Input and Output Module:-
Inputs carry signals from the field (process) to the
controller. Various types of inputs can be switches, pressure
sensors, transmitters etc. The field devices to whom PLC sends the results
of logical operations are the output devices. These are the
actuators that adjusts or control the process, motors, lights,
relays, pumps, etc. Many types of inputs and outputs can be connected to a PLC and they can
be categorised mainly as analog and digital. Digital inputs and
outputs operate on discrete or binary change
i.e. on/off, open/close. Analog inputs and outputs change
continuously with reference to time.
Programming Device:-
The PLC is programmed using a special software using computer
or hand Held Terminal(HHT) that can load and change the logic
inside.
Operation of a PLC system:-
The operation of the PLC is determined by 3 steps.
- Reading the field status form input devices
- Execution or solving the logic, and
- Updating the output devices status.
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