Hello,
my project requires -60C temperature monitoring and for some reason I can't recall any more I bought few MAX31855T with T type thermocouples from a reputable source (Farnell).
Using Teensy 3.2 (just for testing, it's 3.3V so no level shifters required) to talk to the MAX31855, no issues with communication, internal temperature reading is very steady, responds like supposed to, no issues.
However the probe readings are quite erratic, mostly fluctuate +/- 2C, but sometimes as much as -6~8C (and large spikes seem to be only towards low temperature), I'm testing them now in room temperature (+25C).
10n cap is soldered on the thermocouple inputs of the IC, it helped somewhat, reduced the fluctuation amplitude and made it less susceptible to RF noise (cell phone near the probe for instance).
I sample at 1sec intervals, increasing interval doesn't help, same issue present also at intervals below 1sec.
I also have K type thermocouples and 31855K, and that combo doesn't exhibit this behavior, just the T type.
Is this normal for T type thermocouples or I am missing something? Tried 3 different chips, same behavior.
I also tried putting on a shield (knitted mesh, stripped from an audio wire), grounded at IC, had zero impact on stability of the readings.