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'[EE]:Measure liquids temperature with 18S20'
2002\08\14@075859 by Claudio Martin

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Sorry, forgot that point renge of temperature will bw from 10 to 30 celcius
degrees. Thanks


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2002\08\14@081129 by Claudio Martin

picon face
Liquid is wine stored in tanks and the range of temp. is from 10 to 30
degrees. Regarding the response time isn't that important, because it's a
huge mass of liquid. I have to check the temperature at a point located at
the center of the mass of liquid. This point is about 3 meter from the top
cover of the tank. I guess one stainless steel tube could be a good
solution, but one point to work out is how to keep the sensor in contact
with the end of the tube, is there any kind of glue with a good thermal
conductive coeficient?.


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2002\08\14@085630 by a?=

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I suppose that a sealed stainless steel tube, with the sensor inside, and
between sensor and tube, you may put thermal conductive grease.
I think it may be a solution.

 Gabriel.-


-----Mensaje original-----
De: pic microcontroller discussion list
[RemoveMEPICLISTEraseMEspamEraseMEMITVMA.MIT.EDU]En nombre de Claudio Martin
Enviado el: Miircoles, 14 de Agosto de 2002 09:11
Para: RemoveMEPICLISTspam_OUTspamKILLspamMITVMA.MIT.EDU
Asunto: Re: [EE]:Measure liquids temperature with 18S20


Liquid is wine stored in tanks and the range of temp. is from 10 to 30
degrees. Regarding the response time isn't that important, because it's a
huge mass of liquid. I have to check the temperature at a point located at
the center of the mass of liquid. This point is about 3 meter from the top
cover of the tank. I guess one stainless steel tube could be a good
solution, but one point to work out is how to keep the sensor in contact
with the end of the tube, is there any kind of glue with a good thermal
conductive coeficient?.


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2002\08\14@121854 by Brendan Moran

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> Liquid is wine stored in tanks and the range of temp. is from 10 to
> 30 degrees. Regarding the response time isn't that important,
> because it's a huge mass of liquid. I have to check the temperature
> at a point located at the center of the mass of liquid. This point
> is about 3 meter from the top cover of the tank. I guess one
> stainless steel tube could be a good solution, but one point to
> work out is how to keep the sensor in contact with the end of the
> tube, is there any kind of glue with a good thermal conductive
> coeficient?.

Thermally conductive epoxy.....

- --Brendan

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2002\08\14@134726 by Peter L. Peres

picon face
On Wed, 14 Aug 2002, Claudio Martin wrote:

>Liquid is wine stored in tanks and the range of temp. is from 10 to 30
>degrees. Regarding the response time isn't that important, because it's a
>huge mass of liquid. I have to check the temperature at a point located at
>the center of the mass of liquid. This point is about 3 meter from the top
>cover of the tank. I guess one stainless steel tube could be a good
>solution, but one point to work out is how to keep the sensor in contact
>with the end of the tube, is there any kind of glue with a good thermal
>conductive coeficient?.

Use heat conductive paste and ram the sensor down the tube. The tube will
conduct enough heat that there will be no difference with or without paste
at 3m of immersed tube imho.

You could just use a LM35 in each tube, attach terminals using individual
heatshrink and that's it. I think 8mm i.d. tube will be fine. This kind of
sheath is made for thermocouple gauges I think, for the food industry. I
do not know about 3m long though. Make sure the tube is strong or it will
bend as the immersed part tries to float. Maybe put a s.s. weight at the
end. I would put a preamp at the top of the tube and send 4-20mA or other
such signal to further processing.

I think that such modules exist (thermometer in s.s. sheath with 4-20mA
output). I have never used one. The ones I saw were at most 1 meter long.

Peter

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2002\08\14@141804 by Spehro Pefhany

picon face
At 12:10 PM 8/14/02 +0000, you wrote:
>Liquid is wine stored in tanks and the range of temp. is from 10 to 30
>degrees.

