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PGA309: Strain Gage Bridge

emre kaya
Prodigy 90 points
Part Number: PGA309

Hi,

I use PGA309 to detect Strain Gage Bridge changes.
In many projects conducted with PGA309, the Strain Gage Bridge supply voltage appears to be 5V.
For this reason, Vin1 and Vin2 inputs will be 2.5V in a zero-strain state.
The supply voltage of the Strain Gage Bridge I will use appears to be 10V. We must use 10V voltage for the Strain Gage Bridge. This cannot be changed.
For this reason, Vin1 and Vin2 inputs will be 5V in a zero strain state.
When the VSA supply voltage of the IC is 5V, Linear Input Voltage Range VSA − 1.5V = max 3.5V as stated in the datasheet.
For this reason, the situation where the Strain Gage Bridge is supplied with 10V is not suitable for PGA309.

To ensure this compatibility, we plan to reduce the 5V value at the Vin1 and Vin2 inputs to 2.5V levels with Opam+Voltage Divider and read the Strain Gage Bridge with 10V supply using 2 Gain in the PGA309.
When only a voltage divider is required, it disrupts the Strain Gage Bridge structure. For this reason, Buffer Opamp was used. I sharing the circuit below.


If you have a different and effective solution to this issue, I would be very happy

  • 0
    TI__Mastermind 20617 points

    Emre,

    I think your solution is very reasonable.  Any errors introduced by the op amp and voltage dividers will be minimized during calibration.  The only other approach that I could think of would be to use asymmetrical supplies on your bridge.  For example, you can apply 10V across your bridge with a +7.5V supply and a -2.5V supply and the common mode output will be 2.5V.  I think your solution is probably more straight forward, but I though I would mention the idea of asymmetrical supplies.

    Best regards, Art

  • 0 in reply to Art Kay
    Prodigy 90 points

    Hi Art,

    Thank you for your advice. Your solution can be good.
    At my solution, when I use a voltage divider, the Vdiff coming from the strain gage will decrease. Therefore, I need to use 2 V/V internal Gain for my solutions. However, in your solution, there is no need for this. So, at the same Strain Gage value at opamp+voltage divider options will see 49.5 mV, +7.5V supply and a -2.5V supply stiation will see 99 mV.
    I sharing the simulation outputs.

    I will think about your solution. Thank you for your advice.