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simplest way to measure a thermocouple — Parallax Forums

simplest way to measure a thermocouple

laser-vectorlaser-vector Posts: 118
edited 2010-07-30 19:00 in Propeller 1
I need to measure a temperature using a thermocouple. is there a simple object out there that i could use to do this? what is required to build the ADC circuit??
Im a little new to propeller but this would be incredibly helpful as its my first real project. THANKS!!

Comments

  • Duane DegnDuane Degn Posts: 10,588
    edited 2010-07-30 01:37
    laser-vector,

    Thermocouples produce very small voltages and require a voltage amplifier.··I have a couple of thermocouples I use to monitor·oven temperatures.· I use the AD595-AQ and then use a ADC chip to read the increased·voltage.· There is also a digital thermocouple amplifier the MAX6675 which doesn't need an additional ADC.· I'm sure there are other thermocouple amplifiers out there; these are the·two I know of.

    Duane
  • ManAtWorkManAtWork Posts: 2,178
    edited 2010-07-30 15:46
    IMHO, the simplest way to measure a thermocouple is with an LTC2400. It is a 24 bit ADC in a small SO8 package with 1µV resolution. It doesn't need a pre-amplifier or any other external components.
  • Duane DegnDuane Degn Posts: 10,588
    edited 2010-07-30 18:21
    ManAtWork,

    I was just reading skimming through the LTC2400 datasheet.· The thermocouple circuits start on page 33.· They all had external components.· What kind of thermocouple have you used with it?· I'd appreciate additional information.· Do you have schematic you used?· What did you use for a reference voltage?

    As I mentioned, I use several thermal couples and I'd like to now if there is·a better solution than what I'm using.· I used the·thermocouple portion of·a circuit I copied from SparkFun's toaster oven reflow kit.

    I do not recommend the kit I just linked to.· It uses a Pic which is inadequate for this task.

    I'm pretty sure laser-vector wants to make a reflow toaster oven (don't we all?).· Many toaster ovens (mine included) can't heat up fast enough to match most recommended reflow curves (I think you need a temperature increase of 2 degrees C per second).· I've wondered about taking the heating elements of a second oven to add to the first.

    Duane
  • laser-vectorlaser-vector Posts: 118
    edited 2010-07-30 18:46
    hey duane, does Maxim (or anybody) make something similar to that MAX6675 but in a DIP version???
  • Duane DegnDuane Degn Posts: 10,588
    edited 2010-07-30 19:00
    laser-vector,

    I don't know of a·DIP version.· SparkFun sells a SOIC to DIP board which is listed in the related products on the MAX6675 page.

    I've used SOICs several times with this board which is also just right for a surface mount Prop.· I carefull slice appropriate square pads on the back of the board making two rectangles of each sliced square.· These rectangles are just the right spacing for SOIC parts.· Don't tell anyone about these boards, they're my secret.

    Duane
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