s SIMATIC Product Information October 2007
Expansion Module EM 231 Analog Input Thermocouple, 8 Inputs This Product Information contains information about the new EM 231 Analog Input Thermocouple, 8 Inputs expansion module. For more technical information about this module, refer to the S7-200 Programmable Controller System Manual. This manual can be viewed on the STEP 7-Micro/WIN documentation CD, on the Internet at http://www.siemens.com/S7-200, or ordered (order number 6ES7 298-8FA24-8BH0). Description Order Number Dimensions (W x H x D) Weight Dissipation VDC requirements +5 VDC + 24 V Number of inputs Removable connector Isolation Field to logic Field to 24 VDC 24 VDC to logic Common mode input range (input channel to input channel) Common mode rejection Input type Input ranges1 Input resolution Temperature Voltage Measuring Principle Module update time: All channels Wire length Wire loop resistance Suppression of interference Data word format Input impedance Maximum input voltage Input filter attenuation Basic error Repeatability Cold junction error LED indicator 24 VDC supply voltage range 1
EM 231 Analog Input Thermocouple, 8 Inputs 6ES7 231-7PF22-0XA0 71.2 mm x 80 mm x 62 mm 210 g 1.8 W 87 mA 60 mA 8 no 500 VAC 500 VAC 500 VAC 120 VAC > 120 dB at 120 VAC Floating TC TC types (select one per module) S, T, R, E, N, K, J Voltage range: +/- 80 mV 0.1° C/0.1° F 15 bits plus sign Sigma-delta 810 mS 100 meters to sensor max. 100 Ω max. 80 dB at 50 Hz/60 Hz/400 Hz Voltage -27648 to +27648 ≥ 1 MΩ 30 VDC -3 db at 21 kHz 0.1% FS (voltage) 0.05% FS ± 1.5° C 2 (External 24 VDC present and System Fail) 20.4 to 28.8 VDC (Class 2, Limited Power, or sensor power from PLC)
The input range selection (temperature, voltage on resistance) applies to all channels on the module.
6ES7 231-7PF22-0XA0 Copyright 2007 by Siemens Energy and Automation A5E01151572-01
EM 231 Analog Input Thermocouple, 8 Inputs (6ES7 231-7PF22-0XA0) + -
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A+ A- B+ B- C+ C- D+ D- E+ E- F+ FEM 231 AI 8
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Configuration
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The EM 231 Thermocouple module provides a convenient, isolated interface for the S7-200 family to seven thermocouple types: J, K, E, N, S, T, and R. It allows the S7-200 to connect to low level analog signals, ±80mV range. All thermocouples attached to the module must be of the same type.
Compatibility The Thermocouple modules are designed to work with the CPU 222, CPU 224, CPU 224XP and CPU 226. Note The Thermocouple modules are designed to give maximum performance when installed in a stable temperature environment. The EM 231 Thermocouple module has special cold junction compensation circuitry that measures the temperature at the module connectors and makes necessary changes to the measurement to compensate for temperature differences between the reference temperature and the temperature at the module. If the ambient temperature is changing rapidly in the area where the EM 231 Thermocouple module is installed, additional errors are introduced. To achieve maximum accuracy and repeatability, Siemens recommends that the S7-200 Thermocouple module be mounted in locations that have stable ambient temperature.
Noise Immunity Use shielded wires for best noise immunity. If a thermocouple input channel is not used, short the unused channel inputs, or connect them in parallel to another channel.
Configuring the EM 231 Thermocouple Module Configuration DIP switches located on the bottom of the module allow you to select the thermocouple type, open wire detect, temperature scale, and cold junction compensation. For the DIP switch settings to take effect, you need to power cycle the PLC and/or the user 24V power supply. DIP switch 4 is reserved for future use. Set DIP switch 4 to the 0 (down or off) position. The table below shows other DIP switch settings.
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6ES7 231-7PF22-0XA0 Product Information EM 231 Analog Input Thermocouple, 8 Inputs Module A5E01151572-01
Configuring the Thermocouple Dip Switches Switch 1,2,3
Thermocouple Type
SW1,2,3
2 3 4* 5
1
6 7 8
Setting
Description
J (Default)
000
K
001
Switches 1 to 3 select the thermocouple type (or mV operation) for all channels on the module. For example, for an E type, thermocouple SW1 = 0, SW2 = 1, SW3 = 1.
