Level Control Process Loop Trainer Model LVL-1 is intended to study the level control dynamics under closed loop control. This equipment finds applications in Instrumentation laboratory and training organizations. Using this trainer one can study the rudiments of level control. The level control loop trainer has all the required hardware and software needed for controlling level in a tank. The instrument consists of a cylindrical water tank of approximately 30cm high water column with 16cm diameter. A centrifugal pump water from a built-in sump, through a control valve and a Rotometer into this tank. The control valve regulates the rate of flow under software command. A Rotometer displays the flow rate. The level of water in the water tank is displayed by a separate 30cm high sight glass tube. A level transmitter produces current in the range of 4mA to 20mA proportional to the height of water column in the water tank. This level transmitter is used as feedback transducer, to communicate the level to the controller in terms of current. The controller (software driven) determines the current water level. The difference in desired level and current water level is computed. Based on this information the controller determines the desired control action. If the current water level is below the desired level, the control valve allows more water to flow into the tank. As the error reduces, the flow of the water reduces, thus achieving a PID control. If the current water level is above the desired level, a solenoid valve automatically opens and allows the excess water present in the water tank to drain. Hence, the desired level is achieved. In order to provide a disturbance, a hand valve is used. On opening this hand valve, the water from the water tank is discharged into the sump directly, resulting in fall in water level in the tank.
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 Cms 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.
1. Process variable in Cms
2. Controlling variable that is responsible 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 below. All the three parameters overlap one above the other. In this mode all the three parameters namely (a) setpoint (b) process variable, and (c) 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 Combined 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. 1. Study characteristics of a level transmitter. I.e. relation between water level and the current generated by the level transmitter. Plot a graph LEVEL Vs CURRENT. This information is useful to design lookup table, while designing a controller.
2. Study a program to tabulate a relationship between a digital to analog converter (DAC), and the 4 - 20mA current generated. This current can be monitored on an analog and digital indicators. Tabulate this relation DAC number Vs current output (4 - 20mA). Plot a graph. This information is useful in setting a control function to I - P converter.
3. Study a program to understand the relation between current to pressure conversion. In this program, 4 to 20mA currents are used to activate a current to pressure (I to P) converter. For 4mA current, the I-P converter provides 3 PSI (0.2kg/cm2) at it's output port. For 20mA current the output pressure will be 15PSI (1 Kg/cm2). Plot a graph.
4. Study a program to activate the solenoid. This study demonstrates how to discharge water from the water tank.
5. Study a program to change the stem position of control valve, under software control. The stem of the control valve changes its position from one extreme position to the other (usually 0 to 10-15mm) under air pressure. For 3PSI, the stem is in initial position, i.e., and 0mm. For 15PSI, the stem changes its position to the other end. This up/down movement causes, valve to open and close. This action changes the water flow through the pipeline. The water flow can be changed in the range of 3 to 10 Liters/min (LPM). This demonstrates how to change water flow pattern by software.
Tabulate the input pressure (3-15 PSI) VS stem position (0 - 10mm). Plot a graph
6. Study a program to measure, rate of change in the stem's position from 0% to 100% open and 100% to 0% open. This will be used later to study dynamics of control valve. This program demonstrates how quickly water flow can be changed. Plot a graph
7. Study a program to measure the change in water flow rate by observing Rotometer, for different control valve settings.
The setting can be from 0% to 100% open condition and 100% to 0% open.
Tabulate the flow rate (3 to 10LPM) VS valve position (0 to 100%). Plot a graph.
8. RUN PID CONTROL PROGRAM.
Many more experiments can be conducted in the above equipment, as every input and output element is accessible by software. You can formulate an experimental scheme to suit your syllabi needs.
Specifications: a) Control Valve:
Fluid : Water.
Body form : Globe
Size body/port/Cv : 1/2"- 1/4" - 2.0Gpm.
Body material : A216 Gr.WCB
Trim form / Material : Contoured / SS316.
Flow chart/Direction : Linear
Actuator type : Diaphragm.
Spring Range : 0.2 - 1.0 Kg/cm2.
Valve action : Air to open.
Total stem travel : 14.3mm. b) Hand Operated Valves:
Quantity : 1 nos.
Size :1/2".
Coating : Nickel.
Type : Close open close. c) Level Transmitter:
Probe type : Stillwell rod
Probe size : ?? dia
Probe material : ss304
Probe insulation : Teflon Insulated
Enclosure : Weather proof d) Electro-Pneumatic Converter:
Input : 4-20mA.
Output : 3-15 PSI.
Input Resistance : 90 Ohms.
Characteristics : Linear to input current.
Air Supply : 1.4Kg/cm2.
Consumption : 30 L/Hr typical.
Pressure : 1.4 bar.
Connection : 1/4" NPT.
Mounting : Wall. e) Air Filter Regulator:
Service Media : Air
Indicator : Pr gauges
Max input : 10Kg/cm2.
Hose connection : 1/4" BSP. f) Solenoid:
Service : Water.
Coil voltage : 220 VAC.
Service connection : 1/2". g) Current Meters:
Analog : 25mA FSD ?2 Nos h) Rotometer:
Service : Water.
Connection : 1/2". Range : 0 to 10.5 LPM.
Metering tube : Borosilicate.
Float : SS 304.
Needle : Provided, integral. i) Water Pump:
Voltage : 220V AC.
Lift : 2000 Lt./Hr to 20Meters high.
Service : Water
Connection : 3/4" upstream.
1/2" reduced for downstream. j) Water Tank (sump):
Capacity : 25 Lt. 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. |
