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Original question:

ADS112C04: Could ADS112C04 be used in two channel RTDs applications?

ADS112C04: ADS112C04 with two RTDs

Thomas Vollmar
Prodigy 10 points

Part Number: ADS112C04
Other Parts Discussed in Thread: ADS1220

Hi,

https://e2e.ti.com/support/data-converters-group/data-converters/f/data-converters-forum/1327605/ads112c04-could-ads112c04-be-used-in-two-channel-rtds-applications

In this dicussiuson you say, it ts possible that the ADS112C04 to works with two TRDs. In this scematic is used the pins ANI0...ANI4. But theare is no ANI4 on the ADS112C04. Do you mean an other ADS?

  • 0
    TI__Intellectual 1480 points

    Hi Thomas, 

    Welcome to the Texas Instruments E2E forum, thank you for your interest in our ADCs!

    The discussion you linked includes a screen capture from A Basic Guide to RTD Measurements  which shows the use of 5 analog inputs to complete the measurement of two 2-wire RTDs. While this is possible on the ADS112C04 the diagram in that post is not fully accurate for the implementation. 

    High-side reference implementation 

    Use REFP as the IDAC output while connecting RTD1 to AIN0 and AIN1 and RTD2 to AIN2 and AIN3. Rref across REFP and REFN should be at least 4x the resistance expected on either of the RTDs. Current will flow from REFP across Rref through RTD1 and RTD2 and then must have a good connection to ground for best measurement results. 

    Here is an example of this implementation using the ADS1220 that can be used to set up the ADS112C04 (https://www.ti.com/lit/ab/sbaa235a/sbaa235a.pdf)

    In principle you could also set the IDAC to go out through one of the analog input pins but there are some concerns with this. Mainly, you would most likely have to connect without analog input filtering due to the potential voltage drop over the series resistor. So this filter would not be able to provide protection to the device. 

    An additional option would be an external multiplexer to expand the number of analog inputs as well. 

    Regards, 

    Andrew

  • 0 in reply to Andrew Kalthoff
    Prodigy 10 points

    Hello Andrew,

    Thank you very much for your support!

    Unfortunately ths scematic is suboptimal becaus you need both RTDs all times. In my application, it's the decision of the customer to use one or two RTDs. Please do you have a solution for this? Can I use the IDAC1 for the one and the IDAC2 for a second RTD?
    What for a multiplexer do you mean?


    Best regards!

    Thomas

  • 0 in reply to Thomas Vollmar
    TI__Intellectual 1480 points

    Hi Thomas, 

    I understand your concern using both of the at the same time. 

    Another device that might fit your need a little better  ADS114S0x this would allow for the selectable functionality due to the increased analog inputs. Both RTDs would be able to share the low side reference and would be able to switch through the MUX for measurement of each RTD. Here is A Basic Guide to RTD Measurements, Figures 2-9, 2-10 and 2-11 might be helpful depending on the RTDs you have selected to measure multiple RTDs on a single device. 

    Would this device work for your application?

    Regards, 

    Andrew