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Odd Temperature Readings

Grandpas Grub
Grandpas Grub Posts: 14,226
edited November -1 in EggHead Forum
 
What a day we have had. Unusually heavy rain and hail and winds up to 70 mph. Things have calmed down a bit tonight and I decided to cook a 7# butt.

Got egg stabilized and using the Stoker on this cook. The butt has been on for about 25 minutes now. Indirect on raised grid. Lump about to the top of the fire ring.

Dome is at 247° Stoker & 250° BGE therm. Grate temperature is reading 128° and has kept that apx. 120° delta for the entire time, no signs of the dome and grate getting closer together at this point.

2" away from the meat should be enough not to affect the grate read temperature.

The grate probe is about 2" away from the butt and the height is about 1/2 inch off the BGE Grid.

It isn't uncommon to see a 60° delta but never this high.

GG
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Comments

  • 2Fategghead
    2Fategghead Posts: 9,624
    Very interesting Kent.

    It makes me wonder about your burning lump. Could it be your burning lump is down in the bottom of the fire box next to the lump grate. :huh:
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  • PhilsGrill
    PhilsGrill Posts: 2,256
    That's why I would not monitor the grid temperature since you have no control. Just use the dome temperature.
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  • Grandpas Grub
    Grandpas Grub Posts: 14,226
     
    Interesting idea. Just over 4 hrs into the cook and all looks fine. Grate us now 95° below the dome temperature. Butt has climbed from 46° to 119°.



    Just noticed on the stoker log what seems like to be a projection of done time. It is showing 6:47 am,interesting. However, this piece of meat still has to get into and through the plateau. We have rain mixed with snow falling right now. Started at 1 am, just under 7# bone in. Figuring 1.5 hr/# then done time should between 10 and 11 am. I may have to have the computer kick the temperature up onm the stoker somewhat. Kind of interesting looking at the graph history as the cook has progressed.

    Bathroom duties done and back to bed.

    What are you doing up so early, aren't you in the central time zone. Go bug Cindy and tell here hello from the old fart out west.

    tootaloo for now, Kent
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  • Grandpas Grub
    Grandpas Grub Posts: 14,226
     
    Morning young man. I only do because I can. Normally I set the blower to be controlled by the grate temperature. This time I thought I would let the temperature at the dome control the blower. This butt cook has been at 250° throughout the cook. I wonder what would happen if I reassigned the blower down to the grid temperature.

    I am wondering it the grate probe is being affected by the meat. I have the grate probe going through the meat and tip of the probe sticking out the side of the meat about 2-2.5 inches.

    Kemt
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  • 2Fategghead
    2Fategghead Posts: 9,624
    I got up to see how your doing. :laugh:

    Something in me said go check on Kent. :laugh:

    Actually I got up for the same reason you did cept my bathroom toilet don't have a heated seat or phone. :laugh: I'll wait until I get sleepy again and go back to bed. I'll see you later this morning. I'll tell Cindy you said hello if you tell Shelagh the same. ;)

    Here is where I got my bathroom humor from. Read the post it's funny.

    http://www.eggheadforum.com/index.php?option=com_simpleboard&func=view&id=1078075&catid=1
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  • srq2625
    srq2625 Posts: 262
    I use a Stoker and StokerLog for my long cooks and have had good success with it.

    On MY LBGE, I've never seen the temperature delta you are noting. Even at the start of a cook, the largest delta I've ever seen is about 40°F and by the three hour point, the difference between the temperature reading at the grid (that's where I put my pit probe) and the BGE OEM thermometer (which I calibrate right along with all my other temperature probes) is about 15° or 20°. By the end of the cook, the indicated temperature delta is less than 10°.

    From your first post, it appears one of your probes closely agrees with the dome thermometer - which would lead me to believe that probe is correctly calibrated (if the calibration were off, I would not expect to see them agree so closely).

    I have to wonder about the calibration of whatever device you are using to measure the temperature at the grid though.

    As for the StokerLog projection of the finish time .... well, I have never seen that to be anywhere close to accurate. The largest reason, as you alluded to, is it is almost impossible to anticipate when the plateau will be encountered and how long it will take to get through the plateau. Around our house, that finish time estimate is a source of amusement.

