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Original question:

ADS1220: How to choose a proper multiplexer for temperature module

ADS1220: Multiplexer for PT100 2 and 3 wire and Thermocouple typ K.

Vincent Rudolph
Prodigy 40 points
Part Number: ADS1220
Other Parts Discussed in Thread: ADS124S08, ADS124S06, TIDA-00647

Hi Team,

our customer is currently planing an update of a Temperature Sensor hub. The old design is using diffrent ADCs and matching networks, for diffrent sensors.

I suggested that we could only use one ADC like the ADS1220 with a multiplexer to be able to deliver the same performance. The idea is to have 3 diffrents Ports for the sensor that are connected to an Mulitplexer which is connected to the ADS1220. 

Is there something special to keep in mind, while choosing the Multiplexer? And is there somehting like a Guide, for this kind of application?

Best regards
Vincent

  • 0
    TI__Guru** 112705 points

    Hi Vincent,

    I'm sorry for the delayed response.  You may not need to use an external mux, but instead use the highly configurable mux of the ADS1220 (or another alternative the ADS124S06 or ADS124S08).  Which method or device is used will depend on the number of sensors connected to the ADC.  So it is possible to connect multiple sensors to a single terminal block.  Using an external mux is an alternative, especially if there are a number of sensors required to be measured.  The largest consideration when using an external mux is leakage.

    I would suggest taking a look at the following guides for some possible configurations:

    A Basic Guide to Thermocouple Measurements

    A Basic Guide to RTD Measurements

    Best regards,
    Bob B

  • 0 in reply to Bob Benjamin
    Prodigy 40 points

    Hi Bob,

    thanks for your help. The guidelines were helpful. I think I found good examples for diffrent RTD configuration. I think our customer is happy with the performance of the ADS1220.

    I also found the  "TIDA-00647 TIDesign". Which also is pretty helpful. There two Jumpers are used to switch between 4,3 and 2 wire mode. For a prototyp my idea is now to replace these jumpers with switches/transistors. I assume that the same consideration are to be done here - low leakage current etc.

    Does TI maybe have a switch that you can recommend? I am currently unsure for what kind of device I have to watchout.

    Thanks again

    Vincent

  • 0 in reply to Vincent Rudolph
    TI__Guru** 112705 points

    Hi Vincent,

    The world of analog switches and muxes  change often and it is hard for me to keep up.  Most customer applications I have seen use an analog switch or a MOSFET as a switch.  As I mentioned previously, low leakage devices should be used to prevent error from the leakage path.  Which method is used will depend on cost and level of precision required.

    You could take a look at some of the TI devices using the parametric search.  Here is one search example:

    http://www.ti.com/switches-multiplexers/analog/products.html#p480=1;2&p3193max=1e-8;0.009&sort=p3193max;asc

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Prodigy 40 points

    Hi Bob,

    Thanks for the information. Yes it is the same for me, I am not really in touch with these products.

    Thank you again for your support.

    Vincent