• State Resolved
  • Locked Locked
  • Replies 7 replies
  • Subscribers 46 subscribers
  • Views 3189 views
  • Users 0 members are here
Support feedback
Options
Options
Related

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.

How to use ADS1220 to read temperature through thermocouple?

HY CHO
Prodigy 120 points
Other Parts Discussed in Thread: ADS1220, ADS1120

Dear Sirs.

I want to know how to use AD1220 to read temperature through thermocouple.

I don't konw which value set up in configuration register.

If possible, could you give me S/W source to refer?

Also, Please refer to the schematic attached.

Thank you. ADS1220.pptx

  • 0
    TI__Guru** 113765 points

    Hello Hy,

    We are currently in the process of updating the ADS1220 datasheet with more application information.  At this time I would suggest that you take a look at the ADS1120 datasheet that has already had the updates added.  The ADS1120 is essentially the same part except for the maximum resolution size.  The application section (9.2 on page 48) discusses and shows how to make a TC measurment and the process involved. The register settings are also shown in Table 22.

    We do not have specific TC application code, but example code for communication using MSP430 devices can be found at:

    http://e2e.ti.com/support/data_converters/precision_data_converters/w/design_notes/2635.ads1220-example-code

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    TI__Guru** 113765 points

    Hy,

    One of my colleagues mentioned that one of the TI Designs related to the ADS1220 may be helpful.  According to your schematic it appears you want to measure both TC and RTD.  Look at the following link for a similar application.

    http://www.ti.com/tool/TIDA-00018

    Other designs for the ADS1220 can be found at:

    http://www.ti.com/product/ADS1220/toolssoftware

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Prodigy 120 points
    Thank you for your help.
    I try to test with your information.
  • 0 in reply to Bob Benjamin
    Prodigy 120 points
    Hello Bob B
    I have any question.
    Our customer has been using SENCO_P1(AIN0), SENCO_P2(AIN1) with differential mode like last attached file.
    Register setting value is like below.
    ======================================================
    // NORMAL PGA 32 differential. 600 SPS, continuous conversion mode, VREF : internal 2.048
    SPI_Rx_Tx(SPI0, 0x410000 + 0x0AA4, &rxData); // reg write
    SPI_Rx_Tx(SPI0, 0x490000 + 0x1000, &rxData); // reg write
    =======================================================
    When AIN0 supply 2.0V and AIN1 supply ground through power supply, Our customer expected to get 7F FF FF in 24bit max value by using RDATA commend.
    But, Our customer got 7F FF FF value when AIN0 supplied 3.0V.
    Our customer wants to know reason why we get that reponse.
    Please advise me.

    BR
    HY.CHO
  • 0 in reply to HY CHO
    TI__Guru** 113765 points

    Hello Hy Cho,

    It is not clear what the customer is trying to do and why they are overdriving the input.  If I understand correctly the input AIN1 is being referred to analog ground which is in violation of the common mode restriction for the ADS1220 when using PGA gain of 32.  If this is not the case, and a seperate power supply is connected independent of the analog supply being used, you must make certain that the supply output does not cause an issue relative to the power supply ground of the sources.  Sometimes these voltages are much different with respect to a single common point.  You must not violate the ADS1220 absolute maximum voltages for the analog inputs.  When using power line generated supplies you must make sure that when connecting an external source you verify the input voltage relative to analog ground of the ADS1220 is not in violation.

    The configuration chosen has a full-scale range of +/- 64mV, so why is the customer connecting such a large input voltage?  Also please clarify your question.  3V is greater than 2V so why would they not expect to see a full-scale reading?

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Prodigy 20 points
    Hello Bob B,
    I am using a Beaglebone Black to get data from ADS1220 but I have some problems with the reading of data. I have been testing acquisition of data using internal and external voltage reference, I can read the change of voltage since a low voltage to a high voltage. I used a J-type Thermocouple and a Signal Generator (DC). The problem presents when I try to convert the binary code to a voltage data. When I used a internal voltage reference (2.048 V) I used this equation to get the real value:
    Real Value (V)= Binary Data from SPI ADS1220 in INT format (3 bytes) * 2.048 / (2^23)
    When I used a Signal Generator, I read the value from output (Signal Generator) with a Fluke Multimeter. For example, I read 1.103 V but when I get the Real Value from the reading from ADS1220 this value is 0.764.. V. I can't understand which is the reason to this error. The same thing happen when I use an external voltage reference.

    The configuration that I am using it is from the datasheet of ADS1220 (Example - Reading Temperature from K-Type Thermocouple)

    Also, Can you explain me what is the reason to use two types of power supply (Digital and Analog)?

    Please, help me with that.

    Thanks!

    Carlos Saravia Jurado / Lima - Peru

    PS. Sorry for my english
  • 0 in reply to Carlos Saravia Jurado
    TI__Guru** 113765 points

    Hi Carlos,

    What usually happens in the case of connecting external power supplies (signal generators) to the analog input is that they are referenced to analog ground in such a way as the supply input violates the common-mode requirement of the PGA.  I would first try disabling the PGA to see if that changes your reading to the appropriate value.

    You are not required to use two different supplies for analog and digital.  However, there can be some applications where this can be beneficial.  For example, if you use a bridge circuit, you will get more resolution of the bridge output if a higher excitation voltage is used and a ratiometric measurement is also used (excitation and reference voltage are the same voltage source).  In this case, an analog 5V would be appropriate.  Also, some microcontrollers will only accept a maximum of 3.3V.  In this situation you can benefit by having two different supply voltages.

    Best regards,

    Bob B