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Old 05-26-2014, 04:19 PM   #21
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So, to the deeper question... as in the 24 lb turkey.... What part of the "needle is sensitive? the tip or the average of the overall length of the sensor? exactly what part of the big turkey, or the 8 lb. roast is the thermometer actually sensing?

If the cook book says 160 degrees, and the turkey has been in the oven for three hours, won't the meat nearest the outside be warmer than than that 2 inches into the turkey breast? Conversely, if the piece of grilled steak is 1 inch thick, and the probe is inserted to 3/4 of an inch, what about the difference between that, and the center (1/2 inch)?

A mercury thermometer senses the ambient air temperature. Touching the "bulb" at the bottom will easily change the reading.

While this may seem to be a picky issue, consider that the "Safe" temperature for different kinds of meat generally ranges from 140F to 165F, a fairly narrow range.

http://www.foodsafety.gov/keep/charts/mintemp.html
My old style meat thermometer still costs under $2.
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Old 05-26-2014, 07:13 PM   #22
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It behaved itself for the hamburgers we grilled for lunch.

Yes, I think the problem was due to the thinness of the pork chop, and the positions of the probes.

I did give both probes time to come to a stop.

Thanks for the ideas.
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Old 05-26-2014, 07:23 PM   #23
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Ah hah! It was a pork chop as I thought. I have found in the past I tended to overcook thin cuts, due to wanting to be sure that they got fully cooked for sanitary reasons, and my meat was often dried and tough.

By the way, here's another inexpensive probe from Thermoworks with a very thin tip. And it costs but $24 after shipping. The speed is not as fast as the Thermapen, but the accuracy/speed is still a respectable 1F in 5 secs.

I would still stick the tip into the chop edgewise to be sure that the entire tip is in the center of the piece.

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Old 05-26-2014, 08:06 PM   #24
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Ah hah! It was a pork chop as I thought. I have found in the past I tended to overcook thin cuts, due to wanting to be sure that they got fully cooked for sanitary reasons, and my meat was often dried and tough.

By the way, here's another inexpensive probe from Thermoworks with a very thin tip. And it costs but $24 after shipping. The speed is not as fast as the Thermapen, but the accuracy/speed is still a respectable 1F in 5 secs.

I would still stick the tip into the chop edgewise to be sure that the entire tip is in the center of the piece.

In earlier posts, some of the Thermapen fans were lauding the thinness of the tip. It was hard to tell from the pictures if it was significantly thinner than the cheaper ones - the CDN one I have was ~ $10 or maybe $15, and the tip is fairly thin ( OK, trip downstairs to my hole gauge says 3/32" tip, for ~ 3/4", then a 5/32" body). The CDN is pretty good for accuracy and speed.

So is there a significant difference between these cheaper Thermoworks models, the Thermapen, and other brands?

-ERD50
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Old 05-26-2014, 08:56 PM   #25
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That CDN you have may not be bad, considering its price. I just looked at it on Amazon, and they said response time of 6-8 seconds, and nothing about the accuracy. On the other hand, the less expensive Thermoworks I cited earlier claims 1F accuracy within 5 secs, and for about 2x the price. The Thermapen on the other hand is 0.7F within 3 secs.

Is the Thermapen worth $96? I think I would be happy with the lesser Thermoworks, if I did not get the Thermapen as a gift.

About the probe dimension, I just took a photo of some in my arsenal as shown below: an old dial mechanical thermometer, a smaller pocket-size dial thermometer, two probes from two different electronic thermometers, and the Thermapen.





And see the close-up photo of the tips below.







I also took out my caliper to measure the diameter of the probes.

1) Big old dial thermometer: 0.250"
2) The two electronic probes: 0.155"
3) Pocket-sized dial thermometer: 0.150"
4) Thermapen: 0.070"

Note that the shank of the Thermapen is 0.130", tapering down to 0.070" at the last 1/2". The minuscule thermocouple junction is at the very end of that pointed tip.
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Old 05-27-2014, 09:58 AM   #26
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I just put that CDN in some microwaved water. It went from 66 degrees to 158 degrees in 23 seconds!

