Panamentrics Hygrometer / Dew Point Meter

SYSTEM 580 HYGROMETER

USER’S MANUAL

12/19/00

Process Control Instrument Division

System 580 Hygrometer User’s Manual

910-067B

12/19/00

The System 580 Hygrometer

System 580

iii

12/19/00

Warranty

Each Panametrics instrument is warranted to be free from defects in materials and workmanship. Liability under this warranty is limited to servicing the instrument returned to the factory for that purpose and to replacing any defective parts. Fuses and batteries are specifically excluded from any liability. This warranty is effective from the date of delivery to the original purchaser. The equipment must be determined by Panametrics to have been defective for the warranty to be valid. This warranty is effective with respect to the following:

•

one year for electronic failures

•

one year for mechanical failures to the sensor

If damage is determined to have been caused by misuse or abnormal conditions of operation, the owner will be notified and repairs will be billed at standard rates after approval.

Maintenance Policy

If any fault develops, the following steps should be taken: 1. Notify us, giving full details of the difficulty, and provide the model and serial number of the instrument. Upon notification, Panametrics will supply a RETURN AUTHORIZATION NUMBER and/or shipping instructions, depending on the problem. 2. If Panametrics requires the instrument to be returned to the factory, please send it prepaid to the authorized repair station, as indicated in the shipping instructions. 3. If damage has been caused by misuse, abnormal conditions, or if the warranty has expired, an estimate will be made and provided upon request before repairs are started. A Service Form and a list of local offices to contact for service are included in the back of this manual. Use the Service Form to ensure a rapid response to the service order. For additional forms, write to either of the following addresses: Panametrics, Inc. 221 Crescent Street, Suite 1 Waltham, MA 02453-3497 U.S.A. Attn.: Technical Pubs. Dept.

Panametrics Limited Bay 148, Shannon Airport Shannon County Clare, Ireland Attn.: Technical Pubs. Dept.

© Copyright Panametrics, Inc. 2000.

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Table of Contents Chapter 1: General Information Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1-1 Theory of Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1-1 Safety Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1-2 Chapter 2: Installation Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-1 Initial Checkout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-1 Installing the System 580 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-1 Connecting the Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-2 Installing the Probe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-3 Connecting the Probe. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-3 Connecting the Probe Without Zener Barriers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-5 Connecting the Probe With Zener Barriers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-6 Connecting the Recorder Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-7 Connecting the Alarm Relay(s) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-8 Alarm A. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-8 Alarm B. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-8 Chapter 3: Operation Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-1 Applying Power. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-1 Adjusting the Alarm Setpoints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-1 Setting the Dew Point Offset Switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-3 Chapter 4: Calibration and Troubleshooting Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-1 Checking the Fuse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-1 Verifying the Power Supply Jumpers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-1 Checking the Power Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-3 Calibrating the System 580 Electronics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-4 Calibrating the Recorder Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-6 Calibrating the Moisture Probe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-6 Replacing the EPROM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-7 Chapter 5: Specifications Electrical Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-1 Moisture Probe Specifications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-3

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Table of Contents (cont.) Appendix A: Application of the Hygrometer (900-901D1) Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-1 Moisture Monitor Hints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-2 Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-3 Response Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-3 Temperature. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-4 Flow Rate. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-4 Contaminants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-5 Non-Conductive Particulates. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-5 Conductive Particulates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-6 Corrosive Particulates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-6 Aluminum Oxide Probe Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-7 Corrosive Gases And Liquids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-9 Materials of Construction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-10 Calculations and Useful Formulas in Gas Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-11 Nomenclature. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-11 Parts per Million by Volume . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-12 Parts per Million by Weight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-13 Relative Humidity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-13 Weight of Water per Unit Volume of Carrier Gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-13 Weight of Water per Unit Weight of Carrier Gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-14 Comparison of PPMV Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-21 Liquid Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-22 Theory of Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-22 Moisture Content Measurement in Organic Liquids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-22 Empirical Calibrations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-28 Solids Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-34 Appendix B: Outline and Dimension Drawing System 580 Outline and Installation (Dwg. 712-200) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-1

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List of Figures Chapter 1: General Information Figure 1-1: The Moisture Probe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1-1 Figure 1-2: System 580 Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1-3 Chapter 2: Installation Figure 2-1: Figure 2-2: Figure 2-3: Figure 2-4: Figure 2-5: Figure 2-6: Figure 2-7: Figure 2-8:

Power Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-2 A Typical Probe in a Sample Cell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-3 Two-Wire, Shielded Cable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-3 Moisture Probe with Serial Number . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-4 Probe Connections Without Zener Barriers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-5 Probe Connections With Zener Barriers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-6 Recorder Output Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-7 Alarm Relay Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-8

Chapter 3: Operation Figure 3-1: Trimpot and Switch Locations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-2 Chapter 4: Calibration and Troubleshooting Figure 4-1: Power Jumpers, Test Points and Voltage Trimpot . . . . . . . . . . . . . . . . . . . . . . . . . .4-2 Figure 4-2: Component Locations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-5 Chapter 5: Specifications Appendix A: Application of the Hygrometer (900-901D1) Figure A-1: Moisture Content Nomograph for Gases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-20 Figure A-2: Moisture Content Nomograph for Liquids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-32 Figure A-3: Moisture Content Test Apparatus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-33 Appendix B: Outline and Dimension Drawing Figure B-1: System 580 Outline and Installation (Dwg. 712-200) . . . . . . . . . . . . . . . . . . . . . . B-1

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Chapter 1

General Information Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1 Theory of Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1-1 Safety Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2

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Overview

The Panametrics System 580 is a single-channel humidity analyzer that measures water vapor content in gases or non-conductive liquids. It is primarily intended for use with on-line gas or liquid dryers. The System 580 measures the dew/frost point temperature in °C or °F, as specified at the time of purchase. It operates over a full dew/frost range of -80 to +20°C (-112 to 68°F). Other ranges are available as special orders. The System 580 uses a Panametrics moisture probe that is remotely mounted at the process line and connected by a cable to the electronics. The System 580 uses a plug-in EPROM to store moisture sensor probe calibration data. This method eliminates the need for manual adjustments and produces a linear recorder output signal over the specified dew/frost point range. Standard features for the System 580 include:

•

a four-digit LCD, backlit digital display

•

dual form C, 2A alarm relays

•

a 4-20 mA recorder output

•

a NEMA-4 weatherproof case

See Chapter 5, Specifications, for a complete list of options.

Theory of Operation

The System 580 uses a patented Panametrics moisture sensor that consists of a specially anodized aluminum oxide sensor element mounted in a moisture probe (see Figure 1-1 below). The aluminum strip provides a porous oxide layer over which a thin gold coating is vapor deposited. The aluminum base and the gold layer form two electrodes of what is essentially an aluminum oxide capacitor. Sensor

Figure 1-1: The Moisture Probe

General Information

1-1

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Theory of Operation (cont.)

Water vapor is rapidly transported through the porous gold layer, and it equilibrates on the pore walls of the oxide layer in a manner functionally related to the vapor pressure of water in the atmosphere surrounding the sensor. The number of water molecules adsorbed on the oxide structure determines the conductivity of the pore wall. Each value of pore wall resistance provides a distinct value of electrical impedance that may be directly related to water vapor pressure via calibration against moisture standards. The System 580 measures the acceptance (the reciprocal of impedance) of the sensor probe. When properly calibrated, the sensor and associated circuitry yield a precise and repeatable correlation between water vapor pressure and admittance of the sensor. Then, admittance of the sensor is translated by the System 580 electronics into a dew/frost point temperature, which is displayed as an output moisture parameter. Note: Figure 1-2 on page 1-3 shows a complete block diagram of the System 580 circuitry.

Safety Considerations

1-2

Without the use of zener barrier protection, the System 580 is NOT INTRINSICALLY SAFE. However, intrinsic safety CAN BE OBTAINED through the use of the optional internal zener barriers. The zener barriers are certified for use in most hazardous areas. For specific certification information for your application and location, contact the nearest Panametrics company office (see listing at the back of this manual). While Panametrics zener barriers are certified, their use in the System 580 does not imply intrinsic safety certification by an independent agency for the entire system.

General Information

12/19/00

To Probe

Probe Driver

EPROM

Alarm Set Push-Button (S1)

Calibration Circuit

Analog-to-Digital Converter and Linearizer (12 bit)

Probe Signal Conditioning

From Probe

Display Logic

Digital-to-Analog Converter (8 bit)

Display

Recorder Output

Alarm Select Switch (S5)

Display PCB Alarm B Adjust (R58)

Alarm B Circuits

Alarm B Contacts

Alarm A Adjust (R38)

Alarm A Circuits

Alarm A Contacts

Figure 1-2: System 580 Block Diagram

General Information

1-3

Chapter 2

Installation Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1 Initial Checkout. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1 Installing the System 580 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1 Connecting the Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2 Installing the Probe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-3 Connecting the Probe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-3 Connecting the Recorder Output . . . . . . . . . . . . . . . . . . . . . . . . . .2-7 Connecting the Alarm Relay(s) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-8

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Overview

This chapter includes instructions for installing and making all necessary connections for operation of the System 580. Instructions for the following topics are included:

•

initial checkout

•

installing the System 580

•

power, probe, alarm relays, and recorder output connections

Initial Checkout

Panametrics has carefully inspected the System 580 before shipment. However, before installing the unit make sure that the equipment was not physically damaged in transit (for example, shorted or open cables). In addition, make sure the ordered input voltage for the unit matches your line voltage.

Installing the System 580

The System 580 electronics are housed in a standard NEMA-4 weatherproof enclosure. See Appendix B, Outline and Dimension Drawings, for detailed installation requirements. All moisture, power, alarm, and recorder connections are made on the main printed circuit board, which is accessed by opening the front of the enclosure. The connections are made by inserting the stripped and tinned portion of the cables into the appropriate terminals and tightening the screws.

