• State TI Thinks Resolved
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 48 subscribers
  • Views 44 views
  • Users 0 members are here
Support feedback
Options
Options
Related

INA333: Obtaining a single supply 3.3V Vref at half of supply for a full wheatstone strain gauge measurement.

Forrest Hare
Prodigy 10 points
Part Number: INA333
Other Parts Discussed in Thread: OPA197, TLE2426, OPA333, OPA320

Tool/software:

I am trying to design a differential amplifier (INA333) and buffer circuity (OPA197) that measures the strain gauge and conditions the analog signal before it needs to transmit across a 6" wire to an ADC on a micro controller. 

My current design uses an ADR4533 to step down a +5V line to provide a +3.3V precision excitation voltage to the wheatstone bridge.

I then use an INA333 with the +3.3V at V+ and GND at V-. I need help figuring out how to provide a half +3.3V reference since the TLE2426 has a min Vi of 4V.

  • 0
    Prodigy 10 points

    I should also add that for my strain gauge, we can assume that it will only be strained in one direction so I don't necessarily care for + and - bridge output swings. With that being said, could I just tie Vref to GND with the assumption that the voltage differential swings will be in the positive +mV range?

  • 0 in reply to Forrest Hare
    TI__Mastermind 32881 points

    Hello Forrest,

    Thanks for posting on E2E! Fundamentally, you may do the same thing as the TLE2426 discretely with a buffered resistor divider, depending on your application conditions. If you are expecting only strain in a single direction, you still would receive benefit from biasing up the ref voltage, as you would otherwise encounter a "dead zone" at low strains. Even though the INA333 has rail to rail input CM range, the output can only swing (at worst) 50mV from the rail, and the GE spec is only rated to 100mV from either rail, so your range of highest linearity will be 100mV and up.

    Something as simple as a buffered voltage divider can be provided to the INA333, and depending on your precision/noise requirements, you may select the buffer amp accordingly. Since the INA333 is already in a gain of 100, this could relax the specifications needed for your buffer amplifier, as your INA input stage can very easily be your dominant error source.

    Best,
    Gerasimos

  • 0 in reply to Gerasimos Madalvanos
    Prodigy 10 points

    Gerasimos,

    Thank you for your response! I took your recommendation and chose to use a OPA333 and a voltage divider to provide a buffered +500mV reference to the INA333. I also selected a OPA320 to buffer the INA's output in order to condition it before the 6" wire it needs to pass through. 

    This is my first strain gauge specific circuit so I would greatly appreciate any feedback in regards to my component selection; I have attached my schematic for details!  

    Thank you!