Electronics (alt.electronics)

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Adam Preble
 
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Default Detecting heat/temperature -- convection, conduction, radiation

I once got a small lecture of thermocouples at school, but that doesn't
seem to cover much of everything. I'm curious what is all out there for
detecting heat, specifically detecting temperature. I was hoping to
find a device that could determine the temperature of the surface of
food just be "looking" at it. There are IR sensors that can do this
kind of thing, but it'd be nice if the sensor could be rigged to be
plunged inside the food and find the core temperature. Most sensors on
electronic thermometers seem to use conduction, which is sluggish
because the probe was warm up. I'm just trying to think of alternatives.
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Rich Grise
 
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On Wed, 02 Mar 2005 08:03:49 +0000, Adam Preble wrote:

I once got a small lecture of thermocouples at school, but that doesn't
seem to cover much of everything. I'm curious what is all out there for
detecting heat, specifically detecting temperature. I was hoping to
find a device that could determine the temperature of the surface of
food just be "looking" at it. There are IR sensors that can do this
kind of thing, but it'd be nice if the sensor could be rigged to be
plunged inside the food and find the core temperature. Most sensors on
electronic thermometers seem to use conduction, which is sluggish
because the probe was warm up. I'm just trying to think of alternatives.


I've done this, both with a pyrometer and with thermocouples, and the
response time is negligible when you're talking about the temp. of food.
Like, seconds. I wouldn't worry about it. If you're really OC, you
could use a bare thermocouple.

Good Luck!
Rich


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Adam Preble
 
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I've done this, both with a pyrometer and with thermocouples, and the
response time is negligible when you're talking about the temp. of food.
Like, seconds. I wouldn't worry about it. If you're really OC, you
could use a bare thermocouple.

Good Luck!
Rich



I might be that OC in this case. I tried to use a digital thermometer
for making fudge, and the long, metal probe couldn't get warm enough to
accurately report the temperature. I ended up burning the chocolate.
Yes, it's my fault for trying that with a digital thermometer, but when
it advertises it's good for candy, and can handle the temperatures
involved, I don't think I was so naive. This seems to be a common
problem with all the electronic thermometers. They have metal probes
that rely on conduction, which doesn't work when the metal probe cannot
heat consistently.
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larry
 
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When dealing with chocolate, you should use a double pot. bottom pot
has water to heat up the top pot which has the chocolate. if you only
use one pot to melt, you have to use a very, very low heat. it's not
the fault of the temp probe. chocolate burns very easy, and the pot
catches the heat from a very hot flame, and conducts it too fast.

if you used an IR type sensor, you have to worry about getting false
readings off the pan and the heat waves from the side of the pan
eminating from the flame itself.

LarryLarry


On Fri, 04 Mar 2005 07:11:09 GMT, Adam Preble
wrote:


I've done this, both with a pyrometer and with thermocouples, and the
response time is negligible when you're talking about the temp. of food.
Like, seconds. I wouldn't worry about it. If you're really OC, you
could use a bare thermocouple.

Good Luck!
Rich



I might be that OC in this case. I tried to use a digital thermometer
for making fudge, and the long, metal probe couldn't get warm enough to
accurately report the temperature. I ended up burning the chocolate.
Yes, it's my fault for trying that with a digital thermometer, but when
it advertises it's good for candy, and can handle the temperatures
involved, I don't think I was so naive. This seems to be a common
problem with all the electronic thermometers. They have metal probes
that rely on conduction, which doesn't work when the metal probe cannot
heat consistently.


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Adam Preble
 
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larry wrote:
When dealing with chocolate, you should use a double pot. bottom pot
has water to heat up the top pot which has the chocolate. if you only
use one pot to melt, you have to use a very, very low heat. it's not
the fault of the temp probe. chocolate burns very easy, and the pot
catches the heat from a very hot flame, and conducts it too fast.

if you used an IR type sensor, you have to worry about getting false
readings off the pan and the heat waves from the side of the pan
eminating from the flame itself.

LarryLarry

Well I wasn't just melting chocolate, but making fudge from it. There
is a pretty specific temperature I need to reach, just like when making
candy. I don't have a candy thermometer (yet), and I was thinking the
digital one would be able to work. Unfortunately, the probe was
under-reporting the heat, and I ended up scalding the whole mess. I
don't really see why there can't be a way to use a digital thermometer
for that kind of thing.


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Rich Grise
 
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On Sat, 05 Mar 2005 17:39:20 +0000, Adam Preble wrote:

larry wrote:
When dealing with chocolate, you should use a double pot. bottom pot
has water to heat up the top pot which has the chocolate. if you only
use one pot to melt, you have to use a very, very low heat. it's not
the fault of the temp probe. chocolate burns very easy, and the pot
catches the heat from a very hot flame, and conducts it too fast.

if you used an IR type sensor, you have to worry about getting false
readings off the pan and the heat waves from the side of the pan
eminating from the flame itself.

LarryLarry

Well I wasn't just melting chocolate, but making fudge from it. There
is a pretty specific temperature I need to reach, just like when making
candy. I don't have a candy thermometer (yet), and I was thinking the
digital one would be able to work. Unfortunately, the probe was
under-reporting the heat, and I ended up scalding the whole mess. I
don't really see why there can't be a way to use a digital thermometer
for that kind of thing.


What kind of "digital thermometer" was it? If it was a fever thermometer,
then you'd get this kind of result - one, they're not designed to go that
hot, and two, they sacrifice response time for 0.1 deg. F accuracy.

I've used probe-type thermocouples to monitor the temperature of bread
in a vacuum chamber - the product was supposed to be a "vacuum cooler"
for a bakery. Normally, when you get bread out of the oven, you have to
let it sit for hours to cool, so it doesn't gum up the slicer. In a
vacuum cooler, it reaches room temperature in minutes. (the water
evaporating "sucks the heat out" - remember Mr. Wizard, when he froze
and boiled water simultaneously?)

Anyway, the probe thermocouple responded fast enough to track the temp.
within a few degrees. IOW, the speed of response wasn't even an issue.

Do some googling - they're out there. Say,
http://www.google.com/search?q=thermocouple+probe

And, from the book of cooking tips - you sometimes have to stir quite
enthusiastically to keep your mixture from scorching. :-)

Good Luck!
Rich


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Adam Preble
 
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I don't know how inline quoting goes over here, but I'm trying it.

What kind of "digital thermometer" was it? If it was a fever thermometer,
then you'd get this kind of result - one, they're not designed to go that
hot, and two, they sacrifice response time for 0.1 deg. F accuracy.


Here's a similar one on amazon.com:
http://tinyurl.com/4334t

I notice it has a poor rating . . . that might explain something. The
thermometer I have does have some presets for meat, which makes me
wonder if it's meant for meat exclusively. However, it did mention
candy-making in whatever spiel I read about it. That's where I got the
idea to try fudge. It seems the probe that came with it is unsuiteable
though. It's supposed to go up to a thousand degrees Fahrenheit -- note
that I'd try -- so it should be suitable for cooking.

Do some googling - they're out there. Say,
http://www.google.com/search?q=thermocouple+probe


If there's something that plugs fine and dandy into my thermometer then
I'd be content. The base unit itself is nice, but the probe just sucks.

And, from the book of cooking tips - you sometimes have to stir quite
enthusiastically to keep your mixture from scorching. :-)


Of course. I was stirring the whole time. That's to say . . . I had
thoroughly scorched it. I never have made fudge on my own, nor have
I dont any candy making. I wasn't so certain what to expect so I was
relying on the thermometer to help me out.
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