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JiM_cz

Can I wire up Isolated Analog Output card 0-10V to Omron VFD?

18 posts in this topic

Hello Guys, I have an Allen Bradley 1769-OF4VI Isolated Analog Output card 0-10V and I'd like to use it to control speed of an Omron VFD. The VFD has the ordinary frequency analog input where you normally put a potentiometer. Can I connect the +V and -V of the output card to the analog input of the VFD? Please see the attached pics. I'm thinkng about terminals FV and SC..

pic.docx

pic.pdf

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i don;t see a problem.

output is isolated, ranges match, output can handle loads 2k+ (VFD input is 10k) etc. 

 

 

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Posted (edited)

I am not so sure. It looks like the VFD is trying to power the potentiometer.

 

Is that 10vdc on the VFD side internal?  Put a meter on it to see.

 

I guess connecting to "FV (+)" and "SC"(-) should work.

Edited by Mickey

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What worries me is that the manual from the D/A card stresses "Never connect a voltage or current source to an analog
output channel." I don't want to blow the card..

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8 hours ago, JiM_cz said:

What worries me is that the manual from the D/A card stresses "Never connect a voltage or current source to an analog
output channel." I don't want to blow the card..

That is what a voltmeter is for.

Put it across "FV" and "SC".

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never connect two power sources  directly to each other or sparks may fly. (analog output is a source too).

so ... just do NOT use FS terminal... (that is +10V source).

 

you MUST use SC terminal as this is your reference potential.

 

Note: FS terminal would only be needed if potentiometer is connected (passive component). potentiometer provides voltage output on wiper (connected to FV) that is a fraction of supply voltage. in this case that supply would be FS-SC and fraction can be adjusted 0-100% by turning potentiometer knob.

 

 

but since you do have an analog output card, do as mentioned before (output itself already has needed voltage - it is a source)

 

since this is an analog circuit, it need to be shielded. Shield must be connected in one place only, either to GND or to SC. (tape other end).

if connections are short, shielding may not be needed but i would always use it, specially on voltage signal.

 

AO to VFD.png

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Thanks a lot for your help guys, you've been very helpful.

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There could be problems if you want to connect a second output to a second drive (or other device with single-ended input).

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why would that be? as already mentioned, that analog output card is isolated.

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If you tie two isolated circuits to two non-isolated circuits (i.e. grounded), isolation is lost.

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The card has more output points used. Does it mean I could expect some kind of "unpredictable" behavior? What exactly can happen?

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21 hours ago, Gerry said:

If you tie two isolated circuits to two non-isolated circuits (i.e. grounded), isolation is lost.

how exactly? each output channel is isolated individually.

can you show circuit and possible current path that would be concern?

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2 hours ago, JiM_cz said:

The card has more output points used. Does it mean I could expect some kind of "unpredictable" behavior? What exactly can happen?

If the devices connected to the outputs are electrically isolated from each other, then no problem. What I am pointing out is that if one side of two (or more) outputs are effectively tied together through grounded inputs (like the drive as shown above), then the outputs are no longer isolated. I'll leave it to others to analyse the interaction.

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you stated that there can be a problem, don't you think it would be fair that you elaborate and substantiate that claim?

i read the manuals and don't see a reason for such concern.

 

it is no different than using two contacts of a relay in two different circuits.

relay coil and two contacts are isolated from each other (3-way isolated).

 

this is the same thing, only the signals are analog instead of digital:

* yellow region is isolation.

* left of it is circuitry that connects to PLC.

* right side are four channels (analog outputs) that are isolated from each other. i have shown two of them wired

 

5b6d8606c271c_isolatedoutputsmeans-theya5b6d85f5e1b3e_isolatedoutputswiring.thum

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Posted (edited)

He may be referring to the earth connections inside the drives:

IsolatedAnalogs_Edit.thumb.png.5583bcea3

ETA:

I circled the wrong ones. It looks like the analog (-) connection is tied to the SC connection, which is chassis ground.

 

Edited by Joe E.

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that is why i asked for clarification... 

but even if the SC was connected to GND, both VFDs would have their SC referenced to same potential and if this is an issue - it has absolutely nothing to do with wiring to this particular analog output card. presence or absence of the analog card would make no difference.

 

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I agree. I don't think OP will have any issues with this arrangement at all, especially if the drives are in the same cabinet.

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my thoughts exactly... but if there is a concern or different opinion, i am always interested to hear about it. :-)

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