Describe the design and operational characteristics of a PLC system

Learning Outcome 1: Describe the main elements of an electronically controlled industrial system
Learning Outcome 2: Describe the main elements of an electronically controlled industrial system
Learning Outcome 3: Review the main concepts underlying electronically controlled industrial systems
Learning Outcome 4: Analyse the characteristics of an electronically controlled industrial system by applying a variety of techniques to the solution of a given problem
Learning Outcome 5: Critically examine the performance of an electronically controlled system to make recommendations for improvement

Task 1

(a)Review the main concepts underlying electronically controlled industrial systems which makes them ideal for modern industrial systems monitoring and control.
Describe the following two industrial control systems giving practical industrial examples.

1. Motion control
2. Process control
(b)Draw a block diagram of a closed loop showing all the elements of an industrial system. Describe the following elements and explain their function in an electronically controlled industrial system.
• Error detector
• Controller
• Actuator
• Manufacturing Process
• Measurement Devices
(c)Referring to a practical closed loop control system describe the terms manipulated variable, Measured variable and the controlled variable.

Task 2

(a)The drive system in fig 1 shows the three major sections of a DC drive in a feedback configuration. Explain the function of the three sections.
1. Operator controls
2. Drive control
(b)Analyse the two feedback techniques (internal and External) which have been used to monitor the speed of the motor explaining with reasons which method is more accurate.
(c) Explain with the aid of circuit diagrams the terms half wave speed control and full wave speed control

Task 3

(a)Explain the four control modes which can be performed by the controller in a closed loop system.
• On- Off
• Proportional
• Proportional-Integral
• Proportional-Integral-Derivative
(b)A factory is using an electrical system to control the temperature of a furnace. The control system uses a thermostat to turn the solenoid fuel valve ON of OFF. As shown in fig 1.

This system has been identified by a senior engineer as not very effective. It has been noted that the actuator's respond is not adjusting the output to exactly required by the process demand

You have been assigned the project to modify the control system from a simple ON/OFF control to an electronic proportional control by making two changes.

1. Replace the ON/OFF switch(thermostat) by a thermistor in a bridge network
2. Replace the solenoid type of fuel valve in the furnace to a proportional valve

Critically analyse the performance of the simple ON/OFF control and design an electronically controlled system making recommendations for improvements. You should employ your knowledge of operational amplifiers resistors bridge network to design a system which will give a better proportional control. Assume that when the temperature in the furnace is at 70 degrees (set point) then the fuel valve is 50% open.