flow control demonstration panel

LAB 2

FLOW CONTROL DEMONSTRATION PANEL
3) Safety Instructions
3.1 Danger to humans 

 

• DANGER! Exercise caution when handling electrical system components. There is a danger of electric shock. Disconnect the mains plug before accessing any electrical components. Such work should only be performed by qualities personnel.

• DANGER! Never operate the device without a correctly installed ground conductor. A failure to observe this instruction might result in harm to humans and equipment.

3.2 Danger to Equipment and Functionality

• Caution! Do not fill the water tank with more than 15 litres of water. Excess water might overflow into the device and damage it.
• Caution! Never operate the pump without water. Dry running can damage the pump.
• Caution! Do not change the sensor's basic setting. Altered signals can result in a loss of process control.
• Caution! Drain the water tank prior to shutdown periods of more than 3 weeks.
• Caution! Store the model under frost-free conditions. Frost can damage individual components.

4)   Experiments

4.1 Response of the control system

• This experiment is intended to ascertain the properties and response of the control system underlying the model.
• For this purpose, steps in control value are applied successively to the system in the non-regulated mode and the system's response is observed.

Experiment procedure: 

• Turn on the demonstration model via its main switch.
• Fully open the adjustment cock (6). Setting: 0 degree.
• Set the controller to manual operation and the manipulated variable y to 10% =(2.5 litre/min).
• Turn on the pump. After a certain time, the flow rate assumes a constant value. Read and note this value.
• Increment the manipulated variable successively by 10%, waiting briefly each time until the flow rate has attained a constant value. Read and note these values too.

Manipulated variable y in %	10	20	30	40	50	60	70	80	90	100
Flow rate in (litre/min)	0.25	0.27	0.51	0.78	1.47	2.0	3.5	5.8	7.1	7.65

Result: 

• The system evidently responds very quickly to change in the valve setting, much faster than temperature, filling-level and pressure control systems.
• The system is of a compensatory nature, resulting in constant final values each time.
• This characteristics was expected, because every pipe system possesses an intrinsic resistance to flow, thus preventing flow rates from rising indefinitely.
• The characteristic of the control variable x clearly indicates the equal-percentage response of the control valve.

4.2 Flow Control with a PI Controller

• In this experiment, a controller with proportional and integral components is used for flow control, accompanied by variations in parameters. 
• The controller's differential component remains inactive. 
• The control circuit's response to changes in the reference variable w is observed.

4.2.1 Slow PI-Controller

Experiment procedure:

• Turn on the demonstration model via its main switch.
• Set the controller and demonstration model as shown in the following table:

Controller type	PI-Controller
Controller mode	Automatic
P-component                    >>                Pb.1	0.1
I-component                     >>                rt	4 seconds
D-component                   >>                dt	0.0 second
Controller settings                                      Start value:                                                                            Step value:	6 litre/min   (30%)  12 litre/min (60%)
Adjustment cock	Half open, 45 degree

• Observe the flow rate using the readings indicated by the controller and rotameter. After a certain time, the flow rate assumes a constant value of 6 litre/min.
• Increment the reference variable w by setting the controller to 12 litre/min. The flow rate increases and assumes a constant value of 12 litre/min after a certain time.

Result:

• The input signal y reveals that although the controller responds immediately to changes in the reference variable, it takes a long time to achieve a constant target value. The desired flow rate of 12 litre/min is attained very slowly ( t > 1 minute )
• The controller's P-component achieves fast response, while the I-component eliminates persistent deviations. However, the selected integration time is still too long.

4.2.2 Fast PI-Controller

• In this experiment,too, a controller with proportional and integral components is used for flow control.
• The controller's differential components remains inactive.
• Compared with experiment 4.2.1, the integration time.- i.e. the controller's I-component is set to a notably lower value.
• The control circuit's response to changes in the reference variable w is observed.

