• State Resolved
  • Locked Locked
  • Replies 9 replies
  • Answers 1 answer
  • Subscribers 42 subscribers
  • Views 1436 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TIDA-00650: T-type thermocouple

A K
Intellectual 895 points
Part Number: TIDA-00650
Other Parts Discussed in Thread: TIDA-00168, ADS1220

I want to use a T-type thermocouple with the TIDA-00650 reference board. I am using TIDA-00168 example code. I changed to a T-type connector and changed the PGA gain to 64 considering max voltage at 400C is 20.872 mV. Do I need to change filter/biasing circuits to accomodate the change? I am getting a wrong reading with this setup.

Thanks!

  • 0
    TI__Intellectual 800 points

    Hello Adtk,
    Sorry to have kept you waiting. I will get you connected to the right support engineer for an answer to your question as soon as possible.
    Thank you for your patience and I appreciate for choosing TI.
    Regards,
    Yuki Yoshimura

  • 0
    TI__Guru 71516 points

    Please provide some details on how you are making the measurements, register settings, etc, TC part number.

    Here is an E2E post that could be helpful, look especially at the Jun 29 reply with the reference to software examples: http://e2e.ti.com/support/data_converters/precision_data_converters/f/73/t/432533 .

    Also refer to this App Note: http://www.ti.com/lit/an/sbaa189/sbaa189.pdf .

    ~Leonard 

  • 0 in reply to LeonardEllis
    Intellectual 895 points

    Thanks Yuki, for forwarding to the right group.

    Leonard,

    I was out of office so apologize for the late response. I now have a working T-type TC with the TIDA-00650 board. I missed the fact that the code outputs the ADS1220 24-bit register as 32 bits thus forgetting to shift it by 8 during CJC and interpolation calculations.

    My understanding after reading the design theory in tidu574 app note is that the board design would not need any component changes for T-type TC measurements. I would like to verify that my understanding is correct.

    Does TI have any FAEs in Dallas for direct contact?

    Thanks for the help! 

  • 0 in reply to A K
    TI__Guru 71516 points

    Hello AdtK,

      Apologies for the delay, with the holidays and such, having some challenge in resolving this. 

    ~Leonard  

  • 0 in reply to LeonardEllis
    TI__Intellectual 850 points
    Hello AdtK

    sorry for the delayed response.
    As it looks like, you got it working, isn't it?

    As you have described, it doesn't matter which kind of thermocouple type you are using. The only attention you have to pay is the gain setting of the PGA. The Thermocouple generates a certain voltage range (this is dependent on the type of thermocouple you are using) which has to fit to the ADC full scale range. Also you would have to use the look up table for this specific thermocouple type. A Type K TC has a different behavior (LUT) than a Type-T etc.
    I hope this answers your question.

    Regards
    Alex
  • 0 in reply to AlexW
    Intellectual 895 points
    Hello Alex,

    Thanks for your response. I got it working at room temperature, but not at cold temperature.

    I used a cold chain container with ice packs to obtain cold temperatures. I used a Agilent data logger with T-type TC and a Fluke K-type thermocouple as references. Both reference readings were around -3C.

    I have a TIDA-00650 board that I have left original (no hardware or software change). I am using the K-type TC from Omega.
    I have a second board that I modified for the T-type TC with T-type connector. I changed the LUT and PGA gain to 64 for the T-type.

    Using TIDA-00168 software example code I performed following tests with both K-type and T-type boards.

    With CJC from ADS120 internal temp sensor:
    1. Both board and TC at room temperature : ADS1220 temp and compensated TC temp are at room temp
    2. Board at room temp, TC in cold container : ADS1220 is room temp, compensated TC temperature is also room temp
    3. Board in cold container, TC at room temp : ADS1220 is ~0C, compensated TC temperature is ~0C
    4. Both board and TC in cold container : ADS1220 is ~0C, compensated TC temperature is ~0C

    When using the RTD for CJC, I got a totally wrong RTD temperature in 3 and 4 with both boards.

    The compensated TC temperature seems to be following the CJC temperature so not sure what is going on here, especially with the K-type as I have changed nothing there.

    Thanks!
  • 0 in reply to A K
    TI__Intellectual 850 points

    Hello AdtK

    could you please check / measure the value of R12? This is the reference resistor which is connected to REFP0 and REFN0 of the ADS1220. We have on sime boards for test purposes different values for Rref. BTW, from whom do you have you received TIDA-00650 (since it is not orderable)?

    In case, this value is not 3.24k as mentioned in the schematic, this has to be adjusted also in the SW.

    Why are you changing the gain settings to 64? When you change the gain, you have to make sure to satisfy the ADS1220 requirements for common mode etc, as described in its datasheet.

    Since you are using the firmware of TIDA-00168, the firmware might not fit 100% the hardware of TIDA-00650. In TIDA-00168is also a mode where an external reference voltage is used during TC measurement. This configuration is not available in TIDA-00650.

    When you are debugging the firmware, are you able to just look at the measure TC and CJC value? Maybe you can verify if those values are measured correctly.

    Instead of using an actual TC you also can use a precise voltage source for the TC input and a known resistor for the CJC.

    Regards

    Alex

  • 0 in reply to AlexW
    Intellectual 895 points
    Hello Alex,

    We produced the board from the gerber files you have uploaded. I measured R12 to be 3.24K, same as in BOM.
    After my previous post, I found a typo in my TC calculation which I corrected. I had tested T-Type with both 32 and 64 PGA gains but set it to 32 as the K and T-type TCs have similar voltage ranges between -200C and 400C and for the reason you mentioned.

    But while simulating CJC with 100R resistor and a mV source I found that the calculated temp had opposite sign. I compared the schematics after you mentioned that the two boards are different. I realized J2.2 in TIDA-00168 is routed to AIN0 whereas in TIDA-00650 it is routed to AIN1. Both K and T-type are working at all temperatures after reversing the ADS1220 setup.
    I am moving on to testing accuracy. I appreciate your help and thanks for continuing to follow up on my questions!
  • 0 in reply to A K
    TI__Intellectual 850 points
    Hello AdtK

    this sounds great!
    Since this obstacle seems to be solved, would you mind to mark this thread as solved?

    Thanks a lot!
    Regards
    Alex