Powering 2 encoders with a N.I. DAQ

Discussion in 'General Electronics Chat' started by araforn, Nov 18, 2012.

  1. araforn

    Thread Starter New Member

    Jul 26, 2011
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    Hi all.
    I hope this is the right place to post this.

    I'm doing a project at the moment that requires the positional measurement of an x and y axis platform. To achieve this I'm using 2 Renco hollow shaft encoders. Data sheet link: http://www.renco.com/fileadmin/files/Productinfo/RHS15Datasheet.pdf

    The issue I'm having is with the power supply to these encoders. The national instruments DAQ 6211 that I have doing the counting uses both the A & B channels for each encoder and I have attempted to use the on-board 5 volts power supply to power them both but unfortunately it does not provide enough power for 2 simultaneously. They both work individually just fine.

    I since have tried to power 1 from the DAQ 6211 and the other from
    another DAQ 6008. This leads to spurious counting from the encoder connected to the separate DAQ 6008 while the other is fine. I even tried to power both of them from a separate USB device with an on-board 5v supply but both encoders give spurious results in this case.

    Ultimately it seems the only correct operation is when the encoder is powered directly by the device that is doing the counting, the DAQ 6211 but of course this only allows me use 1 encoder, not 2.

    If I use a separate standalone power supply, would it work for my problem??. I'm concerned a separate power supply will give too much current through its signal lines and damage the DAQ 6211.

    I understand that this is a national instruments related question but I thought I would post here to see if anyone has any insight. I appreciate any help or insight as this is really stopping me in my tracks at the moment.

    Apologies for the long winded post and thanks for reading.
     
  2. strantor

    AAC Fanatic!

    Oct 3, 2010
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    I don;t see how it is possible to damage the DAQ, as long as you're using a 5V p/s.
     
  3. araforn

    Thread Starter New Member

    Jul 26, 2011
    18
    0
    For example if I use a 5v 1 amp supply, would the signals lines bring that 1 amp back to the DAQ or do the encoders just take what current they need and use that for the signal lines?
     
  4. t06afre

    AAC Fanatic!

    May 11, 2009
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    You can power the encoders with a separate power. The current they draw will not affect your DAQ units signals in any way. During normal operations.
     
  5. araforn

    Thread Starter New Member

    Jul 26, 2011
    18
    0
    Thanks for your reply. My electrical knowledge is obviously not the greatest.

    So can I assume that the encoder will take its power from any 5v supply even if its current rating is relatively high.i.e. 2/3 amps, and then the encoder will convert it to a lower current ttl output on its signal lines??.

    I was concerned that those signal lines would carry the higher current and damage the DAQ.
     
  6. t06afre

    AAC Fanatic!

    May 11, 2009
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    Your setup is safe. But your understanding about current and voltage is very wrong. You should repeat Ohms law:rolleyes:
     
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