Experiment No.4The 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 integral 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

The following graph is obtained when we set the gain upto 0.005

If we increase the gain upto 0.05 then

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But further increasing the gain upto 0.2 shows us following relation

I ControllerIntegral controlled systems are systems without self-regulation: if the manipulated variable does not equal zero, the integral controlled system responds with a continuous change continuous increase or decrease of the controlled variable. A new equilibrium is not reached.

Liquid level in a tank

In a tank with an outlet and equally high supply and discharge flow rates, a constant liquid level is reached. If the supply or discharge flow rate changes, the liquid level will rise or fall. The level changes the quicker, the larger the difference between supply and discharge flow.This example shows that the use of integral control action is mostly limited in practice. The controlled variable increases or decreases only until it reaches a system-related limit value: the tank will overflow or be discharged, maximum or minimum system pressure is reached, etc.

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