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Old 05-27-2014, 02:13 PM   #41
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Here's another thought.

In order to catch the medical thermometer maker cheating, I can devise a simple test. With the thermometer at room temperature, dip it into a glass of water at 80F for a couple of seconds, then quickly move it to a 2nd glass at 100F. What will the doggone thing read?

Next, start with 100F temperature for the first few seconds, then move to 80F. What will it read?

One can do simple tests to check out various hypotheses.

And people think that thermometer testing is boring.
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Old 05-27-2014, 02:24 PM   #42
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Here's another thought.

In order to catch the medical thermometer maker cheating, I can devise a simple test. With the thermometer at room temperature, dip it into a glass of water at 80F for a couple of seconds, then quickly move it to a 2nd glass at 100F. What will the doggone thing read?

Next, start with 100F temperature for the first few seconds, then move to 80F. What will it read?

One can do simple tests to check out various hypotheses.

And people think that thermometer testing is boring.
You are correct, and there are a lot of papers and patents addressing this issue. One good way to fool an IR thermometer for example is to suddenly move it into a very different ambient temperature. All of them assume stable temperatures for stated accuracy. Temperature measurement and control is indeed much more difficult (and interesting) that it appears at first blush.
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Old 05-27-2014, 03:20 PM   #43
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OK, I am back.

I did some tests similarly to that video, by dunking the Thermapen and other meat thermometers into glasses of water at different temperatures. Nope, never saw the sign of hanky-panky on any of them, other than the different stabilization times to the final reading. I do not have video because that takes way too much work to set up, and this job does not pay all that well.

But it should come as no surprise that the speed demon of them all is my engineering thermocouple. See photo below. The meter this probe plugs into has a display update of perhaps 10Hz, and it reaches final readings in 1/2 to 1 second (too fast to measure without videotaping). Even so, I think the limitation is in the electronics or the meter, which must do some averaging to filter out the noise.

A K-type thermocouple puts out 41uV per deg C, and this low level signal has to be amplified in the presence of noise like AC hum and other emitted radio interference. So, some filtering is needed to prevent fluctuations in the reading and that would cause most of the lag. Just two tiny strands of wire like that thermocouple should not take more than 1/10 of a second to equalize in temperature to the water bath.

I guess my medical thermometer deserves its own later scrutiny, due to the "serious allegations" in previous posts.

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Old 05-27-2014, 07:40 PM   #44
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Just another thought about response time. All of the electronic oral thermometers out there now are linear predictive thermometers. Basically, they look at the rate of change of temperature readings and predict the final temperature. They display and lock that temperature reading long before the actual sensor reaches that temperature. I am guessing that is he case here. You can see how in this case it would be easy to bias a thermometer when you know the testing temperature. Again I am NOT saying that they are doing this, I don't know. But that it is something that is possible and sad to say is probably increasingly common. As T-Al suggests, those "marketing execs"...
Yes, but I don't think the predictive algorithms are really 'cheating' in any way. These thermometers are typically used in liquids or meat, so once they have characterized the response curve in that type of substance (and I assume meat and liquids are similar enough in this regard), they can predict the output based on the the temp change over a short period of time. Each time, they would update it as they approach the 'real' settled temperature, so the absolute error is less with each update. I don't think the temperatures themselves make any difference at all to the algorithm, it's all about that exponential curve, regardless of the specific start/end points.

And I assume they undershoot a bit in their approximation - it probably 'looks' better to the user to see a temp go from say....

72..... 120.....130....135....136....136... than to see it go....

72..... 130.....138....134....136....136...

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I wonder if the problem here is simply one of original calibration. County Meath, Ireland is about ⅓ of the way around the planet from Al's location, and if he's trying to use a Meath thermometer as stated in the thread title he may not be conforming to the manufacturer's intent.


I'm guessing these kinds of thermal dynamics jokes would not go over well with the late night comedians! and I think we lost any non-techy types a while back in this thread

-ERD50
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Old 05-27-2014, 10:05 PM   #45
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Yes, but I don't think the predictive algorithms are really 'cheating' in any way. These thermometers are typically used in liquids or meat, so once they have characterized the response curve in that type of substance (and I assume meat and liquids are similar enough in this regard), they can predict the output based on the the temp change over a short period of time. Each time, they would update it as they approach the 'real' settled temperature, so the absolute error is less with each update. I don't think the temperatures themselves make any difference at all to the algorithm, it's all about that exponential curve, regardless of the specific start/end points.