    FWIW (and I know this goes against the traditional wisdom here), but I use one pit probe about 3" from the meat and about 2" above the grid to control the fire/blower. I have that set to 225° (for the Low-N-Slow cooks) which gives me a dome temperature of about 250° (at the start of the cook anyway). At that temperature, a seven pound pork butt will reach my target temperature (192°F) in 12 to 14 hours.
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  • Grandpas Grub
    Grandpas Grub Posts: 14,226
     
    If I wake Shelagh up she will slug me.

    Before reading this response from you I finished reading max's post. That has got to be one of the most funny things I have seen on here in a long time. You wouldn't believe my mental picture.

    Max with his pepper trou around his ankles and a comforting smile on his face.

    No wonder when you see pictures of Rebecca she is always smiling.

    Kent
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  • srq2625
    srq2625 Posts: 262
    Grandpas Grub wrote:
     
    Morning young man. I only do because I can. Normally I set the blower to be controlled by the grate temperature. This time I thought I would let the temperature at the dome control the blower. This butt cook has been at 250° throughout the cook. I wonder what would happen if I reassigned the blower down to the grid temperature.

    I am wondering it the grate probe is being affected by the meat. I have the grate probe going through the meat and tip of the probe sticking out the side of the meat about 2-2.5 inches.
    Kemt
    Your meat is, literally, sucking the heat out of the probe such that the tip of the probe (where the sensor is actually located) is nowhere near accurately measuring the ambient inside the egg but, rather, some weighted average of the meat temp and the ambient.

    You do not want to use that probe to control the blower - your pit temperature, I'm guessing here, will climb to something over 350°F. Not a goodness.
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  • Grandpas Grub
    Grandpas Grub Posts: 14,226
     
    I have never paid attention to the target times on the log.

    The probe connected to the dome thermometer is controlling the blower at this time. I usually assign the blower to the grate probe but I wanted to see the temperature difference when the fire was being controlled at the dome. Normally I have the blower being controlled a probe at meat level. The delta with the dome probe, with that setup, has been as much as 70°. I have never seen this big a delta between the two levels before.

    If it weren't snowing mixed with rain I would go out and take a picture. I am guessing somehow the probe going through the meat or the tip of the probe is too close to the meat.

    Almost 4 hours into the cook and the dome plot is seeing some dipping in temperature with the blower turning on to bring it back to target. Until a few minutes ago the grate probe had a steady climb. I see a few degree up/down fluctuation. As I type the delta is 85°. The meat probe on a slow but steady climb @ 132° right now. I normally see the plateau about 155° to 165°.

    Kent
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  • Grandpas Grub
    Grandpas Grub Posts: 14,226
     
    "Your meat is, literally, sucking the heat out of the probe"

    I am thinking/wondering the same thing. I would guess when the meat ends the plateau that delta will be much smaller.

    On this cook I have the blower assigned to the dome probe and using the grate probe as a reference. I think I am going to buy a probe tree from the guru folks. I should get a better reference with that.

    Kent
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  • Ripnem
    Ripnem Posts: 5,511
    GG,

    That makes total sense. The meat just won't let the probe heat up. Kinda like a plumber trying to solder a pipe with too much water too close to the end of the pipe.
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  • thirdeye
    thirdeye Posts: 7,428
    well 250°F is about 120°C I wonder if you hit the wrong button on the brain box and it's reading in celsius?
    Happy Trails
    ~thirdeye~

    Barbecue is not rocket surgery
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  • Ripnem
    Ripnem Posts: 5,511
    Thirdeye,

    He said:
    "I have the grate probe going through the meat and tip of the probe sticking out the side of the meat about 2-2.5 inches. "

    That's gotta be it, no?
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  • thegrillster
    thegrillster Posts: 348
    Did you plug your pit probe in after turning on the stoker? I know they should all be plugged in before turning on the unit.
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  • thirdeye
    thirdeye Posts: 7,428
    I thought about that, but most probes have a little dimple or a ring down near the end. That's what anchors the small wires inside, so as long as that portion of the probe is sticking out I wouldn't think the upper part in the meat would cause any weird readings.
    Happy Trails
    ~thirdeye~

