This document discusses various types of industrial control devices including manually operated switches, mechanically operated switches, and electromechanically operated switches. Manually operated switches include knife switches, toggle switches, push buttons, rotary selector switches, and manual starters. Mechanically operated switches include limit switches, mercury switches, snap acting switches, and motor protection switches. Electromechanically operated switches include relays, solenoids, and semi-conductive switches. The document also discusses circuit breakers and their classification, construction, control, and application.

1. Switching and Control Devices

2. Industrial control devices range from simple knife
switches to more complex solid state sensors. The
type of control device selected depends upon the
specific application. There are three distinct ways to
control an application:
Manually Operated Switches
Mechanically Operated Switches
Electromechanical Switches

3. Manually Operated Switches
Manually operated switches are triggered with the use of
human power. There are five types of manually operated
switches:
1. Knife
2. Toggle
3. Push Button
4. Rotary-Selector
5. Manual Starter

4. The knife switch is the oldest and simplest type of switch
consisting of a blade and jaw mechanism.
Knife switches are primarily used in large electrical
distribution situations.
Knife switch
Knife Switch

5. Toggle switches replaced knife switches for safety and
speed of operation. Toggle switches use a lever to
close or open contacts.
Toggle switch
Toggle Switch

6. A pushbutton switch is a two-position switch used to
select a load either on or off.
The pushbutton may consist of one or more contact
blocks; denoting the switch as normally open (NO) or
normally closed (NC), an operator of some type, a legend
plate to denote function and mounting rings or washers
to adjust and hold the device in an enclosure.
Depress Pushbutton
Release Pushbutton
Push Button Switch

7. Rotary-selector switches are constructed in the same
fashion as a pushbutton. A rotary-selector switch
requires the operator to rotate a knob, lever, or key to
open and close contacts. Additionally, rotary-selector
switches are used to select or determine one of several
different circuit possibilities from a two-position on/off
switch to a four-position key switch.
Rotary-Selector Switch
Coin Knob Key
Rotary Selector Switch

8. A manual contactor is a device for any electrical circuit
that repeatedly establishes and interrupts an electrical
power circuit. When a switch is engaged, contacts
touch allowing electrical power to flow.
Manual Contactor
Contacts
Moveable Contacts
Conductive Bar
Contacts
Manual Contactor

9. Manual Starter switches are contactors with an
additional overload protection device used only for
motors. The overload protection device is required to
protect the motor from destroying itself under an
overloaded situation.
Manual Starter Switch

10. Mechanically Operated Switches
Mechanically operated switches are triggered with the use of
some other moving part. There are four types of mechanically
operated switches:
1. Limit
2. Mercury
3. Snap Acting
4. Motor Protection

11. Limit switches are used to convert
mechanical motion into an electrical
signal. They accomplish this
conversion by using some type of
lever to force open or closed a set of
contacts within the limit switch.
Typical applications of limit switches
include conveyors, elevator control,
counting, positioning, detecting,
sequencing, and monitoring.
Limit Switches
Limit Switch

12. For Starting and
stopping a motor in
forward and reverse
with limit switch
providing over-travel
protection
Limit Switch

13. Mercury switches utilize the electrical properties of
mercury to complete a circuit. Within a glass tube, a
pool of mercury is able to move around allowing it to
make contact with different contacts for different
reasons. Usually a mercury switch is used in low
voltage situations such as a household thermostat.
Mercury Switch/ Temperature Switch

14. The most common heat sensing element is the bimetallic
strip that operates on the principle of thermal expansion.
The bimetallic strips are made with two dissimilar metals
(that are having different thermal expansion rates) and
are bonded with each other.

15. The switch contacts are operated when the temperature
causes the strip to bend or wrap. Another method of
operating the temperature switch is to use mercury glass
tube.
When the bulb is heated, mercury in the tube will expand
and then generates pressure to operate the contacts.

16. Motor protection switches
are located on or in a
motor to protect the
motor from overloading
situations. They sense
either the amount of heat
generated or the amount
of current consumed by
the motor. Prior to motor
damage, they directly or
indirectly disconnect the
motor from the power
circuit.
Bimetallic
metal
Before Overload After Overload
Motor Protection Switch

17. Electromechanical Switches
Electromechanical operated switches are triggered with the
use electricity. There are three types of electromechanically
operated switches:
1. Relays
2. Solenoids
3. Semi-conductive

18. Relays
Relays are electromechanical devices that either use a
small input voltage (24v) to control a larger output
voltage (230/460v) or use an input voltage to control
two or more output voltages.
120v
Mechanical
relay switch
operated by a
coil

19. Solenoid switches use simple electromagnetic
attraction and repulsion to create some type of useful
function. The design of the solenoid determines the
type of function created.
Vertical Action
Horizontal Action
N.C. contacts open when energized
N.O. contacts close when energized
Solenoid Switch

20. Semi-conductive switches use semiconductor
technology to control low voltage electricity. Examples
include rectifiers, silicon controlled rectifiers, diodes,
thermistors, photovoltaic cells, photoconductive cells,
resistors, transistors, capacitors and integrated circuits.
Transistors
Integrated Circuits
Diode
Thermistor
Semiconductor Switch

21. To control pressure of liquid and gas
Actuated when a specified pressure is
reached.
Pressure Switch

22. To sense the height of a
liquid, a float is attached
The rising and lowering
of the float trips the
level switch
Level Switch

23. Photovoltaic cell converts light
energy directly into electric
energy.
Photoconductive cell also called
photo-resistive cell. Light energy
falling on the cell will cause
change in resistance