Configuration
T
010
1 - On 0 - Off
E
011
R
100
S
101
N
110
*Set DIP switch 4 to the 0 (down) position.
Switch 5
SW5
± -80mV
111
Open Wire Detect Direction
Setting
Description
Upscale (+3276.7 degrees)
0
0 indicates positive on open wire
Downscale (+3276.8 degrees)
1
Open Wire Detect Enable
Setting
Description
Enable
0
Disable
1
Open wire detection is performed by injecting a 25 µA current onto the input terminals. The open wire enable switch enables or disables the current source. The open wire range check is always performed, even when the current source is disabled. The EM 231 Thermocouple module detects open wire if the input signal exceeds approximately ±200mV. When an open wire is detected, the module reading is set to the value selected by the Open Wire Detect.
Temperature Scale
Setting
Description
Celsius ( °C)
0
Fahrenheit (°F)
1
The EM 231 Thermocouple module can report temperatures in Celsius or Fahrenheit. The Celsiius to Fahrenheit conversion is performed inside the module.
Cold Junction
Setting
Cold junction compensation enabled
0
1 indicates negative on open wire
Configuration 3 4
1 2
5 6
1 - On 0 - Off
7 8
Switch 6
SW6
Configuration 3 4
1 2
5 6
1 - On 0 - Off
7 8
Switch 7 SW7 Configuration 1 2
3 4
5
6 7
8
1 - On 0 - Off
Switch 8 SW8 Configuration 1
2 3
4
5 6 7 8
1 - On 0 - Off
Cold junction compensation disabled
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6ES7 231-7PF22-0XA0 Product Information EM 231 Analog Input Thermocouple, 8 Inputs Module A5E01151572-01
Description Cold junction compensation must be enabled when you are using thermocouples. If cold junction compensation is not enabled, the conversions from the module will be in error because of the voltage that is created when the thermocouple wire is connected to the module connector. Cold junction is automatically disabled when you select the ±80 mV range.
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Note •
The open wire current source could interfere with signals from some low level sources such as thermocouple simulators.
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Input voltages exceeding approximately ± 200mV will trigger open wire detection even when the open wire current source is disabled.
Note •
Module error could exceed specifications while the ambient temperature is changing.
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Exceeding the module ambient temperature range specification could cause the module cold junction to be in error.
Using The Thermocouple: Status Indicators The EM 231 Thermocouple module provides the PLC with data words that indicate temperatures or error conditions. Status bits indicate range error and user supply/module failure. LEDs indicate the status of the module. Your program should have logic to detect error conditions and respond appropriately for the application. The table below shows the EM 231 Thermocouple status indicators. Error Condition
Channel Data
No errors 24 V missing Open wire and current source ennabled Out of range input Diagnostic error3
Conversion data 32766 -32768/32767 -32768/32767 0000
1
SF LED Red OFF OFF BLINK BLINK ON
24 V LED Green ON OFF ON ON OFF
Range Status Bit1 0 0 1 1 0
24 VDC User Power Bad2 0 1 0 0 note3
2
Range status bit is bit 3 in module error register byte (SMB9 for Module 1, SMB11 for Mudule 2, etc.) User Power Bad status bit is bit 2 in module error register byte (SMB 9, SMB11, etc.) Refer to the S7-200 Programmable Controller System Manual, Appendix A for more information
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Diagnostic errors cause a module configuration error. The User Power Bad status bit may or may not be set before the module configuration error.
Note The channel data format is two's complement, 16-bit words. Temperature is presented in 0.1 degree units. For example, if the measured temperature is 100.2 degrees, the reported data is 1002. Voltage data are scaled to 27648. For example, -60.0mV is reported as -20736 (= -60mV/80mV * 27648). All channels are updated every 810 milliseconds if the PLC has read the data. If the PLC does not read the data within one update time, the module reports old data until the next module update after the PLC read. To keep channel data current, it is recommended that the PLC program read data at least as often as the module update rate. Note When you are using the EM 231 Thermocouple module, you should disable analog filtering in the PLC. Analog filtering can prevent error conditions from being detected in a timely manner.
Temperature Ranges for Thermocouple Types For information about the temperature ranges (Celsius and Fahrenheit) and accuracy for Thermocouple Types, please refer to the S7-200 Programmable Controller System Manual, Appendix A.
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6ES7 231-7PF22-0XA0 Product Information EM 231 Analog Input Thermocouple, 8 Inputs Module A5E01151572-01
