FEC's to Drive Fast Acting Actuators

[plotzy]

With all the dampening built into CCT, has anyone had any luck driving 3-5 second fast acting actuators with FECs? Thinking about a VAV box application as an option opposed to a venturi. I'm just worried that the delay in processing time will cause the actuator to slam open and closed and as it chases the pressure.

[mechdorn]

I tried one time, the results were not good. Like you said it just slammed open. Fortunately for me, it really didn't matter the damper just went full open. It was for makeup air into a lab space.

[Ithos]

Try adjusting the time constant in the attributes for the inputs. I had to do that once since the delays were causing havoc. These selftuning PIDs aren't really ideal for dynamic systems. Derivative usually gets more emphasis for rapidly modulating controlled variables.

[Norriski Tech]

I took a PCG/PCT class awhile back, and the loop tuning portion. Started with 60 to 70% of the time the adaptive tuning doesn't work. My next thought was ,why would I use that?? I turn off the adaptive tuning, and self tune all the pids. I've had good success doing that. In your case, I think that would be the only chance, and its still going to be tough!!

[catalina_mike]

Venturi valves are obviously better control because of the way the valve opens a closes. A vav box is hard to control because of the damper. If you can tune the PID and the box is sized correctly you will be able to do it but it is a real pain. We did a small hood and room pressure for one customer using VAV's and VFD's on room and hood exhaust and because of our programming capabilities we are able to do relatively good control. It is in no way the same as the Phoenix or TSI stuff we have done and do, but it met the budget needs of the customer and is reliable.

[Jmartin10]

We have mastered the "art" of using FECs for fast ascitng actuators.

[billcontrols]

On the last 2 JCI NAE jobs that I have followed the branch into, the JCI techs had set a "Tuning Reset" schedule into the NAE to rest the tuning on a Daily or a Weekly basis. I guess the branch has trouble making it work too.

On 1 of those sites I had to turn off the tuning on classroom unit ventilators because, over time, the tuning would get too sluggish and let the room heat a couple of degrees above setpoint for an hour or two in the morning, then come back down to setpoint in the afternoon. Of course the "problem" was the units were "cold" in the afternoon (at setpoint). Manual tuning keeps the room +-0.5°F of setpoint most of the time and complaints seemed to go away. Funny how no one ever tells you it is working better when you make these kind of adjustments.

[Jmartin10]

Auto tuning cause more issues than it prevents. I will rarely use auto tuning to try to find better numbers but the longer I use CCT the more I have figured out what numbers work well and I no longer use auto tuning. Especially with the known issue fo the PID tuning the prop band down to 0 and going unreliable. Before going unrelaible it operates as binary controller toggling between 0 and 100.

[catalina_mike]

Auto tuning cause more issues than it prevents. I will rarely use auto tuning to try to find better numbers but the longer I use CCT the more I have figured out what numbers work well and I no longer use auto tuning. Especially with the known issue fo the PID tuning the prop band down to 0 and going unreliable. Before going unrelaible it operates as binary controller toggling between 0 and 100.

I completely agree, Auto tuning will kill you slowly or fast either way use it to find reasonable numbers then turn it off! Our optimum start will get (learn) some pretty good heat-up & cool-down numbers to start with. But over time because of auto calculating you can miss a mechanical issue creeping up onto the unit. It just keeps starting earlier and earlier as the capacity of the equipment degrades for whatever reason and you wont catch it until its a big issue.

[plotzy]

Thanks folks!