Sign in to follow this  
Followers 0
Phil Izak

Powerflex 4 using Analog Speed Reference

14 posts in this topic

Hey everyone, I am using a Powerflex 4, part number 22A-D8P7N104, and am trying to control the speed with a 0-10V signal from my Micrologix 1400 PLC, part number 1766-L32BWAA. The issue I am running into is anytime I increase my speed, the drive runs straight to my maximum frequency. This happens any time I make a change in the program or sporadically while running. I am receiving the correct voltage when measuring the input to the drive, as well as, seeing the correct readings in the program. My raw input doesn't spike or max out in the PLC. I would appreciate any help on things I may have overlooked as I can't think of any off hand. I have done this set up several times in the past year with similar components. The only way for me to get it to behave correctly is to completely power down the system. Thanks, Phil

Share this post


Link to post
Share on other sites
Can you post a wiring diagram? This doesn't sound right.

Share this post


Link to post
Share on other sites
Here are the drawings for both the drive and vase unit of the micrologix. Glue Application (2)-Model.pdf Glue Application (3)-Model.pdf

Share this post


Link to post
Share on other sites
Thanks for the drawings - though I don't see a problem.

Share this post


Link to post
Share on other sites
Thanks for the quick replay B_Carlton. Like I said, I've done a few machines using the 0-10V reference without any issues, this one however is giving me fits.

Share this post


Link to post
Share on other sites
Sounds like it's time to swap in a spare unit to see if you've got a flaky drive on your hands...

Share this post


Link to post
Share on other sites
To verify if it is a drive problem, I replaced the AB drive with the old Eurotherm drive that we replaced and everything worked as it should. The only difference is that the old drive its incapable of running the required number of motors that are needed.

Share this post


Link to post
Share on other sites
How many motors are you running with this drive? What does the drive show for command frequency when it acts up [d002]? Edited by OkiePC

Share this post


Link to post
Share on other sites
I am running up to 7 motors with the drive. I'm not sure why I haven't checked that setting, but I will make sure to double check it now. When checking the reference voltage at minimum speed, and it acts up, I am reading about .3 volts.

Share this post


Link to post
Share on other sites
You may also want to put your meter on AC volts to check for ripple on the speed reference signal. I suspect that noise is getting to it, perhaps coinciding with the acceleration of the motors. I am not sure if a regular DVOM will show the noise, but it may. It also may be able to pick up a frequency. Are the VFD output wires sufficiently isolated from the speed reference wires? Edited by OkiePC

Share this post


Link to post
Share on other sites
Sorry it took so long to get back, we were running with the old drive yesterday. I put the AB drive back in this morning and did some playing around with it. I am only trying to run a single motor for now. I initially thought that the issue was when our encoder spun the wrong direction, confusing the drive, but that theory was quickly disproved on a power cycle and then trying to run it normally. I checked the the speed reference display, D002, and it shows a speed reference at maximum frequncy. I then checked my speed reference again and I am getting .127 Vdc, which should be turning the motor slowly, but I am running full out. When I switch over to AC to see if there is a ripple, it's holding constant at .025Vac. However, when I check my +speed reference to shiled I am getting .678Vac. I don't know if that's where the issue is or not, but I would think that the issue is with the drive as when I put the old one in, everything worked. Also, my speed reference stays stuck at full frequency, which makes sense since I can only get it to run normal again upon a power cycle. Running the encoder backwards definitely causes the speed reference to shoot to maximum. I am not sure why it causes an issue, when checking my speed reference while having a co-worker spin the encoder backwards, my speed reference does not change. Edited by Phil Izak

Share this post


Link to post
Share on other sites
Okay, so is this VFD running in flux vector mode (closing the speed control loop with an encoder wired to the VFD)? If so, I suspect that the issue is with the encoder configuration/wiring for the drive. You may be able to isolate the problem by running the VFD in sensorless vector mode to see if this alleviates the problem. This may or may not be feasible depending on the application. If the drive still acts goofy in sensorless vector mode, I think it simply has a faulty analog input. I just reviewed the drawings you posted and I think you should remove the connection of the shield from terminal #16 on the VFD. That terminal is for the RS485 shield according to my manual. The shield should be connected to ground. The meter readings sound pretty normal...no big AC ripple, although it doesn't completely rule out noise, but if I had to make a determination, I would say the VFD simply has a bad analog input converter. I have seen this happen with a variety of drives where the signal works okay for part of the range or it scaled incorrectly by the drive because of some sort of internal damage.

Share this post


Link to post
Share on other sites
Thank you everyone. I received a new drive today, made the swap and everything is working correctly. It looks like it was a bad analog converter in the drive. I put this new drive through the paces, both with a single motor running and with all 7 motors running with success. No more ramping to full speed sporadically. Again, thanks for all of the suggestions.

Share this post


Link to post
Share on other sites
Phil, A few more things that I didn't see while speed reading was in regard to the set up of the analog input. For example, if it was expecting 0 - 20 mA or 4 - 20 mA and you put voltage to it, depending on the input impedance, it might see 20 mA already. I have not used the PF4 but I have used the PF40 and 700s. Another way to get in trouble is to have a the wrong source selected for the speed reference. In the 40s and 700s, there are at least 5 options for the speed reference (this is programmed in a register) also some other things like the Start signal are also set up this way (Stop always works). If there is a HIM module, the speed reference could be setup to come from it or it could come from a front panel pot, etc. You will only get one, so if it is an analog input, make sure that it is the right one. Some of the ones that I have used have more than one analog input. To get control of this kind of situation, I like to start from what I know and work through to the end. For example, you could use a signal source Like a Fluke 707 or 715 (email me and I'll tell you where to get a nice one). You get the drive ready to go and then you feed in your signal and verify the 0 volts = 0 Hertz and then check for linearity by going in 25% jumps like 2.5, 5, 7.5 & 10 Volts = 15, 30,45, 60 Hz respectively. A second way that is less sexy, is to put your volt meter on the the speed reference input and compare it for linearity all through your control range. Of course, doing it that way, you have to be able to get your control output to go where you want it. Make sure that the signal coming out of your analog output is what you are expecting. I haven't done the ML1400 but I have done 1000, 1200 and 1500. If I remember correctly, at least some of these are 14 bit but program like 15 bit. So you use 32767 as full scale, but in some, only the even numbers are valid so the LSB is not present. Make sure the math is correct. If you are going to do this work, then you need the right tools. When you need something in the business world and you don't have it, then you wind up paying for it over and over. You are bringing back fond memories...I'm just finishing up the design for an MCC with 17 PF40s in it! So I'm going to be in your shoes for a while later this summer....17 times! If you don't have a current / voltage source tool, sent me an e-mail. <robert.applegate@comcast.net> Best Regards, Bob A. Edited by Bob A.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now
Sign in to follow this  
Followers 0