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Thread: Temp reading errors

  1. #1
    New Member
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    Sep 2018
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    SF Bay Area
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    Temp reading errors

    Hi,

    Sometimes I observe very strange jumps in the temp reading - sometimes it corrects itself, sometimes not. Looks like chaotic jumps up and down. Happened on different jacks - pit and temp1 (haven't checked 2 and 3). Different termistor types - Thermoworks Pro and ET72.
    This is the last screenshot - temp jumped to 113 than corrected back to normal 65:



    Any ideas where to look? The issue is intermittent and happens not too often but when it happens on the pit sensor it screw everything.

    Thanks
    Last edited by YevgenB; 02-22-2019 at 06:29 PM.

  2. #2
    TVWBB Super Fan
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    Dec 2018
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    Louisiana
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    The ONE time i had something simlar occur where my probe went haywire, i think my HM got hot.

    When this happened the food probe and the pit probe also appeared to be coupled together somehow.

    Hanging on handle on side of wsm, (which i did many times), the bottom hung nearer to wall of wsm. The probe ports are at bottom. It didnt feel that warm to touch, but may have been the plastics low conductivity.

    No problems since after moving it off the wsm


    Last edited by MartinB; 02-23-2019 at 02:08 AM.

  3. #3
    New Member
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    Quote Originally Posted by MartinB View Post
    The ONE time i had something simlar occur where my probe went haywire, i think my HM got hot.

    When this happened the food probe and the pit probe also appeared to be coupled together somehow.

    Hanging on handle on side of wsm, (which i did many times), the bottom hung nearer to wall of wsm. The probe ports are at bottom. It didnt feel that warm to touch, but may have been the plastics low conductivity.

    No problems since after moving it off the wsm


    I don't think it's my case - at this particular sample shown there was only one temp probe and HM was laying on the side-table for only 5 minutes - there where no heat and second probe.

  4. #4
    TVWBB Diamond Member
    Join Date
    Apr 2013
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    midwest
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    3,612
    The probe circuits are quite simple, there are only a couple components...
    Probe jack
    10K Pullup resistor (omitted for thermocouple probes)
    100K Resistor for probe filter
    .1uf cap for probe filter
    ATMEGA

    This is the cluster of components between the probe jacks and the ATMega, the probe jacks connect to the four pins from the corner of the ATMega near those components. (Identified on bottom of board)

    Often times issues like this are due to either poor soldering on the above components, or excess flux on the board left behind in this area. I would inspect the soldering in these areas first, reflow if questionable, then wash with isopropyl alcohol and a soft brush... let dry completely before applying power. See if that helps.

    You might want to try another power supply for a while as well...
    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.

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