PRESSURE CONTROL TRAINER
Product Code 314, 314A
Instructi Inst ruction on manual manu al
Contents 1 Description 2 Specifications 3 Installation requirements 4 Installation Commissioning
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5 Troubleshooting 6 Components used 7 Packing slip 8 Warranty
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9 Theory 10 Software 11 Experiments 12 Components’ manuals
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Apex Innovations
Description Pressure control trainer is designed for teaching the basic pressure control principles. Pressure transmitter senses the pressure inside pressure tank and transmits the signals to interfacing unit/control module. The output of interfacing unit/control module is connected to I/P converter. A pneumatic control valve adjusts compressed air flow from the tank outlet. The process parameter (pressure) is controlled through computer or µp controller by manipulating the control valve. These units along with necessary piping are fitted on support housing designed for tabletop mounting. Product No. 314 is DDC (Direct Digital Control) model, in which PID control action is through software by computer. Product No. 314A is SCADA (Supervisory Control And Data Acquisition) model, in which PID controlling is by digital indicating controller. The computer is connected to controller through communication port in supervisory mode.
I/P Converter Air Regulator
Air Supply Supply Pressure
Signal Pressure
Pressure Controller
Set Point Tank Pressure Vent Valve
Pressure Transmitter
N
N
Air Process Tank Supply
Control Valve
Specifications Product Product code Type of control Control unit Communication Pressure Transmitter I/P converter Control valve Process tank Air filter regulator Pressure gauge Overall dimensions Optional
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Pressure control trainer 314 314A DDC SCADA Interfacing unit with Control module with digital ADC/DAC conversion indicating controller RS232 Type Two wire, Range 0–5 bar, Output 4–20 mA Input 4-20mA, Output 3-15 psig Type: Pneumatic; Size: 1/4", Input: 3–15 psig, Air to close, Characteristics: linear Pressure vessel, MS Range 0-2.5 kg/cm 2 Range 0-2.5 kg/cm 2(1No), Range 0-7 kg/cm 2(2Nos) 475Wx430Dx440H mm Compressor
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Product 314 Shipping details Gross volume 0.10m3, Gross weight 43kg, Net weight 18kg Product 314A Shipping details Gross volume 0.10m3, Gross weight 43kg, Net weight 18kg
Installation Installation requirements Electric supply Provide 230 +/- 10 VAC, 50 Hz, single phase electric supply with proper earthing. (Neutral – Earth voltage less than 5 VAC) • 5A, three pin socket with switch (1 No.) • 15A, three pin socket with switch for compressor (if ordered) Air supply
Clean, oil and moisture free air, pressure 6 Bar, Air consumption 7.0 m3 /hr Computer IBM compatible with standard configuration Support table Size: 800Wx800Dx750H in mm.
Installation Commissioning Installation • Unpack the box(es) received and ensure that all material is received as per packing slip (provided in instruction manual). In case of short supply or breakage contact Apex Innovations / your supplier for further action. Place the set up on table. Connect air inlet pipe to process tank and regulator. Pierce hole on the pressure gauges with pin or needle. Connect the cables from interfacing unit/control module to the set up. Connect the interfacing unit/control module with computer to "COM" port.
• • • • • Commissioning • Connect electric supply to interfacing unit/control module. • Ensure the regulator is full open by rotating anticlockwise. Switch on the
compressor. • Adjust the air filter regulator to set supply air pressure at 25 psig. • Set the interfacing unit/digital indicating controller to manual mode by pressing the A/M key. • Increase output of interfacing unit/digital-indicating controller from 0 to 100% in steps of 25%. Check the pressure on pressure gauge at the output of the I/P converter is varying from 3-15 psig and ensure that control valve operates from full open to fully close position. • Switch on the computer and install the software. • Execute the software and ensure correct signals are displayed on computer. NOTE: Maintain the pressure of the process tank below 6 kg/cm2.
