plz explain me in details regarding the di,do,ai,ao concepts with the circuit diagram and theory.

 

DI Digital Input
DO Digital Output
AI Analog Input
AO Analog Output

 

DI is Digital Input which is the contact input to DCS like A contact from pressure switch, level switches etc.

AI is the Analog input which is the current output from transmitters, normally 4 to 20 ma or 0 to 20ma.

DO is the relay output from the DCS this will be used to start/stop commands and fault indication to local panes etc

AO is the analog output from the DCS this will be result of a PID Controls in the DCS and this will be used to control the spped of the motor like VFD etc.

 

- DI or discrete/digital input is the type of PLC input which used to read status of digital input
devices. Digital input device only have 2 status, ON or OFF. ON state mean PLC DI point received status in form of electrical power (can be 24 VDC, 120 VAC, etc.) and OFF state mean PLC DI point received no power from devices. Example of Digital input device is switch.

- DO or discrete/digital output is the type of PLC output which used to control digital output devices. Digital output devices only have 2 status, ON or OFF. ON command mean PLC DO point send command in form of electrical power (24 VDC, 120 VAC, etc.) and OFF command mean PLC DO send no power to devices. Example of digital output devices is relay.

- AI or analog input is the type of PLC input which used to read value from sensor. AI receive
value from sensor in form of electrical current (4-20 ma) or electrical voltage (1-5 V). ADC (Analog to Digital Converter) inside PLC will convert current or voltage to digital value in form of 16 or 12 bit word data to further process. Example of sensor is temperature sensor. Temperature sensor will measure temperature and send measurement value to AI channel in form of current or voltage.

- AO or analog output is the type of PLC output which used to control analog device. AO send command to device in form of electrical current (4 - 20 mA) or electrical voltage. DAC (Digital to Analog Converter) inside PLC will convert digital value (12 bit or 16 bit word data resulted from PLC calculation) to current or voltage and send it to controlled device thru AO channel. Example of AO device is control valve, PLC could control opening percentage of control valve with send 4 - 20 mA current which represent 0 - 100% open command.

Hope this helps.

 

This tutorial will give you agood idea:
https://web.archive.org/web/20081102080750/http://claymore.engineer.gvsu.edu/~jackh/books/plcs/