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Thread: Heatermeter weird issue

  1. #1
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    Heatermeter weird issue

    Hi Guys,
    Im soldering the heatermeter 4.3 incl LCD and I have a weir issue.
    All seems to be working but the TC still is a PITA....
    after some re-soldering and testing, it is working except for one thing….
    as soon as I physically tough the thermocouple wire, temp goes thru the roof.
    I checked for bad connections but cant find any…
    Anyone got an idea what can cause this?

  2. #2
    TVWBB Diamond Member
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    Try an ISOLATED thermocouple....
    I created the Roto Damper, RD3, HMv4.2 sliding back case, "air-burner" and the "ping-pong" valve in my quest for delicious "set and forget" BBQ.

  3. #3
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    that would be the easy guess but since I have made 4 heatermeters and this is the only one that does this... I'm talking about the outside shielding of the tc probe that I touch.
    See pictures:
    https://ibb.co/x2NYd0Z
    https://ibb.co/4PCfMBs
    Weird thing is that there is no connection to the outer wire... I tried with other TCs that I have and they all have this. My other heatermeters don't do this so there is something wrong with the hm..

  4. #4
    TVWBB Honor Circle Bryan Mayland's Avatar
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    I'd check that 1K SMD resistor to GND in the thermocouple circuit and make sure it is well soldered. It helps to eat the noise you're adding when you touch the braid. If that's solid then make sure the 1n and 10n capacitors (differential and common mode noise filters) are soldered well. Finally a therocouple amp with a loose leg can cause this as well.

    Rejecting probe noise is a real problem with these mains-powered temperature sensors and there's always a little bit of magic. You can also upload the hm-noise firmware from the AVR Update page and that will add a new graph to the home screen that shows the raw ADC readings after a few seconds. That would tell you if there's always noise and touching it makes it worse, or if it is 100% fine until you touch it.
    I'm that HeaterMeter guy what ruins everybody's free time.

  5. #5
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    Thanks Bryan! I'll fire up the solder unit tomorrow to check the connections again. The amp is a real menace to get right, especially afterwards when all surrounding stuff is done.
    Will report back asap!

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