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Apex Innovations
Troubleshooting Note: For component specific problems refer components’ manual Problems Possible causes / remedies Control valve does • Valve diaphragm breakage • Faulty I/P converter not operate • No output from Interfacing unit I/P converter does • Insufficient supply air pressure • Faulty electrical input signal not work • Clogged orifice No communication • Improper COM port connection • Computer COM port not working with computer No full screen display • Ensure screen display settings are at 800 x 600 pixels. • On desktop right click mouse button & click properties option. In General option- Settings- set font size- small fonts
Components used Components
Details
Control unit (For 314)
Make Cuadra, Model AX-401, Input 4-20mA (1No), Output 4-20mA (1No), Communication RS232 Make Cuadra, Model AX-403, Input 4-20mA, with RS485 to RS232 converter Make Keller, Model 21S, Output 4-20mA(2 wire), Supply 24VDC, Range 0-5 bar, Process conn. 1/4"BSP(male), Accuracy +/-1% Make Yokogawa, Model UT320-01 (with RS 485 communication) Make Control air inc, Type T500-AC, Input 4-20 mA DC, output 3-15 psig, end connection 1/4 NPT Make Apex, Model MX-101, Size ½”x1/4”, Body SS316, Trim SS316, Travel 10mm, Spring range 3-15 psig, Characteristics linear, Action air to close, Valve coefficient 0.04 Make Airmatic, Model MB10-021-VD-PAP, Range 0-2 Kg/cm^2, Type Relieving Make Waaree, Code: PW2.5GNNNS9 0-2.5 1/4"B, Dia.2.5", Gly. filled, Brass internals, S.S. casing, Range 0-2.5 Kg/cm2, 1/4"BSP (M) back connection Make Waaree, Code: PW2.5GNNNS9 0-7 1/4"B, Dia.2.5", Gly. filled, Brass internals, S.S. casing, Range 0-7 Kg/cm 2, 1/4"BSP (M) back connection
Control unit (For 314A) Pressure Transmitter
Digital indicating controller (For 314A) I/P converter Control valve
Air filter regulator Pressure gauge
Pressure gauge
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Apex Innovations
Packing slip Product No.314 Box No.1/1 1 2 3 4
Size W500xD450xH425 mm; Volume:0.10m3 Set up assembly(Piping set & Male stud 2nos) Communication cable Tool kit Set of instruction manuals consisting of: Instruction manual CD (Apex) I/P converter manual (ControlAir)
Gross weight: 43 kg Net weight: 18 kg 1 No 1 No 1 No 1 No
Product No.314A Box No.1/1 1 2 3 4
Size W500xD450xH425 mm; Volume:0.10m3 Set up assembly(Piping set & Male stud 2nos) Communication cable Tool kit Set of instruction manuals consisting of: Instruction manual CD (Apex) I/P converter manual (ControlAir) User’s manual UT320 (Yokogawa) User’s manual reference CD CD (Yokogawa) (Yokogawa)
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Gross weight: 43 kg Net weight: 18 kg 1 No 1 No 1 No 1 No
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Warranty This product is warranted for a period of 12 months from the date of supply against manufacturing defects. You shall inform us in writing any defect in the system noticed during the warranty period. On receipt of your written notice, Apex at its option either repairs or replaces the product if proved to be defective as stated above. You shall not return any part of the system to us before receiving our confirmation to this effect. The foregoing warranty shall not apply to defects resulting from: Buyer/ User shall not have subjected the system to unauthorized alterations/ additions/ modifications. Unauthorized use of external software/ interfacing. Unauthorized maintenance by third party not authorized by Apex. Improper site utilities and/or maintenance. We do not take any responsibility for accidental injuries caused while working with the set up.
Apex Innovations Pvt. Ltd. E9/1, MIDC, Kupwad, Sangli-416436 (Maharashtra) India Telefax:0233-2644098, Telefax:0233-2644098, 2644398 Email:
[email protected] Web: www.apexinnovations-ind.com
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Theory COMPUTER CONTROL TECHNIQUES Direct Digital Control (DDC) The method of process control described by the term DDC (Direct Digital Control) applies to those cases in which digital dig ital logic circuits or a computer are an integral part of the loop. The software program defines all the control function, setpoint and deviation about the nominal. Direct digital control has the capacity to control multivariable processes with interaction between elements. This is most economically developed process control system basically used for laboratory scale application. In this system the process signals are transmitted to computer through interfacing unit. Along with data acquisition the software has capability of controlling the process. Computer Load Comparator PID Control
Process
Control Element
Controlled Variable
Set Point
Measured Variable
Measurement
Supervisory Control And Data Acquisition (SCADA) In SCADA systems process signals are transmitted the local controller. The controller is in communication with central computer. The software performs the function of data acquisition, display and analysis. The controller settings can be changed from computer. The computer has a supervisory role as controlling is done by local controller. Digital Indicating Controller Load Comparator PID Control
Control Element
Process
Controlled Variable
Set Point
Measured Variable
Computer
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PROCESS CONTROLLER In automatic controlled process the parameter to be controlled is measured and compared with the set point by process controller. The difference between the measured signal and the set point is error. The controller performs on-line calculations based on error and other setting parameters and generates an output signal. The output signal drives the final control elements like control valve or a damper to control the process to the set point. Reference Signal
Error
Controller
Controller Output
Process Parametert
Feedback Signal
Block Digaram of Typical Controller
On/Off controllers
Dead Band
e u l a V t e S
Time
On-Off Controller
A special case of proportional control is On-Off control. If the proportional band of the controller is made very low (=0) the controller out put will move from one extreme position to other for slight deviation of process value from the set point. This very sensitive action is called On-Off control because final control element is either open (On) or close (Off) i.e. operates like a switch. These are the simplest controllers. These controllers incorporate a dead band to keep the output from cycling rapidly between on and off. The controller will not turn on or off until the error signal moves out of the dead band. The process variable controlled by an on/off controller always cycles back and forth about the set point as shown in the fig. Dark line and dotted line shows process parameter and reference values respectively. Hysteresis is a value set in the vicinity of on-off operating point. Upper hysteresis is value or band in which process value is allowed to operate above the set point and lower hysteresis is value or band in which process value is allowed to operate below the set point.
