How to protect a legacy plc module

[fishenguy]

I'm installing a Pro-face HMI/PLC. Some of the outputs will operate air valves (approx. 3-5 watt coils) that are also controlled by an old Symax 400 plc. I intend to use the same 110vac power supply for both plcs. The company is VERY dependent on the Symax, so I don't want to mess with it.
Should I take any precautions connecting the two outputs together to the same coil?
As I said before, I'll be using the same 110vac power.
I just don't want anything to happen to the Symax output modules.

Thanks for the help. Dave

 

[jrwb4gbm]

Probably a small interposing relay driven by the plc output would reduce the risk of plc output failure.

 

[fishenguy]

That's what I was planning..Thanks.

 

[Lancie1]

Will these air valves be driven by two different PLC ouputs (now in parallel configuration)? Will you have a need to know which PLC is doing the driving? Do both PLCs have 120 volt relay-type outputs (or are the outputs of one some other voltage?

(Because they have the same input voltage does not always mean that the output voltage is the same.)

 

[fishenguy]

Will these air valves be driven by two different PLC ouputs (now in parallel configuration)? Will you have a need to know which PLC is doing the driving? Do both PLCs have 120 volt relay-type outputs (or are the outputs of one some other voltage?

(Because they have the same input voltage does not always mean that the output voltage is the same.)

Actualy what will happen is the newer PLC (Pro-Face) will turn on a relay 24vdc coil. The 110vac from the Symax output module supply voltage will go through the NO contact of the relay and out to the valve.

No, I won't need to know which PLC is doing the outputting.

Dave

 

[Lancie1]

Okay, that all makes sense and sounds like it will work.

 

[bce123]

do you need to turn on the valve from both plcs? doing it from the relay only allows you to turn it off from both.