Installation

2-1

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Connecting the Power

Make the input power connections to terminal block TB1 located inside the System 580 on the lower right corner of the circuit board. The specific connections are listed in Table 2-1 below and are shown in Figure 2-1 below. Table 2-1: Power Connections Terminal AC Connection DC Connection TB1-1

Line

+

TB1-2

Neutral

-

TB1-3

Ground

Ground

Figure 2-1: Power Connections

2-2

Installation

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Installing the Probe

Figure 2-2 below shows a typical moisture probe installation, with the probe mounted in a sample cell. Contact the factory to have Panametrics supply a sample cell custom-made to your specifications.

Probe Inlet

Sample Cell

Outlet

Figure 2-2: A Typical Probe in a Sample Cell Before installing the probe, identify the inlet and outlet locations. To install the probe, screw the probe into the sample cell fitting and tighten it securely. Make sure you do not cross-thread the probe. IMPORTANT: For maximum protection of the aluminum oxide sensor, the stainless steel end cap should always be left in place.

Connecting the Probe

Pin D (Green)

The System 580 moisture probe must be connected with a Panametrics two-wire shielded cable as shown in Figure 2-3 below. If the connector is removed from the cable for any reason, be sure to reinstall the connector properly.

Red

Red

Pin A (N.C.)

Foil

Foil

Pin B (N.C.)

Foil

Foil

Green

Green

Pin C (Red)

Bare

Figure 2-3: Two-Wire, Shielded Cable

Installation

2-3

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Connecting the Probe (cont.)

Caution! Excessive cable strain (bending, pulling, twisting, etc.) can cause damage. Do not expose the cable to temperatures above 65°C (149°F) or below -50°C (-58°F). A damaged cable will cause data errors. With the proper cable, the moisture probe may be located at distances up to 1,000 ft (300 m) from the electronics enclosure, with less than 1% reading error. Also, cable lengths may be up to 4,000 ft (1,200 m) with up to 2% reading error. Each System 580 moisture probe has a matching calibration EPROM that bears the serial number corresponding to the probe. (EPROMs are factory installed in the System 580 electronics before shipment.) Figure 2-4 below shows a probe with the serial number on the hex nut. When replacing or recalibrating the probe, replace its matching EPROM with the one supplied by the factory (see Chapter 4, Recalibration and Troubleshooting, for instructions). Serial Number

Figure 2-4: Moisture Probe with Serial Number The wiring for the moisture probe differs, depending on whether or not the optional internal zener barriers are installed in the system. Proceed to the appropriate section for the applicable instructions.

2-4

Installation

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Connecting the Probe Without Zener Barriers

To connect the moisture probe if the optional zener barriers are not being used, insert the lead wires into the appropriate terminal on TB2 and tighten the terminal strip screw. Specifically, refer to Figure 2-5 below, and complete the following steps: 1. Feed the flying lead end of the probe cable through the opening in the bottom left of the System 580 case. (Reserve the right opening for power, recorder, and alarm cables.) 2. Connect the probe cable shield to pin TB2-1. 3. Connect the green probe cable lead (H1) to pin TB2-2. 4. Connect the red probe cable lead (H2) to pin TB2-3.

Figure 2-5: Probe Connections Without Zener Barriers

Installation

2-5

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Connecting the Probe With Zener Barriers

To connect the moisture probe if the optional zener barriers are being used, insert the lead wires into the appropriate terminal on the zener barrier terminal block and tighten the terminal screw. Specifically, refer to Figure 2-6 below, and complete the following steps: Note: The internal zener barrier wiring is done at the factory. 1. Feed the flying lead end of the probe cable through the opening in the bottom left of the System 580 case. (Reserve the right opening for power, recorder, and alarm cables.) 2. Connect a user-supplied ground wire from an independent earth ground to terminal E2 on the zener barrier. The zener barrier ground point must be within 1 ohm of earth ground. 3. Connect the probe cable shield to zener barrier terminal E3. 4. Connect the green probe cable lead (H1) to zener barrier terminal VR1-4. 5. Connect the red probe cable lead (H2) to zener barrier terminal VR2-4.

Probe Cable Ground Wire (user-supplied)

Figure 2-6: Probe Connections With Zener Barriers

2-6

Installation

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Connecting the Recorder Output

The System 580 has one recorder output that is supplied from the factory with a 0-20 mA, 4-20 mA, 0-100 mV, or 0-2 V range. The moisture probe’s matching EPROM indicates the output range of the recorder. Make connections for the recorder output at terminal block TB2 in the following manner (see Figure 2-7 below): 1. Feed the flying lead end of the recorder output cable through the opening in the bottom right of the System 580 case. (Reserve the left opening for the probe cable.) 2. Connect the positive (+) recorder cable lead to pin TB2-4. 3. Connect the negative (–) recorder cable lead to pin TB2-5.

Figure 2-7: Recorder Output Connections

Installation

2-7

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Connecting the Alarm Relay(s)

The System 580 provides two alarm relays. Each alarm has one Form-C SPDT relay rated for 2 A @28 VDC or 120 VAC. For each alarm, the armature (A) moves from the normally-closed (NC) contact to the normally-open (NO) contact when the dew/frost point goes below a programmed set point. The opposite action occurs when the dew/frost point goes above the programmed set point. Refer to Figure 2-8 below, and connect the alarm relays at TB2 as follows: Note: Optional hermetically-sealed alarm relays are available for hazardous area locations.

Alarm A

1. Feed the flying lead end of the alarm cable through the opening in the bottom right of the System 580 case. (Reserve the left opening for the probe cable.) 2. Connect the NC alarm cable lead to pin TB2-6. 3. Connect the Armature alarm cable lead to pin TB2-7. 4. Connect the NO alarm cable lead to pin TB2-8.

Alarm B

1. Feed the flying lead end of the alarm cable through the opening in the bottom right of the System 580 case. (Reserve the left opening for the probe cable.) 2. Connect the NC alarm cable lead to pin TB2-10. 3. Connect the Armature alarm cable lead to pin TB2-11. 4. Connect the NO alarm cable lead to pin TB2-12.

Figure 2-8: Alarm Relay Connections

2-8

Installation

Chapter 3

Operation Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1 Applying Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1 Adjusting the Alarm Setpoints . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1 Setting the Dew Point Offset Switch . . . . . . . . . . . . . . . . . . . . . . . 3-3

12/19/00

Introduction

Applying Power

As soon as the power is applied, the System 580 begins operation. However, a few final adjustments must be made before collecting any data. This chapter contains the instructions for:

•

adjusting the alarm setpoints

•

setting the dew point offset switch Caution! Do not touch any of the exposed AC voltage points on the main printed circuit board.

After making the power connections at terminal block TB1, connect the line cord to an appropriate power source. The System 580 does not have an ON/OFF switch; once the line cord is connected, the unit begins displaying the dew/frost point temperature. Allow the System 580 to warm up for approximately three minutes before proceeding. Note: The display units are set at the factory for °C or °F, as specified at the time of purchase. To turn the unit OFF, disconnect the line cord.

Adjusting the Alarm Setpoints

You may adjust the setpoints for Alarm A and Alarm B using the trimpots on the main printed circuit board. See Figure 3-1 on page 3-2 for the locations of the trimpots and switches. To adjust the alarm setpoints, complete the following steps: 1. Move Switch S5 to either the Alarm A set or the Alarm B set position, depending on the alarm to be adjusted. 2. Press the S1 pushbutton switch and hold it down to display the current alarm setpoint value on the display. 3. While keeping the S1 pushbutton switch depressed, adjust either trimpot R38 for Alarm A or trimpot R58 for Alarm B until the desired setpoint value is displayed. Note: Only the alarm selected in Step 1 above can be adjusted in Step 3 above. 4. Release the S1 pushbutton switch. The display returns to reading the dew/frost point temperature. 5. If desired, repeat steps 1-4 to adjust the other alarm setpoint.

Operation

3-1

12/19/00

C27

U17

C25

C29

U18

C33

U16

C31

C32

U24

U11

U21

U19 C26

C16 U15

C28

C22 C30

U20 U23

S1

U3

U14

Dewpoint Offset Switch

U22

A2

S5

U13

C17

R38

E4

E5

E6

E7

8

4

703-814

E3

W3

E2

W1

S2

W2

R5

S4

S5

R6

S1

R58

T1 S3

TB2

1

W4 TB1

5

F1 E1

1 2 3

Figure 3-1: Trimpot and Switch Locations

3-2

Operation

12/19/00

Setting the Dew Point Offset Switch

The Dew Point Offset switch, S4, is shown in Figure 3-1 on page 3-2. Using a small screwdriver, the rotary switch S4 may be turned to offset the Dew/Frost Point readings by the amounts shown in Table 3-1 below. Table 3-1: Offset Switch Settings Switch Position

Nominal Reading Change in Degrees*

0

Increase 8

1

Increase 6

2

Increase 4

3

Increase 2

4

Null Position

5

Decrease 2

6

Decrease 4

7

Decrease 6

8

Decrease 8

9

Displays MH (FACTORY USE ONLY)

*The actual reading change depends on the system range and units. Note: Position 4 (the null position) displays the factory calibration setting with no applied offset. The recorder output tracks the display reading, so that no recalibration or adjustment of the recorder circuit is required when a dew point offset is applied. IMPORTANT: The alarm setpoints automatically change when the offset switch setting is changed. Thus, the alarm setpoints must be readjusted (see page 3-1) whenever a new dew point offset is applied.

Operation

3-3

Chapter 4

Calibration and Troubleshooting Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1 Checking the Fuse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1 Verifying the Power Supply Jumpers . . . . . . . . . . . . . . . . . . . . . . . 4-1 Checking the Power Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-3 Calibrating the System 580 Electronics . . . . . . . . . . . . . . . . . . . . . 4-4 Calibrating the Recorder Output. . . . . . . . . . . . . . . . . . . . . . . . . . .4-6 Calibrating the Moisture Probe . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-6 Replacing the EPROM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-7

12/19/00

Overview

This chapter describes the calibration procedures for:

•

the System 580 electronics

•

the recorder output

•

the moisture probe

Some basic troubleshooting instructions are also provided to help you locate and correct minor problems. For the service or repair of problems not discussed in this manual, contact Panametrics.