Be *very* sure that the closed end of the tube is made by TIG welding
or some other NSF* approved (US/Canada standard) or equivalent method.
In particular, you want to avoid cadmium-bearing Ag hard solders which
will look nice, but leach out into the wine and cause contamination. The
inert-gas welded probe is all just plain stainless steel and should
last indefinitely under those conditions, unless damaged physically.

For the heat transfer issue, silicone grease should work, and won't
cause stress on the 18S20.

Personally, I'd specify a proper industrial-quality Pt100 DIN RTD probe
and either use a commercial signal conditioner or make one.

* National Sanitary Foundation  http://www.nsf.org

Best regards,

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2002\08\14@144522 by Brendan Moran

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Could always just go with a Fluke type-K thermocouple immersion
probe.  Produces a milivolt/degree C or degree F output.  Scale it
with an opamp, and read with a PIC.  Not too tough.  Little bit pricy
though.  I think it would cost about $300USD for the set.  Though if
you're looking at TIG welding, it could also get that high,
considering the rates for professional welding...

- --Brendan

- {Original Message removed}

2002\08\14@145147 by Spehro Pefhany

picon face
At 11:44 AM 8/14/02 -0700, you wrote:


>Could always just go with a Fluke type-K thermocouple immersion
>probe.  Produces a milivolt/degree C or degree F output.  Scale it
>with an opamp, and read with a PIC.  Not too tough.  Little bit pricy
>though.  I think it would cost about $300USD for the set.  Though if
>you're looking at TIG welding, it could also get that high,
>considering the rates for professional welding...

Probe would be about $75. with a platinum sensor. Signal conditioner
could get it up to the $200 range or higher depending on accuracy
(but they are not that hard to make if you don't need isolation
or industrial-strength EMI immunity). Signal level with RTDs is
about 10* that of a thermocouple.

Thermocouples are not appropriate for that temperature range and
application, the  cold junction compensation contribution will be
as much as the thermocouple, you may as well dump the thermocouple
and stick the compensator down the tube.

Best regards,

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2002\08\14@153714 by Brendan Moran

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> Thermocouples are not appropriate for that temperature range and
> application, the  cold junction compensation contribution will be
> as much as the thermocouple, you may as well dump the thermocouple
> and stick the compensator down the tube.

I hope you don't mind too terribly much if I just disagree with you a
bit there.  The specifications for the Fluke 80TK thermocouple module
seem to belie your opinion about where thermocouples can be used.

Measurement Range:

- -50ºC to 1000ºC (-58ºF to 1832ºF), depending on thermocouple probe
used.

Accuracy:
- -50ºC to -20ºC: 2.5% ± 2ºC
- -58ºF to -4.0ºF: 2.5% ± 3.6ºF
- -20ºC to 350ºC: 0.5% ± 2ºC
- -40ºF to 662ºF: 0.5% ± 3.6ºF
350ºC to 500ºC: 1.75% ± 2ºC
662ºF to 932ºF: 1.75% ± 3.6ºF
500ºC to 1000ºC: 2% ± 2ºC
932ºF to 1832ºF: 2% ± 3.6ºF


You will notice that the 10 to 30 degrees falls well within the
optimum range of -20C to +350C (-40F to +662F)  So, I will have to
say that I am of completely the opposite opinion on this one.  10 to
30 degrees, be it C or F, falls well within the prime operating range
of thermocouples.  Well, Fluke ones, at least.

With regards to the immersion probe which I mentioned,
80PK-2A K-type immersion probe
Measurement range: -40 to 982ºC (-40 to 1800ºF)

It looks like it fits too.

Now, if you were to tell me that the problem was something along the
lines of there being an issue with heat flow, I'd accept that, but,
having read fluke specs before, "Thermocouples don't work in that
range" just doesn't do it for me.

