On/Off Control

Topics: Control theory, Control system, Feedback Pages: 4 (927 words) Published: January 28, 2011
Experiment No. 1


In today’s modern world, automation is one of the things that bring about ease and comfort in our lifestyle – from the temperature of our room to the flushing of the toilet. Automation of these things is run by control systems. A control system is a device or set of devices to manage, command, direct or regulate the behavior of other devices or systems.

Many industrial control systems have approximately first order dynamics and are controlled simply by switching an actuator ON and OFF. Liquid level control systems and heating processes are examples of such systems.

In this experiment, the control system that will be used is the ON / OFF control. And it will be applied in controlling the water level inside a vessel.
The objective of this experiment is to demonstrate On/Off control of water level inside a process tank. And after the experiment, the students should be able to identify the parts of a feedback control loop, commission and operate an on/off controller and be familiar with Solenoid Valves and Motorized Control Valves.

An on/off control is a type of feedback control where the control element is either at its fully-opened or fully-closed position. Figure 1 show the feedback control process where it loops when the final control element is changed bringing about the change in process conditions.

Figure 1. Feedback Control Process

Figure 2 shows the equipment used in the experiment. Where Figure 2a and 2c is the Process part of the system and Figure 2b is the electric part of the system. These equipment are used to demonstrate the on/off Control system.



Figure 2. (a) Front view of PCT 9 (b) PCT 10 (c) Back View of PCT 9.

First, the water level was controlled by manipulationg the inlet flow rate. It can be observed that the system, in order to maintain its level at 80 – 90 mm, the excess water was drained back to the reservoir by opening the solenoid...
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