Checking the Fuse

If your System 580 does not power up when the main voltage source is applied, the power fuse may be defective. The fuse is located on the main printed circuit board, as shown in Figure 4-1 on page 4-2. To check and/or replace the fuse, complete the following steps: 1. Disconnect the main power source. !WARNING! Do not continue with these steps until the main power has been disconnected. 2. Open the electronics enclosure to access the main printed circuit board, and remove the plastic cover that protects the fuse. 3. Check for continuity between the two end caps on the fuse. 4. If the fuse is defective (no continuity was detected in Step 3 above), replace the fuse with a new one having the appropriate rating, as indicated in Table 4-1 below. Table 4-1: Replacement Fuse Ratings System Power Fuse Type Fuse Rating 100/120 VAC

3AG

1/8 A

220/240 VAC

3AG

1/8 A

24 VDC

3AG

1/2 A

5. Replace the plastic protective fuse cover.

Verifying the Power Supply Jumpers

Calibration and Troubleshooting

Based on the supply voltage specified at the time of purchase, power supply jumpers are installed on the main printed circuit board at the time of manufacture. If any voltage other than that specified at the time of purchase is applied to the System 580, the unit will not operate correctly. To verify that you are applying the proper supply voltage, refer to Figure 4-1 on page 4-2 and match the installed power supply jumpers to the list in Table 4-2 on page 4-2.

4-1

12/19/00

Verifying the Power The applied supply voltage must correspond to the jumper settings Supply Jumpers (cont.) actually observed on the main printed circuit board. Table 4-2: Power Jumper Settings Installed Power Jumpers Proper Supply Voltage

C27

U17

C29

U18

W1, W3, W5

100/120 VAC

W2, W5

220/240 VAC

W4

24 VDC

C33

C25

U16

C31

C32

U24

U11

U21

U19 C26

C16 U15

C28

C22 C30

U20 U23 U13

C17

U3

U14

R3 A2

U22

E4

E5

E6

E7

W5

S2

4

W3 W2

W1

8

703-814

E3

W3

E2

Test Points (E2-E7)

W2

S5

R5

S4

R6

S1

T1

S3

TB2

1

W4 TB1

5

F1

W1

E1 1 2 3

1

Fuse

W4 W5

Figure 4-1: Power Jumpers, Test Points and Voltage Trimpot

4-2


12/19/00

Checking the Power Supply

A power supply check should always be performed before electronic calibration and after any repairs. To perform this check, refer to Figure 4-1 on page 4-2 and proceed as follows: 1. Disconnect the main power source. !WARNING! Do not continue with these steps until the main power has been disconnected. 2. Check the fuse and the power jumper settings, as described in the previous two sections. 3. Attach a digital voltmeter to the System 580 by connecting its negative lead to test point E4 and its positive lead to the test points or IC pins indicated in Step 5. 4. Reconnect the main power to the System 580. 5. Test the voltages at the points indicated in Table 4-3 below. Table 4-3: Power Supply Voltages VDC VDC Test Point IC Pin (AC Unit) (DC Unit) E2

U1-1

11–16

12.0±0.6

E3

U1-3

5.00±0.25

5.00±0.25

E4

Common GND

0.0

0.0

E5

U2-5

-4.3 minimum

-4.3 minimum

E6

U8-1

-2.000±0.010

-2.000±0.010

E7

U8-7

+2.000±0.010

+2.000±0.010

Note: Only the voltages at test points E6 and E7 (see Table 4-3 above) are adjustable. 6. If the E6 and E7 voltages are not both within specifications, adjust trimpot R3 until these test voltages are correct. Because trimpot R3 affects both the E6 and E7 voltages, be sure to recheck both voltages after each adjustment.


4-3

12/19/00

Calibrating the System 580 Electronics

The factory calibrates the System 580 electronics prior to shipment, and the unit should not require recalibration before use. However, if any adjustment is made to the power supply or recalibration becomes necessary for other reasons, refer to Figure 4-2 on page 4-5 and use the calibration procedure described below. Note: To simplify calibration, internal reference standards (dummy probe values) are built into the System 580 and are printed on the accompanying calibration sheet. In the following procedure, MH refers to these reference standards. To calibrate the System 580, complete the following steps: 1. Check the EPROM (U3), located in the upper right hand corner of the main printed circuit board, to make sure it is firmly seated in its socket. 2. Apply power to the unit and allow at least ten minutes for the electronic components to warm up. 3. Make sure that the power supply voltages are within specifications (see page 4-3). 4. Set switch S2 on the main printed circuit board to the CAL position. 5. Set switch S3 on the main printed circuit board to the LOW MH position. The display should read 0.175 ± 0.002. If it does not, adjust trimpot R16 until the correct value is displayed. 6. Set switch S3 on the main printed circuit board to the HIGH MH position. The display should read H.955 ± 0.020. If it does not, adjust trimpot R18 until the correct value is displayed. 7. Recheck both the Low MH and High MH readings (the readings interact with each other). If necessary, repeat steps 5-6 until both readings are in the required range. 8. When both MH reference readings are in range, the System 580 electronics are calibrated. Return switch S2 to the OP position.

4-4


12/19/00

C27

U17

C29

U18

C33

C25

U16

C32

U24

C31

Lockscrew U11

U21

U19 C26

C16 U15

C28

C22

U3

C30

U20 U23 U13

C17

U3

U14

U22

A2

R16 S2

E3

E4

E5

E6

E7

8

4

703-814

E2

W3

S3

W1

S2

W2

R5

S4

S5

R6

S1

T1

R18 S3 5

TB1

TB2

W4

1 F1 E1

1 2 3

R36

{

SHLD H1 H2 R+ RNC A NO UNUSED NC A NO

1

R37 Recorder Output

Figure 4-2: Component Locations


4-5

12/19/00

Calibrating the Recorder Output

Refer to Figure 4-2 on page 4-5 and calibrate the System 580 recorder output as follows: 1. Check the EPROM (U3), located in the upper right hand corner of the main printed circuit board, to make sure it is firmly seated in its socket. 2. Apply power to the unit and allow at least ten minutes for the electronic components to warm up. 3. Make sure that the power supply voltages are within specifications (see page 4-3). Then, connect an external meter to the recorder output terminals at pins TB2-4 (R+) and TB2-5 (R-) as follows:

•

an ammeter for 0-20 mA or 4-20 mA units

or

•

a voltmeter for 0-100 mV or 0-2 V units

4. Set switch S2 on the main printed circuit board to the CAL position. 5. Set switch S3 on the main printed circuit board to the LOW MH position. The display should initially read 0.175 ± 0.002. Adjust the trimpot R36 until the lowest value of the appropriate recorder range (0 mA, 4 mA, or 0 V) is displayed. 6. Set switch S3 on the main printed circuit board to the HIGH MH position. The display should read H.955 ± 0.020. Adjust the trimpot R37 until the highest value of the appropriate recorder range (20 mA, 100 mV, or 2 V) is displayed. 7. Recheck both the Low MH and High MH readings (the readings interact with each other). If necessary, repeat steps 5-6 until both readings are correct. 8. When both MH reference readings are in range, the recorder output is calibrated. Return switch S2 to the OP position.

Calibrating the Moisture Probe

Prior to shipment, all Panametrics moisture probes are individually factory calibrated against NBS traceable moisture standards. These calibrations are accurate within ±2°C (±3.6°F) above and within ±3°C (±5.4°F) below the frost point temperature of -65°C (-85°F). Under normal conditions the calibration is valid for one year, but more severe conditions will shorten this time (see Appendix A for details). For maximum accuracy under normal conditions, Panametrics recommends that the moisture probe and its matching EPROM be returned to the factory for a calibration check on a yearly basis. Replacement probes and EPROMs are sold separately and can be used as spares while the original probe and EPROM are being recalibrated at the factory.

4-6


12/19/00

Replacing the EPROM

Because the probe and EPROM (Erasable Programmable Read Only Memory) comprise a matching set, the EPROM must also be replaced whenever the probe is changed or recalibrated. To replace the EPROM, refer to Figure 4-2 on page 4-5 and proceed as follows: Caution! Static electricity may damage the EPROM. Be sure to observe proper grounding and handling procedures before continuing. 1. Disconnect the main power source. !WARNING! Do not continue with these steps until the main power has been disconnected. 2. Using a small screwdriver, rotate the lockscrew just above the U3 location 1/4 turn counterclockwise, so that it is in the “O” (open) position. Then, lift the old EPROM (U3) out of its socket. 3. Replace the old EPROM with the new EPROM. Make sure the notch at one end of the EPROM is facing the lockscrew, and place the new EPROM into its socket. IMPORTANT: The serial number on the new EPROM must match the serial number on the moisture probe. 4. Using a small screwdriver, rotate the lockscrew just above the U3 location 1/4 turn clockwise, so that it is in the “C” (closed) position. Verify that the EPROM is fully seated and firmly locked in its socket.


4-7

Chapter 5

Specifications Electrical Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1 Moisture Probe Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-3

12/19/00

Electrical Specifications

Power: AC: 100, 120, 220, or 240 VAC ± 10%; 50/60 Hz; 4 W DC: 24 VDC ± 10%; 4 W Inputs: A single moisture probe input connected to a plug-in terminal strip. The probe may be mounted up to 4,000 ft (1,220 m) from the electronics enclosure. Zener barriers are available as an option. Ranges: The System 580 is available in any one of four dew/frost point ranges, as follows: -80 to 20°C, in 1°C increments -50 to 0°C, in 0.5°C increments -130 to 70°F, in 2°F increments -50 to 50°F, in 1°F increments Recorder Output: Standard: 4-20 mA Optional: 0-20 mA, 0-100 mV, or 0-2 V All outputs are linear over the selected Dew/Frost Point range. Displays: one four-digit LCD with Electroluminescent (EL) backlight Alarm Relay Outputs: Standard: dual Form-C, SPDT, 2 A @120 VAC or 28 VDC. Each has its own setpoint. Optional: dual hermetically-sealed Form-C, SPDT, 2 A @28 VDC Programming: 101 data points via plug-in EPROM, pre-programming by Panametrics. Electronic Accuracy: better than 1% of full scale Readability: better than ±1% of reading

Specifications

5-1

12/19/00

Electrical Specifications (cont.)