And I assume they undershoot a bit in their approximation - it probably 'looks' better to the user to see a temp go from say....

72..... 120.....130....135....136....136... than to see it go....

72..... 130.....138....134....136....136...





I'm guessing these kinds of thermal dynamics jokes would not go over well with the late night comedians! and I think we lost any non-techy types a while back in this thread

-ERD50
I did not mean to imply that they were cheating by using predictive algorithms, I worked on them myself, only that you might not be able to easily infer the response time of the sensor. And as you show they do lock in the predicted reading, not showing the wiggle at the end. Most algorithms though do have some form of error check, and discard a prediction that results from obviously bad input.

My intention was to indicate the possibility of some vendors "tuning" the test points to make the accuracy and precision look better than it actual was. Not that this is necessarily all that bad either because any device only has to function over a specific range. But any engineer testing the device would need to be aware of these possibilities.

I was however surprised at the time when I saw the built in bias in the ear thermometer. It would certainly give the appearance of lower variation at the 98.6 temperature of a casual tester. My personal opinion was that this was not ethical and I would not do that even if asked. I was never asked.

My bathroom scale also has a reset button, so it computes new results every time I use it. I bought it in Asia, couldn't find one like that here. I do hate the ones with a lock in of the last reading. In mechanical scales and the older electronic ones, you could step on it three times and keep the lowest reading. We want the lowest reading right?
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Old 05-27-2014, 11:00 PM   #46
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All the above talks about the bathroom scale cheating made me think.

OK, what you are saying is if they can sense that it is the same person stepping on the scale to take a repeated reading, they will present the last readout to give the sense of repeatability, which will cause the user to infer accuracy or at least reliability, which of course is not the same thing.

So, how does one devise a test? Simple. If the bathroom scale shows a resolution to 0.1 lb, one can do this test.

1) Step on the scale. The readout says "X".
2) Step off, then back on the scale. The readout says "X" again. Good.
3) Step off, then back on the scale while holding something weighting 0.2 lb. Does the readout say "X+0.2"?

I do that test with my bathroom scale, and the thing keeps saying "X", although I had that extra object in hand. Damn!

So, I now hold a 2nd thing in my other hand, which should cause the scale to read even higher. It does now! Damn! There's a threshold upon which they "release" the lock.

Then, I release both objects, and step on the scale again empty handed. Does it read "X" again? Nope, it reads "X+0.2".

So, the repeatability of the scale is perhaps 0.2 lb, which is worse than its resolution of 0.1 lb. Its absolute accuracy is something else, which I do not know until I can compare it with a calibrated scale.
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Old 05-28-2014, 08:54 AM   #47
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My experiments showed that the variability was even more -- perhaps .6 pounds. That is, weigh self, step off, reset by weighing half of you (one foot on scale), weigh self again. Results could vary by .6 pounds.
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Old 05-28-2014, 08:57 AM   #48
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Back to the original problem...

Last night I cooked a 1.25 inch thick rib-eye to 145 degrees, and used my thermometers to monitor its "resting" back to 125 degrees. So I had the thing on the table, and could conveniently experiment with probe positioning.

I could never get the ChefAlarm and CDN instant read thermometers to agree. The CA was usually 8-10 degrees above the other.
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Old 05-28-2014, 08:49 PM   #49
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I am going to throw out a question since this is getting a lot of attention from engineer types...

What about the probes that you stick in and leave in the meat... the ones with a lead that goes outside the grill... does it really matter if there is speed I would think that accuracy would be more important...
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Old 05-28-2014, 09:05 PM   #50
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I am going to throw out a question since this is getting a lot of attention from engineer types...

What about the probes that you stick in and leave in the meat... the ones with a lead that goes outside the grill... does it really matter if there is speed I would think that accuracy would be more important...
Hey, that would be like asking the owner of a porsche with a 195 mph max speed if that speed is really important. I would probably arrive at the destination in about the same time as him, but I am guessing he would get more girls. Sometimes it is all about bragging rights!
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Old 05-28-2014, 09:09 PM   #51
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Yes, I have one like that, and it is even wireless so that I can leave the grill or the oven site without having the meat burnt.

