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ADS1252: Ads1252 interface K-type, THERMOCOUPLE

sreerama dhanalakshmi
Prodigy 50 points
Part Number: ADS1252
Other Parts Discussed in Thread: ADS1220, ADS124S06, REF5020, REF6025

Hi sir,

I have ADS1252  ADC .

I want to interface    K-type, THERMOCOUPLE   with ADS1252 directly.!

Is there any  application Note ,sample Code for this  Measurement Available?

Thank u

 

 

  • 0
    TI__Mastermind 20765 points
    Hi Sreerama,

    welcome to our forum.

    Is there as specific reason why you want to use ADS1252 for a thermocouple measurement?
    I am asking because we have many ADCs in our portfolio which offer a higher level of integration to ease the implementation of thermocouple measurements.
    With ADS1252 you would need an external voltage reference, a clock and most likely an input buffer to implement a thermocouple measurement.
    Devices such as the ADS1220 or ADS124S06 integrate all those feature. Means they are more or less a single chip analog front end solution.

    Regards,
  • 0 in reply to Joachim Wuerker
    Prodigy 50 points

    Hi sir,

    Thank you for reply.

    In ADS1252 datasheet, I Found below Recommended applications where in Direct T/C Measurement is Mentioned??.. Hence wanted to use the same for similar applications?? Is there any (input impedance) problem?? Why you are suggesting alternate?

    ADS1252- APPLICATIONS


    ●CARDIAC DIAGNOSTICS
    ●DIRECT THERMOCOUPLE INTERFACES
    ●BLOOD ANALYSIS
    ●INFRARED PYROMETERS
    ●LIQUID/GAS CHROMATOGRAPHY
    ●PRECISION PROCESS CONTROL

    Thank u

  • 0 in reply to sreerama dhanalakshmi
    TI__Mastermind 20765 points

    Hi Sreerama,

    no, there is no problem for using the ADS1252 for thermocouple applications at all. You just need a lot of external circuitry around it as I mentioned before. You may actually also need a gain stage in front of the ADS1252 to amplify the small thermocouple signal.

    In our newer devices we integrated all those features (PGA, buffer, voltage reference, oscillator, digital filter that offers 50Hz & 60Hz rejection, etc.) to make our customers' lives easier for implementing thermocouple measurements.
    Those devices also offer more analog input channels, so you can measure the cold junction temperature with the same ADC as well.

    If you are looking for a really good device for thermocouple measurements, then I would recommend the ADS124S06.

    You can search our TI Design (reference design) library for 'thermocouple': www.ti.com/.../refdesignsearchresults.tsp
    You will find some example designs there. We don't have a reference design for ADS124S06 released to the web yet, but it will be almost the same as with the ADS1220.

    Regards,

  • 0 in reply to Joachim Wuerker
    Prodigy 50 points

    Thanks for your advice

    I wish to know ,following.

    1.What is the smallest signal (mV / uV) ,this ADS1252 can measure ?What external REF is recommended for low mV and uV measurement?

    2.For  +ve only signal ,can  i  GND  -Vin (PIN No:2) point, without using any single ended  to differential conversion ?

    Thank u

  • 0 in reply to sreerama dhanalakshmi
    TI__Mastermind 20765 points
    Hi Sreerama,

    the ADS1252 offers a full-scale range of +/-VREF.
    That means the LSB size is LSB = 2xVREF/2^24. That is in theory the smallest signal the ADC can resolve.
    However the noise of the ADC is usually larger than the LSB size. The graphs on p.4 in the datasheet will give you an idea of the noise performance. You can see from there what the smallest signal is that you can resolve (around 10-30uVrms).

    With a k-type thermocouple, which has a sensitivity of about 41uV/°C, you could then only resolve 0.5°C.
    This tells you already that you might be better off by placing a low-noise gain stage in front of the ADS1252 or to use ADS124S06.

    The REF5020 or REF6025 might be suitable voltage references in your case.

    Yes, you can connect -VIN to GND.
    Please remember that your +VIN signal is not allowed to go below GND by more than 300mV in that case. +VIN can swing positive up to +VREF.
    In the end the ADS1252 converts the differential voltage between +VIN and -VIN into a digital code. For the ADC it does not really matter at which voltage level -VIN is.

    Regards,
  • 0 in reply to Joachim Wuerker
    Prodigy 50 points

    Thank you for your reply,

    Request Further clarification for ADS1252 as below..

    1.Do I Need to add any external RC Filter Circuit  before ADC  +VIN  Pin? Alternately Can I Connect Small Signal Directly Without External Capacitor  to ADC +VIN ?

    Thank you

  • 0 in reply to sreerama dhanalakshmi
    TI__Mastermind 20765 points

    Hi Sreerama,

    we do usually recommend placing an RC filter at the ADC inputs. However the RC filter is not necessary for the ADC to work.

    Regards,