Operating Temperature (Electronics Only): 0 to 55°C (32 to 131°F) Alarm Set Point Accuracy: ±1°C (±2°F) Storage Temperature: -20 to 70°C (-4 to 158°F) Warm Up Time: meets specified accuracy within three minutes of power up Electronic Calibration: factory-calibrated Hazardous Areas: Designed for use with optional internal zener barriers for probes and cables located in hazardous areas. Consult Panametrics. Dimensions (NEMA-4 Case): 203.2 mm W x 254.0 mm L x 101.6 mm D (8.0 in. W x 10.0 in. L x 4.0 in. D) Weight (NEMA-4 Case): 4.53 kg (10.0 lb) Current Output/Load Resistance: 0-20 mA/500 Ω max. 4-20 mA/500 Ω max. Voltage Output/Load Resistance: 0-100 mV/10 KΩ min. 0-2 V/10 KΩ min.

5-2

Specifications

12/19/00

Moisture Probe Specifications

Type: aluminum oxide moisture sensor element (patented Panametrics M2J series) Impedance Range: 2 MΩ to 50 KΩ @77 Hz (depending on vapor pressure of water) Calibration: Each sensor is factory calibrated against NBS traceable moisture standards. Dew/Frost Point Range: -80 to 20°C (-112 to 68°F) Operating Temperature: -110 to 70°C (-166 to 158°F) Storage Temperature: 70°C (158°F) maximum Operating Pressure: 5 µm of Hg to 5,000 psig

Specifications

5-3

Appendix A

Application of the Hygrometer (900-901D1) Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-1 Moisture Monitor Hints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-2 Contaminants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-5 Aluminum Oxide Probe Maintenance. . . . . . . . . . . . . . . . . . . . . . A-7 Corrosive Gases And Liquids . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-9 Materials of Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-10 Calculations and Useful Formulas in Gas Applications. . . . . . A-11 Liquid Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-22 Empirical Calibrations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-28 Solids Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-34

3/15/00

Introduction

This appendix contains general information about moisture monitoring techniques. System contaminants, moisture probe maintenance, process applications and other considerations for ensuring accurate moisture measurements are discussed. The following specific topics are covered:

•

Moisture Monitor Hints

•

Contaminants

•

Aluminum Oxide Probe Maintenance

•

Corrosive Gases and Liquids

•

Materials of Construction

•

Calculations and Useful Formulas in Gas Applications

•

Liquid Applications

•

Empirical Calibrations

•

Solids Applications

Application of the Hygrometer (900-901D1)

A-1

3/15/00

Moisture Monitor Hints

Panametrics hygrometers, using aluminum oxide moisture probes, have been designed to reliably measure the moisture content of both gases and liquids. The measured dew point will be the real dew point of the system at the measurement location and at the time of measurement. However, no moisture sensor can determine the origin of the measured moisture content. In addition to the moisture content of the fluid to be analyzed, the water vapor pressure at the measurement location may include components from sources such as: moisture from the inner walls of the piping; external moisture through leaks in the piping system; and trapped moisture from fittings, valves, filters, etc. Although these sources may cause the measured dew point to be higher than expected, it is the actual dew point of the system at the time of measurement. One of the major advantages of the Panametrics hygrometer is that it can be used for in situ measurements (i.e. the sensor element is designed for installation directly within the region to be measured). As a result, the need for complex sample systems that include extensive piping, manifolds, gas flow regulators and pressure regulators is eliminated or greatly reduced. Instead, a simple sample system to reduce the fluid temperature, filter contaminants and facilitate sensor removal is all that is needed. Whether the sensor is installed in situ or in a remote sampling system, the accuracy and speed of measurement depend on the piping system and the dynamics of the fluid flow. Response times and measurement values will be affected by the degree of equilibrium reached within system. Factors such as gas pressure, flow rate, materials of construction, length and diameter of piping, etc. will greatly influence the measured moisture levels and the response times. Assuming that all secondary sources of moisture have been eliminated and the sample system has been allowed to come to equilibrium, then the measured dew point will equal the actual dew point of the process fluid. Some of the most frequently encountered problems associated with moisture monitoring sample systems include:

A-2

•

the moisture content value changes as the total gas pressure changes

•

the measurement response time is very slow

•

the dew point changes as the fluid temperature changes

•

the dew point changes as the fluid flow rate changes.


3/15/00

Moisture Monitor Hints (cont.)

Panametrics hygrometers measure only water vapor pressure. In addition, the instrument has a very rapid response time and it is not affected by changes in fluid temperature or fluid flow rate. If any of the above situations occur, then they are almost always caused by a defect in the sample system. The moisture sensor itself can not lead to such problems.

Pressure

Panametrics hygrometers can accurately measure dew points under pressure conditions ranging from vacuums as low as a few microns of mercury up to pressures of 5000 psig. The calibration data supplied with the moisture probe is directly applicable over this entire pressure range, without correction. Note: Although the moisture probe calibration data is supplied as meter reading vs. dew point, it is important to remember that the moisture probe responds only to water vapor pressure. When a gas is compressed, the partial pressures of all the gaseous components are proportionally increased. Conversely, when a gas expands, the partial pressures of the gaseous components are proportionally decreased. Therefore, increasing the pressure on a closed aqueous system will increase the vapor pressure of the water, and hence, increase the dew point. This is not just a mathematical artifact. The dew point of a gas with 1000 PPMv of water at 200 psig will be considerably higher than the dew point of a gas with 1000 PPMv of water at 1 atm. Gaseous water vapor will actually condense to form liquid water at a higher temperature at the 200 psig pressure than at the 1 atm pressure. Thus, if the moisture probe is exposed to pressure changes, the measured dew point will be altered by the changed vapor pressure of the water. It is generally advantageous to operate the hygrometer at the highest possible pressure, especially at very low moisture concentrations. This minimizes wall effects and results in higher dew point readings, which increases the sensitivity of the instrument.

Response Time

The response time of the Panametrics standard M Series Aluminum Oxide Moisture Sensor is very rapid - a step change of 63% in moisture concentration will be observed in approximately 5 seconds. Thus, the observed response time to moisture changes is, in general, limited by the response time of the sample system as a whole. Water vapor is absorbed tenaciously by many materials, and a large, complex processing system can take several days to “dry down” from atmospheric moisture levels to dew points of less than -60°C. Even simple systems consisting of a few feet of stainless steel tubing and a small chamber can take an hour or more to dry down from dew points of +5°C to -70°C. The rate at which the system reaches equilibrium will depend on flow rate, temperature, materials of construction and system pressure. Generally speaking, an increase in flow rate and/or temperature will decrease the response time of the sample system.


A-3

3/15/00

Response Time (cont.)

To minimize any adverse affects on response time, the preferred materials of construction for moisture monitoring sample systems are stainless steel, Teflon® and glass. Materials to be avoided include rubber elastomers and related compounds.

Temperature

The Panametrics hygrometer is largely unaffected by ambient temperature. However, for best results, it is recommended that the ambient temperature be at least 10°C higher than the measured dew point, up to a maximum of 70°C. Because an ambient temperature increase may cause water vapor to be desorbed from the walls of the sample system, it is possible to observe a diurnal change in moisture concentration for a system exposed to varying ambient conditions. In the heat of the day, the sample system walls will be warmed by the ambient air and an off-gassing of moisture into the process fluid, with a corresponding increase in measured moisture content, will occur. The converse will happen during the cooler evening hours. This effect should not be mistakenly interpreted as indicating that the moisture probe has a temperature coefficient.

Flow Rate

Panametrics hygrometers are unaffected by the fluid flow rate. The moisture probe is not a mass sensor but responds only to water vapor pressure. The moisture probe will operate accurately under both static and dynamic fluid flow conditions. In fact, the specified maximum fluid linear velocity of 10,000 cm/sec for The M Series Aluminum Oxide Moisture Sensor indicates a mechanical stability limitation rather than a sensitivity to the fluid flow rate. If the measured dew point of a system changes with the fluid flow rate, then it can be assumed that off-gassing or a leak in the sample system is causing the variation. If secondary moisture is entering the process fluid (either from an ambient air leak or the release of previously absorbed moisture from the sample system walls), an increase in the flow rate of the process fluid will dilute the secondary moisture source. As a result, the vapor pressure will be lowered and a lower dew point will be measured. Note: Refer to the Specifications chapter in this manual for the maximum allowable flow rate for the instrument.

A-4


3/15/00

Contaminants

Industrial gases and liquids often contain fine particulate matter. Particulates of the following types are commonly found in such process fluids:

•

carbon particles

•

salts

•

rust particles

•

polymerized substances

•

organic liquid droplets

•

dust particles

•

molecular sieve particles

•

alumina dust

For convenience, the above particulates have been divided into three broad categories. Refer to the appropriate section for a discussion of their affect on the Panametrics moisture probe.

Non-Conductive Particulates

Note: Molecular sieve particles, organic liquid droplets and oil droplets are typical of this category. In general, the performance of the moisture probe will not be seriously hindered by the condensation of non-conductive, noncorrosive liquids. However, a slower response to moisture changes will probably be observed, because the contaminating liquid barrier will decrease the rate of transport of the water vapor to the sensor and reduce its response time. Particulate matter with a high density and/or a high flow rate may cause abrasion or pitting of the sensor surface. This can drastically alter the calibration of the moisture probe and, in extreme cases, cause moisture probe failure. A stainless steel shield is supplied with the moisture probe to minimize this effect, but in severe cases, it is advisable to install a Teflon® or stainless steel filter in the fluid stream. On rare occasions, non-conductive particulate material may become lodged under the contact arm of the sensor, creating an open circuit. If this condition is suspected, refer to the Probe Cleaning Procedure section of this appendix for the recommended cleaning procedure.


