How Instant Is A Thermapen?

johnliu_gwFebruary 1, 2012

I was looking for a tap at McMaster-Carr. On a whim, I bought one of their thermometers with a folding probe. It looks a lot like a Thermapen, but was a lot cheaper and a bit uglier.

So, it appears to work fine, but I don't get the final temperature reading "instantly". Its more like I instantly get a reading that is 5 to 10F below the actual temperature, then in 5 to 10 seconds I get the actual temperature.

Example: suppose the meat is 125.0F. As soon as I insert the probe, the display will show 119.2F, then 121.6F, 123.5F, 124.2F, 124.6F, 124.8F, 124.9F, 125.0F - that's an example anyway - and it will take about 10 seconds to stabilize at 125.0F.

Is this about how a Thermapen works? Or are they genuinely "instant" thermometers (let's say that giving an accurate reading in 1 second is instant).

Sounds stupid, I know, but I'm sometimes very impatient. Anyway when you've got your hand stuck in a 450F oven trying to temp the thigh that is all the way at the back of the oven, there is a practical difference between 1 second and 10 seconds.

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My new Thermapen is noticeably faster than my old one (which was still pretty speedy). It should be just under 3 seconds for the usual conditions but that may still not be quick enough for you.

I do insert mine in the oven without discomfort, but I'm not trying to do it way at the back. That might be uncomfortable under any conditions and in that case Kevlar might be the appropriate option regardless of the thermometer.


    Bookmark   February 1, 2012 at 5:04AM
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Well john, I have a thermapen, I do love it but what you describe is pretty much how mine acts. It is not in three seconds but compared to any other thermometer I've ever owned it is great. Mine is a bit over a year old I think...pretty sure I got it around Christmas of last year. I don't know, maybe I should have sent it back? All in all though, I'm happy with mine and use it all the time!

    Bookmark   February 1, 2012 at 9:07AM
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I just got my first Thermapen, and I don't think "instant" is accurate. It does take many seconds, and when your arm is in the oven or over a grill, seconds matter!

The actual package calls it a "Superfast digital thermometer" and the instruction book does, too. But the packing slip and the Amazon ad say "Instant read thermometer." The booklet claims accuracy to +/-0.7 degrees f accuracy in 3 seconds, but I am sure mine still bounces for 10 seconds or so. Booklet says that is because temps within the meat itself vary.

My son swears by his, so gave me mine. I have watched him use his many times; my impression is that his old one does not take as long as my new one. I'll ask him in a few days, as he is out of town all week. I'd like to do a comparison with his, but he lives 5 hours away and we have no plans for a visit for a while.

    Bookmark   February 1, 2012 at 9:12AM
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If you're looking for instant you'll be disappointed. It's quick, though I've questioned the three second claim.

Last time I used mine was for Christmas dinner and it's been lost ever since. I'm willing to bet my 4-year-old "cleaned it up" and it'll remain lost until about a day after I order a new one. Expensive toy to lose.

    Bookmark   February 1, 2012 at 9:21AM
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Just took my Thermapen out and tested it twice. Put hot water in a cup, clocked it to see how long it came up to temperature. It took 4 seconds to reach temp both times. My Thermapen is a couple years old. The newer ones are probably faster then mine. lol But I think 4 seconds is exceptional timing. NancyLouise

    Bookmark   February 1, 2012 at 9:26AM
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I've posted about mine being much slower than 3 seconds. In fact, I have never measured anything that actually stabilized at a temperature. I do believe that's because the temp just doesn't stay the same.

I do have a solution for your arm getting hot. Pull the shelf out or the pan of duck out to where you can reach it easier, then take the temp. ;-)


    Bookmark   February 1, 2012 at 9:29AM
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The electronics that makes a digital thermometer work is not very complex. Basically a voltage stabilizer to maintain constant battery voltage as the power is slowly used up and voltage drops. There is a temperature compensation circuit to automatically adjust operating lineal response whether your room temperature is very low or very high. The sensor, typically a thermocouple, which provides the measurement, is read against an internal reference to give you the readout.

The entire package is inexpensive electronics (less than $10.00) which gives you response time in milliseconds.

Why some thermometer reads faster than the other?

The response time is highly dependent on how small they can make the thermocouple sensor /probe. The smaller it is the shorter the response time.

The problem of making it too small is breakage and difficulty in manufacturing. They need to have the metal casing to be very strong so that when you push the probe into the meat it will not break too easily.

When you push the probe into food, the metal probe travels thru different temperature zones, typically from high (212F) to low, and the metal will carry the heat from high temperature to low temperature and heats up the food in the low temperature zone. It will take time for the temperature to reach equilibrium, depends on the weight (mass) of the probe.


    Bookmark   February 1, 2012 at 1:59PM
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Mine is a year old and takes about 4 seconds. Also, they are on sale today for $69. I got mine as a gift so not sure how good of a sale that is but I think mine was about $100. I love mine.

    Bookmark   February 1, 2012 at 6:31PM
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I bought a reconditioned one and was always concerned with the temp reading, as it seemed to take awhile and didn't match other cheaper models. Found out once I recalibrated it, works great. Probably within 3-4 second range. I love it!

    Bookmark   February 1, 2012 at 8:55PM
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I tested my cheap-thermometer-that-looks-like-a-Thermapen carefully. It doesn't take 10 sec to stabilize, going from 70F to a glass of just-boiled water. It takes 20 seconds!

The Thermapen sounds worth the price, to me.

Still, I'm convinced there has to be an industrial thermometer that is instant-reading and costs under $100. I'm going to keep looking.

    Bookmark   February 1, 2012 at 11:13PM
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