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Ladder logic was originally a written method to document the design and construction of relay racks as used in manufacturing and process control. [1] Each device in the relay rack would be represented by a symbol on the ladder diagram with connections between those devices shown.
In many cases, it is possible to design a relay logic diagram directly from the narrative description of a control event sequence. In general, the following suggestions apply to designing a relay logic diagram: 1. Define the process to be controlled. 2. Draw a sketch of the operation process. Make sure all the components of the system are ...
The National Association of Relay Manufacturers and its successor, the Relay and Switch Industry Association define 23 distinct electrical contact forms found in relays and switches. [12] Of these, the following are commonly encountered: SPST-NO (Single-Pole Single-Throw, Normally-Open) relays have a single Form A or make contact. These have ...
Similarly, a parallel set of instructions will perform a logical OR. In an electromechanical relay wiring diagram, a group of contacts controlling one coil is called a "rung" of a "ladder diagram", and this concept is also used to describe PLC logic. Some models of PLC limit the number of series and parallel instructions in one "rung" of logic.
In his thesis, Shannon, a dual degree graduate of the University of Michigan, proved that Boolean algebra [3] could be used to simplify the arrangement of the relays that were the building blocks of the electromechanical automatic telephone exchanges of the day. He went on to prove that it should also be possible to use arrangements of relays ...
Solid state relay with green LED Solid state contactor PCB mount solid-state DIL relay. A solid state relay (SSR) is an electronic switching device that switches on or off when an external voltage (AC or DC) is applied across its control terminals.
The most common type is a "push-to-make" (or normally-open or NO) switch, which makes contact when the button is pressed and breaks when the button is released. Each key of a computer keyboard, for example, is a normally-open "push-to-make" switch. A "push-to-break" (or normally-closed or NC) switch, on the other hand, breaks contact when the ...
(from top) Single-pole reed switch, four-pole reed switch and single-pole reed relay. Scale in centimeters. A reed relay [i] is a type of relay that uses an electromagnet to control one or more reed switches. The contacts are of magnetic material and the electromagnet acts directly on them without requiring an armature to move them.