You are not registered yet. Please click here to register!


 
 
plc storereviewsdownloads
This board is for PLC Related Q&A ONLY. Please DON'T use it for advertising, etc.
 
Try our online PLC Simulator- FREE.  Click here now to try it.

---------->>>>>Get FREE PLC Programming Tips

New Here? Please read this important info!!!


Go Back   PLCS.net - Interactive Q & A > PLCS.net - Interactive Q & A > LIVE PLC Questions And Answers

PLC training tools sale

Reply
 
Thread Tools Display Modes
Old May 15th, 2019, 09:38 AM   #1
Stankdaddy
Member
United States

Stankdaddy is offline
 
Join Date: Sep 2017
Location: MS
Posts: 12
PowerFlex 525 Unable to Completely Stop Motor

I have a Allen Bradley PowerFlex 525 Drive w/480V. It's connected to a 1/3 HP motor that turns an auger for a feeder. I can drive the motor speed by feeding a manual 4-20 signal to the Drive input so I've taken the control system out of the loop.

The issue that I have is that I can't stop the motor. Even at the 0 set point which should be 4mA, the motor still turns. 20 mA is 100, 4 should be 0 percent. When I increase it, it goes faster, but I can't make it stop completely.

Has anyone see this behavior before? This is eating my lunch. I'm leaning toward getting a new drive if I can't figure this out today.

Please advise.

Last edited by Stankdaddy; May 15th, 2019 at 09:40 AM. Reason: Title not descriptive enough
  Reply With Quote
Old May 15th, 2019, 09:46 AM   #2
alive15
Member
United States

alive15 is offline
 
Join Date: Oct 2015
Location: al
Posts: 288
Where is the drive input coming from? Could you eliminate the 4 mA completely by adding some relay in between, to stop any current from going into the drive?
  Reply With Quote
Old May 15th, 2019, 09:46 AM   #3
tarik1978
Member
Morocco

tarik1978 is offline
 
Join Date: Mar 2010
Location: casablanca
Posts: 488
Check P043 the mimimum frequency Default: 0.00 Hz
also t095 [Anlg In4-20mA Lo] Default: 0.0%
and t096 [Anlg In4-20mA Hi] Default: 100.0%

Last edited by tarik1978; May 15th, 2019 at 09:49 AM.
  Reply With Quote
Old May 15th, 2019, 09:50 AM   #4
Stankdaddy
Member
United States

Stankdaddy is offline
 
Join Date: Sep 2017
Location: MS
Posts: 12
I'm using a Fluke to inject the signal to the drive. Also, let me try the minimum freq. That sounds promising
  Reply With Quote
Old May 15th, 2019, 09:58 AM   #5
Stankdaddy
Member
United States

Stankdaddy is offline
 
Join Date: Sep 2017
Location: MS
Posts: 12
Just checked that parameter and it's was already set to zero. This is bizarre. So I have a HOA switch with a pot as well. Even in the hand mode, it still wants to turn on it's own. Off is the only setting that makes the motor stop turning. Hand and Remote setting, the lowest setting on the pot is the same speed.
  Reply With Quote
Old May 15th, 2019, 09:59 AM   #6
Stankdaddy
Member
United States

Stankdaddy is offline
 
Join Date: Sep 2017
Location: MS
Posts: 12
Let me check These two parameters: also t095 [Anlg In4-20mA Lo] Default: 0.0%
and t096 [Anlg In4-20mA Hi] Default: 100.0%
  Reply With Quote
Old May 15th, 2019, 10:04 AM   #7
Ken Roach
Lifetime Supporting Member + Moderator
United States

Ken Roach is offline
 
Ken Roach's Avatar
 
Join Date: Apr 2002
Location: Seattle, WA
Posts: 14,613
Can this auger be spun by pressure from the load ?

What does the PowerFlex display indicate the output frequency is, when it's running at 4 mA analog command ?

