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ADS114S06B: Temperature calculation for ADS114S06B

Mark Steve
Prodigy 40 points
Part Number: ADS114S06B

Hi,

I have selected ADS114S06B 16 bit ADC for my application. My requirement is to read temperature from 0 deg centigrade to 60 deg centigrade with a accuracy  0.005 degrees and 1% tolerance . As it is 16 bit ADC, and I want to select 5V as reference voltage.

1LSB that I can read for 16 bit and 5V reference is equal to 5/POW (2,16) -1 which corresponds to 76.29 micro volts. My question is am I able to acheive 0.005 degree accuracy with this output or not. Please suggest.

Regards,

Mark Steve

  • 0
    TI__Guru** 113765 points

    Hi Mark,

    It is not clear what the temperature sensor is that you plan to use.  Depending on the sensor, your target may be difficult to reach.  The ability to resolve will also depend on the reference source used.  If the reference source is noisy, the conversion result will also be noisy.  For the ADS114S06B, the ADC converts to binary 2's complement using a full-scale range (FSR) of +/-Vref/GAIN.  The LSB size is determined by the FSR/total number of codes.  So for a 5V reference the FSR is +/-5V or 10V/ (2^16-1) which would then resolve to 152.59uV per LSB at a gain of 1.

    I would recommend looking at the following resource information:

    A Basic Guide to Thermocouple Measurements

    A Basic Guide to RTD Measurements

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Prodigy 40 points

    Hi  Bob, 

    Thanks for the reply.

    I want to use a NTC Thermistor with resistance tolerance of 1% . And as you said,  if I I use a constant reference source of 5V I wl  get 71.6 uV for 1 LSB. 

    I want to use voltage divider configuration with Thermistor resistance of 10K at 25 degrees C and resistance tolerance of 1% by providing 5V input voltage. 

    So, I  will get 2.5V output at Thermistor which is given to ADC. So what will be the 1LSB of temperature I can read for range of 0 to 60 degrees centigrade with 0.005 degrees accuracy 

  • 0 in reply to Mark Steve
    TI__Guru** 113765 points

    Hi Mark,

    I guess you misread my previous response.  The LSB for 5V reference is 152.59uV and not 71.6uV.  Take a look at the circuit in section 2.8.2 in  A Basic Guide to Thermocouple Measurements.  This section discusses measuring a thermistor and includes a circuit diagram.

    Using a voltage divider I would follow the described circuit.  Instead of using 5V use the output of the ADS114S06B reference which is 2.5V.  This circuit has an LSB value of 76.29uV.

    As far as accuracy, you can only be as good as the accuracy of the thermistor and the accuracy/tolerance/temperature coefficient of the bias resistor used.  Depending on the method used for calculation of resistance to temperature (LUT, Steinhart-Hart, polynomials) there can be calculation error as well.

    I don't know what specific sensor you are using, but higher end 10k thermistors have sensor accuracy at greater than 0.5deg C throughout the desired temperature range.  So even though you may be able to resolve to a small temperature value in theory, doesn't mean you will have 0.005 deg accuracy.

    Best regards,

    Bob B