A-5

3/15/00

Conductive Particulates

Note: Metallic particles, carbon particles and conductive liquid droplets are typical of this category. Since the hygrometer reading is inversely proportional to the impedance of the sensor, a decrease in sensor impedance will cause an increase in the meter reading. Thus, trapped conductive particles across the sensor leads or on the sensor surface, which will decrease the sensor impedance, will cause an erroneously high dew point reading. The most common particulates of this type are carbon (from furnaces), iron scale (from pipe walls) and glycol droplets (from glycol-based dehydrators). If the system contains conductive particulates, it is advisable to install a Teflon® or stainless steel filter in the fluid stream.

Corrosive Particulates

Note: Sodium chloride and sodium hydroxide particulates are typical of this category. Since the active sensor element is constructed of aluminum, any material that corrodes aluminum will deleteriously affect the operation of the moisture probe. Furthermore, a combination of this type of particulate with water will cause pitting or severe corrosion of the sensor element. In such instances, the sensor cannot be cleaned or repaired and the probe must be replaced. Obviously, the standard moisture probe can not be used in such applications unless the complete removal of such particulates by adequate filtration is assured.

A-6


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Aluminum Oxide Probe Maintenance

Other than periodic calibration checks, little or no routine moisture probe maintenance is required. However, as discussed in the previous section, any electrically conductive contaminant trapped on the aluminum oxide sensor will cause inaccurate moisture measurements. If such a situation develops, return of the moisture probe to the factory for analysis and recalibration is recommended. However, in an emergency, cleaning of the moisture probe in accordance with the following procedure may be attempted by a qualified technician or chemist. IMPORTANT: Moisture probes must be handled carefully and cannot be cleaned in any fluid which will attack its components. The probe’s materials of construction are Al, Al2O3, nichrome, gold, stainless steel, glass and Viton® A. Also, the sensor’s aluminum sheet is very fragile and can be easily bent or distorted. Do not permit anything to touch it! The following items will be needed to properly complete the moisture probe cleaning procedure:

•

approximately 300 ml of reagent grade hexane or toluene

•

approximately 300 ml of distilled (not deionized) water

•

two glass containers to hold above liquids (metal containers should not be used).

To clean the moisture probe, complete the following steps: 1. Record the dew point of the ambient air. 2. Making sure not to touch the sensor, carefully remove the protective shield from the sensor. 3. Soak the sensor in the distilled water for ten (10) minutes. Be sure to avoid contact with the bottom and the walls of the container! 4. Remove the sensor from the distilled water and soak it in the clean container of hexane or toluene for ten (10) minutes. Again, avoid all contact with the bottom and the walls of the container! 5. Remove the sensor from the hexane or toluene, and place it face up in a low temperature oven set at 50°C ±2°C (122°F ±4°F) for 24 hours.


A-7

3/15/00

Aluminum Oxide Probe Maintenance (cont.)

6. Repeat steps 3-5 for the protective shield. During this process, swirl the shield in the solvents to ensure the removal of any contaminants that may have become embedded in the porous walls of the shield. 7. Carefully replace probe’s protective shield, making sure not to touch the sensor. 8. Connect the probe cable to the probe, and record the dew point of the ambient air, as in step 1. Compare the two recorded dew point readings to determine if the reading after cleaning is a more accurate value for the dew point of the ambient atmosphere. 9. If the sensor is in proper calibration (±2°C accuracy), reinstall the probe in the sample cell and proceed with normal operation of the hygrometer. 10. If the sensor is not in proper calibration, repeat steps 1-9, using time intervals 5 times those used in the previous cleaning cycle. Repeat this procedure until the sensor is in proper calibration. A trained laboratory technician should determine if all electrically conductive compounds have been removed from the aluminum oxide sensor and that the probe is properly calibrated. Probes which are not in proper calibration must be recalibrated. It is recommended that all moisture probes be recalibrated by Panametrics approximately once a year, regardless of the probe’s condition.

A-8


3/15/00

Corrosive Gases And Liquids

Panametrics M Series Aluminum Oxide Moisture Sensors have been designed to minimize the affect of corrosive gases and liquids. As indicated in the Materials of Construction section of this appendix, no copper, solder or epoxy is used in the construction of these sensors. The moisture content of corrosive gases such as H2S, SO2, cyanide containing gases, acetic acid vapors, etc. can be measured directly. Note: Since the active sensor is aluminum, any fluid which corrodes aluminum will affect the sensor’s performance. By observing the following precautions, the moisture probe may be used successfully and economically: 1. The moisture content of the corrosive fluid must be 10 PPMv or less at 1 atmosphere, or the concentration of the corrosive fluid must be 10 PPMv or less at 1 atmosphere. 2. The sample system must be pre-dried with a dry inert gas, such as nitrogen or argon, prior to introduction of the fluid stream. Any adsorbed atmospheric moisture on the sensor will react with the corrosive fluid to cause pitting or corrosion of the sensor. 3. The sample system must be purged with a dry inert gas, such as nitrogen or argon, prior to removal of the moisture probe. Any adsorbed corrosive fluid on the sensor will react with ambient moisture to cause pitting or corrosion of the sensor. 4. Operate the sample system at the lowest possible gas pressure. Using the precautions listed above, the hygrometer has been used to successfully measure the moisture content in such fluids as hydrochloric acid, sulfur dioxide, chlorine and bromine.


A-9

3/15/00

Materials of Construction M1 and M2 Sensors: Sensor Element:

99.99% aluminum, aluminum oxide, gold, Nichrome, A6

Back Wire:

316 stainless steel

Contact Wire:

gold, 304 stainless steel

Front Wire:

316 stainless steel

Support:

Glass (Corning 9010)

Pins:

Al 152 Alloy (52% Ni)

Glass:

Corning 9010

Shell:

304L stainless steel

O-Ring:

silicone rubber

Threaded Fitting:

304 stainless steel

O-Ring:

Viton® A

Cage:

308 stainless steel

Shield:

304 stainless steel

Electrical Connector:

A-10


3/15/00

Calculations and Useful Formulas in Gas Applications

A knowledge of the dew point of a system enables one to calculate all other moisture measurement parameters. The most important fact to recognize is that for a particular dew point there is one and only one equivalent vapor pressure. Note: The calibration of Panametrics moisture probes is based on the vapor pressure of liquid water above 0°C and frost below 0°C. Panametrics moisture probes are never calibrated with supercooled water. Caution is advised when comparing dew points measured with a Panametrics hygrometer to those measured with a mirror type hygrometer, since such instruments may provide the dew points of supercooled water. As stated above, the dew/frost point of a system defines a unique partial pressure of water vapor in the gas. Table A-1 on page A-15, which lists water vapor pressure as a function of dew point, can be used to find either the saturation water vapor pressure at a known temperature or the water vapor pressure at a specified dew point. In addition, all definitions involving humidity can then be expressed in terms of the water vapor pressure.

Nomenclature

The following symbols and units are used in the equations that are presented in the next few sections:

• • • • • • • •

RH = relative humidity

•

PW = water vapor pressure at the measured dew point (mm of Hg)

•

PT = total system pressure (mm of Hg)

TK = temperature (°K = °C + 273) TR = temperature (°R = °F + 460) PPMv = parts per million by volume PPMw = parts per million by weight Mw = molecular weight of water (18) MT = molecular weight of carrier gas PS = saturation vapor pressure of water at the prevailing temperature (mm of Hg)


A-11

3/15/00

Parts per Million by Volume

The water concentration in a system, in parts per million by volume, is proportional to the ratio of the water vapor partial pressure to the total system pressure: PW 6 PPM V = -------- × 10 PT

(5-1)

In a closed system, increasing the total pressure of the gas will proportionally increase the partial pressures of the various components. The relationship between dew point, total pressure and PPMV is provided in nomographic form in Figure A-1 on page A-20. Note: The nomograph shown in Figure A-1 on page A-20 is applicable only to gases. Do not apply it to liquids. To compute the moisture content for any ideal gas at a given pressure, refer to Figure A-1 on page A-20. Using a straightedge, connect the dew point (as measured with the Panametrics’ Hygrometer) with the known system pressure. Read the moisture content in PPMV where the straightedge crosses the moisture content scale.

Typical Problems 1. Find the water content in a nitrogen gas stream, if a dew point of -20°C is measured and the pressure is 60 psig. Solution: In Figure A-1 on page A-20, connect 60 psig on the Pressure scale with -20°C on the Dew/Frost Point scale. Read 200 PPMV, on the Moisture Content scale. 2. Find the expected dew/frost point for a helium gas stream having a measured moisture content of 1000 PPMV and a system pressure of 0.52 atm. Solution: In Figure A-1 on page A-20, connect 1000 PPMV on the Moisture Content scale with 0.52 atm on the Pressure scale. Read the expected frost point of –27°C on the Dew/Frost Point scale.

A-12


3/15/00

Parts per Million by Weight

The water concentration in the gas phase of a system, in parts per million by weight, can be calculated directly from the PPMV and the ratio of the molecular weight of water to that of the carrier gas as follows: MW PPM W = PPMV × ---------M

(5-2)

T

Relative Humidity

Relative humidity is defined as the ratio of the actual water vapor pressure to the saturation water vapor pressure at the prevailing ambient temperature, expressed as a percentage. PW RH = -------- × 100 PS

(5-3)

1. Find the relative humidity in a system, if the measured dew point is 0°C and the ambient temperature is +20°C. Solution: From Table A-1 on page A-20, the water vapor pressure at a dew point of 0°C is 4.579 mm of Hg and the saturation water vapor pressure at an ambient temperature of +20°C is 17.535 mm of Hg. Therefore, the relative humidity of the system is 100 x 4.579/17.535 = 26.1%.

