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multi channel thermocouple application

brian rist
Prodigy 20 points
Other Parts Discussed in Thread: ADS1118

I have an application where I want to measure 40-80 k type thermocouples for temperature control and overtemperature protection.  I played with the ADS1118 eval kit and this part seems to work well for my application (measuring low temperatures < 250 degC, only requires +/-1 deg, low speed).  I want to know if TI offers either:

1) a reference design for addressing multiple ADS1118s on one set of SPI lines, toggling the chip selects

-or-

2) a different a/d part that can read 4-8 thermocouples with built in CJC, etc. and a reference design

Thanks

  • 0
    TI__Guru** 113765 points

    Hi Brian,

    Unfortunately we do not have a reference design for using multiple devices.  Basically it is pretty simple.  Each ADS1118 device needs it's own CS control.  Using a demultiplexer, you can take four lines from your GPIO of your controller to control 16 ADS1118s (as an example). 

    We have other ADC devices that have more input channel count, but this would require external temperature sensors for the CJ.

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Prodigy 20 points
    Thanks. What is a practical limit to the number of ads1118s I can parallel on the same spi lines
  • 0 in reply to brian rist
    TI__Guru** 113765 points

    Hi Brian,

    The practical limit will be more of a function on how many GPIO lines are availble from your controller for CS.  With respect to the communication, routing path and speed of the SCLK will be a factor to maintain the correct phase relationship of the clock to the data out of the ADS1118.  This would relate to layout/cabling of the system as well.

    Best regards,

    Bob B