The ChefAlarm only took about 15 seconds.

One trick is to put your instant read thermometer in a glass of very hot water before sticking it in the meat. Then it only takes a few seconds.
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Old 05-27-2014, 10:10 AM   #27
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I thought I'd found the problem:
I fill up a two-cup measuring cup with water and nuke it in the microwave.

I hold the probe by the little plastic bump (seen here):



I put it in water so that only the narrow half-inch tip is in submerged.

It stabilizes at 152 degrees.

I then put it all the way into the water.

The temperature drops quickly to 142 degrees.
But realized that the water was indeed 10 degrees hotter at the top. If I stirred the water while measuring, there was no difference.
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Old 05-27-2014, 10:14 AM   #28
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Wow, that ChefAlarm of yours is no sloucher.

Oh wait! It is also made by Thermoworks!

I guess you do not need to use anything else. Please disregard my earlier suggestions.

But your actual "speed test" made me want to "race" the Thermapen. Please hold...
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Old 05-27-2014, 10:20 AM   #29
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Originally Posted by TromboneAl View Post
I just put that CDN in some microwaved water. It went from 66 degrees to 158 degrees in 23 seconds!

The ChefAlarm only took about 15 seconds.

One trick is to put your instant read thermometer in a glass of very hot water before sticking it in the meat. Then it only takes a few seconds.
Just to be clear, the CDN that T-Al is talking about is the mechanical kind. The CDN I discussed is ~ $18, digital readout, and is pretty fast (says 6-8 seconds, but seems faster in most cases). It has an 'auto-calibrate' mode for an ice-water bath.

Amazon.com: CDN DTQ450X ProAccurate Quick-Read Thermometer: Kitchen & Dining

No accuracy spec'd, but it sure seems to be good enough, and repeatable enough for home use. We purchased DEC 2009, and I replaced the coin cell just once I think.

I just tried T-Al's test, from a 74F water bath to a dunk in boiled water out of the microwave - moves pretty fast, I caught it at 203 @ 5 seconds, and 211 @ 10 seconds. I'd expect a little faster if I stirred it around, that makes a big difference in heat transfer. I'll check the ice-bath cal later.

-ERD50
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Old 05-27-2014, 11:00 AM   #30
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I was thinking about doing my own test with the Thermapen, and thought that a video would be needed to catch the readings. But then, it occurred to me that surely, someone would have done it already and posted it on youtube.

Yes, see the following video for yourself. Thermapens RULE!

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Old 05-27-2014, 11:43 AM   #31
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I am not saying they are doing this, but manufacturers know how their units are tested and can and do bias their results to account for that. Many years ago when I was testing a competitors ear thermometer I found that they biased the reading towards 98.6. For every degree Fahrenheit that they computed they subtracted or added 0.1 degree towards 98.6. They of course knew that most people who evaluate the thermometers are normal and want to see this temperature.

Anyone who has used a digital scale knows that most of them sold in the U.S. show exactly the same weight when you step off and step on again. Giving you a false sense of their measurement variability. You either have to step off, step on again with half your weight, or wait a period of time to reset it and get the newly computed results. When you do this you will see that there is substantial variability in the measurements.

I am always suspicious of the potential tampering with actual results with microprocessor based instruments and have to account for this possibility when testing.
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Old 05-27-2014, 11:55 AM   #32
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Speaking of measurement accuracy, in a past industrial project I built a circuit to interface a thermocouple to a microcontroller. While the thermocouple sensor itself is so simple and accurate, the tough part is the cold junction compensation. It was tough to get 1deg F accuracy, and in the end we decided that we really did not need that because the object we were trying to measure the temperature of was a turbine engine that ran so damn hot anyway, and an error of a few degrees was of no concern.

But about speed or how fast a thermocouple sensor can come to stabilization, it has no rival other than infrared temperature sensors. However, the latter cannot be as accurate due to its nature.
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Old 05-27-2014, 12:48 PM   #33
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I am not saying they are doing this, but manufacturers know how their units are tested and can and do bias their results to account for that. Many years ago when I was testing a competitors ear thermometer I found that they biased the reading towards 98.6. For every degree Fahrenheit that they computed they subtracted or added 0.1 degree towards 98.6. They of course knew that most people who evaluate the thermometers are normal and want to see this temperature.