Weight of Water per Unit Volume of Carrier Gas

Three units of measure are commonly used in the gas industry to express the weight of water per unit volume of carrier gas. They all represent a vapor density and are derivable from the vapor pressure of water and the Perfect Gas Laws. Referenced to a temperature of 60°F and a pressure of 14.7 psia, the following equations may be used to calculate these units: PW mg of water---------------------------= 289 × -------TK liter of gas

(5-4)

PW lb of water -------------------------- = 0.0324 × ------3 TR ft of gas

(5-5)

6

10 × P W PPM V lb of water -----------------------------------= ---------------- = ----------------------21.1 21.1 × P T MMSCF of gas

(5-6)

Note: MMSCF is an abbreviation for a “million standard cubic feet” of carrier gas.


A-13

3/15/00

Weight of Water per Unit Weight of Carrier Gas

Occasionally, the moisture content of a gas is expressed in terms of the weight of water per unit weight of carrier gas. In such a case, the unit of measure defined by the following equation is the most commonly used: MW × PW grains of water----------------------------------= 7000 × -----------------------MT × PT lb of gas

(5-7)

For ambient air at 1 atm of pressure, the above equation reduces to the following: grains of water----------------------------------= 5.72 × P W lb of gas

A-14

(5-8)


3/15/00

Table A-1: Vapor Pressure of Water Note: If the dew/frost point is known, the table will yield the partial water vapor pressure (PW) in mm of Hg. If the ambient or actual gas temperature is known, the table will yield the saturated water vapor pressure (PS) in mm of Hg. Water Vapor Pressure Over Ice Temp. (°C)

0

2

4

6

8

-90 -80 -70 -60

0.000070 0.000400 0.001940 0.008080

0.000048 0.000290 0.001430 0.006140

0.000033 0.000200 0.001050 0.004640

0.000022 0.000140 0.000770 0.003490

0.000015 0.000100 0.000560 0.002610

-50 -40 -30

0.029550 0.096600 0.285900

0.023000 0.076800 0.231800

0.017800 0.060900 0.187300

0.013800 0.048100 0.150700

0.010600 0.037800 0.120900

Temp. (°C)

0.0

0.2

0.4

0.6

0.8

-29 -28 -27 -26

0.317 0.351 0.389 0.430

0.311 0.344 0.381 0.422

0.304 0.337 0.374 0.414

0.298 0.330 0.366 0.405

0.292 0.324 0.359 0.397

-25 -24 -23 -22 -21

0.476 0.526 0.580 0.640 0.705

0.467 0.515 0.569 0.627 0.691

0.457 0.505 0.558 0.615 0.678

0.448 0.495 0.547 0.603 0.665

0.439 0.486 0.536 0.592 0.652

-20 -19 -18 -17 -16

0.776 0.854 0.939 1.031 1.132

0.761 0.838 0.921 1.012 1.111

0.747 0.822 0.904 0.993 1.091

0.733 0.806 0.887 0.975 1.070

0.719 0.791 0.870 0.956 1.051

-15 -14 -13 -12 -11

1.241 1.361 1.490 1.632 1.785

1.219 1.336 1.464 1.602 1.753

1.196 1.312 1.437 1.574 1.722

1.175 1.288 1.411 1.546 1.691

1.153 1.264 1.386 1.518 1.661

-10 -9 -8 -7 -6

1.950 2.131 2.326 2.537 2.765

1.916 2.093 2.285 2.493 2.718

1.883 2.057 2.246 2.450 2.672

1.849 2.021 2.207 2.408 2.626

1.817 1.985 2.168 2.367 2.581

-5 -4 -3 -2 -1

3.013 3.280 3.568 3.880 4.217

2.962 3.225 3.509 3.816 4.147

2.912 3.171 3.451 3.753 4.079

2.862 3.117 3.393 3.691 4.012

2.813 3.065 3.336 3.630 3.946

0

4.579

4.504

4.431

4.359

4.287


A-15

3/15/00

Table A-1: Vapor Pressure of Water (Continued) Aqueous Vapor Pressure Over Water Temp. (°C)

0.0

0.2

0.4

0.6

0.8

0 1 2 3 4

4.579 4.926 5.294 5.685 6.101

4.647 4.998 5.370 5.766 6.187

4.715 5.070 5.447 5.848 6.274

4.785 5.144 5.525 5.931 6.363

4.855 5.219 5.605 6.015 6.453

5 6 7 8 9

6.543 7.013 7.513 8.045 8.609

6.635 7.111 7.617 8.155 8.727

6.728 7.209 7.722 8.267 8.845

6.822 7.309 7.828 8.380 8.965

6.917 7.411 7.936 8.494 9.086

10 11 12 13 14

9.209 9.844 10.518 11.231 11.987

9.333 9.976 10.658 11.379 12.144

9.458 10.109 10.799 11.528 12.302

9.585 10.244 10.941 11.680 12.462

9.714 10.380 11.085 11.833 12.624

15 16 17 18 19

12.788 13.634 14.530 15.477 16.477

12.953 13.809 14.715 15.673 16.685

13.121 13.987 14.903 15.871 16.894

13.290 14.166 15.092 16.071 17.105

13.461 14.347 15.284 16.272 17.319

20 21 22 23 24

17.535 18.650 19.827 21.068 22.377

17.753 18.880 20.070 21.324 22.648

17.974 19.113 20.316 21.583 22.922

18.197 19.349 20.565 21.845 23.198

18.422 19.587 20.815 22.110 23.476

25 26 27 28 29

23.756 25.209 26.739 28.349 30.043

24.039 25.509 27.055 28.680 30.392

24.326 25.812 27.374 29.015 30.745

24.617 26.117 27.696 29.354 31.102

24.912 26.426 28.021 29.697 31.461

30 31 32 33 34

31.824 33.695 35.663 37.729 39.898

32.191 34.082 36.068 38.155 40.344

32.561 34.471 36.477 38.584 40.796

32.934 34.864 36.891 39.018 41.251

33.312 35.261 37.308 39.457 41.710

35 36 37 38 39

42.175 44.563 47.067 49.692 52.442

42.644 45.054 47.582 50.231 53.009

43.117 45.549 48.102 50.774 53.580

43.595 46.050 48.627 51.323 54.156

44.078 46.556 49.157 51.879 54.737

40 41

55.324 58.340

55.910 58.960

56.510 59.580

57.110 60.220

57.720 60.860

A-16


3/15/00

Table A-1: Vapor Pressure of Water (Continued) Aqueous Vapor Pressure Over Water (cont.) Temp. (°C)

0.0

0.2

0.4

0.6

0.8

42 43 44

61.500 64.800 68.260

62.140 65.480 68.970

62.800 66.160 69.690

63.460 66.860 70.410

64.120 67.560 71.140

45 46 47 48 49

71.880 75.650 79.600 83.710 88.020

72.620 76.430 80.410 84.560 88.900

73.360 77.210 81.230 85.420 89.790

74.120 78.000 82.050 86.280 90.690

74.880 78.800 82.870 87.140 91.590

50 51 52 53 54

92.51 97.20 102.09 107.20 112.51

93.50 98.20 103.10 108.20 113.60

94.40 99.10 104.10 109.30 114.70

95.30 100.10 105.10 110.40 115.80

96.30 101.10 106.20 111.40 116.90

55 56 57 58 59

118.04 123.80 129.82 136.08 142.60

119.10 125.00 131.00 137.30 143.90

120.30 126.20 132.30 138.50 145.20

121.50 127.40 133.50 139.90 146.60

122.60 128.60 134.70 141.20 148.00

60 61 62 63 64

149.38 156.43 163.77 171.38 179.31

150.70 157.80 165.20 172.90 180.90

152.10 159.30 166.80 174.50 182.50

153.50 160.80 168.30 176.10 184.20

155.00 162.30 169.80 177.70 185.80

65 66 67 68 69

187.54 196.09 204.96 214.17 223.73

189.20 197.80 206.80 216.00 225.70

190.90 199.50 208.60 218.00 227.70

192.60 201.30 210.50 219.90 229.70

194.30 203.10 212.30 221.80 231.70

70 71 72 73 74

233.70 243.90 254.60 265.70 277.20

235.70 246.00 256.80 268.00 279.40

237.70 248.20 259.00 270.20 281.80

239.70 250.30 261.20 272.60 284.20

241.80 252.40 263.40 274.80 286.60

75 76 77 78 79

289.10 301.40 314.10 327.30 341.00

291.50 303.80 316.60 330.00 343.80

294.00 306.40 319.20 332.80 346.60

296.40 308.90 322.00 335.60 349.40

298.80 311.40 324.60 338.20 352.20

80 81 82 83

355.10 369.70 384.90 400.60

358.00 372.60 388.00 403.80

361.00 375.60 391.20 407.00

363.80 378.80 394.40 410.20

366.80 381.80 397.40 413.60


A-17

3/15/00

Table A-1: Vapor Pressure of Water (Continued) Aqueous Vapor Pressure Over Water (cont.) Temp. (°C)

0.0

0.2

0.4

0.6

0.8

84

416.80

420.20

423.60

426.80

430.20

85 86 87 88 89

433.60 450.90 468.70 487.10 506.10

437.00 454.40 472.40 491.00 510.00

440.40 458.00 476.00 494.70 513.90

444.00 461.60 479.80 498.50 517.80

447.50 465.20 483.40 502.20 521.80

90 91 92 93 94

525.76 546.05 566.99 588.60 610.90

529.77 550.18 571.26 593.00 615.44

533.80 554.35 575.55 597.43 620.01

537.86 558.53 579.87 601.89 624.61

541.95 562.75 584.22 606.38 629.24

95 96 97 98 99

633.90 657.62 682.07 707.27 733.24

638.59 662.45 687.04 712.40 738.53

643.30 667.31 692.05 717.56 743.85

648.05 672.20 697.10 722.75 749.20

652.82 677.12 702.17 727.98 754.58

100 101

760.00 787.57

765.45 793.18

770.93 798.82

776.44 804.50

782.00 810.21

A-18


3/15/00

Table A-2: Maximum Gas Flow Rates Based on the physical characteristics of air at a temperature of 77°F and a pressure of 1 atm, the following flow rates will produce the maximum allowable gas stream linear velocity of 10,000 cm/sec in the corresponding pipe sizes. Inside Pipe Diameter (in.) 0.25 0.50 0.75 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0 12.0

