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PGA309: PGA309 INTERNAL TEMP SENSOR MOVING

Lori Ferger52
Intellectual 495 points
Part Number: PGA309

We use the internal temperature sensor of the PGA309 in the signal conditioning circuitry of a pressure sensor. The external EEPROM is loaded with temperature correction coefficients which the PGA309 indexes to correct for temperature errors. 

In a controlled oven at cold temperature, when full scale pressure is applied to the sensor,  the output of the PGA309 is slowly moving.  We have tracked this to movement of the internal temperature sensor.  The temperature correction is fairly large so a small movement of the temperature sensor causes noticable/unacceptable movement on the output of the transducer.  The temperature sensor reading moves about  six degrees celsius in the first two minutes that pressure is applied.  The temperature sensor does not move when no pressure is applied.  

Why is the temperature sensor moving and is there a way to stop it from doing so?  Please note that the temperature of the sensor and electronics are stable and the temperature sensor does not change when no pressure is applied to the sensor. 

  • 0
    TI__Guru 55466 points

    Hi Lori,

    The PGA309 internal temperature sensor accuracy is ±2C typical and unfortunately there is no guaranteed maximum spec provided. In general, sensors requiring a fairly large temperature coefficient correction or where high accuracy of temperature reading is required, will require the use an external higher accuracy RTD or temp sensor.

    Some standard oven or thermal chambers can exhibit temp gradients and/or air turbulence creating errors of a couple of degrees Celsius. In many cases, when quantifying the temperature sensor accuracy on a device, within an error below of a couple of degrees Celsius, an oil bath or specialized thermal chamber will be required.

    If I understood the question correctly, the temp reading slowly changes after applying pressure to the sensor, inside a thermal chamber with controlled temperature. What type of thermal chamber is used? I assume the sensor is placed inside the chamber at cold temperature, is this correct?. How is the pressure applied on the sensor inside the chamber after the temperature is stable? If you wait many minutes (for soak) on the chamber after applying pressure, does the temperature reading with the applied pressure agree with the temperature reading at the low pressure? Would it be possible to perform an experiment, and use a stable, high accuracy, low noise voltage source to emulate the sensor low pressure and high pressure, and monitor the PGA309 temperature reading after changing the input voltages?

    If possible, please share the schematic, and let me know the PGA front end and output stage gain settings as well as the input voltages corresponding to low pressure and high pressure of the sensor.

    Thank you and Regards,

    Luis