Has anyone ever checked the WSF temperature?

[wow400]

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.

 

[wow400]

And 300°f equates to around 255°f

 

[WillM]

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

 

[Dassman5]

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

 

[Dassman5]

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]

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]

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.

 

[wow400]

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]

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).

 

[wow400]

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]

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.

 

[Canuck55]

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

My EX6 is new, my second cook. I had issues with the first with temp spikes and drops, but I went on. In this cook I set my Inkbird to monitor internal temps and while I have it set to 200, the temp fluctuates between 240 and 275. I get that there will be some fluctuations and that things average out but I am consistently 50 degrees hotter than what the controller is saying. That just doesn’t seem right. At the moment I have inkbird probe sitting on the top grate. I will move it next time but it just seems to be very inconsistent. I am using Weber pellets.

 

[Dassman5]

in my humble opinion, you have now entered an area ripe for discussion…one of: Accuracy, Repeatability and Manufacturing tolerances of the equipment in question.

All of these enter the equation when converting the bi-metal probes reaction to heat into a visual feedback; something that also involves the electronics of the unit, as well as the PID bandwidth in which it reports the set point and feedback probe as essentially being “close enough”.

Lots of variabilities to consider, but my suggestion is that you should first place the inkbird probe in the immediate vicinity of the Weber ambient air probe and make sure that the tips are not contacting one another or any solid surface, as it is the air temp that is being measured. Remember that the SF, like all pellet grills use forced air-combustion that necessarily creates combustion air currents that circulate throughout the unit and will vary from place to place within the unit. (For instance, in my ex4, the upper grate typically reads 10-15F higher than the left side of the lower grate.)

There are lots of articles on this topic, but essentially I have learned to cook/smoke more by site, touch and feel

 

[MrPhilGrillTX]

Lots of variabilities to consider, but my suggestion is that you should first place the inkbird probe in the immediate vicinity of the Weber ambient air probe and make sure that the tips are not contacting one another or any solid surface, as it is the air temp that is being measured. Remember that the SF, like all pellet grills use forced air-combustion that necessarily creates combustion air currents that circulate throughout the unit and will vary from place to place within the unit. (For instance, in my ex4, the upper grate typically reads 10-15F higher than the left side of the lower grate.)

This. My EX6 temps vary considerably all over the grill. I guarantee you the built in probe and the lower grate just to the right of the firebox are not the same temperature at grilling (vs smoking) temperatures.

But only getting into the 400's seems cause for concern, especially if you are using fresh Weber pellets.

 

[Dassman5]

This. My EX6 temps vary considerably all over the grill. I guarantee you the built in probe and the lower grate just to the right of the firebox are not the same temperature at grilling (vs smoking) temperatures.

But only getting into the 400's seems cause for concern, especially if you are using fresh Weber pellets.

Only getting into the 400s is a cause for concern.. if that is the case you need to look at the pellet slide, make certain that the firebox cover totally covers front and rear, the firebox. If all that checks out, and you have removed the finger guard, you may either have a bad Weber ambient air probe, or a bad controller.