4.3 Interface card
The interface card is used between the sensors output and PLC for
interfacing. In this card we use opto coupler is used for short the two
pins i.e. pin # 1 and pin # 25. When the input is approaches from
sensor then a current limiting resistor is used for reducing the current
and drops the voltage for a specific limit.
When sensors provide output then a resistor is used in series with the
opto coupler and the output terminal of the opto coupler is attached
with pin no 1 and lower terminal is connected with pin no 25. When
the opto coupler gains supply at its input then the output terminal is
short and behaves like a switch, so PLC receive a interrupt from pin
no 1 and than take decision about that.