Has anyone ever checked the WSF temperature?

wow400

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I’ve been using my WSF for about a year now and have a separate thermometer system (FireBoard V1) and I’m always seeing the WSF temps to be about 20-40°f low.
I’m doing some beef short ribs at the moment and the WSF has been rock solid at 250°f for the past 4hrs but the FireBoard is showing 218°f and pretty stable at that.
🤷‍♂️
 

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wow400

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And 300°f equates to around 255°f 😬
 

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WillM

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Yes. Have started to watch my Ex6. Seeing similar results. Wish there was a way to recalibrate.
 

Dassman5

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I apologize fir this long winded response, but to answer your question in lay-terms is a bit long-winded.

With PID controllers the feedback signal (the permanent ambient air probe) sends a signal to the controller that is compared to the set point you select. Hence, within a given bandwidth (temperature range) the ambient grill probe does not show variation by design, but will do so if it goes out of the designed tolerance (bandwidth). Hence the reported grill temperature appears to hold steady while using a separate probe, without that controller dampening, will show actual variations within its individual design tolerance or accuracy.

Why does this happen?

First, PID controllers are designed to iteratively “learn” and constantly adjust feed, and airflow to approximate match a set point., largely the job of the “I” function.

Second, but minor variations are typically tolerated and counteracted by the “D” function, something we used to call the “Do, Don’t Do Function”. This is because small variations have no discernible impact on production (cooking the food) over time. Essentially that “D” function keeps the controller from constantly chasing itself and over or under feeding within a programmed “tolerable” bandwidth.

Third, a pellet grill/smoker is dealing with a solid fuel that has a natural lag time between sensing the actual grill temperature, comparing it to set point, calling for more or less heat, adjusting the pellet feed, waiting for ignition, and sensing the resulting heat output change via the grill probe. Note that this lag is not as much of a case with liquid ignition control systems like cruise control on an automobile for example which has a much closer correlation and timing between wheels sensors and fuel feed to the engine.

Fourth, in smoking and cooking a 10-30 degree temperature variation has very little real impact on the final product...your dinner. [By the way, the same happens with your oven to a lesser extent as you seldom, if ever, see the actual temperature of the oven, unless you are using a separate probe]. This is not the case with industrial control applications where tolerances are much tighter as the product requires.

Fifth, it keeps the operator (the cook) from constantly adjusting and fiddling with the controls; something that would happen if every degree in temperature variance from set point were shown.

I use a separate Weber ambient air probe connected to port #4 every time I cook and have learned to rely on it to monitor what is actually going on in the grill. I also have a separate Maverick probe unit and instant read thermal pens. However, I seldom need to make adjustments on my ex4 as I consider most variances within tolerance.

But even without that or your other probes, you can observe PID bandwidth override by letting your unit stabilize at a given temperature and then adjusting the temperature upward or downward by 5 or 10 degrees and noting how, almost instantaneously it reports that set point has been achieved. But if you change by 40 or 50 degrees it takes a while to report that set point has been achieved,

Again, sorry for the long post and what, undoubtedly is TMI
 
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Dassman5

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And 300°f equates to around 255°f 😬
Perhaps, and perhaps not. Not only do all temperature probes have a built in “design tolerance” or repeatability or accuracy (not all the same thing) that is part of the manufacturing process, but then when comparing two different systems, that variance can change significantly, as they are essentially bi-metal probes.

Scientific and medical grade probes are more “accurate” but much more expensive and largely overkill for our applications. Also build-up of coatings, age, rough usage and exact location in comparison to one another all impact these sensors.
 

WillM

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Hmmm. Thanks for the very technical explanation. However, what I think I'm observing is not variation within a given bandwidth, but a consistent difference between reported and actual temperature. And 25 degrees in my case and 45 degrees in wow400's case, seems significant to me. I get that a constant reading of 225 degrees is actually 225 +/- 25 degrees (i.e., 200-250), but presume it averages out to 225. However, if the actual temp is 200 +/- 25, that's still 25 degrees (average) below the set point. Granted that at smoking temperatures, the impact on the quality of the end product is probably not that great. But the impact on the time to reach terminal temperature can be significant.

What I want is confidence that when I set the smoker at 225, on average that's what temperature I will get. Right now, I don't think that's the case. I think setting the smoker at 250 is giving me an average temp of 225.

I think.
 

Dassman5

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Hmmm. Thanks for the very technical explanation. However, what I think I'm observing is not variation within a given bandwidth, but a consistent difference between reported and actual temperature. And 25 degrees in my case and 45 degrees in wow400's case, seems significant to me. I get that a constant reading of 225 degrees is actually 225 +/- 25 degrees (i.e., 200-250), but presume it averages out to 225. However, if the actual temp is 200 +/- 25, that's still 25 degrees (average) below the set point. Granted that at smoking temperatures, the impact on the quality of the end product is probably not that great. But the impact on the time to reach terminal temperature can be significant.

What I want is confidence that when I set the smoker at 225, on average that's what temperature I will get. Right now, I don't think that's the case. I think setting the smoker at 250 is giving me an average temp of 225.

I think.
Sorry, I misunderstood. It could be a number of things in that case: A bad ambient air probe in the unit. A coating in that probe that is insulating it. A mis-calibrated control board, etc.

The only way to tell for certain would be verify the calibration of the two ( or preferably more) probes against a known value. Boiling water is one option, another is against an infrared gun that has known accuracy, Barring that, you could also use two or three other probes all located at the exact point of the tip of the permanent probe and graph the results.

depending on the manufacturer, different probes may result in different variations at various temperatures as most are not linear across an entire range. Hence the difference between true accuracy and linearity or repeatability.
 
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wow400

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Thanks for the replies - glad it’s not just me then!
I did Moroccan lamb last night & needed to get the WSF as hot as it could go to start with - it only managed to get to 450°f indicated which was only 408° on the FireBoard.
A significant difference that appears to get bigger the hotter the temperature.
I checked the fireboard probe with boiling water & within 1° so unlikely the probe is out.
So that & the ability to only reach 450° instead of 600° is a real shame.
I’ll be contacting Weber & see if they can offer any insight….
 

AHoneyman

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Check your pellets - new, shiny pellets that are small diameter. Several board members have discovered this fact. Pellets can absorb humidity and greatly effect performance (top temp).
 
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wow400

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Thank you for that - though I’ve only been using Weber pellets that have been stored in airtight containers so unfortunately don’t think they’re to blame!
 

TwoWheeler

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I did Moroccan lamb last night & needed to get the WSF as hot as it could go to start with - it only managed to get to 450°f indicated which was only 408° on the FireBoard.
A significant difference that appears to get bigger the hotter the temperature.
I have had the opposite experience. I put my Thermoworks Smoke pit probe right next to the Weber pit temp one and found that, at higher temps its spot on, but at lower temps the Weber is pretty consistently about 40 degrees low. 🤪
 
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