Does the control system have discrete On/Off control of the motor, or is this meant to be a stop-on-analog control scheme ?

Parameter D361 should display the 4-20 mA command as a percentage of full scale; that will at least show you whether the drive thinks it's receiving an analog speed command.

Be sure you've stopped the drive (like with they keypad or a discrete stop) before changing the Analog Min/Max parameters, or they won't take effect.

Parameter T097 is the mA Loss action; you can set the drive up to stop if it sees less than 2 mA.

Also have a look at the User Manual for the functions of parameter T100 through T104, the "Sleep/Wake" analog threshold feature.
  Reply With Quote
Old May 15th, 2019, 10:14 AM   #8
Stankdaddy
Member
United States

Stankdaddy is offline
 
Join Date: Sep 2017
Location: MS
Posts: 12
Quote:
Originally Posted by Ken Roach View Post
Can this auger be spun by pressure from the load ?

What does the PowerFlex display indicate the output frequency is, when it's running at 4 mA analog command ?

Does the control system have discrete On/Off control of the motor, or is this meant to be a stop-on-analog control scheme ?

Parameter D361 should display the 4-20 mA command as a percentage of full scale; that will at least show you whether the drive thinks it's receiving an analog speed command.

Be sure you've stopped the drive (like with they keypad or a discrete stop) before changing the Analog Min/Max parameters, or they won't take effect.

Parameter T097 is the mA Loss action; you can set the drive up to stop if it sees less than 2 mA.

Also have a look at the User Manual for the functions of parameter T100 through T104, the "Sleep/Wake" analog threshold feature.
I get Zero Hz as the output Freq when we're giving it a 4 mA signal. There is no discrete on/off or start/stop in the control scheme. If I'm giving it a zero set point, the motor should not be turning. Let me look at the rest of your suggestions.
  Reply With Quote
Old May 15th, 2019, 10:48 AM   #9
Ken Roach
Lifetime Supporting Member + Moderator
United States

Ken Roach is offline
 
Ken Roach's Avatar
 
Join Date: Apr 2002
Location: Seattle, WA
Posts: 14,613
Quote:
If I'm giving it a zero set point, the motor should not be turning.
There's really no such thing as zero in the analog speed control world. How many RPM would you say the motor is actually turning ?

The Analog Sleep feature on the PowerFlex 525 is intended for applications like yours. As long as your normal range of operation isn't down in the weeds, it ought to do the trick.
  Reply With Quote
Old May 15th, 2019, 11:07 AM   #10
Stankdaddy
Member
United States

Stankdaddy is offline
 
Join Date: Sep 2017
Location: MS
Posts: 12
Quote:
Originally Posted by Ken Roach View Post
There's really no such thing as zero in the analog speed control world. How many RPM would you say the motor is actually turning ?

The Analog Sleep feature on the PowerFlex 525 is intended for applications like yours. As long as your normal range of operation isn't down in the weeds, it ought to do the trick.
According to my calculations, it's turning around 8 RPM @ 4 mA.
  Reply With Quote
Old May 15th, 2019, 11:31 AM   #11
kamenges
Member
United States

kamenges is offline
 
kamenges's Avatar
 
Join Date: Nov 2002
Location: Brillion, WI
Posts: 3,739
Is it 8 RPM fast at all speeds?

I have had some issues with moderately to heavily loaded PF525 drives in external speed control applications. In effect the drive is generating a slip comp frequency offset based on the detected load. From what i was told several years ago there is no way to really turn this off. What I was told to do at the time was set the nameplate frequency value to 1800. Since slip comp is based on the difference between nameplate and synchronous RPM, if there is no difference, there is no slip comp. Zero speed command became zero speed.
That worked for me.

Keith
  Reply With Quote
Old May 15th, 2019, 11:49 AM   #12
Ken Roach
Lifetime Supporting Member + Moderator
United States

Ken Roach is offline
 
Ken Roach's Avatar
 
Join Date: Apr 2002
Location: Seattle, WA
Posts: 14,613
Assuming an 1800 RPM motor at 60 Hz, 8 RPM is about 0.44% of the full command range for the drive.