Gas Flow Rate (cfm) 7 27 60 107 429 966 1,718 2,684 3,865 5,261 6,871 8,697 10,737 12,991 15,461

Table A-3: Maximum Liquid Flow Rates Based on the physical characteristics of benzene at a temperature of 77°F, the following flow rates will produce the maximum allowable fluid linear velocity of 10 cm/sec in the corresponding pipe sizes. Inside Pipe Diameter (in.) 0.25 0.50 0.75 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0 12.0

Flow Rate (gal/hr) 3 12 27 48 193 434 771 1,205 1,735 2,361 3,084 3,903 4,819 5,831 6,939


Flow Rate (l/hr) 11 46 103 182 730 1,642 2,919 4,561 6,567 8,939 11,675 14,776 18,243 22,074 26,269

A-19

3/15/00

10,000

1,000

8,000

800 10,000

6,000 5,000

8,000 6,000 5,000

4,000 3,000

4,000 3,000

2,000

600 500 400 300 200

2,000 1,500

1,000 800

100 80

1,000

400 300

30 20

10.0 8.0 6.0 5.0 4.0 3.0

+10

30

0

600 500

40

400

30

300

10 0

-10

-20

-10 -20

-30

-30 -40

-40

-50 -60

-50

-70 -80

-60

20

200 150

PRESSURE, PSIG

40

60 50 40

DEW/FROST POINT, °C

60 50

60 50

20

DEW/FROST POINT, °F

80

MOISTURE CONTENT, PPM by volume

200

100

800 +20

100 80 60 50 40 30

10 8.0 6.0 5.0 4.0 3.0

20 2.0 10 5 0

1.0 .8

-90

PRESSURE, ATMOSPHERES

600 500

.6 .5

-70 -100

.4 .3

-110 -80

2.0

1.0

.2

-120

-130

.10

-90

0.8

.08

0.6 0.5

.06 .05

0.4

.04

0.3

.03

0.2

.02

0.1

.01

Figure A-1: Moisture Content Nomograph for Gases

A-20


3/15/00

Comparison of PPMV Calculations

There are three basic methods for determining the moisture content of a gas in PPMV:

•

the calculations described in this appendix

•

calculations performed with the slide rule device that is provided with each Panametrics hygrometer

•

values determined from tabulated vapor pressures

For comparison purposes, examples of all three procedures are listed in Table A-4 below. Table A-4: Comparative PPMV Values Calculation Method Dew Point (°C) -80

-50

+20


Pressure (psig) 0 100 800 1500 0 100 800 1500 0 100 800 1500

Slide Rule 0.5 0.065 0.009 0.005 37 4.8 0.65 0.36 N.A. 3000 420 220

Appendix A 0.55 N.A. N.A. N.A. 40 5.2 0.8 0.35 20,000 3000 400 200

Vapor Pressure 0.526 0.0675 0.0095 0.0051 38.88 4.98 0.7016 0.3773 23,072.36 2956.9 416.3105 223.9

A-21

3/15/00

Liquid Applications Theory of Operation

The direct measurement of water vapor pressure in organic liquids is accomplished easily and effectively with Panametrics’ Aluminum Oxide Moisture Sensors. Since the moisture probe pore openings are small in relation to the size of most organic molecules, admission into the sensor cavity is limited to much smaller molecules, such as water. Thus, the surface of the aluminum oxide sensor, which acts as a semipermeable membrane, permits the measurement of water vapor pressure in organic liquids just as easily as it does in gaseous media. In fact, an accurate sensor electrical output will be registered whether the sensor is directly immersed in the organic liquid or it is placed in the gas space above the liquid surface. As with gases, the electrical output of the aluminum oxide sensor is a function of the measured water vapor pressure.

Moisture Content Measurement in Organic Liquids

Henry’s Law Type Analysis When using the aluminum oxide sensor in non-polar liquids having water concentrations ≤1% by weight, Henry’s Law is generally applicable. Henry’s Law states that, at constant temperature, the mass of a gas dissolved in a given volume of liquid is proportional to the partial pressure of the gas in the system. Stated in terms pertinent to this discussion, it can be said that the PPMW of water in hydrocarbon liquids is equal to the partial pressure of water vapor in the system times a constant. As discussed above, a Panametrics aluminum oxide sensor can be directly immersed in a hydrocarbon liquid to measure the equivalent dew point. Since the dew point is functionally related to the vapor pressure of the water, a determination of the dew point will allow one to calculate the PPMW of water in the liquid by a Henry’s Law type analysis. A specific example of such an analysis is shown below. For liquids in which a Henry’s Law type analysis is applicable, the parts per million by weight of water in the organic liquid is equal to the partial pressure of water vapor times a constant: PPM W = K × PW

(a)

where, K is the Henry’s Law constant in the appropriate units, and the other variables are as defined on page A-11.

A-22


3/15/00

Henry’s Law Type Analysis (cont.) Also, the value of K is determined from the known water saturation concentration of the organic liquid at the measurement temperature: Saturation PPM W K = -------------------------------------------PS

(b)

For a mixture of organic liquids, an average saturation value can be calculated from the weight fractions and saturation values of the pure components as follows: n

Ave. C S =

∑ Xi ( CS )i

(c)

i=1

where, Xi is the weight fraction of the ith component, (CS)i is the saturation concentration (PPMW) of the ith component, and n is the total number of components. In conclusion, the Henry’s Law constant (K) is a constant of proportionality between the saturation concentration (CS) and the saturation vapor pressure (PS) of water, at the measurement temperature. In the General Case, the Henry’s Law constant varies with the measurement temperature, but there is a Special Case in which the Henry’s Law constant does not vary appreciably with the measurement temperature. This special case applies to saturated, straight-chain hydrocarbons such as pentane, hexane, heptane, etc.

A: General Case Determination of Moisture Content if CS is Known: The nomograph for liquids in Figure A-2 on page A-32 can be used to determine the moisture content in an organic liquid, if the following values are known:

•

the temperature of the liquid at the time of measurement

•

the saturation water concentration at the measurement temperature

•

the dew point, as measured with the Panametrics hygrometer


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A: General Case (cont.) Complete the following steps to determine the moisture content from the nomograph: 1. Using a straightedge on the two scales on the right of the figure, connect the known saturation concentration (PPMW) with the measurement temperature (°C). 2. Read the Henry’s Law constant (K) on the center scale. 3. Using a straightedge, connect above K value with the dew/frost point, as measured with the Panametrics’ hygrometer. 4. Read the moisture content (PPMW) where the straight edge crosses the moisture content scale. Empirical Determination of K and CS If the values of K and CS are not known, the Panametrics hygrometer can be used to determine these values. In fact, only one of the values is required to determine PPMW from the nomograph in Figure A-2 on page A-32. To perform such an analysis, proceed as follows: 1. Obtain a sample of the test solution with a known water content; or perform a Karl Fischer titration on a sample of the test stream to determine the PPMW of water. Note: The Karl Fischer analysis involves titrating the test sample against a special Karl Fischer reagent until an endpoint is reached. 2. Measure the dew point of the known sample with the Panametrics hygrometer. 3. Measure the temperature (°C) of the test solution. 4. Using a straightedge, connect the moisture content (PPMW) with the measured dew point, and read the K value on the center scale. 5. Using a straightedge, connect the above K value with the measured temperature (°C) of the test solution, and read the saturation concentration (PPMW). Note: Since the values of K and CS vary with temperature, the hygrometer measurement and the test sample analysis must be done at the same temperature. If the moisture probe temperature is expected to vary, the test should be performed at more than one temperature.

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B: Special Case As mentioned earlier, saturated straight-chain hydrocarbons represent a special case, where the Henry’s Law constant does not vary appreciably with temperature. In such cases, use the nomograph for liquids in Figure A-2 on page A-32 to complete the analysis. Determination of moisture content if the Henry’s Law constant (K) is known. 1. Using a straightedge, connect the known K value on the center scale with the dew/frost point, as measured with the Panametrics hygrometer. 2. Read moisture content (PPMW) where the straightedge crosses the scale on the left. Typical Problems 1. Find the moisture content in benzene, at an ambient temperature of 30°C, if a dew point of 0°C is measured with the Panametrics hygrometer. a. From the literature, it is found that CS for benzene at a temperature of 30°C is 870 PPMW. b. Using a straightedge on Figure A-2 on page A-32, connect the 870 PPMW saturation concentration with the 30°C ambient temperature and read the Henry’s Law Constant of 27.4 on the center scale. c. Using the straightedge, connect the above K value of 27.4 with the measured dew point of 0°C, and read the correct moisture content of 125 PPMW where the straightedge crosses the moisture content scale. 2. Find the moisture content in heptane, at an ambient temperature of 50°C, if a dew point of 3°C is measured with the Panametrics hygrometer. a. From the literature, it is found that CS for heptane at a temperature of 50°C is 480 PPMW. b. Using a straightedge on Figure A-2 on page A-32, connect the 480 PPMW saturation concentration with the 50°C ambient temperature and read the Henry’s Law Constant of 5.2 on the center scale. c. Using the straightedge, connect the above K value of 5.2 with the measured dew point of 3°C, and read the correct moisture content of 29 PPMW where the straightedge crosses the moisture content scale.


