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Thread: Thermocouple variation -defect?

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    Thermocouple variation -defect?

    Put my probes in ice and boiling water to check offsets, since wasnt reading same.

    Noticed......thermocouple reading at 212, bounces 215-217. Tried another, bounced 216-217.

    This reflects what i see cooking too...the reading is unsteady by 1-2F. The reading is not unsteady in my multimeter.

    The thermistor probes are not unsteady either

    Thus....seems to be a defect in the heatermeter thermocouple amplifier? Bare wire thermocouples could bounce around rapidly....a probe cannot.

    Anyone else see this? Is there a fix? I've observed others online cooks that bounced around by one degree or more also.

    As someone who used a lot of lab equipment that stable at 0.1 degree.... This seems kind of poor. It did not fluctuate like that at cold temperature on ice.

    Is there some kind of grounding issue?
    Last edited by MartinB; 01-26-2019 at 04:24 PM.

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    TVWBB Honor Circle Bryan Mayland's Avatar
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    HeateMeter is definitely not a lab-grade device, but if the temperature is fluctuating that much then there's no way it would ever be able to control a pit as the fluctuations would confuse the PID controller.

    You can see live graphs of the internal ADC measurements by installing the LinkMeter -> AVR Firmware -> Online Repository -> Flash hm-noise.hex. Then go back to the home webui and in a few seconds you'll see a new graph with a cycle's worth of ADC. It is easier to see from there if noise is being coupled into the probe somehow from there. You should see something like this

    with the variation extending one or maybe two ticks on each side of a center. It's ok if there's a ton of blips, as long as they're only 1-2 units tall. If you're seeing a jaggedy line going all over then that's noise coming in from the AC power, or being coupled through the braid of the thermocouple. If it matches mains AC frequency, you can cancel that out in the config page by turning on the "A/C input line noise filter" in the config.
    I'm that HeaterMeter guy what ruins everybody's free time.

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    Quote Originally Posted by Bryan Mayland View Post
    HeateMeter is definitely not a lab-grade device, but if the temperature is fluctuating that much then there's no way it would ever be able to control a pit as the fluctuations would confuse the PID controller.

    You can see live graphs of the internal ADC measurements by installing the LinkMeter -> AVR Firmware -> Online Repository -> Flash hm-noise.hex. Then go back to the home webui and in a few seconds you'll see a new graph with a cycle's worth of ADC. It is easier to see from there if noise is being coupled into the probe somehow from there. You should see something like this

    with the variation extending one or maybe two ticks on each side of a center. It's ok if there's a ton of blips, as long as they're only 1-2 units tall. If you're seeing a jaggedy line going all over then that's noise coming in from the AC power, or being coupled through the braid of the thermocouple. If it matches mains AC frequency, you can cancel that out in the config page by turning on the "A/C input line noise filter" in the config.
    Why not smooth this noise in thermocouple?

    Ive used ac line filter, no effect

    It doesnt really occur at room temp, only at higher temps
    Last edited by MartinB; 01-27-2019 at 06:46 AM.

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    RE: grounding issue... I do prefer ISOLATED thermocouples as opposed to grounded ones.
    What kind of thermocouple are you using?
    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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    TVWBB Honor Circle Bryan Mayland's Avatar
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    Quote Originally Posted by MartinB View Post
    Why not smooth this noise in thermocouple?
    It is smoothed / oversampled / filtered but if your noise is bad, even the hundreds of samples that are combined will have enough variation that your number is going to jump up and down by a few degrees. Remember a few degrees is around 5mV peak-to-peak, which is not a lot compared to what can be coupled into a HeaterMeter. Did you try the noise firmware to get a visualization of what you're dealing with?
    I'm that HeaterMeter guy what ruins everybody's free time.

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    Quote Originally Posted by Bryan Mayland View Post
    It is smoothed / oversampled / filtered but if your noise is bad, even the hundreds of samples that are combined will have enough variation that your number is going to jump up and down by a few degrees. Remember a few degrees is around 5mV peak-to-peak, which is not a lot compared to what can be coupled into a HeaterMeter. Did you try the noise firmware to get a visualization of what you're dealing with?
    Not yet.

    I will try a shorter thermocouple and twisted pair instead of parallel too .

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    Ok, did as instructed
    Below . First is without ac filter. Second is with. At room temp.

    Dont look like yours....

    Thx








    And with it hot.....with the filter.

    Last edited by MartinB; 02-05-2019 at 06:11 PM.

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    And a pic on 12 v dc in my truck....not running...no alternator noise. Direct battery voltage

    Last edited by MartinB; 02-05-2019 at 07:27 PM.

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    I tried on a 5a regulated fitered 12 v dc supply i have.....same thing.


    Then i changed thermocouples to different one with stainless cover over wire. (Auber)

    At least in my house when calibrating on boiling water, appears lower noise than other and more stable. Still has the sinusoidal rhythm. Height of variations are 1/2 tic.

    Now can i get rid of this add-in wo reflashing firmware?

    Last edited by MartinB; 02-09-2019 at 11:35 AM.

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    There's some interference somewhere. Have you tried on an isolated AC outlet? Grabbing at straws at this point.

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