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Old January 8th, 2003, 08:09 PM   #1
harryg
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Exclamation VFD Question

This is an off topic question, but, I'm hoping you VFD and control experts will give me some help as the manufacturer can't seem to. I'm retrofitting a starter controlled pump with a VFD. It's a Baldor 15V series 5hp drive. I'm running the drive in process control using the PID loop to maintain a constant pressure, my feedback signal is coming from a 2 wire pressure transducer giving me a 4/20ma signal. For the life of me I can't get this to work. Usually i run the 4/20ma to a voltage transducer to convert it to 10-1vdc, and it works fine which BTW I ended up doing. But there's got to be a way to make it work with the 4/20ma. Any help would be greatly appreciated, I wasted 2 hours with tech support today and came up empty. Here's a link for the manual. Also a crude wiring diagram, forgive me I was in a rush.
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Old January 8th, 2003, 08:17 PM   #2
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What exactly didn't work? Does your process provide the 24V for the pressure transducer, and your drive must utilize its own power source? Did you measure the current to prove the circuit worked when connected to the drive (I understand that it did when connected to the signal isolator)? Just looking for a little more info to go with.
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Old January 8th, 2003, 08:56 PM   #3
jrwb4gbm
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In the manual in your link you posted, on page 20 of 119, JP-2 needs to be changed from pins 2-3 to pins 1-2.(See Table 3-5) On page 34 of 119, it said to use analog input #2. (See Figure 3-23).There are some parameters that must be set also.(Refer to Analog Input #2).
Maybe this helps.
Sid
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Old January 8th, 2003, 11:10 PM   #4
harryg
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Thanks for the replies,

Sid,

JP-2 was changed to 1-2, Analog input #2 was used, Don't see a parameter Analog Input #2. Level 1 Input, Operating Mode is set as Process CTRL. The next parameter; Command Select is set as None. Level 2 Block Process Control parameter Process Feedback is set at
4-20mA. The next parameter; Setpoint Source is set at Setpoint Command.

What's not working is I can't get a feedback signal. The pressure transducer is supplied 24vdc from the drive. Also measured current and exercised the transducer up and down it's scale. It just seems like the drive isn't recognizing the input. I also swapped the drive to rule out faulty drive. I've got to be overlooking something.
Man I hate to lose!! mddr

Thanks for the help beerchug
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Old January 9th, 2003, 09:13 AM   #5
jrwb4gbm
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On Table 4-1 (page 63 of 119) under INPUT Command Select try setting it at 4-20 ma. Also Table 4-2 (page 70 of 119) shows the Process Control parameters. I can't help you much on the settings for that without being on site. I also have had problems setting up Baldor Drives.
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Old January 9th, 2003, 10:12 AM   #6
Tarrell Martin
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Earth

You might want to consider checking out a differant name brand drive. In the harse envirement of the carpet industry the Danfoss Drives seem to be holding their own and even out performing the more reconized brands with PID,Self Centering and good prices. I hope this will help in you future applications.
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Old January 9th, 2003, 10:17 AM   #7
Tom Jenkins
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I'm not familiar with Baldor specifically, but if you are measuing 4-20 mA at the input to the signal board then the VFD is obvioulsy powering the transmitter. I am assuming the polarity is correct - an easy thing to swap. In that case I would guess that the problem is in your set-up parameters.

Most VFDs let you monitor the actual input signal values from the set up keypad. Start with a 4-20 simulator if you have one, get to that monitoring display, and make sure the signal tracks. Then put the sensor back in the loop, mointor the mA with your meter, and make sure the display shows the same value.

And by the way, don't accept "I don't know" from your local distributor. If he doesn't know it is his job to find out who does and get you in touch with them!
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Old January 9th, 2003, 05:41 PM   #8
icky812
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Is your input a sinking or sourcing type?