    Barbecue is not rocket surgery
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  • Ripnem
    Ripnem Posts: 5,511
    I would think it would be a constant fight between the hot tip and the cold center of the probe and the dimple would be someplace in between. :S
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  • Grandpas Grub
    Grandpas Grub Posts: 14,226
     
    Nope... all probes plugged in then Stoker On. I once tried to add a probe and the Stoker would not 'hot swap', the Stoker had to be turned off then back on to read or see the new probe.

    Kent
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  • Grandpas Grub
    Grandpas Grub Posts: 14,226
     
    All in Fahrenheit. About an hour and a half ago the dome probe spiked to 174°, pit probe went down and the meat had a slow steady climb. Now that is odd... see the update 1 post below.

    Kent
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  • Grandpas Grub
    Grandpas Grub Posts: 14,226
     
    Interesting readings...

    About 1.5 hours ago the dome probe (the probe controlling the blower) spiked from 253° to 278° all in about a 15 minute period.

    At the apex of the spike, the grate probe was still on a smooth steady climb and then at 173.4° withing a few minutes dropped to 162.6°, A 10.8° drop within 15 or so minutes.

    At about 6.5 hrs into the cook and the dome spike and grate dip both dome and grate began to drop equally in temperature with a constant 93.3° delta between the dome and grate.

    From the point of the spike in the dome the meat was 154.5° (about 1.5 hours ago) and until it hit 162° about 15 minutes ago. Too short of a time but it looks like the meat is holding steady or going into a little of a drop. I am guessing the beginning of the plateau. For me the plateau begins at about this meat temperature.

    There has been no blower on time since 15 minutes before the dome spike up to now. The dome is 150.8°, .8° above target.

    About an hour ago the dome probe dropped below the meat temperature. Right now the meat is at 163.5°, grate 150.8 - a delta of 12.7°.

    Dome 241.4° grate temperature 150.2° - a delta of 91.2°. No blower activity yet.

    GG
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  • gdenby
    gdenby Posts: 6,239
    To clarify:

    There is one probe in the dome, one in the meat, and one sticking thru the meat, with an end extending over the grill?
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  • Grandpas Grub
    Grandpas Grub Posts: 14,226
     
    Yup, that's it. Stoker probe clipped to the dome probe just above the crimp on the BGE thermometer.

    Meat probe. Food probe stuck through the edge of the butt sticking out over the grate by about 2 to 2.5 inches.

    This delta was bugging me so I decided to go out and look to see what was going on.

    The grid probe had positioned parallel with the meat within about 1/4" of the meat. So what evidently was happening is the cool meat caused the huge delta. I pulled the grate probe and repositioned it through the meat again but made sure the tip was 2.5 to 3 inches away from the meat.

    The delta between the dome immediately changed to a 30° delta and with only 15 minutes of tracking since the change so far parallel with the dome temperature.

    The meat is in the plateau for 1.5 hrs now. The plateau temperature has been flat during that time, no dip so far on this cook.

    Looks like I am going to have to push the temperature in order to achieve serve time. I was hoping to let this cook complete without raising the cook temperature.

    Kent
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  • gdenby
    gdenby Posts: 6,239
    The delta between the dome immediately changed to a 30° delta and with only 15 minutes of tracking since the change so far parallel with the dome temperature.

    O.K. That clears up a lot of my confusion. Evidently the probe stem can't be in both meat and grill air.

    Also, because there is still a 30 D even with the meat in plateau, I have to suppose the the grill level is almost always cooler than the dome because of both position and presence of the heat absorbing meat. This is good to know.
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  • Grandpas Grub
    Grandpas Grub Posts: 14,226
     
    I on purpose left the grid temp probe passing through the meat and the tip hanging over the grid.

    The temperature delta between dome and grate is more normal with previous cooks.

    I just had the computer change the cook temperature to 350°.

    Kent
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