24. Bar code system consists of : bar code symbol, a scanner ,
and a decoder.
Bar code symbol contains up to 30 characters encoded in
a machine-readable form.
Barcode Technology

25. Mostly based on UPC (universal product code)
UPC type (1 char)
Manufacturer or vendor ID (5 chars)
Item number (5 chars)
Check digit (1 char)
Barcode Technology

26. A light source illuminates the bar code symbol, those bar
absorb light , and spaces reflect light.
A photo detector collects this light in the form of an
electronics signal pattern.
The decoder received the signal and converts these data
into character data.
Barcode Technology

27. An ultrasonic sensor operates by sending sound waves
toward the target and measuring the time it takes for the
pulses to bounce back.
Its bounce back time proportional to the distance
Ultrasonic Sensor

28. A strain gauge transducer converts a mechanical strain
into an electric signal.
Strain gauge are based on the principle that the
resistance of a conductor varies with length and cross-
sectional area.
Level Switch

29. Strain Gauge Sensor

30. Purpose
• To make, break or change the connections in an
electric circuit, under either normal or abnormal
conditions

31. Fuses
• Used to protect circuits of small capacity against
abnormal currents such as overloads or short
circuits.
Types:a)cartridge fuses b)transformer
fuse block and cutout c)expulsion
fuses

32. Classification of Circuit Breakers
Interrupting medium - air, air blast, oil
Service - indoor, outdoor
Operation – gravity opened, gravity closed, horizontal
break
Action – nonautomatic, automatic
Mode of control – direct control, remote control (manual,
electrical [motor/solenoid], pneumatic)
Tank construction – all poles in one tank, one tank for each
pole
Mounting – panel mounting, rear of panel

33. Air Circuit Breakers
•
•
•
“carbon circuit breaker” have 2 or 3 contacts
Protect the main contacts against arcing or pitting,
secondary copper contacts and also carbon contacts
are provided
Carbon contacts take most of the arcing, and since
•
carbon is very refractory, the contacts are not
damaged very much
In case of damage to either the secondary or carbon
contacts, it is possible to replace these easily.

34. Circuit Breakers
classified
• Standard oil circuit breakers may be
according to their method of operation as
a) Gravity opened
b)Gravity closed
c) Horizontal break
• But several variations of these types are nevertheless
found

35. a) gravity-opened type
•
•
Most common type wherein contacts are operated
by an insulated rod which projects outside the tank
Tendency is for the contacts to fall open due to
gravity

36. b) gravity-closed type
•
•
•
It will close under the action of gravity
Terminals are at the bottom of the tanks, the circuit
being completed through contact rods
Equipped with a set of main contacts located at the
top of the tank which opens before the arcing-rod
contacts are opened and, hence, are not subjected
to arcing and can, therefore, be located outside the
tanks

37. c) horizontal-break type
• In both of earlier types, the circuit is broken by
contacts moving in a vertical plane, however, this
type has its contacts arranged for horizontal motion.

38. d) air-blast circuit breakers
•
•
•
Introduced in the United States practice in 1939
Blow out the arc with a jet of air that is supplied from
a pressure tank
Arc is blown into a set of arc chutes, where it is
subdivided into several parts, making the task of
extinguishing somewhat easier.

39. e) magnetic-blast circuit breakers
•
•
Designed for 5,000V and less
These are air circuit breakers that extinguish their
arcs by blowing them magnetically into arc chutes
where they are lengthened, cooled and interrupted.

40. f) impulse oil circuit breakers
• Arc is extinguished by an oil blast produced by a
spring-driven piston.

41. Contact Details
•
•
simplest type of contact is using of either flat or
curved metal surfaces as terminals of CBs
Butt contact
•
– when moving contactors are held firmly against the
stationary terminals by means of heavy springs
– For low voltages and capacity
Wedge design
– Wedge-shaped terminal on the moving element, which
when in the closed position is forced between spring jaws

42. • Bayonet or rod type
•
– Arcing tips are connected to the contact arms through
heavy springs
– Essential when contacts be opened at very high speed
Oil-blast explosion chamber
– Consist of an upper, an intermediate, and a lower element
– In the closed position, these three elements are pressed
together

43. Circuit Breaker Construction
Mechanical details of CB vary a great deal, depending
on the particular requirements that must be met
•Indoor
– In most cases, lower voltage ratings and therefore present
a different appearance. Generally, they are mounted in
cells
•Outdoor
– Must naturally be water and moisture proof, the bushings
must be designed for all weather conditions and, as a
general rule must be given greater clearance

44. • For very low capacity and voltages all poles of a
polyphase circuit breaker are sometimes placed in
the same tank, but for medium- and high-capacity
units it is necessary to enclose the separate poles in
individual tank

45. Circuit Breaker Control
•
•
•
Remote electrical control may be obtained by means
of an operating motor or solenoid
Operating voltages used are either 125 or 250 volts
DC is generally obtained from storage batteries,
which give continuous service w/ maximum possible
reliability
•
•
Pneumatic method of CB control, owing to its
positive and unusually fast action
relays are placed in ckt in order that CB may be
opened automatically in case of abnormal condition.

46. Application of Circuit Breakers
To apply CBs: normal current of circuit, rated voltage, &
the interrupting capacity in amperes must be known
•Interrupting capacity of circuit breaker is also affected
by the frequency of the circuit, p.f. prior to the short
ckt, the temperature, and also the altitude of the
breaker above sea level
•Stored electrostatic and magnetic energy of system
has definite effects upon
•also limited by the safe operating temperature
•Up to an elevation of 3,300 ft above sea level ther is
no perceptible decrease in rating