Proportional (P) controllers
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Offset
e u l a V r e t e m a r a P
Time
Propertional Controller
In proportional controller the control algorithm generates a linear control output proportional to deviation. In proportional action the amount of change in the measured value (or deviation) is expressed in percent of span that is required to cause the control output to change from 0 to 100 % is called the proportional band. The controller output is given by:
OP = b +
100 PB
⋅e
Where, OP is the output, PB is proportional band in %, b is the bias value, and e is the error signal. If there is no biasing, output OP will become zero when error is zero. Hence bias value decides the value of output when error is zero. The proportional controllers usually show some difference between the set point and process variable called offset. The offset can be reduced by decreasing proportional band or by readjusting the bias. With decrease in proportional band the process becomes oscillatory. There are two types of controller actions: 1) Increase-increase in which output increases as measurement increases. (error e = measurement – set point) 2) Increase-decrease in which output decreases as measurement increases. (error e = set point –measurement)
Proportional- Integral (PI) controllers
e l a V r e t e m a r a P
Time
Propertional - Integral Controller
The offset in proportional proportional controller can be overcome by adding adding integral action. The control algorithm that applies changes in output as long as deviation exits, so as to bring the deviation to zero, is called integral action. Output of proportional-Integral controllers is given by:
OP = b +
1 × e + ∫ e ⋅ dt PB Ti
100
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Where OP is the output, b is the bias, PB is the proportional band in %, e is the error signal, Ti is integral time; this is the time required to repeat proportional action.
Proportional-Derivative (PD) controller This mode of control is described by t he relationship
OP = b +
100 de e + Td ⋅ PB dt
Where OP is the output, b is the bias, PB is the proportional band in %, e is the error signal, Td is derivative time. Larger the derivative time larger is the action. Smaller is the proportional band the larger is the derivative action. In order to achieve faster response and more stable operation in slow processes derivative action is added to apply an output component proportional to the rate of change of input (error). Derivative action is used with P action or PI action.
Proportional–Integral–Derivative (PID) controllers PID controllers are used for controlling almost all process variables like temperature, flow, level, pressure etc. in a continuous or batch process. The output of a PID controller is given by:
OP = b +
100 1 de e ⋅ dt + Td ⋅ e + PB Ti dt
∫
Where OP is the output, b is the bias, PB is the proportional band in %, e is the error signal, Ti is the integral time and Td is derivative time. Selection of proportional band, integral time and derivative time to achieve desired process response to load changes is called tuning of controller.
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CONTROLLER TUNING The three-mode controller (PID) is the most common feedback controller used in industrial control. The method of determination of the optimum mode gains, depending on the nature and complexity of the process is known as loop tuning. tuning. The three parameters should be selected to meet a set of defined goals. These goals typically require a plant response with minimum steady state error, insensitivity to load disturbances and an acceptable transient response to set point changes and disturbances. In practice the choice of proportional band, integral time and derivative time is a compromise between the set point tracking and disturbances. If a mathematical model of the process is known, selecting the controller parameters is relatively simple. But in many industrial applications, a reliable mathematical model is not available or it is difficult to determine. So empirical rules are developed for PID tuning which do not require mathematical model. A widely used set of rules is proposed by Ziegler- Nichols by open loop method and close loop method in 1942.
Open loop method (Process reaction curve metood) In open loop method the process is assumed to be model of first order. The step response i.e. process reaction curve, allows to obtain the approximate values of P, I and D parameters. With the feedback loop open, a step response is applied to manipulated variable and the values of P, I and D are estimated.
