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ADS1118: What is the resolution of temperature sensor?

Part Number: ADS1118
Other Parts Discussed in Thread: ADS1018, ADS1120

Dear TI experts,

My customer is looking for the IC which can measure temperature with K-type thermocouple.

I found ADS1118(16bit) and ADS1018(12bit).

my customer wants to use the function with less than 0.25℃ step.

ADS1118 datasheet says that the resolution of temperature sensor is 0.03125℃/LSB. does it mean that I cam measure the temperature with 0.03125℃ step?

Please check my question, and please recommend cheaper IC that can measure the temperature with K-type thermocouple.

measuring with less than 0.25℃ step is mandatory, I2C interface is preferred. (does not matter with SPI either.) cheaper is more important than interface type.

Best regards,

Chase 

  • Hi Chase,

    The ADS1118 is one of the cheaper solutions for doing K-type thermocouple measurements. 

    From the data sheet, there is a +/- 0.5°C accuracy variation for temperatures between 0°C to 70°C and +/-1°C for temps between –40°C to +125°C, which might not satisfy the 0.25°C step requirement. 

    Doing temperature measurements is not trivial and achieving that level of resolution is not an easy task to achieve with K-type thermocouples measurements. A different solution might be necessary. 

    We have an application note on thermocouple measurements that is hopefully useful in gaining a better understanding of these measurements: A Basic Guide to Thermocouple Measurements (Rev. A) (ti.com)

    We also have a circuit design for thermocouple measurements that uses an ADS1120 that can be used as a reference: K-type thermocouple measurement circuit with precision ADC (ti.com)

    Best Regards,

    Angel

  • Dear Angel,

    Thank you for your support.

    I think that accuracy and resolution have little different meaning.

    I accept a +/- 0.5°C accuracy. on the other hand, I have to check the resolution(steps) of temperature sensor of ADS1118.

    Please check this issue. Thanks.

    Best regards,

    Chase

  • Hi Chase,

    Yes, 0.03125℃/LSB is the resolution of the internal temperature sensor of the ADC. 

    It does not mean that this is the resolution in which you will be reading temperature from the thermocouple. 

    The thermocouple measurement is a separate voltage measurement, and the accuracy depends on the thermocouple. What the ADC is measuring is the voltage generated by the thermocouple.

    There are two measurements, the internal temperature sensor that measures the ADC die temperature, and the voltage reading from the thermocouple. Both of these are used together in order to make temperature measurements.

    The explanation is in the basic guide that I sent in the previous reply. 

    Best Regards,

    Angel