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Entry  Tue Jan 12 08:21:47 2021, anchal, HowTo, CDS, Acromag wiring investigation SingleEndedNonFloatingWiring.pdfSingleEndedFloatingWiring.pdfDifferentialSignalWiring.pdf
    Reply  Tue Jan 12 11:42:38 2021, gautam, HowTo, CDS, Acromag wiring investigation 
       Reply  Wed Jan 13 16:09:29 2021, Anchal, HowTo, CDS, Acromag wiring investigation SimpleTestsStriptoolImages.pdf
          Reply  Tue Jan 26 12:59:51 2021, Anchal, HowTo, CDS, Acromag wiring investigation TestingDifferentialSignalWithFloatingRTNwrtIN-.pdf
             Reply  Tue Jan 26 15:37:25 2021, Anchal, HowTo, CDS, Acromag wiring investigation GeneralLabWiring.pdfGeneralLabWiring2.pdfGeneralLabWiring3.pdf
                Reply  Fri Jan 29 17:57:17 2021, Anchal, HowTo, CDS, Acromag wiring investigation GeneralLabWiringDiffWith2Wires.pdfGeneralLabWiringDiffWith3Wires.pdfDiffReadResistorbtwnINandRTN.pdf
Message ID: 15779     Entry time: Tue Jan 26 15:37:25 2021     In reply to: 15778     Reply to this: 15785
Author: Anchal 
Type: HowTo 
Category: CDS 
Subject: Acromag wiring investigation 

Here I present few wiring diagrams when using Acromag to avoid noisy behavior and ground loops.


Case 1: Only single-ended sources

  • Attachment 1 gives a functioning wiring diagram when all sources are single ended.
  • One should always short the RTN to IN- pin if the particular GND carried by that signal has not been shorted before to RTN for some other signal.
  • So care is required to mark different GNDs of different powersupply separately and follow where they inadvertently get shorted, for example when a photodiode output is connected to FSS Box.
  • Acromag should serve as the node of all GNDs concerned and all these grounds must not be connected to Earth GND at power supply ends or in any of the signal sources.
  • I think this is a bit complicated thing to do.

Case 2: Some single and some differential sources

  • Connect all single ended sources same as above keeping care of not building any ground loops.
  • The differential source can be connected to IN+ and IN- pins, but there should be a high resistance path between IN- and RTN. See Attachment 2.
  • Why this is the case, I'm not sure since I could not get access to internal wiring of Acromag (no response from them). But I have empirically found this.
  • This helps IN- to float with respect to RTN according to the negative signal value. I've found that 10kOhm resistance works good. See 40m/15778.
  • If RTN is shorted to nearby Earth GND (assuming none of the other power supply GNDs have been shorted to Earth GND) shows a reduction in noise for differential input. So this is recommended.
  • This wiring diagram carries all complexity of previous case along with the fact that RTN and anything connected to it is at Earth GND now.

Case 3: Signal agnostic wiring

  • Attachment 3 gives a wiring diagram which mimics the high resistance shorting of RTN to IN- in all ports regardless of the kind of signal it is used for reading.
  • In this case, instead of being the node of the star configuration for GND, acromag gets detached from any ground loops.
  • All differences in various GNDs would be kept by the power supplies driving small amounts of current through the 10 kOhm resistors.
  • This is a much simpler wiring diagram as it avoids shorting various signal sources or their GNDs with each other, avoiding some of the ground loops.

Edit Wed Jan 27 13:38:19 2021 :

This solution is not acceptable as well. Even if it is successfull in reading the value, connecting resistor between IN- and RTN will not break the ground loops and the issue of ground loops will persist. Further, IN- connection to RTN breaks the symmetry between IN-  and IN+, and hence reduces the common mode rejection which is the intended purpose of differential signal anyways. I'll work more on this to find a way to read differential signals without connecitng IN- and RTN. My first guess is that it would need the GND on the source end to be connected to EarthGND and RTN on acromag end to be connected to EarthGND as well.

 

Attachment 1: GeneralLabWiring.pdf  30 kB  | Hide | Hide all
GeneralLabWiring.pdf
Attachment 2: GeneralLabWiring2.pdf  37 kB  | Hide | Hide all
GeneralLabWiring2.pdf
Attachment 3: GeneralLabWiring3.pdf  38 kB  | Hide | Hide all
GeneralLabWiring3.pdf
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