I am trying to help a friend/client with a pinch valve actuator controlled by a Moore 348 Fieldpac controller.

The folks at Seimens would only help so far as they say the device is obsolete. If someone could start a dialogue troubleshooting the device for a setpoint "hunting" problem I would appreciate it.

I am not a programmer or an engineer, just a humble former refrigeration tech trying to help a guy out.

 

Yokogawa now makes a compatible replacement. Y-348M

> I am trying to help a friend/client with a pinch valve actuator controlled
> by a Moore 348 Fieldpac controller.

 

Technically, setpoints do not 'hunt'. Setpoints are fixed and the process variable 'hunts' for any number of reasons.

The 348 manual is here:
http://tinyurl.com/9g6swbj

Try retuning the controller.

Find the 'gain' and whatever number it is, divide it by 2, enter the lower value, then see what the process response is.

It appears that the TUNE pushbutton might take you to 'gain':

TUNE Pushbutton (from the manual)
Pressing the TUNE button will first cause 'LOOP 1 TUNE' to appear in the 4-character display if FB13 has been configured.

When 'LOOP _ TUNE' has been selected, repeated pressing of the STEP DOWN button will step through the tuning parameters for that loop controller. STEP UP will reverse the sequence.

 

Is this a NEW problem or has it always hunted from the day you bought it?

If this is an old plant and the controller used to work OK then its much more likely that your tuning is fine and your valve is worn out. Rather than try to work around the problem by re-tuning you should probably check the valve positioner. If this valve is OK then have a good look around at other bits of the plant connected to this process. I'd lay money that you're dealing with an equipment maintenance problem that has nothing to do with the controller tuning.

Of course, if the controller never worked from the day it was supplied (or the day somebody replaced it and didnt set it up) then halving the gain will either make it swing slower or may have a decent chance of fixing it.

Rob
www[.]lymac.co.nz