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Dual thermocouple measurement via Excel in real time — Parallax Forums

Dual thermocouple measurement via Excel in real time

KatyBriKatyBri Posts: 171
edited 2012-10-18 12:18 in Accessories
Hello,

I have a project where I need an interface between two thermocouples and a PC's USB port, to allow me to capture their temperature values in Excel (with the appropriate add in) in real time.

Looking for ideas on a low cost interface with cold junction compensation, and a source for a free Excel add in. If Parallax product, must be BASIC STAMP, Not propeller. If no Parallax products available (either as kit, ready to use, or build from scratch), please advise of other low cost solutions.

Thanks

Comments

  • WBA ConsultingWBA Consulting Posts: 2,933
    edited 2012-10-16 17:34
    I would start with looking at thePLX-DAQ Excel Plugin:
    http://www.parallax.com/tabid/393/Default.aspx

    It appears that the DS2760 Thermocouple Kit #28022 is discontinued, so I am not sure if there are other thermocouple kits available through Sparkfun or elsewhere for use with the stamp. You could piece one together as well by using the schematic on the last page of the 28022 PDF which is still available.
  • Tracy AllenTracy Allen Posts: 6,658
    edited 2012-10-17 16:07
    The 8-pin MAX31855, direct thermocouple to SPI digital, is very easy to use. It has built-in cold junction and gain compensation, so that the BS2 SHIFTIN command can read the actual temperature value directly. There is Stamp code for reading the MAX6674 and MAX6675 on my web site. The new MAX32855 appears to have the same interface.

    What type of thermocouple? You have to know or decide that before you can order the corresponding version of the chip. Also, be careful, because tricky instrumentation issues can arise when deploying thermocouples.

    The chip is an soic8. I noticed that Mikroelektronika has it available for type K (Chromel-Alumel) mounted on a PC board with a connector, Thermo click. There may be others, or DIY.

    There are more general approaches that use a low level ADC, a separate reference temperature sensor, and firmware to apply the cold junction compensation and gain corrections. For example, the ADS1118 is a 16 bit analog to digital converter, SPI interface, that is meant specifically to read two independent thermocouples, plus on-chip reference sensor. The evaluation module, ADS1118EVM, is a direct to USB interface for a pair of type K couples. It would seem to be ideal, IFFF if it can be adapted for your direct to PC/Excel data capture.
  • KatyBriKatyBri Posts: 171
    edited 2012-10-18 12:18
    Tracy, thanks very much for your suggestions. I will check them out. BTW, I really like your web site.
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