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.