ab analog wiring

irondesk40

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Join Date
Jan 2008
Location
nc
Posts
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have a question about how a machine that we just recieved yesterday that has a ab micrologix 1100 with a 1762-of4 analog output card.
They tried to run the machine, but the speed control is having some issues, so took a quick look at it this morning, but not had a chance yet to look at it in detail, but did notice something about how the analog output card is wired that did not look right.
For example there is a analog output labeled Iout0_drive1 that is I out 0 on the module. There is a shielded cable that has one of the wires connected to the IOut 0 terminal on the analog card, then the other wire in the cable is connected to Com on the analog output module, which to me is correct, but there is also a wire going from the com on the output module that goes over and connects to the -24 terminal blocks in the machine that comes from the powersupply.
Is this a good idea, i have not done that many analog projects, but it appears to me the cable coming from the analog card should be connected to the Iout0, and the Analog output common, but not to the -24v of the DC power supply as well. I called AB tech connect and the engineer I spoke to seemed to agree with me that the wire going from the analog output common should not be connected over to the -24vdc terminal that is fed from the power supply that is being used to power a display.
the micrologix is powered by 110vac.
I hope this makes sense.
Would there be a problem with how this is wired?
Thanks
 
look at the resolution

check to make sure the card is set up the way you need it in the adv.confg. you have to chose current or voltage output also you have to choose the format Raw/proportional or Scaled for PID.
http://literature.rockwellautomation.com/idc/groups/literature/documents/in/1762-in016_-en-p.pdf

also look at the resolution: Knowledgebase answer ID 38470

Even though the IO configuration indicates that the 1762-OF4 is configured for 4-20mA the module actually operates at 0-21mA. 0-16383 PID output will drive OF4 output from 0-21mA.
8192 (expected 50% mark) should result in 12mA. The actual value is 9362, half of the range of 0-21mA.
An SCP can be used to rescale the output for correct 4-20mA range (3120 - 15603).
 
I have a ML1100 with the same card and also use it for sending an analog reference to a drive. I would agree with AB support and say that there is not any need to tie the -24 V of the Ml1100 supply to the common of the analog output card. The wire may not be the problem, but it is definitely worth trying.
 
fabric feeding through machine was not running constant speed. Speed was set, but appeared to be drifting, took wire to DC- off, appears to be running okay.
 

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