0 4
0 e 3 l b a i r a V d 0 e 2 l l o r t n o C 0 1
0
Y
L
X
10
20
30 Time
40
Open loop response for input step change (Process reaction curve) Where Slope R: Slope of line drawn tangent to the point of inflection.
R
=
%ChangeinVariable time(min)
=
Y X
Dead time L: Time between the step change and the point where tangent line crosses the initial value of the controlled variable (in min.) ∆P = Step change applied in %
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Using these parameters, the empirical equations are used to predict the controller settings for a decay ratio of 1/4. For P, PI and PID controller the parameters are calculated as follows. Mode Proportional band Integral time Derivative time (in %) (in Min) (in Min) P 100RL/∆P P+I 110RL/ ∆P L/0.3 P+I+D L/0.5 0.5L 83RL/ ∆P
Closed loop method (Ultimate gain method) This method is also called as ultimate gain method. The term ultimate was attached to this method because its use requires the determination of the ultimate proportional band and ultimate period. The ultimate proportional band, PBu is the minimum allowable value of proportional band (for a controller with only proportional mode) for which the system continuously oscillates at constant amplitude. The ultimate period, Tu is the period of response with the proportional band set to its ultimate value. To determine the ultimate proportional band and ultimate period the proportional band of the controller (with all integral and derivative action turned off) is gradually reduced until the process cycles continuously. t u t u O
Tu
Continuous Cycli Cycling ng
Time
Response curve for ultimate gain and period The process is placed in the closed loop with a proportional controller. The Proportional band is decreased until the process goes to continuous oscillations. The corresponding value of proportional band is called as ultimate proportional band PBu and the period of oscillation is called the ultimate period Tu. The PID controller parameters are selected from the following table. Mode P P+I P+I+D
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Proportional 2 PBu 2.2 PBu 1.65 PBu
Integral
Derivative
Tu/1.2 0.5 Tu
Tu/8.0
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FREQUENCY RESPONSE ANALYSIS Laplace transform techniques are used to express mathematical models in terms of transfer functions in order to calculate transient response. An alternative way to interpret the transfer function model, refereed to as the complex transfer function or the frequency response. It shows how the output response characteristics depend upon the frequency of the input signal. This is the origin of the term, frequency response.
Stability analysis by using bode plots Frequency response may be plotted in three ways: i. The rectangular plot with amplitude ratio ratio verses frequency frequency and phase lag verses frequency. ii. A polar plot with magnitude magnitude and phase shown shown in vector form with frequency as a parameter. iii. A phase margin plot with magnitude shown verses a function of phase with frequency as a parameter. If the system is linear, the output signal for sine wave input must be a sine wave having the same frequency as the input. Assume that the input to the first order system is suddenly switched from a constant input to a sine wave input. The initial slope of the sine wave input signal may be approximated by a ramp input or even exponential input. If the input frequency is very low, period of the sine wave will be very long. Stated in another way, period is very much larger than the system time constant. Under this condition the output will have sufficient time to approach the condition, which is nearly in equilibrium with the input signal. Thus, at low frequencies both magnitude and phase angle of the output signal will be close to magnitude and phase angle of the input signal. However as the frequency increases period decreases, and the system does not have sufficient time to achieve the equilibrium status between input and output. Under these conditions output magnitude will decrease, and output phase angle will fall behind or lag the input phase angle. Thus it is evident that any solution must show a decrease in ratio of output to input magnitude as frequency increases. Magnitude and phase angle calculation: Let, M Magnitude ratio A1 Input amplitude (%) A2 Output amplitude (%) φ Phase angle (degrees) x lag (seconds) T Period (seconds) f frequency (cycles per seconds) = 1/T. Then, M = A2/A1 φ = (x (x /T) x 360
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u p t u O
u p n I
T X A2
A1
Frequency Response
Time
BODE diagram In Bode diagram the magnitude ratio verses frequency is plotted on log-log co ordinates and the phase angle verses frequency on semi-log coordinates. 0 1
M o 1 i t a R e d u . t i 1 n 0 g a M
Log Scale 0.01
0.1
1 10 Frequency
0
g 0 e 9 D e l g n A 0 e 8 s 1 a h P
0.01
0.1 Frequency
1
10
Bode Diagram
Stability criteria • A system is stable if the phase lag is less than 180 Deg. at the frequency for which the gain is unity (one). • A system is stable if the gain is less than one (unity) at the frequency for which the phase lag is 180 Deg.
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Software Windows based control software package provided is designed to fulfill basic pressure control study. It helps in understanding PID logic and combinations of different control actions.
