Hello All,

I have this challenge with a controller I am trying to program. I need to understand what is actually happening and that is the reason why I have written to this forum. I plan to contact the manufacturers of the controller for help in addition but I do not want to be lazy. I want to do my research first.

Basically my controller reads a PV (pressure) and varies the output (actuator). When I break the input or remote setpoint signal, I get a controller error, which is normal. On restoration of the input or PV signal, the controller error clears, which is also fine. It is what happens to the output which is of concern for me.

The actuator output does not 'freeze' when I break the input signal but goes down to zero. On restoration of the signal, the actuator output falls to zero, stays there for some time (maybe "integrating") and then rises to the value it was before the signal break.

I would like a bumpless transition from loss of signal to restoration, where the controller just continues acting from where it was without having to ramp the output first to zero, 'soak' for some time, and then rise again to the value pre-signal break.

Has anyone successfully accomplished this bump-less transfer on any controller?

Regards.

 

What type of controller are you using?

 

is this a PLC of some sort? if so, you can readily program this behavior.

if it is a DCS, it may or may not be possible to do so with an existing logic block, but you could probably program it.

personally, I would program the loop to switch into manual on loss of PV. normally this results in a bumpless transfer and the output should not change. when the pv is restored, program it to return to auto, again, this should be bumpless.