What type does the vfd take?
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Old January 9th, 2003, 09:56 PM   #9
harryg
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Thanks Tom,

Pretty much tried your suggestions still have 0% feedback. And sadly it was tech support at the factory that I dealt with.
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Old January 10th, 2003, 11:58 AM   #10
DickDV
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I'll try to help you, harryg, but I need a little time to study the link to the manual. I probably won't get to it until this weekend, having been out of town and just buried in work.

Hang in there.
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Old January 10th, 2003, 01:15 PM   #11
awalinski
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I did have the same problem with Baldor drive once. In my case transducer input + was wired to analog #2 + on the drive, minus to minus. Did not work.
It is working now, because I wired it like that:

Separate 24 VDC + to Transducer +
Transducer minus to analog #2 + on the drive
Analog #2 minus to 24VDC-

Try it. All my drives are working this way though we are using analog cards not stright wiring to the drive.
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Old January 10th, 2003, 02:38 PM   #12
Tom Jenkins
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Harry, when you say you have 0% feedback, do you mean that the input signal to the VFD from the pressure transmitter is 0%? And does that mean both at the VFD keypad AND using a meter right at the VFD terminal strip? In that case the problem is probably wiring. I have had problems with "ground loops" with 4-20 mA when there is a pot on the front panel for speed adjustment - sometimes the pot leg and the 4-20 mA common are tied together. An isolator fixed this.

Or does that mean 0% at the VFD keypad but 4-20 mA on the meter right at the VFD terminal strip? In that case the problem is probably VFD configuration. Many have the ability to take either 0-10 VDC or 4-20 mA and you have to tell it which signal and which set of terminals to look at. Often there is a separate speed reference input and process feedback input terminal on the drive. And some drives default to 0-20 mA instead of 4-20 mA.

Or, by 0% feedback does that mean the signal is getting in OK, but the output of the PID loop to the drive is a 0% speed command. In that case the problem is almost certainly in the configuration of the VFD.
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Old January 10th, 2003, 04:57 PM   #13
DickDV
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harryg, first, I don't want to upset the train of thought of others working with you on this. So, if you want to continue with them, just say so and I'll step back and wait for your signal, if you end up wanting my help.

If you want me to jump in here, then I need your information on the following items:

1. on pg 3-34 of the manual (on the link you provided), please
give me a pin by pin description of what you have wired to
terminal strip J4.
2. please describe exactly how you have the 4-20ma loop wired.
At minimum you should have a 24vdc power supply, the pressure
transducer, and the input terminals to the drive. You may
also have a signal conditioner or isolator in the loop. If so
please explain how you've wired it.

I think we can get you going with a step-by-step process here. PID controllers are always tricky and getting used to Baldor's terminology is taking me a little time, as well.
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Old January 10th, 2003, 07:32 PM   #14
harryg
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Tom,

0% at the VFD keypad but 4-20 mA on the meter right at the VFD terminal strip.

awalinski,

I did get that much from the factory the tech said the terminals are labeled backwards. Job security I guess!!

DickDV,

Definitely glad to hear from you! I know you're an ABB guy but your expertise will be greatly appreciated. OK, pins 1,4,8,13 and 17 are jumpered together Pins 39 & 40 are jumpered. Transducer 24v+ terminates at pin 39, xducer signal terminates at pin 5. I have a NO contact between pins 1 & 9 for the run command. I verified that the transducer is good, but at the keypad it still reads 0% feedback. See my earlier post for key parameter settings. I may have just overlooked one but I'll tell you I will know this drive WELL by the time this is done. A plug for you, I like the ACS much better!
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Old January 10th, 2003, 08:50 PM   #15
Tom Jenkins
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"Tom, 0% at the VFD keypad but 4-20 mA on the meter right at the VFD terminal strip."

In that case I suspect the problem is in the VFD configuration. I am assuming, of course, that the drive anaolg input can physically accept the 4-20 mA signal. You might try to put the transmitter signal accross a 500 Ohm resistor to get a 2-10 VDC signal. (Or use a 250 Ohm resistor to get 1-5 VDC if the transmitter is limited on load). Then repeat the readings at the keypad and see what you get.

Dick has more expertise in this area than I do, so maybe he can point you in the right direction.
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