Programmable Logic Controller are factory centered. with communications occurring over LAN with high speed and controls that are closed feedback loops.

History

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How works a PLC?

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We have, for example, 2 liquids that have to go into this tank to be mixed until is full, for this reason we have a FLOAT SWITCH. We have a TIMER (this type of information will go inside an Holding Register for example!) that we need to set to how long to stir them and then we have a SOLENOID here for the output.

The control circuit operates as follows:

  1. When the start button is pressed, solenoids A and B energize. This permits the two liquids to begin filling the tank.
  2. When the tank is filled, the float switch trips. This de-energizes solenoids A and B and starts the motor used to mix the liquids together.
  3. The motor is permitted to run for one minute. After one minute has elapsed, the motor turns off and solenoid C energizes to drain the tank.
  4. When the tank is empty, the float switch de-energizes solenoid C.
  5. A stop button can be used to stop process at any point.
  6. If the motor becomes overloaded, the action of the entire circuit will stop.
  7. Once the circuit has been energized it will continue to operate until it is manually stopped.