Installing the software package • Switch on computer. Ensure display settings are 800x600 pixel and font size is
• • •
small fonts. Create separate directory and copy software files & instruction manual from the CD supplied with the product. Create a short cut on the desktop d esktop for the executable file. Click on the icon created on the desktop to execute the software.
Getting started Real time data access For DDC model: Select Data Access | Interface. Select Start . For SCADA model: Select Data access| Microprocessor| COM1 or COM2 as the case may be. Select Start . Studying data logging from file Select Data Access, Access , control and control and then Data File. File. By default data file for PID control is opened using a dialog box to select file name.
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Menus
Data Access This menu gives three options to start the experiments. Interface/ microprocessor microprocessor Selecting this option, accesses real-time data from field using interfacing unit/control module. Data File This option accesses data from stored file. Results and data of experiment conducted are observed. A file open window lets you open t he desired file. There is a predefined file extension. While opening the file user need not know the file extensions, software lists the files related to the experiment. User can see the data, stored in file, in the form of tables as well as graphs. Simulator This option accesses data from PID simulation logic. The user has to enter process value and set point. With different values of the PID parameters, user can observe the change in the controller output to the error produced. Changing set point produces error to the controller. Control This menu gives two options to select control mode. Closed loop: This option enables, close loop control action. In this action, controller calculates output to the process based on process parameters automatically. Open loop: This option enables the open loop control action. Selecting this option control loop is opened i.e. output to the controller can be changed manually. Controller does not work in open loop. Controller
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It provides four different modes of controller for controlling the process variable. Each controller is provided with separate controller setting facility. Select respective controller and set the desired control parameters. Various types of controller are mentioned below. On Off: This option allows selecting on-off controller. P: This option allows selecting Proportional controller. PD: This option allows selecting Proportional + Derivative controller. PID: This option allows selecting Proportional + Integral + Derivative controller. Note: PI controller can be set in PID controller option by keeping the derivative time equal to zero. Function Generator This option is used to apply the dynamic input to the process. The dynamic (sinusoidal) wave form is applied to the process. During the close loop operation the function is applied to the set point, in open loop operation the function is applied to output. On: Enables the function generator selection. Amplitude and period is entered to the wave. Off: Stops the function generator. Log On: Enables the data logging. Off: Stops the data logging. Print Use Print for printing graphs and data table from Data File. Graph: To print graph click pause when you reach at the desired data plotting. Select print then graph to get a window for printer selection. Select a printer and click OK to print selected graph. Again clicking the run switch will start the plotting of the remaining data. Tables: Data table for PID values is available. Select any option for printing. PID Tune contains tuning values set during experiment. Select Print then Table with option to get a window for printer selection. Select a printer and click OK to print selected graph. Start Click Start to activate selected Data Access option. Stop Click Stop to deactivate selected Data Access op tion. Shutdown Select Shutdown for closing software application.
Basic functions ON- OFF Control On - off control compares set point and process value and gives output an O N or OFF signal according to the positive or negative deviation. Hysteresis: A value set in the vicinity of the on/off operating point is referred to as the hysteresis. Upper hysteresis and lower hysteresis can be set. To set hysteresis values Tune button is provided on the screen. PID control PID controller compares set point and process value. It gives output by calculations based on PID logic. To set PID values Tune button is provided. Set values for P, I, D; Output high, high, Output low and Action. Action. Use Download for applying new values for controller. P Proportional band value for this controller is denoted by P. Set proportional band values. 26-03-2005
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I Integral time for controller denoted by I and it is applied in seconds. D Derivative time for controller denoted by D and it is applied in i n seconds. Bias Bias is the value of normal output of controller at zero error. This option appears if Proportional controller or Proportional + Derivative controller is selected.. Output High Higher bound of the controller output Output Low Lower bound of the controller output Action In INC-INC mode, increase in process variable increases controller output & viseversa. For INC-DEC mode, increase in process variable decreases controller output & vise-versa. Download Use Download for applying new values for controller. PID Tune screen
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Switching between auto and manual You can use a button, marked Auto (by default) for switching between the two modes. Click to change the mode from Auto to Manual. Manual. Click again to change the mode from Manual to Auto. Auto . In Auto mode output of process is controlled by software and in Manual user controls mode output of process. Pause or Run trend graph in offline In Data File, Data access mode a button marked Pause (by default) is used to stop the trend graphs. To run the trend graph click RUN display. Stored data screen
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Setting parameters for digital indicating controller (For product no. 314A ) [Refer instruction manual operation]. Operating parameter table LED Display Value Press ENT for 3 sec.
