controlling presure with VFD

Hi
I'd to control hydraulic holding pressure (almost no flow) with rpm via ABB VFD and fixed pump. This drive has no PID inputs
I can "almost" do with a pid loop in micrologix 1500, but it still hunts.
Is there an economical gizmo that can take a 0-10 input from a pressure transducer, a 0-10 input from plc (for setpoint) and a 0-10v output to vfd to close the loop? Only for pressure, my flows are working fine for all other functions as is.
For what it's worth, most modern injection molders are using a servo drive/motor with fixed pump to control flow and pressure. No more proportional flow or pressure valves.
This a poor mans version of that...
Thanks a Happy Holidays

You could try a process controller. You may have to send the setpoint from the PLC to the controller over Modbus. However, the process controller will only perform a PID calculation, just like the PLC does.

My suggestion is to use a pressure relief valve to prevent over-shoot. You might find an air-pilot variable pressure valve that you can control with your PLC

You should be able to do it with PID logic in the controller.
Maybe its not tuned well enough.

I'm with GTUnit, what is the value of a standalone controller? Hunting you say? Try detuning, try adding deadband, try lengthening the update time of your PID block, ensure you are properly updating your PID block, etc.

Check the scan rate in the PLC, the conversion time of your analogue I/O, and the response time of the pressure sensor.

You need to run the PID loop very fast but the limiting factor wil be your I/O. You cannot run the PID loop faster than the I/O will update or you will process the same error twice.

You probably also need to map the response of the pump in terms of rpm X = pressure Y. Build a lookup table from the data and interpolate it to predict what speed the pump needs to run at to achieve a given pressure and sum that with your PID correction.

Nick

You could always resort to some op-amps, resistors and a couple of capacitors if you need more control bandwidth.

Nick

I'll try working with the PID more. I really thought it should do the job, but I searched and found a bunch of posts and so many times someone on the forum would say "plc isn't fast enough" get a motion controller.
This should be less demanding than closing a velocity loop.
It's a lack of tuning skill on my part.
Thanks

see post #2 opinion, using process controller.

check the digital input function,

www automationdirect com/adc/Overview/Catalog/Process_Control_-a-_Measurement/Pressure_Sensors/Pressure_Transmitters

www automationdirect.com/static/manuals/processctrlm_08_09/processctrlm_08_09.pdf


www acdrivesguide com/fluxvectorcontrol html

https://library.e.abb.com/public/14f3a3ad8f3362bac12578a70041e728/ABB_Technical_guide_No_1_REVC.pdf

https://www02.abb.com/global/dkabb/dkabb501.nsf/0/7741814b4738da7bc125793d00357e6c/$file/Frekvensomformerh%C3%A5ndbog-TechnicalGuideBook_1_10_EN_REVF.pdf

AC drives - flux vector control using PWM

Most ABB drives have PID capability built in. What model do you have?

osmanmom said:

see post #2 opinion, using process controller.

check the digital input function,

www automationdirect com/adc/Overview/Catalog/Process_Control_-a-_Measurement/Pressure_Sensors/Pressure_Transmitters

www automationdirect.com/static/manuals/processctrlm_08_09/processctrlm_08_09.pdf


www acdrivesguide com/fluxvectorcontrol html

https://library.e.abb.com/public/14f3a3ad8f3362bac12578a70041e728/ABB_Technical_guide_No_1_REVC.pdf

https://www02.abb.com/global/dkabb/dkabb501.nsf/0/7741814b4738da7bc125793d00357e6c/$file/Frekvensomformerh%C3%A5ndbog-TechnicalGuideBook_1_10_EN_REVF.pdf

AC drives - flux vector control using PWM

Click to expand...

The "process controller" suggestion is what I was fishing for....
This model doesn't have PID inputs. It's quite old.
I do have another on a different press that does. Maybe I could switch it out.

If you go process controller route.....
I would recommend Azbil SDC35 or 36.
Azbill used to be Yamatake and they make a lot of process controllers for Honeywell.


The controllers work great and are easy to set up, and they have a fantastic and fairly fast auto-tune function.
I have used/setup/tuned almost every process controller out there and these are my favorite.

Thanks, I'll check those out.
Autotune is my friend...

dougpdf said:

The "process controller" suggestion is what I was fishing for....
This model doesn't have PID inputs. It's quite old.
I do have another on a different press that does. Maybe I could switch it out.

Click to expand...

In order for it to not have PID functionality built-in, it would have to be an old GX or LC series analog drive, from when Asea bought the old Parameterix company, right before Asea merged with Brown Boveri to create ABB. That drive was only sold with an ABB name on it for about a year before the ACS400 was released, and I'm pretty sure every ACS series drive since then has PID functionality built-in. It's essentially a "freebie" once you have a digital drive. If you do have an old GX or LC series drive, and it still runs (shocker!), it's time to replace it anyway. Those drives were made obsolete over 25 years ago when ABB went all digital, there are no parts available any more.

There are no special "PID inputs" for a VFD, it uses the basic Analog input for the PV feedback, then the SP is entered via the keypad, and the CV is the VFD output frequency. Since the days of the original ACS 500 and 350 products, there has been a very simple and easy to use user macro fro setting up a PID control loop, probably one of the best things about that drive.

It's old, but not that old. I'll study it more.
Thanks, you guys have given me some great info.. as usual

dougpdf said:

It's old, but not that old. I'll study it more.
Thanks, you guys have given me some great info.. as usual

Click to expand...

DickDV is an ABB guy, I'm sure if you say which series you have, he can help you get started.

I used to be an ABB guy, but I dropped one of the "B"s and can't find it now...

Haha, cute.
Looks like I have an ACH550 and ACH400. I need to figure out this PID that's built in to the drive.