connect voltmeters to make 8.5 digit display?????

Discussion in 'General Electronics Chat' started by sophisto007, Nov 20, 2013.

  1. sophisto007

    Thread Starter New Member

    Nov 20, 2013
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    Is it possible to connect volt meters together to get a 8.5 digit display. For example; I want to see 2.4999998 vdc. Not 2.499. Please help me.
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,999
    745
    No...................
     
  3. JohnInTX

    Moderator

    Jun 26, 2012
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    As DD says, no. You are asking for 24+ bits of precision. That is a serious voltmeter. You can't get it by simply chaining 2 together. Sorry.
     
  4. paulktreg

    Distinguished Member

    Jun 2, 2008
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    ... and you probably won't get the accuracy it sounds like you want without spending serious money.
     
  5. wayneh

    Expert

    Sep 9, 2010
    12,151
    3,058
    Precision and accuracy in the 100nV range is an odd request. What are you doing that could possibly require this?

    There are many, many things that can skew a voltage reading by a µV. Measuring anything to 8 significant figures is a huge challenge. Just having the digits on a readout doesn't mean they're meaningful.
     
  6. sophisto007

    Thread Starter New Member

    Nov 20, 2013
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    0
    Well. Im trying to take some analog signals to a whole other level. I would need a static powe source of course. I used resistors to drop the voltage, but that interferes with the sensors voltage range. I was thinking of using an aray of transistors to filter out the higher voltages and be able to see whats happening on the micro volt level.
     
  7. wayneh

    Expert

    Sep 9, 2010
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    That may make sense in your head, but not in mine. :confused:

    Maybe someone else has a clue as to what you're talking about. I don't.
     
  8. MrChips

    Moderator

    Oct 2, 2009
    12,449
    3,364
    What you are asking for is wider dynamic range, i.e. ability to measure 3V with 10nV steps.

    Two things will prevent you from doing this (1) limited resolution of the meter and (2) noise.

    What you can do is subtract the large overhead DC voltage, i.e. subtract 2.4999V and then measure the remainder.

    However noise is still going kill your efforts.
     
  9. Dr.killjoy

    Well-Known Member

    Apr 28, 2013
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    What he is trying to do is take a simply voltage diplay and measure the voltage and another voltage display to display further past the deciaml point for a more accurte reading...
     
  10. WBahn

    Moderator

    Mar 31, 2012
    17,768
    4,804
    As others have pointed out, you are chasing a pipe dream.

    To give you some idea of how small 100nV is, if 1V were the distance from the surface of the earth to the moon (~225k miles), 100nV would be about 120 feet.

    When I was at NIST we measured voltages along superconductors and those measurements were down in the 10nV to 100nV range. It took very specialized meters to do this and great care in experimental setup. Everything had to use low-thermal indium solder because the inadvertent thermocouple junctions you create would otherwise swamp the measurement. The meter itself used aligator clips and if you turned them upside down you trashed your measurement because now the signal had to go through the rivet connecting the jaws. All of the junctions also had to be packed with lead shot otherwise the air currents in the room would send the needle on the chart recorder flailing as it produced thermal voltages in the junctions. One day I was standing on the far side of the room idly playing with about a three foot length of rubber vacuum hose and the folks making the measurements were trying to figure out why they had a large low frequency signal in their data that was totally overwhelming the signal from the voltage taps. I then noticed that the sound of the chart recorder pen moving was synchronized to the movements of the vacuum hose. What was happening was the slight electrical charge on the hose was inducing a current in the twisted pair voltage leads that was huge relative to the signal.

    That's what you can look forward to if you want to play around in the deep sub-microvolt range.
     
    Papabravo, GopherT and JohnInTX like this.
  11. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    WB,
    Thanks for that story, I was going to tell the OP that simply moving your hands near the circuit will cause mIllivolt-scale fluctuations in standard test leads making a loop (antenna). Twisted pair test leads are required.

    Cheers
     
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