of the controller (separately provided) for controller Setup parameter table
Input output related
LED Display Value LED Display Value OP.PA (press FUnC (press up/down): up/down): I/o (press ENT) STUP (press ENT) Pyd 0 I/O FUnC In 41 SPH (**) 100.0 RH 5.000 SPL (**) 0.1 RL 1.000 AL1 1 SdP 1 AL2 2 SH 100.0 AL3 1 SL 0.0 Hy1 0.5 bSL 1 Hy2 0.5 Ot 2 Hy3 0.5 rEt 3 dY1 (**) 0.00 rtH (**) 100 dY2 (**) 0.00 rtL (**) 0 dY3 (**) 0.00 diS 1 Ct 30 C.S1 oFF Po 0.0 C.S2 oFF C.md 0 C.S3 oFF Zon oFF C.S4 oFF Ar Auto LoCK oFF tmU 1 P.SL 0 bPS 4 PrI 0 StP 1 dLn 8 Adr 1 rP.t 0 test 0
oP.PA LL (**) oFF A1 100.0 A2 0.0 A3 100.0 At oFF SC oFF SP.no 1 PId MenU or FL oFF bS 0.0 UPr oFF dnr oFF oH 100.0 oL 0.0 dr 0 Hb1 oFF Hb2 oFF HC1 0.0 HC2 0.0 orb 1.0 orH 100.0 orL 0.0 or 0 1.SP 50.0 2.SP 0.1 3.SP 0.1 4.SP 0.1 (**) Marked steps are not visible in some controller models.
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Experiments Note: The experiment nos 1 thr 6 are to get feel of the process and PID settings.
1 Study of open loop response (Manual control) Procedure • Start up the set, adjust the vent valve. • Select open loop option from software. • Close the control valve by increasing the controller output to 100%. • Apply the step change by 10% to controller output in manual mode, wait for process value to reach the steady state value. • Repeat the above step until the controller output reaches to minimum 0%. Observations Tabulate the observations as follows Controller output in % Process Value in % 100 90 80 … 0
• •
From the above data, note the output required for maintaining the process at desired set points. (for particular vent valve opening). Set the output of the controller to the noted value and at steady state apply the load change to the process. Load change can be given by slightly varying the vent valve. Observe new steady state process value.
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2 Study of on/off controller Procedure • Start up the set up and select close loop option for control from software. • Set the controller to On/Off mode. On/Off mode. • Press Tune & set the upper and lower hysteresis of the controller. • Change the values of the set point and observe the On-Off control operation. Observations Observe that if process value exceeds the set point, controller closes the valve and if process value decreases below the set point control valve opens, i.e. the controller operates like On/Off switch.
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3 Study of proportional controller Procedure • Start up the set up and select close loop option for control from software. • Set the controller to proportional control (P) mode. • Adjust the process value by switching the controller to manual mode to a particular pressure (say 50 %) on the screen and apply output of the controller as bias value. Change the proportional band to 100%. • Switch the controller to auto mode. • Apply step change of 10% to set point. • Switch the controller to manual mode. Decrease proportional band to half of the previous value. With each decrease, obtain a new response of the step change. Ensure that the set point changes are around the same operating point (Say 50%). Observations • Observe the effect of very low proportional band values (system works as on-off control). • Observe the response of the system at load change. Load change can be given by slightly manipulating the vent valve of the tank.
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4 Study of proportional integral controller Procedure • Start up the set up and select close loop option for control from software. • Select PID controller. Set the proportional band estimated in Proportional control. Set derivative time to 0 sec and integral time 6000 sec, which will cut off the derivative action and widen the effect of integral action. • Set the set point to desired flow value. Allow the process to reach at steady state. Record the steady state error. • Switch the controller to manual mode. Reduce the integral time to half of the previous value. Switch to Auto mode and apply step change(+/- 10%) to the set point. Note the response of the system. • Repeat above step to observe the effect of changes in Integral setting. Observations • Observe the effect of reducing integral time on the response of the process.
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5 Study of proportional derivative controller Procedure • Start up the set up and select close loop option for control. • Select PD controller. Set the proportional band estimated from Proportional control (P only) Set derivative time to 0 and integral time=6000 sec. • Set the set point to desired value. Allow the process to reach at steady state. Note the response of the system. • Switch the controller to manual mode Increase the derivative time by 1 sec. Switch to Auto mode and apply step change to the set point by 5 to 10%. Note the response of the system. • Increase the derivative time gradually and observe the process response for step change. Observations • Compare the steady state response of the PD controller with PI controller obtained in the previous experiment.
