The Pressure Control Loop Trainer Model PCLT-1 is a WINDOW based system. This is intended to study and experiment, on methods to maintain a constant pressure, in a pressure vessel. The pressure in a pressure vessel may fall, if the air is withdrawn by an external instrument or vented out. Therefore, there is a fall in pressure. It is necessary to regain the lost pressure in the pressure vessel back to original (predetermined) pressure in the shortest time. A controller achieves this. Proportional (P) and Proportional Integral Derivative (PID) controllers are used to achieve this. To study control dynamics, a pressure vessel is used. The PCLT-1 has all the monitoring and control elements to study and experiment the above objective. The instrument helps the student/trainee to study the dynamics of control valve, valve positioning mechanism, pressure measurement of the valve, simulation of fault / disturbance, valve characteristics, hysterisis, linearity error, response time and closed loop analysis. The Pressure Control Loop Trainer consists of:
1. An IBM PC/XT/AT/PS-1 computer or compatible instrument, with atleast one ISA slots for inserting dedicated Input output card. Supply of computer is not in the scope of supply. This must be supplied at your cost at the time of installation.
2. A dedicated interface Data Acquisition Instrument in the front panel assembly.
3. Pressure Loop Trainer on movable stand. In order to assist in conducting the experiment, several WINDOW based features are provided. They are:
This is the process screen. This screen is used to do the following Input Parameters:
1. Set point
Of desired level in PSI or
Set the variable set point by using function generator inputs as SINE, SQUARE, TRIANGLE, SAW TOOTH.
2. Set the Proportional (kp) gain in the range of 1 to 100%
Set the Integral (ki) gain in the range of 1 to 100%
Set the Differential (kd) gain in the range of 1 to 100%
Sampling time in terms of mS. Output Parameters: These are displayed in response to the above parameters. These are displayed as a function of comparing the feedback parameters. Process variable in Cms
Controlling variable that is responsible for controlling the process to restore close to the set point.
Graphs: These are stored dynamically, and will be displayed any time. When ?show graph? option is selected, the controlling process stops, and gets ready to display the trend. There are varieties of statical graphs that can be generated as a consequence of data logging. These graphs can also be printed.
How to view the graphs: The following possibilities are available to view the graph. They are: Show Combined Graph: When this option is selected, all the process parameters appear in a single graph, as shown here. All the three parameters overlap one above the other. In this mode all the three parameters namely setpoint process variable, and Controlling force are all displayed in the same screen.
Show Individual Graph: When this option is selected, the process parameters are displayed as individual graphs in the same screen, as shown below. This distinguishes one graph from the other. Show Complete Graph: When this option is selected, the whole run is displayed at once, as shown below. When this is selected, the complete trend from the start is displayed. Zoom: This feature allows the user to zoom into a specific portion of the graph. Move the cursor to the point where you want the zoomed portion to start, as shown below. Insert markers: A marker will appear as a gray line on the graph. For each marker, indicator labels appear, indicating the values of the corresponding process parameters. By inserting markers, a specific portion of the trend may be observed more closely. This option is necessary as, some times the process takes long time to settle down. At this time, it is a good method to move your cursor to a specific portion of your process and view that zone, which is critical for analysis. Using this trainer, we can perform the following experiments.
There are independent study programs to understand the above rudiments, both for open loop and closed loop controls, in the form of EXPERIMENTS listed here. Each experiment is designed to highlight one or more important aspects of data logging and control. The communication between the computer and the pressure control loop trainer is through 4-20mA current transmitter (TX) and receiver (Rx). Hence all control/measurement parameters (Viz.) positioning the stem of control valve, pressure in the PV are all co-related in terms of 4-20mA only, because the display on computer should appear in engineering units.
The following experiments help in understanding the techniques to measure, compute, control, display and store on-line. These programs are supplied in BASIC Language. Study a program to tabulate a relationship between DAC and the 4-20mA current generated, which activates I/P converter.
Study a program to read stem position and record the actual displacement to create a Data file for future use.
Study program to determine the displacement from previous position to the current position.
Study a program to position the stem of control valve anywhere from 0-100% opening/closing with a time delay (Td), not exceeding cycle time.
Study a program to measure the valve dynamics in moving from 0-100% opening/closing using a stopwatch.
Study a program to determine the relationship between I/P converter to that of control valve.
Study a program to tabulate the controller setting of I/P Vs the displacement of control valve in mm
Study a program to display ON-LINE pressure directly.
