Answer / senthilkumar saudi aramco

AI- Analog input (that means 24volt dc with 4-20madcdriving
the loop)

AO- Analog Output (that means only 4-20 madc driving the
loop)
D/I - Digital input (5volt/15volt/24volt/110volt supply
given from plc to the field switches
(pressure,level,limit,flow)to close the circuit or breake
the circuit.
D/O - Digital Output (PLC giving output voltage mode
24volt/110 volt to the field either solenoid valve or
electrical driven equipments

Answer / raja

AI - analog input
AO - analog output
DI -digital ""
DO- digital ""

these are the input and output types used in external cards
inserted in a plc . this ensures a proper selection and
processing of signals by PLC .

Important point is that they may not be the direct output of
a field sensor but a modulated one .

e.g - thermistor is provided in a plc itself for temperature
measurement . then it will be connected in analog input card.
2. pressure control to a p to i converter will be connected
in analog output card .

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