Experiment procedure:

• Turn on the demonstration model via its main switch.
• Set the controller and demonstration model as shown in the following table:

Controller type	PI-Controller
Controller mode	Automatic
P-component    >>           Pb.1	0.1
I-component    >>           rt	0.5 seconds
D-component    >>           dt	0.0 second
Controller    Start value:      settings      Step value:	6 litre/min   (30%) 12 litre/min (60%)
Adjustment cock	Half open, 45 degree

• Observe the flow rate using the readings indicated by the controller and rotameter. After a certain time, the flow rate assumes a constant value of 6 litre/min.
• Increment the reference variable w by setting the controller to 12 litre/min. The flow rate increases and assumes a constant value of 12 litre/min after a certain time.

Result:

• The input signal y reveals that the controller quickly generates values which are notably higher than in the previous experiment. In fact, the control variable now distinctly overshoots the target value of 12 litre/min and starts to oscillate about it. 
• The oscillations decay in 30 seconds to a permanent level of roughly +/- 5% about the target value.
• The parameters selected here do not result in satisfactory control performance. The selected integration time is obviously too short.

4.2.3  PI-Controller with Improved Parameters

• In this experiment, too, a controller with proportional and integral components is used for flow control.
• The controller's differential component remains inactive.
• The results obtained in experiments 4.2.1 and 4.2.2 are used as a basis for adapting the controller's integration time here.
• The control circuit's response to changes in the reference variable w is observed.

Experiment procedure:

• Turn on the demonstration model via its main switch.
• Set the controller and demonstration model as shown in the following table:

Controller type	PI-Controller
Controller mode	Automatic
P-component           >>         Pb.1	0.1
I-component           >>         rt	0.75 seconds
D-component           >>         dt	0.0 second
Controller                 Start value:   settings                   Step value:	6 litre/min   (30%) 12 litre/min (60%)
Adjustment cock	Half open, 45 degree

• Observe the flow rate using the readings indicated by the controller and rotameter. After a certain time, the flow rate assumes a constant value of 6 litre/min.
• Increment the reference variable w by setting the controller to 12 litre/min. The flow rate increases and assumes a constant value of 12 litre/min after a certain time.

Result:

• The input signal y rises immediately after the step in the reference variable to achieve a nearly constant value in just ~5seconds.
• The control variable initially overshoots the target value by ~5% and never becomes completely stable, instead oscillating irregularly about the target value.
• However, the control performance is acceptable for a fast system such as this one.
• The control parameters in this operating mode are nearly ideal for responding to change in the reference variable. This configuration is a compromise between response and control performance.

4.3 Note on Further Experiments

• The experiments and associated parameters described above are a subset of the available possibilities.
• The addition variants of this demonstration model also easily allow a realization and evaluation of control systems with different settings and control parameters.

Possible Variants:

- Use of just a P-controller

- Use of a PID-controller

-Variations in reference variable step

- Disturbance variable control: Introduction of a disturbance variable z by means of the adjustment cock (6) and comparison of the results with those obtained from reference variable control.

- Optimization of reference and disturbance variable control parameters for various operating points.

Production-related factors, fluctuations in ambient conditions and operational modifications can cause the control system's properties to change.

level control demonstration panel

LAB 1

JM507

CONTROL SYSTEM

Experiment 1 : Level Control Demonstration Panel

Control technology is now an integral part of nearly all areas of engineering.Accordingly, a description of its basic principles is a standard feature of technical training programs.

The demonstration model of the RT-6x4 series from G.U.N.T make it possible to ascertain relationship between control parameters in practical experiments and demonstrate these relationships so that they are clear and easily mobilizable.

Every model comprises a fully functional system of process with it own control circuit.An extensive use of modern industrial component makes the model are realistic as possible.students thus not only obtain knowledge of basic control principles  but also an overview of the control element's design, functionality and application.

The models have a desktop design and require very little maintenance.They are ideal as training aids for laboratory experiments at technical college and universities and intended exclusively for educational purposes.

1. Devices description

• The RT 614 demonstration model is a desktop device to control filling levels.
• Water is used as the operating medium here.Filling levels are controlled by an electronic industrial unit which can be configured as a P, PI, or PID controller.
• Experiments with demonstration model involve modification and adaptation to system control parameters.