A 4-20 mA command signal has a 16 milliampere span. That output result suggests that the drive is seeing 0.0044 x 16 = 0.071 mA as the command reference.

The PowerFlex 525's analog input resolution is a 10-bit A/D converter, and the "Frequency Accuracy" section in Appendix A of the user manual says the resolution of the frequency command is 0.5 % of the maximum output frequency.

Looking at it mathematically, the resolution of the A/D converter is 16 mA/ 1024 = 0.015 ma. The apparent command speed of the drive is a little under 5 counts out of 1024, or about 0.5 % of the maximum output frequency.

What I'm getting at is that a drive with an analog reference set very close to zero is probably still going to turn as long as it's being told to run, because it's hard to tell the difference between 4.0 mA and 4.015 mA with a ten-bit A/D converter.

The Analog Sleep mode allows you to set an input signal threshold under which the drive will actually stop. The drive helpfully flashes the display to let you know it's in "Sleep Stop" mode.
  Reply With Quote
Old May 15th, 2019, 11:56 AM   #13
FactoryTalktotheHand
Member
United States

FactoryTalktotheHand is offline
 
Join Date: Nov 2013
Location: Michigan
Posts: 508
You shouldn't be stopping the drive with a 4-20ma Signal. You should be stopping it by breaking the loop between terminals 1 and 11.
  Reply With Quote
Old May 15th, 2019, 12:01 PM   #14
alive15
Member
United States

alive15 is offline
 
Join Date: Oct 2015
Location: al
Posts: 288
Quote:
Originally Posted by FactoryTalktotheHand View Post
You shouldn't be stopping the drive with a 4-20ma Signal. You should be stopping it by breaking the loop between terminals 1 and 11.
I second this, you should cut the infeed somewhere on the drive.
  Reply With Quote
Old May 15th, 2019, 03:34 PM   #15
Stankdaddy
Member
United States

Stankdaddy is offline
 
Join Date: Sep 2017
Location: MS
Posts: 12
First off gentlemen, thanks for all the help. We were able to get back running so I can continue to commission my line.

We had to bring in a Drive expert to assist us. The culprit wound up being our Torque performance model setting. In order for the drive to not move the motor at 4 mA, we needed to change that model setting to Sensorless Vector Control. Immediately we saw a difference. Our expert liked you guys' idea about the sleep/wake threshold. He was concerned that the current could "creep" up and eventually start moving the motor if we have long periods of idle time. That setting would alleviate that.

He tried to implement the sleep/wake settings but couldn't get it to work. He's going to call me after he get's it worked out on his workbench back at his office.

So, in conclusion, Sensorless Vector Control (SVC) on parameter 39 was the solution. Going forward we are probably going to also employ the wake/sleep settings in tandem with this change to get us where we want to be.

I want to thank everyone that provided input on this problem.
  Reply With Quote
Reply
Jump to Live PLC Question and Answer Forum

Bookmarks


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Topics
Thread Thread Starter Forum Replies Last Post
DOL chnaged to PowerFlex 525 Issue lanester LIVE PLC Questions And Answers 3 March 28th, 2017 12:25 PM
PowerFlex 525 - Lobe Pump Flow PID Control freju LIVE PLC Questions And Answers 7 February 7th, 2017 08:55 AM
Simple way to program a lot of drilled holes?? neilfl LIVE PLC Questions And Answers 103 March 20th, 2012 10:23 AM
Help Rodter LIVE PLC Questions And Answers 18 April 24th, 2006 05:37 PM
how do I 'queue' machines using PLC & relays hickman LIVE PLC Questions And Answers 42 September 2nd, 2003 09:16 PM


All times are GMT -5. The time now is 09:16 AM.


.