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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: 15785     Entry time: Fri Jan 29 17:57:17 2021     In reply to: 15779
Author: Anchal 
Type: HowTo 
Category: CDS 
Subject: Acromag wiring investigation 

I found a white paper  from Acromag which discusses how to read differential signal using Acromag units. The document categorically says that differential signals are always supposed to be transmitted in three wires. I provides the two options of either using the RTN to connect to the signal ground (as done in Attachment 3) or locally place 10k-100k resistors between return and IN+ and IN- both (Attachment 2).

I have provided possible scenarios for these.

Using two wires to carry differential signal (Attachment 1):

  • I assume this is our preferential way to connect.
  • We can also assume all single-ended inputs as differential and do a signal condition agnostic wiring.
  • Attachment 3 show what were the results for different values of resistors when a 2Hz 0.5V amplitude signal from SR785 which as converted to differential signal using D1900068 was measured by acromag.
  • The connection to RTN is symmetrical for both inputs.

Using three wires to carry differential signal (Attachment 2):

  • This is recommended method by the document in which it asks to carry the GND from signal source and connect it to RTN.
  • If we use this, we'll have to be very cautious on what GND has been shorted through the acromag RTN terminals.
  • This would probably create a lot of opportunities for ground loops to form.

Using an acromag card without making any connection with RTN is basically not allowed as per this document.

Attachment 1: GeneralLabWiringDiffWith2Wires.pdf  35 kB  | Hide | Hide all
GeneralLabWiringDiffWith2Wires.pdf
Attachment 2: GeneralLabWiringDiffWith3Wires.pdf  34 kB  | Hide | Hide all
GeneralLabWiringDiffWith3Wires.pdf
Attachment 3: DiffReadResistorbtwnINandRTN.pdf  391 kB  | Hide | Hide all
DiffReadResistorbtwnINandRTN.pdf DiffReadResistorbtwnINandRTN.pdf DiffReadResistorbtwnINandRTN.pdf
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