Wire two output channels to one solenoid
- Thread starter elmatador
- Start date
harryting
Lifetime Supporting Member
I don't think that's a good way of doing thing... why not use PLC logic? What's your intend action for one on, both on, etc..?
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milldrone
Member
I can think of several reasons to do this ranging from "I'm bored, let's do something" to "I have two PLC's and I need them to both turn on the same field device". The reasons you want to do this determine how.
We have this whole new SIL-2 system. They want to have redundancy for the control to the ESD valves. So we need to wire a single solenoid to two seperate output channels
Christoff84
Lifetime Supporting Member + Moderator
It depends if both PLCs use the same power source or not. If they do, just put the 2 wires together (generally a diode would be a good idea to have on both lines). If not, you'll have to figure out something with relays connected in parallel to the solenoid coil.
When your dealing with safety, why not use 2 valves as stated above?
When your dealing with safety, why not use 2 valves as stated above?
I have been trying to explain it to the guys to use two valves. This would be a much better method.
I have noticed in SIL-3 systems where they have three pressure transmitters on the line.
We have around 20 esd valves on this site. I am not sure if the process company is just trying to cheap out. they are keeping me in the dark
I have noticed in SIL-3 systems where they have three pressure transmitters on the line.
We have around 20 esd valves on this site. I am not sure if the process company is just trying to cheap out. they are keeping me in the dark
harryting
Lifetime Supporting Member
Maybe someone who does safety circuit can enlighten me. Isn't a safety relay typically used in such situation?
OP said it's for a ESD (emergency shutdown valve), so the output from PLC is Normally energized and the ESD shuts when EITHER signal is lost. Correct?
OP said it's for a ESD (emergency shutdown valve), so the output from PLC is Normally energized and the ESD shuts when EITHER signal is lost. Correct?
sthompson
Lifetime Supporting Member + Moderator
I would not connect two outputs together, that is a good way to damage them if they are fighting each other. Your options depend on what you want to do. Is it an either or situation, or do both outputs need to be on to allow the Solenoid to engage? What if one PLC says solenoid off, and the other PLC says solenoid on? What needs to happen then?
It is certainly a solvable problem, but you have to set out your exact parameters first.
Stu.....
It is certainly a solvable problem, but you have to set out your exact parameters first.
Stu.....
normally these ESD valves close on a hard ESD pushbutton, fire, or hi hi h2s/lel. In such a situation we normally drop the power to the output cards. So the ESD valves would loose power and would return to their fail-safe position which is FAIL CLOSED. This would also apply to blowdown valves which would just go Fail Open on loss of power
BudW
Member
Long ago this configuration was the standard for places like Chrysler. Two (dual) outputs for each solenoid. One output from the high side of the line voltage or + for DC was placed on one side of the solenoid and a output from the low side of the line voltage or – (return) for DC was used on the other side of the solenoid. This was done just in case one of the output (relay) contacts were to weld together (stick together). If this happened and the solenoid was connected to only one output of course the solenoid would not de-energize (turn off). Now that the outputs have been changed from relay contacts to triac/SCR (electronic) with on/off feedback you do not see the dual output for solenoids as much.
Hope this helps
Bud
Hope this helps
Bud
well as far as i know it will have to be an either or situation. We will most likely have it timed in such a way where one output will try an open that valve. Once a certain amount of time has passed and the open switch has not registered then we would attempt to fire the other output to open the valve. If both commands dont register and OPEN status then we would ESD the Plant.
BudW
Member
Dual output to a solenoid, see attached PDF.
milldrone
Member
http://www.gminternationalsrl.com/?pid=D1047S
?
Edit: they have some sil3 stuff for NE loads here
http://www.gminternationalsrl.com/?pid=D1098S
?
Edit: they have some sil3 stuff for NE loads here
http://www.gminternationalsrl.com/?pid=D1098S
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