1.Push Button and Switches 2

04/17/2023Mahadzir Mat Rabi 1

PUSH BUTTON AND SWITCHESMAHADZIR MAT RABI


PUSH BUTTON AND SWITCHES

A Pushbutton Switch is a switch designed so that its contacts are opened and closed by depressing and releasing a pushbutton(momentary switches)


PUSH BUTTON Operation Explanation

Momentary operationThe pushbutton returns to its original position after it is released.

Alternate operationThe first time the pushbutton is pressed, an internal lock mechanism holds it in the same position. The next time it is pressed, the lock is released and the pushbutton returns to its original position.

Push-pull operationWhen the pushbutton is pressed, an internal lock mechanism holds it in the same position. The pushbutton is returned to its original position when the pushbutton is pulled to release the lock.

Push-lock, turn-reset operation

When the pushbutton is pressed, an internal lock mechanism holds it in the same position. The pushbutton is returned to its original position when the pushbutton is twisted to release the lock.


Push button

SYMBOLS (IEC STD)

NORMALY OPEN CONTACT

SYMBOLS(IEC STD)

Normaly closed contact


EMO PUSH BUTTONS

• Emergency Stop Push Button Is A Twist-to-reset IEC 60947-5-5 specifies the

requirements for devices used to initiate the emergency stop function.These all specify that it shall not be possible for the device to latch without generating the OFF (stop) command or to generate the OFF (stop) command without latching.


Electrical Switches

Terms To Know:“SPST” – Single Pole / Single Throw“SPDT” – Single Pole / Double ThrowGanged Switch (MPMT)Mercury SwitchElectromagnetic SwitchPosition Switch Pressure Switch


Electrical SwitchesIntroduction:

Commonly used to control the “on/off function” of a component and/or circuit

Also used to “direct the current” in an electrical circuit

May also be used as “momentary contact” switches

The term “pole(s)” refers to the number of input circuits of the switch

The term “throw(s)” refers to the number of output circuits of the switch

Switches may be “normally open” (NO), or “normally closed” (NC) depending upon the application

May be used on either power or ground side of circuit


Electrical Switches

Classifications of Switches

04/17/2023 Mahadzir Mat Rabi 9

Electrical SwitchesSPST Switches

Single pole input Single pole output A set of contacts inside the

switch opens or closes the circuit

The contacts carry the current load of the circuit when closed


Electrical Switches

The “Momentary” Switch A SPST type switch Switch contacts are spring

loaded Closing the circuit requires

overcoming spring pressure

Circuit is opened by spring Switch is (NO)


Electrical Switches

SPDT Switches One input circuit (pole) Two output circuits (throws) Only one output is energized at a

time Contacts carry the current load of

circuit


Electrical Switches

Ganged Switches (MPMT)

Contain multiple “wipers” that operate in unison

Contacts may carry current load of circuit

Contacts may supply current to an “electromagnetic switch”


Electrical Switches

Mercury Switches A SPST type switch Uses mercury as the

conductor for the contacts

Accurate mounting of mercury switches is essential to proper operation

Used on ground side of circuit


Electrical SwitchesElectromagnetic

Switches Also called a “relay” Uses a small amount

of current to control a higher amperage circuit

Relays are (NO) type circuits

Often controlled by low amperage switch circuit


Electrical SwitchesAn Electromagnetic Switch in a Horn Circuit


Electrical Switches

Position Switches May be used on power or ground side of circuit Used to indicate whether a component is in the on or

off position Only provides a “high/low” signal to a solid state

control device A low current circuit


Electrical SwitchesPressure Switches

Can be used on either power or ground side of circuit

Switch is turned on/off by “pressure” rather than a component’s movement

Switch may carry current load of circuit Switch may be used as a type of position switch for

a solid state control device


Electrical Switches

Switch/Circuit Diagnosis



Tools and Methods: Test Light Continuity Light Jumper Wire DVOM


Switch/Circuit DiagnosisSPST Switches



Position Switches / Pressure Switches Basically a SPST switch Can be tested using SPST methods Always refer to appropriate wiring diagrams

for the current flow information It is a good idea to remove the switch from

the circuit before testing to prevent accidental damage to solid state components