Electrosonic shows the 80TK thermocouple module at $124 each, and the
80PK-2A immersion probe at $83 each.

All in all, I think it's quite a viable solution.

- --Brendan

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2002\08\14@155639 by Peter L. Peres

picon face
www.google.com/search?hl=en&lr=&ie=ISO-8859-1&q=immersion+temperature+probe+food+flange

Be sure to check out omega's page linked above ;-)

Peter

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2002\08\14@162836 by Spehro Pefhany

picon face
At 12:36 PM 8/14/02 -0700, you wrote:

>I hope you don't mind too terribly much if I just disagree with you a
>bit there.  The specifications for the Fluke 80TK thermocouple module
>seem to belie your opinion about where thermocouples can be used.

Excuse me? I did NOT say it could not be used or would not "work" (in
the sense of giving some indication of temperature), I did
say that it was *inappropriate* for this application.  Straw man?

>Measurement Range:
>
>- -50ºC to 1000ºC (-58ºF to 1832ºF), depending on thermocouple probe
>used.
>
>- -20ºC to 350ºC: 0.5% ± 2ºC


Yes, not very good, for this kind of biological application, is it?
And what warm-up time do they specify to achieve this level of
accuracy? And what thermal gradients can be expected outside this
tub of relatively constant temperature liquid?  What kind of
errors in any panel jacks etc. that might be involved? Errors
due to the compensation leadwire not being quite the same alloy?
There is an inaccuracy due to the probe as well, typically
special limits of error alloys are used, but still the errors
are significant. A decent RTD system would be around five times
better accuracy at a similar price, and have completely
interchangeable probes. Which is why they are used
almost exclusively in industry for this sort of thing.

Do you know anything about thermocouples and their conditioning
circuitry?  There is a temperature sensor inside the Fluke that
must *track* the junction between the copper wire inside the
circuit and the thermocouple materials more accurately than
the desired system accuracy. This can't be done perfectly,
particularly not on a very inexpensive instrument like this one
which doesn't have a lot of effort put into maintaining isothermal
conditions around the junctions. A 2' error in tracking means
a 2' error in the reading (the thermocouple voltage is (to a
first approximation, it's not exact, nor is it linear)
proportional to the difference in temperature from one end to
the other. This introduces lots of sources of error.

>You will notice that the 10 to 30 degrees falls well within the
>optimum range of -20C to +350C (-40F to +662F)

Optimum? Hardly.

>So, I will have to
>say that I am of completely the opposite opinion on this one.  10 to
>30 degrees, be it C or F, falls well within the prime operating range
>of thermocouples.  Well, Fluke ones, at least.

No, it is an area of temperature that is *usually* best served by
other types of sensors. Most temperature sensors will "work" in this
temperature range- semiconductor, precision thermistor, base-metal
RTD, precious metal RTD, most thermocouple types (not type B or some
exotics), IR, etc. etc. T/C's are best reserved for applications
where their ruggedness, speed of response, high or low temperature
capability (or potential, anyway) etc. justify their disadvantages.
This, quite simply, is not such an application.

>With regards to the immersion probe which I mentioned,
>80PK-2A K-type immersion probe
>Measurement range: -40 to 982ºC (-40 to 1800ºF)
>
>It looks like it fits too.

Yes..  believe it or not, you can get probes and/or protection
tubes made to whatever length you want, within reason. Cheaply.

>Now, if you were to tell me that the problem was something along the
>lines of there being an issue with heat flow, I'd accept that, but,
>having read fluke specs before, "Thermocouples don't work in that
>range" just doesn't do it for me.

"Heat flow" would be B.S. A big tub of liquid like this is about the
easiest type of system to measure accurately.

>Electrosonic shows the 80TK thermocouple module at $124 each, and the
>80PK-2A immersion probe at $83 each.
>
>All in all, I think it's quite a viable solution.

If you don't look too close.

