Wednesday, May 23, 2018

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Discrete Process Measurement - Hand Switches

A hand switch is exactly what the name implies: an electrical switch actuated by a person’s hand motion. These may take the form of toggle, pushbutton, rotary, pull-chain, etc. A common form of industrial pushbutton switch looks something like this:


an industrial push button switch showing its contacts at its terminals

The threaded neck inserts through a hole cut into a metal or plastic panel, with a matching nut to hold it in place. Thus, the button faces the human operator(s) while the switch contacts reside on the other side of the panel.

When pressed, the downward motion of the actuator breaks the electrical bridge between the two NC contacts, forming a new bridge between the NO contacts:

An industrial push button switch on its actuated state.

The schematic diagram symbol for this type of switch looks much like the real thing, with the normally-closed contact set on top and the normally-open contact set below:

A normally closed contact symbol at its normal state
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