Help with configuring digital panel meter

Discussion in 'The Projects Forum' started by DougB, Nov 29, 2010.

  1. DougB

    Thread Starter New Member

    Sep 11, 2010
    24
    0
    I purchased a DPM and I am having trouble based on the instructions provided figuring out how and what resistors/jumpers I need to make the unit function as needed. The DPM is going to be used to readout a LM35CAZ precision temperature sensor. The output of the sensor in my instance will be from about -300mv(maybe a little less) to +400mv. I need the meter to read 40.0 when the voltage is 400mv and -30.0 when the voltage is -300mv. Everything else in between is linear. The vendor is of little help and my knowledge of electronics only helps get me in trouble. Any help would be appreciated. Attached are the supplied instructions and the datasheet.
     
  2. wayneh

    Expert

    Sep 9, 2010
    12,123
    3,047
    Look at the instructions for the "Generic Meter". You'll want about ±0.5v to cover your range. That range isn't shown as an example, but I think you can calculate the resistor values following the examples given and then tweak for accuracy as described.
     
  3. DougB

    Thread Starter New Member

    Sep 11, 2010
    24
    0
    I was thinking that was one of the ways I could go. Having said that there are some values I have to plug into the formula to calculate R3. I am unsure as to what the difference is between full display value(FDV) and full scale(FS). The other option would be the voltage meter option in the -.2 to +1.0 volt range and modifying R1 and R3 slightly which are now at 100K R1, 11K R3 respectively. This is very close to my needs as is. A little more neg voltage allowance and I am there. Not sure here if we would have to change R1 and R3 to another value, but I would think that R3 only may do. This is only a guess and this is where I get myself into trouble.
     
  4. wayneh

    Expert

    Sep 9, 2010
    12,123
    3,047
    I believe FDV is 199.99, the highest reading the display can produce, whereas FS is the input value that will produce FDV.
     
  5. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    5,692
    901
    I think you want R1=1Meg; R3=10K; and Edit:short D1.

    That gives you a rage of -2 to 10 V, but the proportionality is correct. That is, 400 mV will read 40.0

    Messing with other values of resistance will change that "1:1" proportionality.

    John

    Edit: Otherwise, you will not get the lower limit you need.
    Oops, I think you want to short D1. It goes to +9.999
     
    Last edited: Dec 1, 2010
Loading...