Information about DCS

  • Thread starter santosh kumar patro
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santosh kumar patro

In AI card we are getting 4-20mA from transmitter as output and giving this to AO card slot and from this AO card's output 4-20mA is given to the contol valves but why can't we give the output of AI card slot to the control valve present in the field directly? plz explain the reason in detail sir for which i shall thankful to you.

Ashok Kumar Hait

Something is wrong in your understanding. Normally the AI card will not have any output. If you are using a DCS, the sensor signal from a field transmitter will go to a AI card first. The signal goes to the PID block inside the Controller module for PID control. The output from the PID controller goes to the AO card for physical interface with the final element. The AI card can't give a 4-20 mA output. Pl. check again what you are using.

Ashok Kumar Hait
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I'm sure you can direct a transmitter's output directly to a valve in any DCS; hence the bigger question, why would you want to?

A DCS is a CONTROL system. A process variable from the transmitter is not the same as the control output from a controller.

Why use a DCS if all you have to do is wire a transmitter to a valve?

There's something missing here . . . .