1. Industrial Machine Control
EKT 451
CHAPTER 7
Industrial Machine Control

2. Basics of Industrial Motor Control
When applied to machinery, it involves the starting, acceleration, reversal, deceleration and stopping of a motor and its load.
In this chapter we will study the electrical (not electronic) control of a alternating current motor.
However, the basic principle covered here apply to any system of control.

3. Control Devices Disconnecting switches Manual circuit breaker
Isolates the motor from the power source.
3 knife-switches and 3 line fuses
Manual circuit breaker
Opens and closes a circuit.
Trip automatically when the current exceed the predetermined limit.

4. Control Devices Cam switches Pushbuttons
Has a group of fixed contacts and an equal number of movable contacts.
The contacts can be made to open or close by rotating a handle or knob.
Are used to control the motion and position of hoist, machine tools and so on.
Pushbuttons
Is a switch activated by finger pressure.
Usually spring loaded so as to return to normal position when pressure is removed.

5. Control Devices Control relays Thermal relays
Is an electromagnetic switch that opens and closes when the relay coil is energized.
Mainly used in low-power circuits.
Thermal relays
Is a temperature sensitive device.
The current flow will increase the temperature of the relay.
The contacts open or close when the current exceeds a preset limit.

6. Control Devices Magnetic contactors Pilot lights
Basically a large control relay designed to open or close a power circuit.
Possess of a relay coil and a magnetic plunger.
When the relay coil is energized, it attracts the magnetic plunger, thereby closing the power circuit.
Pilot lights
Indicates the on/off state of a remote component in a control system.

7. Normally open and normally close contacts
Control circuit diagram always show components in a state of rest, that is, when they are do not energized (electrically) or activated (mechanically).
Normally open contacts (NO)
Normally closed contacts (NC)

8. Control Diagrams
A control system can be represented by four types of circuit diagrams.
Block diagram
One-line diagram
Wiring diagram
Schematic diagram

9. Control Diagrams Block diagram
Composed of a set of rectangles, each representing a control devices, together with a brief description of its function.
The rectangles are connected by arrow that indicate the direction of power or signal flow.
Block diagram of a combination starter

10. Control Diagrams One-line diagram
Similar to block diagram, except that the components are shown by the symbols rather than rectangles.
The symbols give us an idea of the nature of the components.
Consequently, one-line diagram yield more information.
One-line diagram of a combination starter

11. Control Diagrams Wiring diagram
Shows the connection between the components
These diagrams are employed when installing equipment or when troubleshooting a circuit.
wiring diagram of a combination starter

12. Control Diagrams Schematic diagram
Shows all the electrical connections between the components, without regard to their physical location or terminal arrangement.
These diagram is indispensable when troubleshooting a circuit or analyzing its mode of operation.
Schematic diagram of a combination starter

13. Starting Methods A motor control circuit contains two basic components
A disconnecting switch
A starter
Manual across-the-line starters
Composed of a circuit breaker and either two or three thermal relay; mounted in appropriate enclosure.
The thermal relays trip the circuit breaker whenever the current exceeds the rated value for a significant length of time.
Manual starter for single phase motor

14. Starting Methods Magnetic across-the-line starters
Whenever a motor has to be controlled from a remote location.
Has 3 main components:
a magnetic contactor
A thermal relay
A control station
Magnetic starter

15. Reversing the direction of rotation
We can reverse the direction of rotation of a 3-phase motor by interchanging any two lines.
This can be done by using 2 magnetic contactors and a manual 3-position cam switch.
Schematic diagram of a reversible magnetic starter

16. Reduced-voltage starting
Some industrial loads have to be started very gradually.
Example : coil winders, printing presses, conveyor belts.
A motor cannot be directly connected to the line because the starting current is too high.
reduce the voltage applied to the motor by connecting resistor in series with the line.

17. Reduced-voltage starting
connecting resistor in series

18. Computer and Controlled
With the advent of computers, it is now possible to simulate the behavior of many relay coils and relay contacts.
Instead of using relays, contacts and time delay dashpots , we simply program these device on a computer.
Programmable Logic Controllers (PLCs)

19. Programmable Logic Controllers
The fundamental difference of the electric machine control diagram is the way the control devices are interconnected.
An automated system is composed of control devices and controlled devices.
Black box is a computer and designed to simulate the relays, relay coils and relay contacts.

20. Programmable Logic Controllers
PLCs consists of five basic parts.
CPU
Input module
Output module
Programming unit
Power supply

21. Programmable Logic Controllers