4-20MA AO to AB PF400 issues

g.mccormick

Lifetime Supporting Member
G
Join Date
Jul 2012
Location
IN
Posts
961
All,
I have a 2 channel isolated 4-20MA Opto22 AO card
http://opto22.com/site/pr_details.aspx?cid=7&item=SNAP-AOA-23-iSRC


The two channels on this card are suppose to be isolated from each other.
The two channels are wired to two seperate PF400 drives at terminals 13+ and 14-.

If I run one drive, the drive behaves as one would expect driving from 0-60hz from 4-20MA. If I attempt to run both drives at the same time, one of the drives will work and the other will jump around all over the place as if the 4-20MA was oscillating wildly. It seems to track that which ever drive I command secondly will have the issue.

If I put a DMM in series to meaasure the 4-20MA, I always see a nice steady signal. Putting the DMM in series also seems to fix the issue, as both drives can be driven around correctly.
Somesort of noise or crosstalk is happening, but I can't figure out how/what.


For the meantime, I have put a second 4-20MA card in the next slot on the rack and I spit the commands to the two drives to the two seperate cards.

We just recently had no trouble at all using the same exact 4-20MA card to two different PF400 drives (both drive commands comming from same card).


Drive A right next to cabinet, Drive B is about 50ft away, the signal wiring is not in the same conduit as any of the 3phase power wiring.

Any thoughts?
 
g.mccormick said:
If I put a DMM in series to meaasure the 4-20MA, I always see a nice steady signal. Putting the DMM in series also seems to fix the issue, as both drives can be driven around correctly.
Click to expand...
The DMM has a low resistance shunt resistor in its current measuring circuit. So how could an ohm or less of resistance, essentially floating, quiet down a noisy current signal?

Being current control signals, the drives have a resistor on its analog input to convert the current to a voltage signal. An additional trivial resistance in the circuit should be unremarkable.

I'm stumped.
 
I would make sure that the 4-20mA wires aren’t getting some induction from the drives. It’s a bit of a stretch but I could see a DMM adding just enough of a load (they shouldn’t but a lot of them do) to squelch a small amount of induced current. Like I said it’s a shot in the dark but its good practice to shield the 4-20mA lines from high current sources anyway.
 
g.mccormick said:
All,
I have a 2 channel isolated 4-20MA Opto22 AO card
http://opto22.com/site/pr_details.aspx?cid=7&item=SNAP-AOA-23-iSRC


The two channels on this card are suppose to be isolated from each other.
The two channels are wired to two seperate PF400 drives at terminals 13+ and 14-.

If I run one drive, the drive behaves as one would expect driving from 0-60hz from 4-20MA. If I attempt to run both drives at the same time, one of the drives will work and the other will jump around all over the place as if the 4-20MA was oscillating wildly. It seems to track that which ever drive I command secondly will have the issue.

If I put a DMM in series to meaasure the 4-20MA, I always see a nice steady signal. Putting the DMM in series also seems to fix the issue, as both drives can be driven around correctly.
Somesort of noise or crosstalk is happening, but I can't figure out how/what.


For the meantime, I have put a second 4-20MA card in the next slot on the rack and I spit the commands to the two drives to the two seperate cards.

We just recently had no trouble at all using the same exact 4-20MA card to two different PF400 drives (both drive commands comming from same card).


Drive A right next to cabinet, Drive B is about 50ft away, the signal wiring is not in the same conduit as any of the 3phase power wiring.

Any thoughts?
Click to expand...



We're all assuming that its wired correctly, of course - that is, both drives in series.
We're also assuming that the drive analog input 'COMMON' is NOT GROUNDED.
.
Don't forget that some drives can accept either a 0-10VDC input -OR- a current input. BUT, there's usually a jumper device on the drive that selects CURRENT input, or VOLTAGE. If one were wrong, it might just create a goofy impedence that would make the symptom you describe.

What happens if you disconnect your OPTO device, and try to send a reference to the drives using a Transmation or other similar current signal simulator?
 
More info.

I measured the tried adding a 100ohm (had it in the bag) resister in series with signal to no avail.

I have checked the wiring at the vfd, 4-20MA+ to term 13 (as it should be), 4-20MA- to terminal 14 (as it should be). The AI1 switch is on 0-20ma setting (which should be).

4-20MA is ran on Belden 8760, shield is grounded in my panel only, and ran in seperate conduit from any AC.

I will have to see if anyone has a current sourcing meter. I need to tell the wife to get me one for early christmas :)
 
Well in the land of absurdity, I set the accel time for the drives from 1 to 2.5secs. I then powered down the drives and changed my wiring in my panel back so that both are coming from same AO card. Powered drives back up and all seems to have "fixed" itself.

WTS (what the s**t)??

Is there something potentially if the drives were powered before the AO card was powered that could have been causing weirdness????
 

Similar Topics

J
4-20mA loop grounding
Hi all, I'm connecting several 4-20mA sensors together in parallel (only one shown below) The enclosure is ABS plastic with metal backplate DAQ...
Replies
5
Views
273
Jenny8711
J
A
Looking for a 4 or 8-channel converter for 4-20mA inputs and 0-135Ohm outputs
Problem: Our PLC can only output 4-20mA, but the actuators it needs to control, modulate based on a 0-135Ohm signal. Buying 4 or 8 individual...
Replies
7
Views
275
AdaptnOvercome
A
D
4-20ma isolator.
What's your go to 4-20ma isolator. I've got some 4 wire 4-20ma from several flow meters and scales that I would like to isolate before it gets to...
Replies
10
Views
1,688
jdbrandt
J
S
4-20mA analog output from DCS
Hi, I need to read three 4-20mA signals from a DCS(ABB) in a remote 6 channel analog input module with RS485 modbus port. When I connected...
Replies
2
Views
486
danw
danw
V
4-20ma loops with multiple supply's on different inputs can you the commons together
Hello this is my first post. Looking forward to being more involved in this community to learn and hopefully help others. Any help or guidance...
Replies
7
Views
789
lfe
L
Back
Top Bottom