Experiment No.3The objective of this practice is to carry out a closed loop control by an on/off controller by the closing and opening of the A VS-I, AVS-2, AVS-3 solenoid valves and the activation of pump 2 using proportional controller.

Apparatus: UCP-L Control and Acquisition Software Water

Diagram:

Procedure: Connect the interface of the equipment and the control software Select the control on/off option Make a double click on the on/off control, select the flow wanted. there are a certain flow, a

tolerance and a performance time set by default. It allows the students to play with these parameters and see the influences of each one

The level control can be carried out by the activation of a single actuator, or of several ones, to which different tolerances are allowed. These controllers work as security system measures when the controlled variable exceeds in a tolerance the set value. To activate or to disable any of these controllers you may have to double click on each of them and press the button "PAUSE"

Calculate the inertia of the system for an on/off response and determine the limit time for an exact control

This is the graph when we set gain 1

But when we increase the gain to 3.5, we get following relation

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1 5 9 13 17 21 25 29 33 37 41 45 49 53 57 61 65 690

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Further increasing the gain upto 5 gives us following behaviour

Proportional controllerIn controlled systems with proportional action, the controlled variable x changes proportional to the manipulated variable y. The controlled variable follows the manipulated variable without any lag. Since any energy transfer requires a finite amount of time, P control actionwithout any lag does not occur in practice. When the time lag between manipulated and controlled variable is so small, however, that it does not have any effect on the system, this behavior is called proportional control action of a system or a P controlled system.

1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 490

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PROPORTIONAL CONTROLLER GRAPH

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Flow controlIf the valve travel changes in the pressure control system illustrated in the following figure, a new flow rate q is reached (almost) instantaneously. Depending on the valve flow coefficient, the controlled variable changes proportional to the manipulated variable; the system has proportional control action.

In the following figure, it shows the block diagram symbol for proportional action and the dynamic behavior of a P controlled system after a step change in the input variable. The characteristic curves clearly show that a proportional controlled system is a system with self-regulation, since a new equilibrium is reached immediately after the step change.

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