Industrial Control Devices: Switch, Relay, Solenoid and Timer

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  • Topic: Switch, Relay, Electromagnet
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  • Published : October 5, 2010
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Abbreviations NO (Normally Open) and NC (Normally Closed) represent the electrical state of this switch contacts when the switch is not actuated.

Manually Operated Switches
- Switch is controlled by hand.
- Forms of switches
i) Toggle switch
(Types of switches:-
➢ Single Pole Single Throw (SPST)
➢ Single Pole Double Throw (SPDT)
➢ Double Pole Single Throw (DPST)
➢ Double Pole Double Throw (DPDT)
( Electrical ratings are expressed in terms maximum interrupting voltage and current; should not be exceeded. ( AC and DC ratings are not the same for a given switch. The DC current rating of a switch would have a lower magnitude than the ac rating.


Figure 1: Toggle Switches

ii) Slide switch
( uses a simple slide action to produce the same connections as a toggle switch. (used as a mode switch to select a certain mode of operation such as HIGH and LOW. [pic]
Figure 2: Slide Switch

iii) DIP (dual in-line package) switches
( small switch assemblies designed for mounting on PCB. ( The pins or terminals on the bottom of the DIP switch are the same size and spacing as an IC chips. [pic]
Figure 3: DIP Switch
iv) Rotary switch
( often used for more complex switching operations, such as oscilloscopes and multimeters. ( wafer switch
# the main shaft passes through the center of one or more ceramic, fiberglass or phenolic wafers on which the terminals and contacts are mounted. # the center section of each wafer can be rotated, passing a common contact to one of the many stationary contacts mounted around the wafer’s perimeter. [pic]

Figure 4: Rotary Switch

v) Thumbwheel switches
( used on numerical and computer-controlled equipment to input information from the operator to the computer. ( Their specially made decks output binary coded decimal (BCD), decimal, or hexadecimal codes necessary to communicate with digital computers.

Figure 5: Thumbwheel Switch

vi) Selector switch
( switch positions are made by tuning the operator knob right or left. ( selector switches may have two or more selector positions, with either maintained contact position or spring return to give momentary contact operation.


Figure 6: Selector Switch

vii) Pushbutton switches
Types of switches:-
- NO pushbutton: makes a circuit when it is pressed and returns to its open position when button is released. - NC pushbutton: opens the circuit when it is pressed and returns to the closed position when the button is released. - Break-make pushbutton: used for interlocking controls. i. top section – NC

ii. bottom section-NO
- when the button is pressed, the bottom contacts are closed after the top contacts open. - one or more pushbuttons: pushbutton station
|[pic] |[pic] | |[pic] |[pic] | |[pic] |[pic] |

Figure 7: Various types of pushbutton symbols and switches

Mechanically Operated Switches
- Switch is controlled automatically by factors such as pressure, position, and temperature. - Forms of switches
i) Limit Switch
← limit switches are designed to operate only when a predetermined limit is reached and usually actuated by contact with an object. |[pic] |[pic] |...
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