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Thread: New Heatermeter Build - Pit Probe Temp drops intermittently

  1. #1
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    New Heatermeter Build - Pit Probe Temp drops intermittently

    Good afternoon,

    I just completed my first heatermeter build V4.0 for the raspberry pi. I powered everything up on my counter top and have noticed that I get an intermittent drop of the pit temperature reading...maybe for a second or so and notice that the blower stops and then starts right back up to 100 % when the temperature locks back in. Then it may stay locked in for 5 minutes and then happen again. My probes are Maverick 732's. Any suggestions on how to troubleshoot this behavior?

    Thanks,

    Dan

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    TVWBB Gold Member Bryan Mayland's Avatar
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    From the Wiki
    The response curve of these [ET-732] probes bottoms out around room temperature when used with the standard 10kohm HeaterMeter resistance, which causes them to read as "off". To get more usable range, replace the standard 10k resistors with 22k or even 47k 1% tolerance resistors.
    EDIT: They also have an issue where they can be inserted too far, so make sure they're not just pushed too far in.
    Last edited by Bryan Mayland; 06-07-2013 at 01:50 PM.

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    I'd also suggest doing a search on ET732. There is lots of discussion about common issues with ET732 probes.

    dave

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    I saw the issue about pushing them in too far, so that is not the issue. What does replacing the resistors do if I end up changing probes in the future. I knew 732s were not recommended....but I already had them. Again I was just testing on the countertop so it was reading 70 degrees F....is it fair to assume that it won't drop out at regular grilling temps?

    Thanks,

    Dan

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    Typically yes. Once you get over 90F or so it is pretty stable. You can carefully put them in a cup of hot water and see if they drop out on you.

    dave

    Quote Originally Posted by Dan Seaver View Post
    I saw the issue about pushing them in too far, so that is not the issue. What does replacing the resistors do if I end up changing probes in the future. I knew 732s were not recommended....but I already had them. Again I was just testing on the countertop so it was reading 70 degrees F....is it fair to assume that it won't drop out at regular grilling temps?

    Thanks,

    Dan

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    There are TWO minor issues with the 732 probes that I have seen.

    The first is that the plug is longer than the 72/73 plugs (too long) so if you push them all the way in they will not work. Back them out and that problem is solved.

    The second problem is the braided shield is not connected to the ground for some reason, and it does not give a reading when it is not connected to ground. The reason the 732 probes work intermittently (my theory) is when the braid of the 732 touches the braid of a 72/73 (which is grounded) the 732 gets the ground it needs and works. If the braid of the 732 does not touch the braid of another probe (or another ground) it will not give a reading. With my 732 if I isolate the braid (not touching any ground) I get no reading, if I tap the braid to another probe (72/73) or any other ground (the LAN port on the rPi works conveniently) I DO get a reading. This was reproducible and consistent, give it a try....

    The simple (but not very pretty) fix I came up with to fix BOTH problems is this. I just soldered a little wire around the ground shield on the plug (which prevents it from inserting too far) and then very lightly soldered the other end to the braid (which gives it constant ground). Now my probe plugs in and works every time...

    Here's a pic...


    My 732 has worked pretty solid as my pit probe since I did this, but I am gonna toss the 732 aside and get a Maverick high heat probe because I just got me a Kamado style grill that is supposed to be able to smoke low and slow and cook hot enough to grill pizza's!
    Last edited by RalphTrimble; 06-07-2013 at 03:33 PM.

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    On a side note about probes...
    Initially I was unaware of how sensitive to water the probes are, so mine got plenty wet. I ended up with one probe that was reading way high when clipped to my other two (due to taking on water I guess). I've read somewhere that putting the probes in a deep fryer will boil the water out of them and make then work again, so I fired up the deep fryer, figured what the hey, I can't use it the way it is. I dipped the probe in the oil gingerly at first, seemed uneventful though I recall reading about the water boiling out of the probe? So I figured to see that the end of the probe (with the braided wire coming out of it) would have to be in the oil too... So I dipped the probe past the braid and boy did it boil out some water! It went on for a bit and then stopped, I guess when the water was gone. I went straight from the fryer to the grill with the probe and what do you know, the probe tracks temp right on target with the other two probes again! I don't know the long term effects of this cause I just did it tonight, but if you have a probe that is reading hopelessly high perhaps give this a try...

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    Thanks for the suggestions everyone! I put the probes in a mug with boiling water and I had no drop outs. So at this point I am good to go. I need to order some additional probes, so I will make sure to order the recommended 73 probes.

    Thanks for all you help. I now have to figure our my blower mount for my Primo Oval XL grill!

    Dan

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    Dan, you might want to consider the Maverick high temp probes (or at least one). Besides not being very water proof I didn't realize the standard Maverick probes aren't rated for higher temperatures. The standard probes are fine for my smoker where I always cook low and slow, but I have a new Kamado style grill that I hope to cook pizza on soon and I need the HM to work at higher temperatures for that. The High Heat probes are good up to 700 degrees, Maverick has them on their website and they are not expensive or anything. They do free shipping in the USA so the price you see is what you pay. I paid $24 for two high heat probes the other day, still waiting for delivery though....
    Last edited by RalphTrimble; 06-08-2013 at 09:50 AM.

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    You will need to get the Steinhart-Hart coefficients if you want to use them with the heatermeter. I don't think they will be the same as the ET732 or ET73 as they will have a different thermistor.

    You may have luck emailing their tech support and asking for the temperature vs resistance data. I know that they were willing to email me the ones for the ET732, but they only had them for the ET73 probes.

    PM me if you want a contact email. I worked with a guy there with the ET732 probes and he was very helpful. Maybe he is still there.

    dave

    Quote Originally Posted by RalphTrimble View Post
    Dan, you might want to consider the Maverick high temp probes (or at least one). Besides not being very water proof I didn't realize the standard Maverick probes aren't rated for higher temperatures. The standard probes are fine for my smoker where I always cook low and slow, but I have a new Kamado style grill that I hope to cook pizza on soon and I need the HM to work at higher temperatures for that. The High Heat probes are good up to 700 degrees, Maverick has them on their website and they are not expensive or anything. They do free shipping in the USA so the price you see is what you pay. I paid $24 for two high heat probes the other day, still waiting for delivery though....

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