Pt100 Wheatstone bridge arduino

Discussion in 'Embedded Systems and Microcontrollers' started by viri, Nov 7, 2015.

  1. viri

    Thread Starter New Member

    Jun 23, 2012
    4
    0
    Hello,

    i need help designing a Wheatstone bridge for pt100 temperature sensor
    firstly i need recommendation for a good amplifier to amplify the output of my Wheatstone bridge that is going to be connected to my arduino and displayed to an lcd, if there is a one that has (i2c or spi) control then that would be plus.
    and secondly, any though about replacing the other 3 resistor of the Wheatstone bridge by (spi or i2c) controlled potentiometer, i am thinking about that to over come calibration problem
    that might show up due to environment temperature change or other changes that might affect the performance of the circuit.
    finally, any thought about general improvement that can be added to the bridge circuit to make it more accurate

    Thanks
     
  2. eeabe

    Member

    Nov 30, 2013
    59
    9
    I just did a quick search on PT100, and I don't see a bridge type sensor. It looks like a simple resistive type sensor. Some of them have four wires, but just for the connector. They are internally connected to two points.

    If you need to measure the resistance, you can apply a small current and measure the resulting voltage across the element. I'd recommend some type of instrumentation op-amp, such as the INA333 from TI for an off-the-shelf method of measuring very small voltages.

    If you have specific accuracy requirements, you should mention them because the techniques required for various levels of accuracy can be quite different.
     
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  3. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    Over any given temperature range, there are certain values of the bridge resistors that give the best linearity using the PT100. Here is an example for 0 to 200degC:

    The reference shows how to cover different temperature ranges....
    pt100.gif
     
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  4. viri

    Thread Starter New Member

    Jun 23, 2012
    4
    0
    MikeML: The temperature range from 0-200 c is fine, what was the amp used in the circuit, could you please attach the spice circuit you have used in the screenshot, and what do you think about using Digital pot instead of normal resistor, any experience with them, could you suggest a model.

    eeabe: Thanks for your help :), the required accuracy is just one decimal point but using Wheatstone bridge, any though about improving bridge circuits in general ? .
     
  5. viri

    Thread Starter New Member

    Jun 23, 2012
    4
    0
    MikeML just saw the link on the circuit and saw that OPA188 were used but honestly i was thinking about MCP6N11. which do you think is better (INA826,MCP6N11,OPA188,INA333)???
     
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