+ Post New Thread
Results 1 to 7 of 7
  1. #1
    Newbie level 3
    Points: 1,765, Level: 9
    Achievements:
    7 years registered

    Join Date
    Apr 2009
    Posts
    5
    Helped
    0 / 0
    Points
    1,765
    Level
    9

    Pressure Sensor Resistance Variation

    I'm making use of a pressure sensor to produce an output voltage range depending on pressure but the sensor to sensor resistance variation is throwing off the output range.

    Is there an analog compensation method for the varying resistances of Wheatstone bridge sensors?

    •   AltAdvertisement

        
       

  2. #2
    Advanced Member level 5
    Points: 24,863, Level: 38
    barry's Avatar
    Join Date
    Mar 2005
    Location
    California, USA
    Posts
    4,763
    Helped
    1055 / 1055
    Points
    24,863
    Level
    38

    Re: Pressure Sensor Resistance Variation

    The whole point of a Wheatstone bridge is that it's the RATIO of the resistors that matters, not the absolute resistance. What kind of sensor are you using?


    1 members found this post helpful.

    •   AltAdvertisement

        
       

  3. #3
    Newbie level 3
    Points: 1,765, Level: 9
    Achievements:
    7 years registered

    Join Date
    Apr 2009
    Posts
    5
    Helped
    0 / 0
    Points
    1,765
    Level
    9

    Re: Pressure Sensor Resistance Variation

    I'm using the sensor linked below:
    https://www.stw-technic.com/wp-conte...ment-Cells.pdf
    Click image for larger version. 

Name:	Sensor.jpg 
Views:	5 
Size:	264.9 KB 
ID:	142909

    I've attached the schematic for the circuit. The problem that I'm running into is that the output voltage range is different for each sensor. I would like to find a method to keep the output voltage range stable for any sensor used.



    •   AltAdvertisement

        
       

  4. #4
    Super Moderator
    Points: 30,125, Level: 42
    andre_teprom's Avatar
    Join Date
    Nov 2006
    Location
    Brazil
    Posts
    8,995
    Helped
    1138 / 1138
    Points
    30,125
    Level
    42
    Blog Entries
    9

    Re: Pressure Sensor Resistance Variation

    The variation of values between components of a given manufacturing lot is expected within a tolerance range. The calibration process at the firmware side, or addition of extra resistors in series are possible solutions to minimize the effect of this variation from part to part.
    --------------------------------------------------------------------------------------------------
    Part of the world that you live in, You are the part that you're giving ( Renaissance )


    1 members found this post helpful.

  5. #5
    Advanced Member level 5
    Points: 24,863, Level: 38
    barry's Avatar
    Join Date
    Mar 2005
    Location
    California, USA
    Posts
    4,763
    Helped
    1055 / 1055
    Points
    24,863
    Level
    38

    Re: Pressure Sensor Resistance Variation

    It's a little difficult to tell what's going on with that sensor from the data sheet. Is it a half-bridge? Full-bridge? quarter-bridge? It LOOKS like it's a full bridge, in which case, as I said, the absolute resistance shouldn't matter. However, it looks like the SPAN variation is enormous, i.e., the first column has "2.5...5.4"-That's greater than 100% tolerance. Does that mean the value for a particular sensor is 'somewhere' in that range? If so, you'll have to calibrate each unit.

    And why are you using 741 opamps? Those are about 40 years old. I think you want a more modern precision opamp.


    1 members found this post helpful.

    •   AltAdvertisement

        
       

  6. #6
    Super Moderator
    Points: 81,179, Level: 69
    Achievements:
    7 years registered
    Awards:
    Most Frequent Poster 3rd Helpful Member

    Join Date
    Apr 2014
    Posts
    16,461
    Helped
    3736 / 3736
    Points
    81,179
    Level
    69

    Re: Pressure Sensor Resistance Variation

    Hi,

    If I remember right then there are "signal conditioning ICs" with non volatile calibration features especially for bridge sensors.
    But I don't remember the name.

    But I think the cheaper and more flexible solution is a microcontroller.

    Klaus
    Please don´t contact me via PM, because there is no time to respond to them. No friend requests. Thank you.


    1 members found this post helpful.

  7. #7
    Newbie level 2
    Points: 19, Level: 1

    Join Date
    Apr 2018
    Posts
    2
    Helped
    0 / 0
    Points
    19
    Level
    1

    Re: Pressure Sensor Resistance Variation

    Hi,
    this is a stainless steel sensor with a great variance in offset an span. There is no other way than to do an an individual calibration for each sensor or to buy a calibrated and compensated sensor.
    Do you need a stainless stell product ?



--[[ ]]--