Discrete DCS <--> PLC interfacing without a Gateway

[Scott180zip]

I need to control a solenoid currently connected to a PLC from an ABB DCS in a remote part of a plant. So the PLC and DCS would "share" control of the 24VDC Solenoid. Any ideas on the best way to do this without a gateway? Ex: Use a PICO controller as interposting relay, etc..?

 

[godfrey]

Use an interposing relay but it can be a cheap SPDT type like an ice cube for about $15. Use the ABB to energize the relay when solenoid action is needed. Wire the contacts at the relay to an unused PLC input. Program the PLC to recognize the digital input as a call to energize the solenoid.

 

[Scott180zip]

Thank you. Currently the solenoid is operating air to a diaphragm pump. This pump runs when the PLC calls for it. Doesn't Adding this interposing relay now opens up a conflict between the DCS and the PLC when both call for the pump at the same time?

 

[milldrone]

Doesn't Adding this interposing relay now opens up a conflict between the DCS and the PLC when both call for the pump at the same time?

Not if you use the same control power supply.

 

[godfrey]

There would be no conflict if the original call by the plc and the digital input representing the ABB-activated relay were programmed in parallel (an OR statement). That way if either the PLC or the ABB called for the solenoid, it would actuate.

 

[Scott180zip]

I appreciate the wiring diagram. Thanks for your help.

 

[Scott180zip]

Thanks Godfrey, that answers my question precisely. The next response also covers the power supply issue - which I was about to think about next.

 

[Scott180zip]

Reply to Power Supply (Re:Milldrone):

If I use for the interface a dry contact relay, wouldn't the power supplies be isolated? Therefore it would not matter, correct?

Thanks...