Switch/Circuit DiagnosisSPST Momentary Switches


Switch/Circuit DiagnosisSPDT Switches


Switch/Circuit Diagnosis“Ganged” / MPMT Switches


Switch/Circuit DiagnosisMercury Switches


Switch/Circuit DiagnosisElectromagnetic Switches


SWITCHES


CHANGE OVER CONTACT A switch with both types of contact is called a changeover switch. These may be "make-before-break" ("MBB" or shorting) which momentarily connect both circuits, or may be "break-before-make" ("BBM" or non-shorting) which interrupts one circuit before closing the other.


WHAT HAPPENED DURING SWITCH CLOSED AND OFF

high-power electric circuits. The exposed conductors in a knife switch make accidental contact with the circuit a distinct possibility, and any sparking that may occur between the moving blade and the stationary contact is free to ignite any nearby flammable materials. Most modern switch designs have their moving conductors and contact points sealed inside an insulating case in order to mitigate these hazards


EMERGENCY STOP DEVICESIs a safety mechanism used to shut off a device in an emergency situation in which it cannot be shut down in the usual manner. Unlike a normal shut-down switch/procedure, which shuts down all systems in an orderly fashion and turns the machine off without damaging it, a kill switch is designed and configured to a) completely and as quickly as possible abort the operation, even if this damages equipment and b) be operable in a manner that is quick, simple (so that even a panicking user with impaired executive function can operate it), and, usually, c) be obvious even to an untrained operator or a bystander


EMERGENCY STOP CONSTRUCTION

Emergency Stop Button This is an emergency stop button

and it differs from a standard stop button as follows:

It has a large, easy to operate, mushroom shaped actuator.

This actuator must be mounted on a yellow background.

When operated, the actuator latches in the “Off “ position.

The actuator is released by twisting the mushroom shaped head.


Emergency stop criteria

Must be ready to use at any time.

One actuation must result in immediate disconnection (shutdown).

Resetting an E-Stop switch must not initiate restarting.

The switching device must latch when pressed.

Unambiguous identification (red/yellow


EMERGENCY STOP DEVICES WITH NO(NORMALY OPEN CONTACT )

This additional normally open contact of is used, for example, to inform a monitor or additional safety master of Emergency-Stop operation and to localise and the Emergency-Stop button which has been pressed. Faults can thus be immediately and clearly identified and, if required,. In particular with large installations with several Emergency-Stop buttons, downtimes can thus be reduced because the service technicians can immediately localise where the Emergency-Stop button was pressed.


Emergency off vs emergency stop

Emergency switching-off with mechanical latching

These have direct opening action. The speed of opening of the NC

contacts, and therefore the generation of the OFF command, is dependent on the speed with which the button is pressed.

The OFF command can (under some circumstances) be generated before the latching mechanism has operated, that is a momentary OFF command can be generated without the mechanism latching.

Emergency stop with trigger action and mechanical latching.

These also have direct opening action. The opening of the NC contacts, and the operation of the latching mechanism, are independent of the speed with which the button is pressed.

Stored energy in a spring is used to operate both the latching mechanism and the opening of the NC contacts, so that the mechanism cannot latch without the OFF command being generated, and cannot generate the OFF command without latching the mechanism


Safety limit switch limit switch is a switch operated by

the motion of a machine part or presence of an object.

They are used for control of a machine, as safety interlocks

When an object comes into contact with the actuator, the device operates the contacts to make or break an electrical connection

Limit switches are used in a variety of applications and environments because of their ruggedness, ease of installation, and reliability of operation.

Documents

1.Push Button and Switches 2