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6 Study of proportional integral derivative controller Procedure • Start up the set up. Select close loop option for control from software. • Select PID controller. • Switch the controller to manual mode. • Change the proportional band to the value that estimated in proportional controller. Set integral time and derivative time based on the responses in previous experiments. • Adjust the set point to @ 50 %. Switch the controller to auto mode. Apply step change of 10%. Observe the process response. • Change the proportional band, integral time, derivative time and observe the response of the process for step change for each change in setting. Observations Compare the steady state response of the PID controller with P. PI and PD controller obtained in the previous experiments.
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7 Tuning of controller (Open loop method) Procedure • Start up the set up and select Open loop option for control. • Adjust controller output, so that the process value is maintained at 50%. • Start data logging. • Apply a 20 - 30 % change to controller output. (Open the control valve) Record the step response. Wait for the steady state. • Stop data logging. • Plot the step response (Process reaction curve) from stored data. Find out the value of slope at the point of inflection and time lag. • Calculate P I D settings for different d ifferent modes. • Select close loop, switch auto manual key to auto mode and then select controller to study. Set the PID values obtained from the calculations. Apply the step change & observe the response of the system. Allow the system to reach steady state. Observations (Refer theory for formulae.) • Step change to the system ∆P = Initial output - Final output of the controller. • Plot the graph of process value Vs Time on a graph paper. From process reaction curve: • Slope of the process reaction curve R = • Time lag L= Calculate P, PI, PID setting from above values. • Observe response of the system for different PID settings.
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8 Tuning of controller (Closed loop method) Procedure • Start up the set up and select close loop control. • Select P controller only. Set the proportional band value to maximum (Say 200). Set the controller to manual mode and adjust the output so that the process value reaches to 50%. • Switch the controller to auto mode and decrease the proportional band and apply the step change to the set point and observe the process response. • Repeat the above procedure and find out correct value of proportional band for which the system just goes unstable i.e. continuous oscillations are observed in the output of controller. • Record the ultimate proportional band and ultimate period from the response. • Calculate the PID values from the table. Select the PID controller and apply the parameter values obtained from the above steps. Observe the response of the process to a step change with these settings. Observations • Record the ultimate proportional band (Pbu) and ultimate period (Tu) from above experiment. • Calculate PID values by referring theory part for different control actions. • Observe the process response for these settings. • Compare the values obtained with open loop re sponse method.
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9 To study stability of the system (Bode plot) Procedure • Start up the set up and select open loop option from software • Start data logging. • Select function generator to apply the sinusoidal input to the output of the controller. • Enter Reference point, Amplitude and Period. • Observe the sinusoidal output of the controller and sinusoidal response of the process. • Log the data for records. • Change the period and repeat the observation for 3-4 different values of the period. • Repeat above procedure for different amplitude and period values. Observations • From the data file stored observe the output response of the process and note down the output amplitude. • Measure output wave period and note down as T sec. Measure the phase lag x and note down in sec. Obs. Input Output Output Lag X Frequency No. amplitude amplitude Period In sec A1 % A2 % Tin sec
Calculations • Calculate for each observation Magnitude ratio as M = A2/A1 Phase angle = (X/T) x 360 Frequency = 1/T cycles / sec. • Draw the graphs of: Magnitude Vs frequency on log - log scale Phase angle Vs frequency on semi-log coordinates. • Study the graph for stable conditions mentioned in t heory.
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Components’ manuals
Electro pneumatic transducer (I/P) The ControlAir Type 500X converts a current input signal to a linearly proportional pneumatic output pressure.
Technical specifications Model Make Input Output Min./Max supply pressure Linearity Repeatability Hysteresis Air consumption Port size
500X-AC ControlAir 4-20 mA 3-15 psi Min. 18 psig, Max 100 psig +/-0.75 % of span <0.5% of span <1% of span 0.05 scfm midrange typical ¼ NPT
Principle of operation The unit is a force balance device in which a coil is suspended in the field of a magnet by a flexure. The flexure moves towards the nozzle and creates back pressure which acts as a pilot pressure to an integral booster relay. Input signal increase causes increase in proportional output pressure. Zero and span are calibrated by turning adjust screws on the front face of the unit. Adjustment of the zero screw repositions the nozzle relative to the flexure. The span adjustment is a potentiometer that controls the amount of current through the coil.
