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Crazy Analog Output...

Crazy Analog Output...

Crazy Analog Output...

(OP)
Modiccn Compact DAU-204 Analog Output card configured for 4-20mA.  Everything is configured correctly (switches and software), but the outputs are acting weird.  Raw value is 0-4095 which should correspond to 4-20mA but the output signal (on at least 2 of the channels (didn't test the other 2)) is not linear and is not proportional to the raw output value.  0 raw gives 3.82 mA....that I can live with, but 409 gives a 1.93 mA output, 2047 gives .99 mA, 2866 gives 13.16, but 3685 gives 2.03 mA.  I think the card must be bad but wondering if anyone has ever encountered this?  The device being controlled is not causing the problem...connected mA meter and calibration device directly.  Thanks!

RE: Crazy Analog Output...

Is this a new problem with existing hardware or are you commissioning a new system? I seem to recall having a similar problem that turned out to be a configuration error.
It almost seems like the D/A is not responding to the more significant bits e.g as you go from 0111-- to 1000--  it's not seeing the MSbit. Either that or the module is getting some value you don't see in decimal format.
I suggest you look at the output word in bit format, you might see something there, try turning on one bit at the time.
Roy

RE: Crazy Analog Output...

(OP)
Hi Roy....it's a 10 year old system that has been out of use for a few years.  Not at the site now, or I'd try the one bit thing.  I agree about the D/A thing.  Trying to get a replacement card to try, as well.  Thanks!! B

RE: Crazy Analog Output...

I just had a look at an old file, there is a 30xxx register associated with the module, I think thats status.
Check bits 12 thru 15 of the 40xxx they should all be 0
It's also strange that zero gives you less than 4 mA. I wonder if one of the electrolytic capacitors has failed du to being powered down for a long period.
If you do an upload of the program you will be able to look at the register values off site.
Good Luck
Roy

RE: Crazy Analog Output...

Never hurts to check AC current if you are seeing strange results on a DC system.  You can get really weird readings from it.

Keith Cress
kcress - http://www.flaminsystems.com

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