Study a program to determine the relationship of valve position (mm) to the actual pressure measured at pressure transducer gauge (Kg.cm2)
Execute Proportional (P) control program and observe a change in the pressure indicator and control valve position, for disturbance created by venting the air of pressure vessel into atmosphere.
Execute the above Proportional and Integral (PI) controls and observe the trend on the computer's display.
To aid the above tasks, the instrument is provided with momentary switches, which can be programmed to actually open or close solenoid valves to simulate faults at the inlet and outlet of the pressure loop. 4-20mA current meters to study behavior of I/P converter, stem position of the control valve, and measure pressure of pressure transducer gauge. There are pressure gauges at appropriate places, solenoid valves, hand operated changeover switches, air filter regulators, couplings etc. The instrument offers enough scope to write control programs in any language: like PASCAL, ASSEMBLER, C, C++, BASIC, TURBO C, TURBO BASIC etc as long as they support I/O instructions. The documentation provides study programs in BASIC with necessary comments. Window based software on CD includes Proportional (P), Proportional Integral (PI) and Proportional Integral Derivative (PID) controls, trend charts. Specifications: FESTO make couplings and fittings are used.
a) Control Valve:
Size : 15mm.
Type : 2way s/seat.
Body : A216Gr.WCB
Stroke : 14.3mm
Air Failure : open.
Max Incremental
Pressure in closed :30 PSI position
Air connection : Brass. b) Electro-Pneumatic Converter:
Input Signal : 4-20mA DC.
Input Resistance : 90 ohms ?5 ohms.
Output Pressure : 3-15 PSI.
Characteristics : Linear to input current.
Air supply : 1Kg/cm2.
Consumption : 30L/hr typical.
Pressure Connection : 1/4" NPT thread.
Mounting Method : wall.
Mounting Position : Horizontal. c) Pressure Transmitter:
Input : 3 ? 15PSI
Output :4-20mA DC.
Maximum working Pr :29 PSI
Enclosure :W/P
Mounting :Direct On line
Sensor and Wetted parts: SS 316 d) Filter Regulator:
Quantity used : 2 nos.
Service medium : Air.
Indicator : Graduated pressure gauge.
Max Pressure : upto 250 PSI.
Max input rating : 18Kg/cm2.
Outlet Pressure : 0-30 PSI (0-2.1) Kg/cm2.
Size of output hose : 1/4".
Ambient Temperature : upto 80? C. f) Pressure Vessels:
Quantity : 1 No
Housing :Chromium plated MS
Service : Air
Capacity : 1 Lt
Max Pressure : upto 2Kg/cm2.
Connection : 1/4"BSP external thread. g) Pressure Gauges:
Quantity : 4Nos
Pressure : 3-15PSI.
Size : 1/4"BSP external thread. h) Rotometer:
Service : Air.
Flow Range : 0-100 LMP.
Max.Pressure : 10Kg/cm2.
Metering tube : Boro-silicate glass.
Float SS304.
Packing Neoprene.
Needle Valve : Provided integral.
End connection size : 1/4" NPT (F). i) Solenoid:
Quantity : 2 nos.
Service : Air.
Type : 2/2 way Normally closed.
Pipe size : 1/4".
Orifice size : 6mm.
Flow factor (Kv) : 0.4.
Coil type : 230V AC. j) Meters:
Quantity : 2 nos.
Type : Moving coil.
Range : 0-25mA.
Purpose :To monitor. What you must provide the following facilities at your cost, at the time of installation: You have to provide compressed air @ 5kg/cm2 from your in-house compressor.
Constant water line to be provided by you for filling the water tank and discharge pipelines must be provided to drain the water from the tank after the completion of the experiment.
You must provide an IBM Computer or Compatible system. It must have at least one vacant ISA slot on the motherboard, to enable the ADD-ON card to be inserted, which will communicate with the trainer. The minimum configuration of the system must be any Intel make standard CPU, 32MB RAM, one 1.44?FDD, HDD with any capacity, CD ROM drive, and a color monitor.
You must provide the necessary electrical fittings at 230V AC single phase, and accessories, observing all the safety standard features, like circuit breakers, safety switches and fuses etc, so that the operator will work under safe environment. Proper electrical grounding (earth) must be provided to the instrument setup as a whole.
This requires 10 Sq.ft floor space for conducting experiments by the students or trainee.
Good electrical connection, with proper earthing is required.
Mobility: Mounted on robust caster wheels
Dimensions: 4' X 2' X 6' (L, B, H)
Specifications are subject to change without notice. Changes in specifications may be effected even after receiving confirmed purchase ORDER. |
