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PGA900: Load Cell design

Kum Hoo Lee
Expert 1855 points
Part Number: PGA900
Other Parts Discussed in Thread: ADS124S06, ADS122C04, PGA300

Dear Sir/Madam,

Understand that PGA900 can be use for Load Cell application. Can i use both P Gain and T Gain for load cell? Is it possible that I am not using the T GAIN for temperature because I would like to connect that input for my second load cell, may I know is there any way i can do that?

Thanks for you help and hope to hear from you soon!

 

Best regards,

KH

  • 0
    TI__Mastermind 31655 points
    Hello,

    The P and T signal paths are not exactly the same. The temperature path's performance is not quite as good as the pressure path. For instance, the noise floor is higher on the temperature side, and the number of gain bits is only 2, so the options are limited. If the characteristics of the temperature path ADC and gain blocks are acceptable, then you can certainly use it to measure differential voltage from a pressure load cell.

    One other thing to keep in mind is that you will need an external excitation source for the load cell bridge, since the internal VBRIDGE voltage source cannot supply enough current for 2 separate bridges.

    Regards,
  • 0 in reply to Scott Cummins
    TI__Mastermind 22385 points

    Hi Kum Hoo Lee,

    if you are only looking for an ADC solution - without the integrated MCU, DAC, etc. - then ADS124S06 would be a great solution to measure two load cells.

    Regards,

  • 0 in reply to Scott Cummins
    Expert 1855 points
    Dear Scott,

    Thank you so much for the advise, I will not need to have a very high accuracy on the T gain path.

    How can I do the connection if I am using the T gain path for load cell?
    And i do have 2 more questions as below:
    1) the pga900 comes with the initial code programmed into the chip? That means I can use it as it is without having to program it?
    2) If i am not using the T gain path, can I leave the temperature sensor (optional) unconnected? will it affect anything?

    Hope to hear from you soon
    Thanks and best regards,
    KH
  • 0 in reply to Joachim Wuerker
    Expert 1855 points
    Hi Joachim,

    Thanks for the advise, i will look into your advise on the 24 bit ADC,. Is there any I2C device with similar specs?

    Thanks and best regards,
    KH
  • 0 in reply to Kum Hoo Lee
    TI__Mastermind 22385 points
    Hi Kum Hoo Lee,

    the only suitable 24-bit ADC we have with I2C interface would be ADS122C04. It is not as high-performance as the ADS124S06, but could be sufficient depending on your requirements.

    The ADS122C04 datasheet shows a ratiometric measurement implementation for a load cell in the application section.
    To measure two load cells you would power/excite both load cells with the same excitation voltage.

    Regards,
  • 0 in reply to Kum Hoo Lee
    TI__Mastermind 31655 points

    Hello KH,

    1. The PGA900 does not have the firmware programmed onto the device. The PGA300 is the device you are looking for. It comes with the OTP preprogrammed with firmware for the embedded microcontroller.

    2. Yes, you can leave it disconnected. Just make sure to disable it in the EEPROM when not in use.

    Regards,