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TIPD209: Thermocouple Signal Conditioning

Carson Running
Prodigy 30 points
Part Number: TIPD209
Other Parts Discussed in Thread: TIPD109, ADS1263, ADS1118

Hi I will be using 5 T-type thermocouples in my work. I already have a sophisticated DAQ to conduct the ADC but would like a convenient way of filtering/amplifying each of my T.C. signals as well as implementing reference junctions. In the future I may be using more and/or different type T.C.'s. Is there a good solution for this? Thanks in advance.

  • 0
    TI__Mastermind 23050 points

    Hi Carson,

    Are you just looking for a simpler solution than what is presented in TIPD209? If your ADC is not set in stone you may also want to take a look at TIPD109, which is an ADC solution using the ADS1118, which includes an integrated temp sensor for cold junction compensation. For an upgrade, you could consider something like the ADS1263 which has 11 analog inputs you can mux between to accommodate all of your thermocouples with one device.

  • 0 in reply to Zak Kaye
    Prodigy 30 points

    The TIPD209 looks like the best option, it is just unclear if all type thermocouples are supported, how to connect to the thermocouple, and purchase ability.

  • 0 in reply to Carson Running
    TI__Mastermind 23050 points
    Carson,

    The interface to thermocouples doesn't vary with different types, so you should be able to connect any thermocouple and adjust your gain and cold junction compensation as necessary. Thermocouples are two-wire interfaces you can connect however you see fit (terminal block, soldered to board, etc.).
  • 0 in reply to Zak Kaye
    Prodigy 30 points

    Zak, thanks for your help. Am I correct in thinking that there is not a physical cold-point reference junction in the circuit but that the different resistors in the bridge make up a cold junction? If so, would you have to change these resistor values for different type thermocouples. Also, I know you cannot purchase this part as is. Is the best thing to do order the materials off the BOM and make your own?

  • 0 in reply to Carson Running
    TI__Mastermind 23050 points
    Hi Carson,

    That's not quite right. The cold junction is going to be wherever you make the connections from the thermocouple to the copper of the pcb. The connection points should be kept very close together to minimize any temperature difference between them so that you can treat the two junctions as a single reference junction. If you look at section 2.2 in TIPD209 it discusses how compensating for the change in thermocouple voltage requires an equal change in RTD voltage. Thus if you use a different thermocouple with a different Seebeck coefficient, then you will need to adjust R2 to satisfy this condition. If you want some more information on thermocouples, I found a great application note that gives some more insight into thermocouple operation and cold junction compensation. You can find it here: www.ti.com/.../sloa204.pdf

    While we do not offer assembled board for sale, we do provide all of the design files and the BOM so that you can easily integrate the design into your own board or send it to a manufacturer as is. Let me know if there is anything else I can help with!