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INA333: RTD sensor measurement with INA333

Bulent Kupelı
Prodigy 160 points
Part Number: INA333

Hi all,

Can I measure RTD sensor( NTC or PTC) using INA333? In INA333, the VIN + pin is connected to the RTD output and VIN - pin is conected to the ground line.Do I have to use differential input or can ı amplification the singel input as shown in the schematic. 

I would highly appreciate and suggestions for improvement.

Thanks in advance.  

  • 0
    TI__Genius 10850 points

    Hi Bulent,

    You cannot ground one of the inputs, this would violate the input common mode voltage range of the INA as specified in the datasheet on page 5. Can you share more detail on the expected input and output signal? I want to make sure you are operating in the linear range.

    Also, here is an INA & RTD reference design you may find helpful for your application: http://www.ti.com/lit/ug/tidu969/tidu969.pdf

    -Tamara

  • 0 in reply to Tamara M Alani
    Prodigy 160 points

    Hi Tamara,

    Firstly, thank you for answer. I am using RTD sensor for input signal, it has 4 wire but I use it as two wire. First wire is using as input signal and pull up with 56K ohm resistance and other wire is ground. I want to amplifier my input signal using ina333 and I expect my output signal that will changes between 0.5 - 4.5 V but I am not sure this circuit that works or not and I cant find a example that is like it for ina333. Also 33K ohm and 33n Farad are using low pass filter.

    Thanks in advence,

    Bülent Küpeli

  • 0 in reply to Bulent Kupelı
    TI__Genius 10850 points

    Hi Bulent,

    I can help you put together a circuit using the INA333. I need you to answer a few questions first so we can make sure we are putting together a proper circuit:

    • What is the expected input signal into the INA333? What range of voltage do you need to amplify? This information will help us determine if the INA333 is the right amplifier and what gain we need.
    • I understand you want Vout to be 0.5V to 4.5V

    Note: 2-wire RTD measurement is very sensitive to lead resistance. it is recommended to put the RTD as close to the INA to minimize the error drop across a long lead or additional resistance. Two-wire RTDs yield the least accurate RTD measurements and are used when accuracy is not critical or when lead lengths are short. 

    Here is a basic guide to RTD measurement which you may find useful: http://www.ti.com/lit/an/sbaa275/sbaa275.pdf

    -Tamara

  • 0 in reply to Tamara M Alani
    Prodigy 160 points

    Hi Tamara,

    My input is analog DC signal that is changing in milivolt ranges.For example, it is changing between 0.02 and 0.05 V and I want Vout to be 0.5 to 4.5V. Gain is changing according to my pull up resistance so I dont need to specific gain.

    Bülent

  • 0 in reply to Bulent Kupelı
    TI__Genius 10850 points

    Hi Bulent,

    The 33k-ohm resistor and 22nF capacitor are not doing what I think you are expecting. The 33nF capacitor is a DC-blocking component so Vin+ is always 5V regardless of the input signal.

    I would recommend removing these components and trying the measurement again. 

    -Tamara

  • 0 in reply to Tamara M Alani
    Prodigy 160 points

    Hi Tamara,

    The 33k ohm and  33nF capacitor are part of RC low pass filter of which cut off frequency is 150 Hz. I dont have INA333 and  so I can not try it :) Thank you for answer. 

    Best regards,

    Bülent