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Troubleshooting Problem No output or low output
Leakage Low or improper span
Erratic operation
Check Zero adjustment Supply pressure too low Clogged orifice Connections Zero and span adjustments Supply pressure too low Output leakage Electrical input signal Loose wires or connections Liquid in air supply
Calibration 1 Open protective covers to expose zero and span adjustment screws. 2 Connect the recommended air supply to the inlet of the transducer and an accurate pressure gauge at the outlet. 3 connect the electrical input and set it to 4 mA. 4 Observe the output pressure. If necessary adjust zero screw until reaching minimum output pressure setting (3 psi). Turn zero screw counter clockwise to increase pressure, clockwise to decrease pressure. If unable to achieve output during calibration process, turn zero adjustment screw counter clockwise for up to 30 revolutions, until output pressure rises. 5 Increase electrical input to 20 mA
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6 Observe the output pressure. If necessary adjust the span screw until output pressure reaching 15 psi. Turn span screw counter clockwise to increase pressure, clockwise to decrease pressure. 7 The zero span adjustments are interactive. After adjusting the span it will be necessary to recheck the zero. Repeat steps 3-6 until both end points are at the required values.
Manufacturer’s address If you need any additional details, spares or service support for this unit you may directly communicate to the manufacturer / Dealer / Indian Supplier. Control Air Inc. 8 Columbia Drive, Amherst, NH 03031 USA Email:
[email protected] [email protected]
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Indian supplier: Control teknics 5,Aboorva Flats, old No.6, New No. 11 7th main road, Raja Annamalaipuram Chennai - 600 028 Email:
[email protected]
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Mini combination air filter regulator These modular series filter regulator are high flow, low pressure, and high accuracy.
Technical specifications Make Model Range Type Connection Body Bowl Element Drain Seals Diaphragm Spring pressure Spring valve Spring cage and nob Gauge ports Element rating Drain Bowl capacity Max. pressure Max. temperature Overall dimensions Weight
Airmatic MB10-021-VD-PAP 0 – 2 Kg/cm2 Diaphragm, Relieving ¼”BSP Aluminium Polycarbonate Porous material Brass Buna – N Buna – N Spring steel Zn plated Stainless steel Acetyl resin Two 25 micron Manual 30 ml 12kg/cm2 500C 40diameter x 155 H mm 220 gm
Manufacturer’s address If you need any additional details, spares or service support for this unit you may directly communicate to the manufacturer / Dealer / Indian Supplier. Shah pneumatics 28/30, Navketan Industrial Estate, Mahakali Caves Road, Andheri (E) Mumbai – 400 093. E-mail:
[email protected] [email protected] .in Web: www.shahpneumatics.com www.shahpneumatics.com
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Pressure gauge Introduction Pressures gauges are suitable for use with air, oil, water or compatible gases. The phosphor bronze bourdon tube is housed within a rugged SS case. The aluminum dial and pointer are protected by an impact resistant polycarbonate window. Accuracy is +/- 3-2-3% per ASME grade B. Brass back connection is ¼” male NPT.
Technical specifications Make Code Pressure gauge Liquid filled Internals part Housing Range Connection Accuracy Media Bourdon tube Dial/pointer Wetted parts Temperature range Mounting Overall dimensions Weight
Waaree Instruments PW2.5GNNNS9 0-2.5 ¼”B 2.5” diameter Glycerin Brass SS 0 – 2.5 and 0 – 7 Kg/cm2 ¼” center back +/-3-2-3% per ASME grade B. Clean, no corrosive liquid Phosphor bronze Aluminum dial with black enameled pointer Phosphor bronze bourdon tube with brass stem -10 to 800C Panel mounting 70diameter x 55mmL 140 gm
Manufacturer’s address If you need any additional details, spares or service support for this unit you may directly communicate to the manufacturer / Dealer / Indian Supplier. Waaree Instruments Ltd. 10, Damji Shamji Industrial Complex, Off Mahakali Caves Road, Andheri (E), Mumbai – 400 093. E-mail:
[email protected] [email protected] Web: www.waaree.com www.waaree.com
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Pressure Transmitter Pressure transmitters are use for air, fluid and gas pressure in the close tank.
Technical specifications Model Make Output Supply Pressure Range Process connection Accuracy
21S Keller 4-20mA (2wire) 24 VDC 0-5 Bar ¼”BSP (Male) +/-1%
Troubleshooting Problem No output at the output pin No variation in the output Pressure not holding at constant input pressure
Check Check Check Check Check Check
the wiring configuration. the input + Vcc supply. for the leakage at pressure port. for the span set of indicator ind icator / controller. for the leakage at pressure port.
Manufacturer’s address If you need any additional details, spares or service support for this unit you may directly communicate to the manufacturer / Dealer / Indian Supplier. Web: www.keller-druck.com www.keller-druck.com
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Supplied by: Waaree Instruments Ltd. 36, Damji Shamji Industrial Complex, Off. Mahakali Caves Road, Andheri (East), Mumbai – 400 093. Email:
[email protected] Web:www.waaree.com
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