Outputs fluctuates between on and off


An OPTO22 system has been installed at LBC Antwerp since 2009.
This is a plant with tank parks for the storage of chemical and petrochemical products.
Input: Reading error messages / high pressure / low pressure / flow switching / level switching …
Output: Operating sprinkler for cooling the tanks.
The controls are started and stopped from the graphic package.
All hard and software already installed works without problems.
Now a new tank park has been added.
The inputs work normally.
Everything goes wrong with the outputs.
the graphical package sets a Numeric variable “True => FLAG_MOV_T204_ON_OFF”
if this variable is True => FLAG_MOV_T204_ON_OFF, output is sent “Turn On => MOV_T204_OPENEN” and stops when the level switch “On => LS_MOV_T204_OP” is active.
The output fluctuates between on and off.
To perform a test, I modified the program from start block 0 to a simple program FLAG_MOV_T204_ON_OFF = True => Turn On RES_Q8_2
and FLAG_MOV_T204_ON_OFF = False => Turn Off RES_Q8_2 and back to start block 0.
The rest of the program is still there but is no longer controlled.
This output “RES_Q8_2” has never been used and works normally on, but output MOV_T204_OPENEN was also controlled fluctuating on / off while this is impossible because this part of the program is no longer used.
It seems that a part of the old program remains present during programming.
Gladly help because this program had to work yesterday and the delivery date is Friday.


Quick thought - pretty sure PIDs that you don’t deliberately clear in PAC Manager keep their old settings if they’re not asserted in a new strategy, perhaps this is the case for you?


Possible causes:

  1. As JimmyTime states, an old PID is setup (using TPO too)
  2. Event Reactions are setup
  3. Another strategy on another controller is communicating to your IO Unit
  4. There is a problem with your strategy logic

The first two options would be cleared by a reset to defaults on the IO Unit: PAC Manager, Tools, Inspect for your device then go to Status Write and run the “Reset to defaults and Restart Device” and then re-program and run your strategy.

The third and fourth possibilities would be confirmed by temporarily removing the network cable from the IO Unit while the oscillation is happening and see if the oscillation stops. (Unless this is an R1 or R2 and the problem is the strategy logic - in which case the problem would stop if you stop the strategy).