Wheatstone bridge to op amp (741)

Discussion in 'Homework Help' started by OLP, Feb 13, 2012.

  1. OLP

    Thread Starter New Member

    Feb 9, 2012
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    0
    Hi all, I'm building a weather station and using a PT100 RTD as the variable resistor in a wheatstone bridge. I have the bridge sorted out but I'm no entirely sure what to do now with the output voltage from the bridge, how do I bring it to the op amp? And how do I determine what feedback I need from the system?

    Thanks
    Chris
     
  2. Wendy

    Moderator

    Mar 24, 2008
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    You mention a 741. It is one of the oldest op amps created for an IC. It's specs are among the worst you can find. The reason this matters is stability. You are using a Cadillac of a sensor with a Model T amplifier.

    The first thing you need to do is show us the schematic you are using. If you are stuck on this then my suggestion is to find a instrumentation type amplifier (not a op amp, but based off of precision op amps) and use it instead.

    Other people may have better ideas.

    I am guessing you are fairly new to electronics. What you need is an instrumentation amplifier, which also come in IC form. You can usually feed the low voltage signal into a DAC instead, and have it fed directly into a computer if this is your goal.
     
  3. OLP

    Thread Starter New Member

    Feb 9, 2012
    2
    0
    Well it's a college project, the whole thing will incorporate sending the various signalsto a PLC then on to a computer to be displayed on a webpage.

    Here's a quick schematic I just did of the bridge we have set up at the moment

    [​IMG][​IMG]http://www.flickr.com/photos/76661617@N03/6878817593/
    (Don't know why I can't put it in IMG tags)

    The only op amp we've studied is the 741 and I just assume this is what will be available to us in college.
     
  4. Wendy

    Moderator

    Mar 24, 2008
    20,765
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    I recommend a TL074, or similar. There are thousands of op amps to choose from, it is an embarrassment of riches, and can make choosing one hard.
     
  5. t06afre

    AAC Fanatic!

    May 11, 2009
    5,939
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    Take a look at the LM35 or LM34 IC. It could make your measuremnts more easy. The LM35/34 chip is cheap and quite common(easy to get)
     
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