Oscillating PSI

[ptonsparky]

The default setting for the yaskawa IQ1000 is 2.00 for P(b5-03) and 3.0 seconds for I(b5-03). If I were you, I'd call the tech line at yaskawa and get their advice. They've always been very helpful for me.

i see your using the drive wizard. I save all my modified parameters for each installation on my laptop with it. I haven't used the trend recorder before. I'll have to try it out. I usually just use the signal monitoring mode while I have the laptop hooked up to the drive.

The tech line is very helpful and I will call them again if I need to. I feltthe control is a bit tight for my application

Defaults for the P1000 are both 1.

 

[Smart $]

Regardless of what I is set to, the graph shows approximately 7 changes in control state every two seconds. ...

That's just it. The I setting controls how often a change is made via the PID control. A setting of 10 seconds says the PID is not making the changes. It is possible for the derivative function to destabilize a system, but he did not report a "D" setting, which suggests he has it turned off.

 

[ptonsparky]

That's just it. The I setting controls how often a change is made via the PID control. A setting of 10 seconds says the PID is not making the changes. It is possible for the derivative function to destabilize a system, but he did not report a "D" setting, which suggests he has it turned off.

D is turned off. Default.
I'm looking at changing the Primary Delay Time Constant, which, if I understand, will slow up the response. (One of the hints a few pages latter in the manual.)

 

[retirede]

I had a similar issue with a hydraulic servo system many years ago, before today's sophisticated controllers. We added a dampener to the hydraulic side to solve it. It was basically a small air bladder inside a metal tube.
I don't know if something equivalent exists for an irrigation system. It would probably need to be too large to be practical.

 

[Ingenieur]

I had a similar issue with a hydraulic servo system many years ago, before today's sophisticated controllers. We added a dampener to the hydraulic side to solve it. It was basically a small air bladder inside a metal tube.
I don't know if something equivalent exists for an irrigation system. It would probably need to be too large to be practical.

You can put a subber on the press xdcr

P is always active
I integrates error over a period then adds to P
Output = P x e + I x int e + D x de/dt

I did not think I was the actual int time
I thought The loop time was
and I was a gain applied to it

P is a gain
if error (desired - act feedback) is 2% and P is 2 the output is changed by 4%

honestly I don't see an issue?
Lower P to say 0.25 and I to 1
rule of thumb is I = P x 4 for a starting point

 

[ptonsparky]

Had customer let me know when the system would be running again so we could do our tweak to the Primary Delay Time Constant. I figured the oscillation was about .29 per second and we were to enter a delay just a bit over. We used .3.

When we got there the pivot was in full operation with end gun and swing arm in full bloom. Motor HZ was maxed at 60 with amperage and PSI bouncing around 124 and 49. (Surprised it was in operation as we thought we had changed the FLA to 117.) We entered the .3 variable even though we did not expect to see any results while the pivot was in this field position. Wrong. Amperage dropped to 116 and PSI stabilized at 50.

I did not expect the amperage to go down. Was the previously tight control causing this? It would seem so.

 

[Smart $]

Had customer let me know when the system would be running again so we could do our tweak to the Primary Delay Time Constant. I figured the oscillation was about .29 per second and we were to enter a delay just a bit over. We used .3.

When we got there the pivot was in full operation with end gun and swing arm in full bloom. Motor HZ was maxed at 60 with amperage and PSI bouncing around 124 and 49. (Surprised it was in operation as we thought we had changed the FLA to 117.) We entered the .3 variable even though we did not expect to see any results while the pivot was in this field position. Wrong. Amperage dropped to 116 and PSI stabilized at 50.

I did not expect the amperage to go down. Was the previously tight control causing this? It would seem so.

Seems so.

Doesn't a VFD use measurement of the output as sort of a feedback controller... of which the Primary Delay Time Constant is part of that control loop? I'm just wanting to verify it was the PID control that was not causing the oscillation.

 

[ptonsparky]

Seems so.

Doesn't a VFD use measurement of the output as sort of a feedback controller... of which the Primary Delay Time Constant is part of that control loop? I'm just wanting to verify it was the PID control that was not causing the oscillation.

My guess is that it was the PID control causing the oscillation, by responding to quickly.

What amazes me even more is that the 100 HP motor pumping 900-1000 GPM can respond that quickly.

 

[gadfly56]

My guess is that it was the PID control causing the oscillation, by responding to quickly.

What amazes me even more is that the 100 HP motor pumping 900-1000 GPM can respond that quickly.

I think what was happening is that the VFD and PID were running in the same "control space", but because there is a delay as each reads the variable it's trying to control, they were perfectly arranged to oscillate. By increasing the delay you smoothed out the interaction, probably allowing the "I" function on the controller to operate properly.

 

[Smart $]

My guess is that it was the PID control causing the oscillation, by responding to quickly.

I'm thinking it was not caused by the PID. PID can respond quite quick, especially digital ones... but only when the "I" setting is quite low. At 10 seconds I do not see how the PID control was making an adjustment several times per second.

What amazes me even more is that the 100 HP motor pumping 900-1000 GPM can respond that quickly.

My understanding of VFD's is that they use output measurement as a form of feedback loop... which is where the Primary Delay Time Constant setting you adjusted comes into play. My guess is that the pumping system has a little bit of cavitation or bubble oscillation going on.

 

[ptonsparky]

I'm thinking it was not caused by the PID. PID can respond quite quick, especially digital ones... but only when the "I" setting is quite low. At 10 seconds I do not see how the PID control was making an adjustment several times per second.


My understanding of VFD's is that they use output measurement as a form of feedback loop... which is where the Primary Delay Time Constant setting you adjusted comes into play. My guess is that the pumping system has a little bit of cavitation or bubble oscillation going on.

Went back this AM and did short recording while well is feeding short pivot. PSI was steady at 50. Wouldn't the cavitation still be apparent on the PSI if that was the cause?

 

[Smart $]

Went back this AM and did short recording while well is feeding short pivot. PSI was steady at 50. Wouldn't the cavitation still be apparent on the PSI if that was the cause?

Good point.

 

[Cow]

We've been using quite a few Yaskawa IQPump controllers lately, and our Yaskawa rep has been praising the software. I really need to take a stab at programming one with the software just so I can see all the cool trending you can do, that I've been missing out on....

 

[ptonsparky]

We've been using quite a few Yaskawa IQPump controllers lately, and our Yaskawa rep has been praising the software. I really need to take a stab at programming one with the software just so I can see all the cool trending you can do, that I've been missing out on....

Beats the heck out of trying to read and thumb thought the HMI that can't be read in daylight.
Price is good too.