ADA4528-2 drive AD7172-2 + 10VDC load cell

My question is if It´s possible to connect a load cell (+10VDC supply) with zero drift amplifier ADA4528-2 (+5VDC supply) for driving diferential input of AD7172-2 AD converter.

You can see the schematic attached.

regards.

  • 0
    •  Analog Employees 
    on Jul 17, 2018 12:09 AM

    Hi,

    May I know what is your load cell's sensitivity? What is your target gain and target resolution? ADA4528-2 is suitable for driving AD7172, however for a 10V excitation voltage a ratio metric configuration is not possible as the AD7172 can only accept a 5V supply and reference voltage. Thus, any variation in reference voltage or excitation voltage may results errors or variations in your measurements. If you have any further questions regarding ADA4528-2, I think someone from the  Amplifiers  Community may be able to help you. It is necessary to take note some important considerations in designing your signal conditioning to meet your required specifications.

    Thanks,

    Jellenie

  • Hi Jellenie,

    It´s a 350 Ohm load cell, with sensitivity of 2mV/V. The gain and reference target depends of test. I think this circuit works in ratio metric configuration, what do you think? Please, you can see the measurements that i have made in schematic. Also, I have left the circuit ready to work with different voltages, I have a variable power supply (VDC). In the attached schematic you can see the voltage values measured of signals and reference with different power supply voltages. With +10VDC load cell supply, AGND-SIGNAL+ is < 5VDC, so this circuit would must work.

     

    Regards,

    Javier.

    SCHEMATIC1_H_CONVERSOR_AD.pdf
  • 0
    •  Analog Employees 
    on Jul 19, 2018 8:14 PM

    Hi, Javier.

    Ratio metric configuration means that the excitation for the bridge will also used for the ADC's reference. In this case, the input to the converter and its reference are derived from the same excitation source, changes in the excitation do not introduce measurement errors. However, the reference for AD7172 can only accept up to 5.5V and typically 5V. So if you use a 10V excitation voltage you cannot directly use this as your reference input. I see that you used a voltage divider, is that correct? but any errors in the divider circuit will not be related to the inputs, thus they are not fully ratio metric. So I would suggest that you can lower that your excitation voltage to 5V.

    Thanks,

    Jellenie 

  • Hi, Jellenie.

    I know what you say, that's why I use a voltage divider, so this voltage is proportional to excitation voltage. I´m not sure if i have any benefits of power supply to 10VDC instead 5VDC, Do you have any idea about this?

     

    Regards.

  • 0
    •  Analog Employees 
    on Jul 22, 2018 5:07 PM

    Hi,

    Higher excitation voltage gives much higher performance resolution. But it will still depends on your target performance and also on your system noise. Noise is affected by ODR, Gain and Filter choice. Correct the voltage in the divider is proportional to excitation, however, any noise or errors on the resistors divider itself is not related to the inputs.

    Thanks,

    Jellenie