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ECET 211 Electric Machines & Controls

Lecture 4-1 Motor Control Devices: Part 1. Manually Operated Switch

Part 2. Mechanically Operated Switch

Text Book: Electric Motors and Control Systems, by Frank D. Petruzella,

published by McGraw Hill, 2015.

Paul I-Hai Lin, Professor of Electrical and Computer Engineering

Technology

P.E. States of Indiana & California

Dept. of Computer, Electrical and Information Technology

Purdue University Fort Wayne Campus

Prof. Paul Lin

Lecture 4 Motor Control Devices

Chapter 4. Motor Control Devices

• Part 1. Manually Operated Switches

• Part 2. Mechanically Operated Switches

• Part 3. Sensors

• Part 4. Actuators

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Part 1. Manually Operated Switches

Primary and Pilot Control Devices

Toggle Switches

Push Button Switches

Pilot Lights

Selector Switch

Drum Switch

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Manually Operated Switches

Primary and Pilot Control Devices

Control device

• A component that governs the electric

power delivery to an electrical load

• Must be capable of handling the voltage

and current to be switched

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Two classes of control devices: Primary control and Pilot

control device

Primary control device:

• Motor contactor, Starter, or Controller that connect the load

to the line

• Contactor can also be used as pilot control device

Pilot control device:

• Relay, Switch contact that used to activate the primary

control device

• Should not be used to switch horsepower load

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Manually Operated Switches – Push Button SW

Figure 4-1 Primary and Pilot Control

Devices

• A typical motor control switch that

include both a Primary Control

(contactor), and a Pilot Control

device (toggle switch)

• Theory of operation

1. Turn toggle switch on to

complete the control circuit:

Power source (L1, L2) Toggle

switch Contactor’s coil M

2. Contactor energized => close

the M’s NO contacts => Deliver

power to the Motor

3. Turn toggle switch off =>

Contact M de-energized => the

M’s NO contacts open => Motor

stop Prof. Paul Lin 5

Manually Operated Switches – Toggle Switches

Types of toggle switch

• SPST – Single pole, single throw

• SPDT – Single pole, double throw

• DPST – Double pole, double throw

• DPDT – Double pole, double throw

Figure 4-2 Toggle switches

Electrical Rating for Switches

• Maximum interrupting voltage and current

• AC rating higher than DC rating for an equivalent amount of

voltage

• AC current is at zero level twice during each cycle

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AC 120V 60Hz Since Wave

% sine120v.m

% MATLAB simulation

% 2014/1/13

% By Paul Lin

f = 60; %Frequency in Hz

T = 1/f; %Period in Second

dt = T/100; %Samlping time interval

Vrms = 120; % Root Mean Square voltage

t = 0: dt: 2*T; % Time vector

theta = 0; % Initial offset angle

e = 120*sqrt(2)*sin(2*pi*f*t + theta); % Voltage equation

% e = 120*1.414*sin(2*pi*f*t + theta); % Voltage equation

plot(t, e), grid on; %Plot the voltage waveform

xlabel('time Second'), ylabel('Volts')

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0 0.005 0.01 0.015 0.02 0.025 0.03 0.035-200

-150

-100

-50

0

50

100

150

200

time Second

Volts

Manually Operated Switches – Push Buttons

NO Push button (Normally open) –

START

NC Push button (Normally close) –

STOP

Break-Make Push button – NC contact

on the top section, NO contact on the

bottom section

Application example2

• 1) Motor starting/stopping control

• 2) Control and override process

functions

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Figure 4-3 Pushbutton

symbols and switching action

Figure 4-5 Pushbutton station – NEMA type 1

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Manually Operated Switches – Pushbutton SW

Figure 4-4 Break-make push button

and typical motor control circuit

Jogging Application – Momentary

operation to give small movement of a

driven machine.