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B: Special Case (cont.) Note: If the saturation concentration at the desired ambient temperature can not be found for any of these special case hydrocarbons, the value at any other temperature may be used, because K is constant over a large temperature range. 3. Find the moisture content in hexane, at an ambient temperature of 10°C, if a dew point of 0°C is measured with the Panametrics hygrometer. a. From the literature, it is found that CS for hexane at a temperature of 20°C is 101 PPMW. b. Using a straightedge on Figure A-2 on page A-32, connect the 101 PPMW saturation concentration with the 20°C ambient temperature and read the Henry’s Law Constant of 5.75 on the center scale. c. Using the straightedge, connect the above K value of 5.75 with the measured dew point of 0°C, and read the correct moisture content of 26 PPMW where the straightedge crosses the moisture content scale. 4. Find the moisture content in an unknown organic liquid, at an ambient temperature of 50°C, if a dew point of 10°C is measured with the Panametrics hygrometer. a. Either perform a Karl Fischer analysis on a sample of the liquid or obtain a dry sample of the liquid. b. Either use the PPMW determined by the Karl Fischer analysis or add a known amount of water (i.e. 10 PPMW) to the dry sample. c. Measure the dew point of the known test sample with the Panametrics hygrometer. For purposes of this example, assume the measured dew point to be -10°C. d. Using a straightedge on the nomograph in Figure A-2 on page A-32, connect the known 10 PPMW moisture content with the measured dew point of -10°C, and read a K value of 5.1 on the center scale. e. Using the straightedge, connect the above K value of 5.1 with the measured 10°C dew point of the original liquid, and read the actual moisture content of 47 PPMW on the left scale.

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B: Special Case (cont.) Note: The saturation value at 50°C for this liquid could also have been determined by connecting the K value of 5.1 with the ambient temperature of 50°C and reading a value of 475 PPMW on the right scale. For many applications, a knowledge of the absolute moisture content of the liquid is not required. Either the dew point of the liquid or its percent saturation is the only value needed. For such applications, the saturation value for the liquid need not be known. The Panametrics hygrometer can be used directly to determine the dew point, and then the percent saturation can be calculated from the vapor pressures of water at the measured dew point and at the ambient temperature of the liquid: PW C % Saturation = ------ × 100 = -------- × 100 CS PS


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Empirical Calibrations

For those liquids in which a Henry’s Law type analysis is not applicable, the absolute moisture content is best determined by empirical calibration. A Henry’s Law type analysis is generally not applicable for the following classes of liquids:

•

liquids with a high saturation value (2% by weight of water or greater)

•

liquids, such as dioxane, that are completely miscible with water

•

liquids, such as isopropyl alcohol, that are conductive

For such liquids, measurements of the hygrometer dew point readings for solutions of various known water concentrations must be performed. Such a calibration can be conducted in either of two ways:

•

perform a Karl Fischer analysis on several unknown test samples of different water content

•

prepare a series of known test samples via the addition of water to a quantity of dry liquid

In the latter case, it is important to be sure that the solutions have reached equilibrium before proceeding with the dew point measurements. Note: Karl Fisher analysis is a method for measuring trace quantities of water by titrating the test sample against a special Karl Fischer reagent until a color change from yellow to brown (or a change in potential) indicates that the end point has been reached. Either of the empirical calibration techniques described above can be conducted using an apparatus equivalent to that shown in Figure A-3 on page A-33. The apparatus pictured can be used for both the Karl Fischer titrations of unknown test samples and the preparation of test samples with known moisture content. Procedures for both of these techniques are presented below.

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A. Instructions for Karl Fischer Analysis

To perform a Karl Fisher analysis, use the apparatus in Figure A-3 on page A-33 and complete the following steps: 1. Fill the glass bottle completely with the sample liquid. 2. Close both valves and turn on the magnetic stirrer. 3. Permit sufficient time for the entire test apparatus and the sample liquid to reach equilibrium with the ambient temperature. 4. Turn on the hygrometer and monitor the dew point reading. When a stable dew point reading indicates that equilibrium has been reached, record the reading. 5. Insert a syringe through the rubber septum and withdraw a fluid sample for Karl Fischer analysis. Record the actual moisture content of the sample. 6. Open the exhaust valve. 7. Open the inlet valve and increase the moisture content of the sample by bubbling wet N2 through the liquid (or decrease the moisture content by bubbling dry N2 through the liquid). 8. When the hygrometer reading indicates the approximate moisture content expected, close both valves. 9. Repeat steps 3-8 until samples with several different moisture contents have been analyzed.


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B. Instructions for Preparing Known Samples

Note: This procedure is only for liquids that are highly miscible with water. Excessive equilibrium times would be required with less miscible liquids. To prepare samples of known moisture content, use the apparatus in Figure A-3 on page A-33 and complete the following steps: 1. Weigh the dry, empty apparatus. 2. Fill the glass bottle with the sample liquid. 3. Open both valves and turn on the magnetic stirrer. 4. While monitoring the dew point reading with the hygrometer, bubble dry N2 through the liquid until the dew point stabilizes at some minimum value. 5. Turn off the N2 supply and close both valves. 6. Weigh the apparatus, including the liquid, and calculate the sample weight by subtracting the step 1 weight from this weight. 7. Insert a syringe through the rubber septum and add a known weight of H2O to the sample. Continue stirring until the water is completely dissolved in the liquid. 8. Record the dew point indicated by the hygrometer and calculate the moisture content as follows: 6 weight of water PPM W = -------------------------------------------------- × 10 total weight of liquid

9. Repeat steps 6-8 until samples with several different moisture contents have been analyzed. Note: The accuracy of this technique can be checked at any point by withdrawing a sample and performing a Karl Fischer titration. Be aware that this will change the total liquid weight in calculating the next point.

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C. Additional Notes for Liquid Applications

In addition to the topics already discussed, the following general application notes pertain to the use of Panametrics moisture probes in liquid applications: 1. All M Series Aluminum Oxide Moisture Sensors can be used in either the gas phase or the liquid phase. However, for the detection of trace amounts of water in conductive liquids (for which an empirical calibration is required), the M2 Sensor is recommended. Since a background signal is caused by the conductivity of the liquid between the sensor lead wires, use of the M2 Sensor (which has the shortest lead wires) will result in the best sensitivity. 2. The calibration data supplied with Panametrics Moisture Probes is applicable to both liquid phase (for those liquids in which a Henry’s Law analysis is applicable) and gas phase applications. 3. As indicated in Table A-3 on page A-19, the flow rate of the liquid is limited to a maximum of 10 cm/sec. 4. Possible probe malfunctions and their remedies are discussed in the Troubleshooting chapter of this manual.


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Figure A-2: Moisture Content Nomograph for Liquids

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Stainless Steel Tubing (soft soldered to cover)

3/4-26 THD Female (soft soldered to cover)

M2 Probe Rubber Septum

Exhaust Soft Solder

Metal Cover with Teflon Washer

Liquid Glass Bottle

Magnetic Stirrer Bar

Magnetic Stirrer

Figure A-3: Moisture Content Test Apparatus


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Solids Applications A. In-Line Measurements Panametrics moisture probes may be installed in-line to continuously monitor the drying process of a solid. Install one sensor at the process system inlet to monitor the moisture content of the drying gas and install a second sensor at the process system outlet to monitor the moisture content of the discharged gas. When the two sensors read the same (or close to the same) dew point, the drying process is complete. For example, a system of this type has been used successfully to monitor the drying of photographic film. If one wishes to measure the absolute moisture content of the solid at any time during such a process, then an empirical calibration is required: 1. At a particular set of operating conditions (i.e. flow rate, temperature and pressure), the hygrometer dew point reading can be calibrated against solids samples with known moisture contents. 2. Assuming the operating conditions are relatively constant, the hygrometer dew point reading can be noted and a solids sample withdrawn for laboratory analysis. 3. Repeat this procedure until a calibration curve over the desired moisture content range has been developed. Once such a curve has been developed, the hygrometer can then be used to continuously monitor the moisture content of the solid (as long as operating conditions are relatively constant).

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B. Laboratory Procedures

If in-line measurements are not practical, then there are two possible laboratory procedures: 1. The unique ability of the Panametrics sensor to determine the moisture content of a liquid can be used as follows: a. Using the apparatus shown in Figure A-3 on page A-33, dissolve a known amount of the solids sample in a suitable hydrocarbon liquid. b. The measured increase in the moisture content of the hydrocarbon liquid can then be used to calculate the moisture content of the sample. c. For best results, the hydrocarbon liquid used above should be pre-dried to a moisture content that is insignificant compared to the moisture content of the sample. Note: Since the addition of the solid may significantly change the saturation value for the solvent, published values should not be used. Instead, an empirical calibration, as discussed in the previous section, should be used. d. A dew point of -110°C, which can correspond to a moisture content of 10-6 PPMW or less, represents the lower limit of sensor sensitivity. The maximum measurable moisture content depends to a great extent on the liquid itself. Generally, the sensor becomes insensitive to moisture contents in excess of 1% by weight. 2. An alternative technique involves driving the moisture from the solids sample by heating: a. The evaporated moisture is directed into a chamber of known volume, which contains a calibrated moisture sensor. b. Convert the measured dew point of the chamber into a water vapor pressure, as discussed earlier in this appendix. From the known volume of the chamber and the measured vapor pressure (dew point) of the water, the number of moles of water in the chamber can be calculated and related to the percent by weight of water in the test sample. c. Although this technique is somewhat tedious, it can be used successfully. An empirical calibration of the procedure may be performed by using hydrated solids of known moisture content for test samples.


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Appendix B

Outline and Dimension Drawing System 580 Outline and Installation (Dwg. 712-200). . . . . . . . . . B-1

Figure B-1: System 580 Outline and Installation (Dwg. 712-200)

12/19/00

B-1

PANAMETRICS WORLDWIDE OFFICES PANAMETRICS

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MAIN OFFICES:

INTERNATIONAL OFFICES:

USA Panametrics, Inc. 221 Crescent St., Suite 1 Waltham, MA 02453-3497 USA Telephone 781-899-2719 Toll-Free 800-833-9438 Fax 781-894-8582 E-Mail [email protected] Web Site www.panametrics.com ISO 9001 Certified

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10/30/00

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ISO 9001 CERTIFIED

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Panamentrics Hygrometer / Dew Point Meter

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