• State Resolved
  • Locked Locked
  • Replies 6 replies
  • Subscribers 46 subscribers
  • Views 616 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.

Compiler/ADS1118EVM: Understanding conversion register on ADS1118

Shubham Tandon
Prodigy 250 points
Part Number: ADS1118EVM
Other Parts Discussed in Thread: ADS1118

Tool/software: TI C/C++ Compiler

Hello,

I have an ADS1118EVM - and I am trying to get a better understanding of the conversion register.

Using the tool - I can see that the conversion register returns 0B8Ch. This chip is in temperature sensor mode. 

I understand that the above value is 2's complement - which would be 0474h. How is a temperature sensor value of 23C derived and the thermocouple voltage determined from this one register? 

FS = .256V

Thank you in advance. I am sorry if the question is vague and i'll try my best to regurgitate. 

  • 0
    TI__Guru* 97415 points

    Shubham,



    The ADS1118 reports temperature sensor data based on Table 4 on page 20 in the datasheet. Just to be sure, I would definitely re-read that section.

    First, the FSR value is ignored for temperature sensor data, so regardless of setting, it will report the value back based on the table.

    Going to your conversion register value you get 0B8Ch. However, the ADS1118 reports back the temperature data as a 14-bit number that is left justified in the conversion register. To get the proper value you truncate the last two bits of the conversion register. The equivalent function would be to divide by 4 to get the proper value.

    With this, 0B8Ch becomes 02E3h. Converting this to decimal, this becomes 739d. Converting to temperature, each code represents 0.03125°C. So:

    739 * 0.03125°C = 23.09°C



    Joseph Wu

  • 0 in reply to Joseph Wu
    Prodigy 250 points

    OK thank you for that.

    Does the ADC output also get communicated over the conversion register? I am guessing section 9.5.6 of the data sheet would help with that. 

    I am using this device for a type-t thermocouple.

  • 0 in reply to Shubham Tandon
    TI__Guru* 97415 points

    Shubham,

    The ADC output data also gets sent to the conversion register. There is only one ADC in the device and a multiplexer at the front end. Normally, the MUX[2:0] bits set the multiplexer to the input pins, but the TS_MODE sets the multiplexer to measure the temperature sensor instead of the input pins.

    Joseph Wu

  • 0 in reply to Joseph Wu
    Prodigy 250 points

    If I am using temp sensor mode, how quickly are the two temperatures relased? Also can I use the EVM to read the conversion register outputting the ADC output [not temperature sensor value]

  • 0 in reply to Shubham Tandon
    TI__Guru* 97415 points

    Shubham,


    The readings for the temperature sensor mode come out at the same data rate as set by the ADC. If you're in DR=128SPS for the ADC, then the temperature sensor comes out at the same rate.

    For the EVM, it's more of a reference design instead of a evaluation module. Because of this, the data is reported only in degrees.  

    I would note that if you are doing a thermocouple application, there is some background information for you to read:

    Here's a basic guide to thermocouple measurements:
    www.ti.com/.../sbaa274.pdf

    Here's a TI design using the ADS1118 for thermocouple measurements:
    www.ti.com/.../slau509.pdf

    It should guide you through some of the design considerations for a thermocouple application.


    Joseph Wu

  • 0 in reply to Joseph Wu
    Prodigy 250 points

    Joseph I figured it out.

    The config register needs to be switched to temperature mode to store the ambient temperature and the config register needs to be switched from temperature sensor mode to obtain the far end temperature data..

    I am fairly new to the embedded world so I really do appreciate your patience with me on this topic.

    Cheers!