2. Device layout

• The RT614 demonstration model for filling level control has following layout :                                                           

 

1. Filling-level sensor
2. Drain cock with scale
3. Water tank
4. Pump
5. Electric proportional wave
6. Pump switch
7. Jack for the Y control signal
8. Switch for internal/external changeover of the Y control signal
9. Controller
10. Jacks for the X signal from the filling-level sensor

3. Process scheme

         

1. Filling-level cylinder
2. Filling-level sensor
3. Controller
4. Control valve
5. Pump
6. Drain cock
7. Water tank

4. The controller

• The digital universal controller is equipped with a microprocessor with digitally process input signals and converts them back to analog variable prior to output.

5. Question

                                                                                                                                              

Block diagrams are ways of representing relationships between signals in a system.  Here is a block diagram of a typical control system.  Each block in the block diagram establish a relationship between signals.                            

Here are the relationships for this particular system :

• E(s) = U(s) - Y(s)
• This relationship is for the summer/subtractor (shown with a green circle)
• W(s) = K(s)E(s)
• This shows how W(s) - the control effort that drives the system being controlled, G(s) - is related to the error.  The controller is probably an amplifier - probably a power amplifier - that provides an output to drive the plant, G(s).
• Y(s) = G(s)W(s)
• This shows how the output, Y(s), is related to the control effort that drives the plant (system being controlled ) with a transfer function, G(s).

        Next, you can combine all of those relationships and get an overall relationship between the input and the output in the system.  Here is the process.

• Note that Y(s) = G(s)W(s)
• Note that W(s) = KE(s), and use that in the equation for Y(s).  That gives you:
• Y(s) = G(s)W(s) = G(s)KE(s)
• Note that the error is given by E(s) = U(s) = Y(s), and use that in the equation for Y(s).
• Y(s) = G(s)W(s) = G(s)KE(s) = G(s)K[U(s) = Y(s)]
• Now, solve for Y(s), and you get:
• Y(s) = U(s)KG(s)/[1 + KG(s)]

        That's what you need to know, and the final relationship will allow you to compute the output given knowledge of the system components and the input.         What if you have a more complex system?  Here is a block diagram of a slightly more complex system.

 

A description of this system is as follows.

• The plant being controlled includes a pump motor.  The output is the height of a liquid in a tank.
• It takes some threshold voltage on the pump to get it started.  After the voltage exceeds the threshold, the flow rate into the pump depends upon the amount by which the threshold is exceeded.
• In the block diagram model above, the threshold voltage (V_T)and attendant effects are modelled using another summer.
• The controller has a transfer function, G_C(s).
• The sensor has a transfer function, G_S(s).
• We can write the mathematical relationships that exist in this block diagram.
• Y(s) = G_P(s)[W(s) - V_T(s)]
• Y(s) = G_P(s)[G_C(s)E(s) - V_T(s)]
• Y(s) = G_P(s)[G_C(s)(U(s) - G_S(s)Y(s)) - V_T(s)]
• Now, solve for Y(s), and you get:
• Y(s) = U(s)G_P(s)G_C(s)[1 + G_P(s)G_C(s)G_S(s)] - V_T(s)G_P(s)[1 + G_P(s)G_C(s)G_S(s)]

        Now, notice that the output has two components.  One of those components is due to the input - something we know about.  The other component of the output is due to the threshold voltage - something we might not have expected.         What do we make of all this?  Actually, representing offsets and thresholds like this is a particularly good way to incorporate some simple nonlinearities into our block diagram algebra even though the block diagram representation was originally used only for linear systems.  It's not hard to incorporate those offsets into your analysis.  Here's what you can do.

1. Generate a complete block diagram for the system and be sure that you incorporate all of the offsets in your block diagram model.
2. Using your block diagram model write out the algebraic equations for each block.
3. Solve the equations you have written to determine the output of the system (or the error if that is what you are interested in).  Note that the output will probably depend upon the input and all of the offset quantities you added.
4. Use the solution to determine numerical values for the output.  Remember, you are often interested in steady state solutions (DC solutions) and you can get that by using DC gains with s = 0 in your transfer functions.