Draw the block diagram of discrete input module & explain each block.
Power conversion: It consists of rectifier which converts the incoming AC signal to a pulsating dc level, which is passed through filter and other logic in order to deliver a clean and denounced dc signal.
Threshold detector:
It detects if monitoring signal has reached or exceeded a predetermined value. A valid ON sate will be between 80- 132V ac. The upper voltage limit for a valid OFF state is below 20V. The voltage between 20V and 80V is called undefined zone.
Isolation: It is made up of an optical isolator which separate high voltage from CPU‟s low voltage control logic.
Logic section: It passes the input signal to the module‟s input address LED and the CPU.