Anyone who has used a digital scale knows that most of them sold in the U.S. show exactly the same weight when you step off and step on again. Giving you a false sense of their measurement variability. You either have to step off, step on again with half your weight, or wait a period of time to reset it and get the newly computed results. When you do this you will see that there is substantial variability in the measurements.

I am always suspicious of the potential tampering with actual results with microprocessor based instruments and have to account for this possibility when testing.
98.6 is a bogus number anyway...

Normal Body Temperature : Rethinking the Normal Human Body Temperature - Harvard Health Publications
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Old 05-27-2014, 01:02 PM   #34
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Yes of course you are correct. But it is what people "expect" to see.
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Old 05-27-2014, 01:24 PM   #35
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Based on that video, I would definitely want to use a thermapen when I want a very quick measurement of something that is 33 degrees Fahrenheit. Does anyone ever need to do that?

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Anyone who has used a digital scale knows that most of them sold in the U.S. show exactly the same weight when you step off and step on again.
Yes, Health-o-meter caught me with that once. I tried one at someone's house, got three readings the same, and said "Wow, I'm buying one of these!"

It is the worst kind of lie. I'll bet a marketing exec said "We can't sell a scale that goes up and down by 2 pounds as you stand on it, go find a solution."
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Old 05-27-2014, 01:50 PM   #36
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Based on that video, I would definitely want to use a thermapen when I want a very quick measurement of something that is 33 degrees Fahrenheit. Does anyone ever need to do that? ...

I assume it applies to any temperature delta of that magnitude. Room temp to meat cooking temperatures are a similar delta. Yes, the time constant is in % of the delta, so delta doesn't really change things much, except that the typical 'within a few degrees' we shoot for will be a larger part of the total for small deltas, so it will get in that range quicker (absolute rather than relative).


Quote:
Yes, Health-o-meter caught me with that once. I tried one at someone's house, got three readings the same, and said "Wow, I'm buying one of these!"

It is the worst kind of lie. I'll bet a marketing exec said "We can't sell a scale that goes up and down by 2 pounds as you stand on it, go find a solution."
I'm not sure if I'm more disgusted by the trickery, or impressed by the creative 'solution'. Pretty darn clever! BTW, I was hoping they didn't do this with our kitchen scale, as there you can be adding deleting small amounts for a recipe. Looks like it gives it its best shot w/o too much filtering.

I looked at that kitchen sale a while back, and it is also quite clever. They have a separate pressure transducer floating in each of the four legs, and sum the outputs of each. It doesn't matter where you place the item, any corner or center of the platform and it reads the same.

-ERD50
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Old 05-27-2014, 01:54 PM   #37
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I assume it applies to any temperature delta of that magnitude. Room temp to meat cooking temperatures are a similar delta. Yes, the time constant is in % of the delta, so delta doesn't really change things much, except that the typical 'within a few degrees' we shoot for will be a larger part of the total for small deltas, so it will get in that range quicker (absolute rather than relative).

-ERD50
+1

The temperature rise (or drop) of a thermometer as it comes into stabilization with the media is approximately an exponential decay. So, the time to be within, say 1F of the final reading (which may not be correct), is a function of the time constant of the thermometer, and also proportional to the temperature change.
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Old 05-27-2014, 02:01 PM   #38
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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"...
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Old 05-27-2014, 02:04 PM   #39
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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.

Just a thought.
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Old 05-27-2014, 02:08 PM   #40
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I understand how one can cheat with a medical thermometer where the expected human body temperature has a narrow range. I do not see how one can apply this "technique" to a food thermometer that in the case of the Thermapen claims to cover a range from -58F to 572F.

Of course, I could be wrong. But the easiest way is for me to do some tests on the Thermapen myself, as I own one. I need to get off this forum for a little while though.
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