1) Start PB pushed => M coil

energized => Motor running;

contact M is closed and

remembering the Start operation

2) Push down the Jog PB

momentary, M coil de-energized,

Motor stopped;

3) Then when Jog PB is pressed all

the way down, it then energize M

coil again and contact M is also

closed again

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Manually Operated Switches – Pushbutton SW

Figure 4-6 Typical pushbutton

assembly

Figure 4-7 Flush pushbutton

operator: used for start button that

need to be protected from accidental

initiation

Figure 4-8 Extended pushbutton

operator:

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Manually Operated Switches – Pushbutton SW

Figure 4-9 Mushroom head

pushbutton operator: easily seen

and actuated, used as emergency

stop PBs

E-Stop

Emergency Stop Pushbutton White

Paper, 2012,

http://literature.rockwellautomation.

com/idc/groups/literature/document

s/wp/800-wp008_-en-p.pdf

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Manually Operated Switches – Pushbutton SW

Figure 4-10 Half-rounded

pushbutton operator

Figure 4-11 Illuminated

pushbutton operator: LED

integrated

Figure 4-13 Pushbutton assembly

Legend Plates (Labels) for

Pushbuttons: START, STOP, FWD,

REV, JOG, UP, DOWN, ON, OFF,

RESET, and RUN

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OSHA Safety Requirement: Emergency Stop Pushbutton

OSHA requirements on Emergency Stop: Requires that once

the emergency stop switch has activated, the control process cannot be

started again until the actuating stop switch has been reset to the on

position.

• Safeguarding Equipment and Protecting Employee from

Amputation, 2007,

https://www.osha.gov/Publications/osha3170.pdf

• Section IV: Chapter 4 Industrial Robots and Robot System

Safety, OSHA Technical Manual,

https://www.osha.gov/dts/osta/otm/otm_iv/otm_iv_4.html

Other References

Electrical Requirements, Safeguarding Cutting and

Turning Machine – The Safety Library,

http://www.readbag.com/sti-ltr2-access-php-5

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Emergency Stop Pushbutton

Figure 4-14 Emergency Stop

Pushbutton – motor control circuit

Theory of Operation

An Emergency Stop PB is added

(in series) with the typical

START/STOP motor control circuit

The normally closed maintained

contacts of the Emergency Stop

push button will open when the

push button is pressed and remain

open until its is manually reset.

Motor will not operate

To restart the motor, you must first

reset the emergency PB, and then

press the Start button

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Mechanically Operated Switches – Pilot Lights

Pilot Lights

• provide visual indication of the

status for many motor-controlled

processes permitting personnel at

remote locations to observe the

current state of the operation.

• Full-voltage type – with

transformers (Figure 4-16)

• Low-voltage type – operate at 6 to

24 V, AC or DC

Figure 4-15 Remote start/stop station

with run pilot light

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Mechanically Operated Switches – Pilot Lights

Figure 4-17 Push-to-test pilot

light

• Designed to reduce the time

required to troubleshoot a

suspected faulty lamp.

Theory of Operation

1) Normal operation – R light on

2) If R light out, push and release

the Push-to-test light to see if the R

light is at fault rather that the motor

control circuit.

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Selector Switch

Selector Switch

A rotated switch for opening and

closing contacts of the attached

contact block

Operator knob:

• turning right or left

• May have two or more

selector positions

Figure 4-17 Three-position

selector switch: Pump Control

• Hand – it allows for manual

control via Manual Control

Switch

• Auto – It allow only for pump

to be control via Liquid-level

switch

• Off

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Drum Switch

A drum switch consists of a set of

moving contacts and a set secondary

contacts that open and as close as the

shaft is rotated

Figure 4-19 Drum switch used for

reversing the direction of rotation of

a three-phase motor

• FWD position

T1 L1

T2 L2

T3 L3

• REV position

T1 L1

T2 L3

T3 L2

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Part 2 Mechanically Operated Switches

Limit Switches

• A mechanically operated switch is

one that is controlled automatically

by factor such pressure, position,

and temperature

• Designed to operate only when a

predetermined limit is reached

• Often used in the control circuits of

machine processes to govern the

Starting, Stopping, or Reversal of

motors

Temperature Control Devices

Pressure Switches

Float and Flow Switches

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Part 2 Mechanically Operated Switches Limit Switches

• Two parts: the body

and the operator

head (actuator)

