PIDFF tuning help needed Unity Pro

[ganutenator]

I am being thrown to the wolves and am driving to New York on Monday to tune a PIDFF loop. I am the wrong person to do this.

Back in the day when I was using Proworx Nxt I had some good starting numbers for the P and the I for processes that I routinely ran into.

The process.. what I know so far...

Centrifugal Water Pump (300gpm max flow rate)
Aft of the Water Pump is a flow meter (paddle wheel type)

PIDFF needs to keep the flow at the flow rate sp.

Any body have any experience w/ tuning this particular PID instruction?

 

[scalelar]

I don't have the software with me at the moment so this is from memory(and my memory is bad). It is still a PID loop. I like it a lot more than than the old 984 PID2. The proportional, integral and derivative are to me more straight forward. The loop has a PIDFF parameter data type where most of the loop is set up ie the gains and limits. You can use the TRI and TRS inputs to manually set the loop output to do some tuning.
Good luck

 

[MRobert]

Look at this site for starting values for PID tunings
http://www.expertune.com/tutor.aspx#InitialPID

 

[ganutenator]

I read all of the help files and still no units. i.e. repeats/min on integral?
I talk to tech support and he says it is in repeats/min yet when I ask him for some starting values he recommends 3 for gain and 10 sec for integral. I ask if I type in 10 and he says yes. This seems to go against his repeats/min previous answer. Has anyone used this instruction. I have read all of the help and links.

 

[ganutenator]

5) Attempted to tune the PID loop for the water injection pump. The dead range between 0 and 20 hertz and the change in pressure made this extremely difficult. If I tried to make the PID function fast reacting to changes in flow , then it would immediately go out of control when pressures changed and the new dead range was between 0 and some other hertz number. I made a compromise so that the flow would chase the set point, but still react to process changes. This caused a new problem of a slow start up.

6) Fixed new slow start up problem. Put a conditional statement in front of enable pin on PID block so that PID is reset on startup and mistakenly overshoots on start up to ramp the water injection pump up quickly. More tuning and tech support is needed on this issue. Multiple Social Engineering Calls to Schneider tech support only yielded "the entire tech support staff is in a meeting".

 

[ganutenator]

the help for the PIDFF instruction does not show the units for the PIDFF function (minus formulas that I don't understand). Tech support said that P is gain (larger # means more gain), and I is repeats per minute ( larger number means more error checking ?). In reality, any gain more than .02 causes the loop to go unstable w/ a mixed mode of 20 seconds of I and a 5 second sampling time on the PIDFF block. And a max 5.5 units per second max output modifications limit. HELP!

 

[scalelar]

ganutenator
Yes an increase in gain will give a larger output per error. The integral would be t#10s for 10 seconds. On the enable input of the PIDFF I used a clock input so the loop wasn't solving all the time. To solve your slow startup problem a bias might help. I'm not sure about dead range.

If you search for control guru on this site you should find a link to the controls guru website. I used his method to tune several loops and the integrals were dead nuts.

 

[ganutenator]

The problem that I am having is this...

My centrifugal pump is pumping into an injection manifold in which the pressure changes.
Some times the vfd has to be running at 25hz to start flow, then flow increases rapidly. If the vfd backs down only to 19hz then everything is ok. If it drops below that, then flow stops again. How can I possibly tune this loop.

It is working poorly now at 0.02 gain & t#10s integral w/ a 1 second sampling time. This is ****.