Actuator PLC Timeout

S

Shuntme

Member
Location
San Diego California
Occupation
Instrument Control Tech
Replacing a hydraulic 24" vertical Sluice Gate controls with an electric actuator. Hydraulic specs was 6in/min travel. New actuator(re-purposed) cycle time is much slower in the 10min range. Full open and full close limits are set correctly and Open and Close indications are also set correctly. Problem is the PLC is so outdated connection to it to change the cycle time is virtually out of the question. PLC is looking for the Open or Close indication with a 4min cycle time and the electrical actuator cycle time being 10min, the PLC shuts it down after 4min timeout either way and to continue the cycle I have to reset the command switch.
Is there an alternative solution if I can not access the PLC to increase the cycle time to 10minutes. Upgrading the PLC is not an option at this time as it is an RTU that controls other SCADA communications. Your ideas most welcome.
Thank you
 
ptonsparky said:
Depends on what happens in that six seconds difference.
Click to expand...
It's more like 6minutes difference. The PLC is looking for a 4minute time out indicating fully Open or Fully closed but the actuator cycle time is 10 minutes either way.
alan_505 said:
Add a separate timer, trigger it by the gate and use its output into the PLC.
Click to expand...
Not following on the add a timer approach feeding into the PLC as the actuator cycle time is 6 minutes too long. The PLC shuts down(times out) the actuator(40% Open/Close) after 4 minutes. Please explain/include more details
 
As Peter says, you need to change the PLC program. If that is infeasible, you could try a hack. Add stand alone timers that start 4 minutes after the actuator is told to move, closing the input circuit to the PLC, and time out after 6 minutes if the actual end of travel switch is not made, opening the input circuit to the PLC.

This explanation might not be the best. A logic diagram and wiring diagram would make it clearer. Gotta get to work. Maybe others can flesh out the idea.
 
Yes, minutes.
What is supposed to happen in those six minutes after the gate was opened originally?

Adding a timer to give the input at four minutes would work as long as you can tell the gate is in motion and it's positioning is not critically sensitive. Is the position at closing time another issue?
 
alan_505 said:
Add a separate timer, trigger it by the gate and use its output into the PLC.
Click to expand...
Awesome responses you all. I have been thinking along the same line for a count down timer to intercept the PLC shut down signal at the 4 minute mark. I will be looking at the control schematic today to see where I can intercept the PLC shut down signal and hold it for 6 minutes until the actuator stop limit switch times out then resets everything(auto). It's 460V - phase actuator with 120V Local control, Remote/Local(RTU) and a Remote/Remote(SCADA)
1. Local control at the actuator no issues
2. Remote/Local(RTU) is a Open/Off/Close maintained switch - times out and shuts unit down 6 min(40%) but reset with OFF then goes 100%
This is not a big issue since I'm at the RTU I can just reset it(Off-Open/Close)and it completes the 100% Open/Close commands.
3. Remote Remote(SCADA) is a Open/Close maintained. Stops at 40%. No Stop/Off to reset it from SCADA
Following TwoBlocked's scenario, a timer that kicks in in the 4 minute mark(40%) gives the PLC a fake cycle complete signal sounds like the solution. However will the actuator still continue to open/close 60% more to Full Open/Close positions. I tried that last week not with a timer but with a toggle switch but the PLC still shut down the actuator due to No Movement detected time out Fault. I will test that theory out again asap as my test last week was flawed. I used the 6 minutes timeout as that is when the current actuator actually shut down(PLC timeout) not taking into account the current actuator is very slow so 6 minutes was not what the PLC cycle time out was set for but 4 minutes. I calculated the 4 minutes later from the Hydraulic specs of 24" gate and 6in per minute travel = 4 minutes. So I will set my over-ride switch at 3min 45sec and see if the actuator continues to Open/Close 100%
Thank you all.
PS: A schematic for the timer if possible is greatly appreciated
 
ptonsparky said:
To be clear, what is RTU?
Click to expand...
Sorry. Remote Telemetry Unit. Just a Remote panel/Unit that houses PLC controls for remote instruments, communications, Back up Uninterruptible Power supply(UPS) etc. that relays field data to a Main Control Center(SCADA). It's a Remote mini control room if you may.
 
ptonsparky said:
Yes, minutes.
What is supposed to happen in those six minutes after the gate was opened originally?

Adding a timer to give the input at four minutes would work as long as you can tell the gate is in motion and it's positioning is not critically sensitive. Is the position at closing time another issue?
Click to expand...
Close Limit and Open Limit are working properly with no issues at end of travel
 
Sounds like you need to access the logic to make the actual timer adjustments, that or use a faster actuator... unless there is there a way to utilize mechanical leverage that can increase the stroke time.... any other work around seems to increase issues. Curious as to what you do, please update us.
 
4-20mA said:
Sounds like you need to access the logic to make the actual timer adjustments, that or use a faster actuator... unless there is there a way to utilize mechanical leverage that can increase the stroke time.... any other work around seems to increase issues. Curious as to what you do, please update us.
Click to expand...
Not sure where this comment fits into the phantom voltage issues discussion. Wrong post⁉️
 
Ok. Now I see where this fits. I think this is for my other Actuator PLC time out issue with the longer actuator travel time than the original plc programmed travel time which my SCADA integrator can't access the plc(they just want more $$$ to upgrade, lol) to change the cycle time.
I actually tested out my timer circuit today (work in progress). I figured out a wiring diagram to have the timer Delay Off contact to over-ride the plc time out at the 4 minutes 30secs mark until the actuator limit switch Open/Close stops the actuator(8min 20secs). However the timer power has to be reset at the end of the timer time out to reset the timer for the next command/action.
I've tested it on the Remote/Local and Remote/Remote(Scada) and voila!, it seems to work. Actuator does not stop at the 4min 30secs anymore. It goes the full 8min 20secs then actuator stops and the Timer resets ready for the next cycle. I just have to fine tune it now so the Timer setting matches the actuator cycle time of 8min 20secs or pretty close to it. (y) :).
 
Shuntme said:
Ok. Now I see where this fits. I think this is for my other Actuator PLC time out issue with the longer actuator travel time than the original plc programmed travel time which my SCADA integrator can't access the plc(they just want more $$$ to upgrade, lol) to change the cycle time.
I actually tested out my timer circuit today (work in progress). I figured out a wiring diagram to have the timer Delay Off contact to over-ride the plc time out at the 4 minutes 30secs mark until the actuator limit switch Open/Close stops the actuator(8min 20secs). However the timer power has to be reset at the end of the timer time out to reset the timer for the next command/action.
I've tested it on the Remote/Local and Remote/Remote(Scada) and voila!, it seems to work. Actuator does not stop at the 4min 30secs anymore. It goes the full 8min 20secs then actuator stops and the Timer resets ready for the next cycle. I just have to fine tune it now so the Timer setting matches the actuator cycle time of 8min 20secs or pretty close to it. (y) :).
Click to expand...
Sometimes you just need to lie to make logic work.

Eta: (Please, don't take that as a political statement, it wasn't meant to be.)
 
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