• Contact types

NO, NC,

Momentary

(spring returned),

Maintained-

contact type

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Limit Switches Figure 4-12 Limit

switch symbols and

configuration

• NEMA Symbols

• IEC Symbols

• A limit switch with

both NO and NC

contacts, you must

wire the Load on the

same side of line;

and be sure to form a

COM on the line side

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COM

Limit Switches Figure 4-12 Limit switch operator

• Level type

• Fork type

• Wobble stick

• Push roller

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COM

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Common Applications for Limit Switches To limit the travel of

electrically operated Doors,

Conveyors, Hoists, Machine

tool worktables, and similar

device

Figure 4-12 Limit switches

providing over travel

protection operator

Forward Direction Movement

• 1) Push Forward PB, energize

F coil that control the motor to

rotate in one direction, F’s NO

contact maintained; F’s NC

contact open to provide

interlock that prevent the

reverse director of motor

• 2) If it is overtravel in FWD

direction, FWD LS is pushed

Open, deenergized the F coil,

and then turn off the motor

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Reverse Direction Movement

1) Push Reverse PB, energize R coil

that control the motor to rotate in the

reverse direction, R’s NO contact

maintained; R’s NC contact open to

provide interlock that prevent the

reverse director of motor

2) If it is overtravel in REV direction,

REV LS is pushed Open, deenergized

the R coil, and then turn off the motor

Limit Switches Micro Limit Switch (Figure 4-24)

• Provide rapid closing and/or opening

action

• Single-pole double throw that has

COM, NO, and NC

• Offers a limit amount of electrical

insulation and physical protection for

contacts

• Normally mounted within encloses

with lower risk of physical damage

Rotating Cam Limit Switch (Figure 4-

25)

• Senses angular shaft rotation within

360° and the activates contacts

• Used with machinery having a

repetitive cycle of operation

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Part 2 Mechanically Operated Switches

Temperature Control Devices

• Monitoring temperature or changes in

temperature for a particular process

Temperature switch (Thermostats),

Figure 4-26

• Used in heating or cooling

applications where temperature must

be maintained within preset limits

Figure 4-27 Capillary tube temperature

switch

• Temperature-sensitive liquid will

expand and contract with a change in

temperature

• Pressure in the system changes in

proportion to temperature and is

transmitted to the bellow through a

bulb and capillary tube

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Temperature Controlled Fan Motor Application

Figure 4-28 Temperature

switch utilized as part of a

motor control circuit

• 230 V fractional HP fan

motor

• Selector Switch: Auto,

OFF, Hand

• In Auto position,

Temperature sw

actuated

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Part 2 Mechanically Operated Switches

Pressure Switches

• Used to monitor and control the

pressure of liquids and gases

• Pressure => activate electrical

contacts

• Three types

Positive pressure

Vacuum (negative pressure)

Differential pressure

• Figure 4-29 Pressure switch

symbols

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Part 2 Mechanically Operated Switches

Theory of Operation

1) Pressure sw with high cut off and low

turn on differential setting (dean band)

is preselected

2) System on/off sw is set to on position

=> energize Compressor motor starter

coil => Motor is on

3) Compressor system pressure is

reached, Pressure sw off, de-energize

M coil => Motor stopped

4) Compressor system pressure

dropped below the low level =>

Pressure sw On, M coil energized again

=> Motor start to run again

5) Repeat step 3 through 4

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Figure 4-30 Pressure switch used as

part of air-compressor control

system

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Part 2 Mechanically Operated Switches

Float Switches

• A float-level switch is used to sense

the height of a liquid

Applications: providing automatic

control for motors that pump liquid from

a sump or into a tank

Figure 4-31 Float switch symbols and

circuit

• Motor stop level => Float SW Off

=> M coil de-energized => Pump

Motor Off

• Motor start level => Float SW On

=> M coil energized => Pump

Motor On

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Part 2 Mechanically Operated Switches

Flow Switches

• A flow switch is used to detect the

movement of air or liquid through a

duct or pipe

Applications: providing automatic

control for motors that pump liquid from

a sump or into a tank

Figure 4-32 Flow switch symbols and

circuit

• Paddle-type flow SW moves to

close the electrical contacts of flow

SW when the flow is sufficient to

overcome the spring tension on the

paddle

• When flow stops, the contacts open

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Summary & Conclusion

Questions? Contact Prof. Lin through:

Email: lin@ipfw.edu

LINE Group discussion forum

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