I need to shift 0-10 Vdc to -5 to +5 Vdc

Discussion in 'The Projects Forum' started by ebrook, Nov 1, 2010.

  1. ebrook

    Thread Starter New Member

    Nov 1, 2010
    I am a MecE trying to get an instrumentation package to work again. I have a Larel TM8100QD counter that I am using to measure the rate of counts from a rotary sensor. The problem is the Laurel's analog output is 0-10 Vdc and the data acquisition system I am using (an Instrunet) will only accept +-5Vdc. I have seen lots of voltage shifting circuits to take a bilaterally symmetrical signal and convert it to a one sided signal, but I haven't seen anything yet for going the other direction.
    Any help with this would be much appreciated, please keep in mind that I have very little knowledge of circuit theory. I am hoping to get a turnkey solution, tell me what bits to buy and what order they need to get soldered together.
  2. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    If both are powered by AC mains voltage you may be able to use an isolation transformer on one and use the signal "as is" directly to the other. For example feeding the 0 to 10 Volt signal to an isolated AC mains driven Instrunet, leave its shield terminal open, just go straight to the +5 and -5 input terminals from the hi low terminals of the Laurel. If one side of its output is referenced to actual ground it won't matter, since the other instrument will be floating, with no reference to ground itself.

    Be sure and meter between the two units after hooking things up but before applying power to 'insure' that one units ground pin has no connection to the other units ground pin, through chassis or earth
    ebrook likes this.
  3. ebrook

    Thread Starter New Member

    Nov 1, 2010
    Hmm...an interesting approach Kermit, I hadn't thought of that, thanks for your input. I just did a little looking at prices for isolating transformers and they are pretty close to the prices for a pre-fab signal conditioning unit from RedLion that says it will do the required voltage shift. The problem is I have to complete this project on the cheap, which was why I was trying to build the voltage shifter myself.
    I think I'm going to try using a simple voltage divider (0-10vdc to 0-5vdc) and see how much precision I lose in the data. If it gives me acceptable results then that will be the cheapest easiest way to do it.
  4. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    Something like This Op Amp Circuit, but with a dual rail supply may do what you are looking for.

    The circuit would need a few tweaks.

    Is the input a squarewave? What frequency/bandwidth do you need to cover (high to preserve squarewave, how many pulses/second)?

    --ETA: Here is another, slightly more elegant level shifter.

    I think Maxim IC's may have what you are looking for, as they have shifters for +5/-5v for serial comms.
    Last edited: Nov 5, 2010
  5. gootee

    Senior Member

    Apr 24, 2007
    Look at application notes AN-20 and AN-31, at http://www.national.com . Both include basic opamp circuits for difference and summing amplifiers. To convert your 0 to 10V to -5 to 5V you need to either subtract 5V (with a differenc amplifier) or add -5V (with a summing amplifier). If you use a +/-15V supply for an opamp difference amplifier or an opamp summing amplifier, you can do it either way and use a potentiometer to get the 5V or -5V to subtract or add, from one of the DC power rails. Just adjust the pot to get -5V output when the input is 0V.