Accuracy is more important there than speed, but sadly that piece of junk has neither, as I found out. So, I still use it, but now set the alarm at a lower temperature, then use the Thermapen for the final check.

And the speed of the Thermapen lets me poke and measure temperature at half a dozen spots in the same time someone with a lesser thermometer can get a single reading!
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Old 05-28-2014, 09:12 PM   #52
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Yes, I have one like that, and it is even wireless so that I can leave the grill or the oven site without having the meat burnt.

Accuracy is more important there than speed, but sadly that piece of junk has neither, as I found out. So, I still use it, but now set the alarm at a lower temperature, then use the Thermapen for the final check.

OK... thanks... Kinda what I wanted to know.... right now I still use the 'push the meat' method which is OK for steak... but have found that it is not always good with pork...
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Old 05-29-2014, 05:24 AM   #53
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I am going to throw out a question since this is getting a lot of attention from engineer types...

What about the probes that you stick in and leave in the meat... the ones with a lead that goes outside the grill... does it really matter if there is speed I would think that accuracy would be more important...
I use both. A long term (leave in) probe that tells me when I am getting in the ballpark - I use it to time the one turning of the meat. And the fast accurate one to take each piece off the grill at just the right moment.
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Old 05-29-2014, 05:29 AM   #54
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And the speed of the Thermapen lets me poke and measure temperature at half a dozen spots in the same time someone with a lesser thermometer can get a single reading!
+1!!!

Quick checks near the finish, then close the grill lid. Some pieces might come off the grill minutes before others.

8 lamb loin chops with some size variation, and you can get each one just right.
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Old 05-29-2014, 01:49 PM   #55
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Note that the whole point of the electronic version, which is the only reason to use it as opposed to a traditional meat thermometer, is this:

It beeps when the meat is done.
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Old 05-29-2014, 07:54 PM   #56
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Note that the whole point of the electronic version, which is the only reason to use it as opposed to a traditional meat thermometer, is this:

It beeps when the meat is done.
The way I use my remote wireless thermometer is this: It beeps when the meat is about done.

When the meat is removed from the grill or oven, the internal temperature continues to rise as the heat soaks in from the surface. So, I set the alarm temperature 5 or 10 deg F below the target temperature to allow for that coasting to a higher temperature, and time for me to take it off the grill or oven.

I also want to babysit a nice cut of meat to the right temperature. So, I put the wireless thermometer on the thinnest or smallest piece, because it cooks the fastest, and remove it first. I then measure and watch the larger pieces as they come up to temperature.
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Old 05-29-2014, 09:31 PM   #57
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I think I'm going to give up on this device. Today it told me the chicken thighs were done after 23 minutes:

ChefAlarmChicken.jpg

What can it be? The probe was in a lot, it wasn't touching bone, and it wasn't touching the pan.
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Old 05-29-2014, 09:35 PM   #58
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I think I'm going to give up on this device. Today it told me the chicken thighs were done after 23 minutes:

Attachment 19082

What can it be? The probe was in a lot, it wasn't touching bone, and it wasn't touching the pan.
Try moving the probes around. The numbers might swap. I'm not sure you can 'blame' one probe or the other.

Sure, you would not expect the meat to be done in 23 minutes, but maybe some part of it is at 169F?

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Old 05-29-2014, 09:46 PM   #59
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Again, your thermometers have a disagreement of 30F, and at about the same (unknown) temperature as before. And again, the digital is high, while the mechanical one is low. Yet, you said they agreed at 32F and 212F.

Shouldn't you run a comparison across the range? But of course you then need a tie-breaker. I once ran a comparison of 3 probes (before I got the Thermapen) and saw that they agreed at room temperature but then differed by 10F at around 140F. At close to boiling, one of them became awfully off by more than 20F.

I did the above test when I tended to overcook steak with one of them, and got suspicious.
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Old 05-29-2014, 10:06 PM   #60
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Shouldn't you run a comparison across the range? But of course you then need a tie-breaker. I once ran a comparison of 3 probes (before I got the Thermapen) and saw that they agreed at room temperature but then differed by 10F at around 140F. At close to boiling, one of them became awfully off by more than 20F.
When I put them in a glass of water, they always agree, no matter what the temperature of the water.

I tried a lot of different positions when measuring the temp of the resting steak, couldn't get them to agree.
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