Best regards,

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2002\08\14@164137 by Brendan Moran

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> Yes, not very good, for this kind of biological application, is it?
> And what warm-up time do they specify to achieve this level of
> accuracy? And what thermal gradients can be expected outside this
> tub of relatively constant temperature liquid?  What kind of
> errors in any panel jacks etc. that might be involved? Errors
> due to the compensation leadwire not being quite the same alloy?
> There is an inaccuracy due to the probe as well, typically
> special limits of error alloys are used, but still the errors
> are significant. A decent RTD system would be around five times
> better accuracy at a similar price, and have completely
> interchangeable probes. Which is why they are used
> almost exclusively in industry for this sort of thing.

Couldn't a little careful calibration fix that?

Well, anyways, what do you think of the LM35 solution that someone else
offered?  It would require the TIG welded tube that I was saying would be
expensive, but other than that, I think I remember it being a relatively
good sensor, and with a thermal epoxy bond to the stainless steel tube, it
should measure temperature fairly well, I think.

--Brendan

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2002\08\14@170224 by Spehro Pefhany

picon face
At 01:40 PM 8/14/02 -0700, you wrote:

>Couldn't a little careful calibration fix that?

Not if it shifts with the breeze, which is the issue. Under lab
conditions, sure, but usually you'd prefer to have the sensors
interchangeable so when one gets wrecked it can be replaced
quickly. And you do not want the reading to change when the
door opens or when someone touches or gets near to something.

>Well, anyways, what do you think of the LM35 solution that someone else
>offered?

It's not bad at all, IMHO, in this temperature range.
Pretty good accuracy (about the best I've
seen in a cheap semiconductor sensor), and inexpensive.

I'm not sure exactly what method they use for the actual
temperature measurement, and when I asked Pease about it,
he clammed up tight, there are obviously some proprietary
aspects to it, but it seems to be in capable hands anyway.

And doesn't have the somewhat dubious history that the 18S20's
predecessor had with moisture ingress issues causing the reading
to drift.

The "one-wire" bus also has its issues. It works great for short
distances and is quite easy to use, but is suspect for long runs.

>It would require the TIG welded tube that I was saying would be
>expensive, but other than that, I think I remember it being a relatively
>good sensor, and with a thermal epoxy bond to the stainless steel tube, it
>should measure temperature fairly well, I think.

I'd try to avoid the epoxy in favor of something with more "give", but sure.
At an immersion over 10* the tube diameter you don't have to worry about
accuracy so much as slow response (which isn't an issue here).

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
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2002\08\14@171743 by Olin Lathrop

face picon face
> Thermocouples are not appropriate for that temperature range and
> application, the  cold junction compensation contribution will be
> as much as the thermocouple, you may as well dump the thermocouple
> and stick the compensator down the tube.
>
> > I hope you don't mind too terribly much if I just disagree with you a
> > bit there.  The specifications for the Fluke 80TK thermocouple module
> > seem to belie your opinion about where thermocouples can be used.

I think you are missing the whole point Sphero was making about the
compensation circuit.  Thermocouples are only *relative* measures of
temperature.  This is a bit simplified, but they measure the temperature
difference between one end of the bi-wire cable and the other.  One end is
in the probe, and the other end on a circuit board.  To know the absolute
temperature at the probe, the circuit on the board needs to measure its own
absolute temperature, then "compensate" the thermocouple signal.  Sometimes
this is referred to as an "electronic icepoint".  This is still a win if the
probe is in a flame, oven, or cryogenic chamber where the circuit wouldn't
survive.  In that case small variations introduced by errors in compensating
for the circuit temperature are relatively insignificant, especially in
relative terms compared to a flame temperature.

However, thermocouples lose much of their advantage if you only want to
measure human scale absolute temperatures where circuits survive and operate
nicely.  The circuit has to measure absolute temperature anyway.  At human
temperatures, you can ditch the thermocouple and just measure the absolute
temperature at the probe like you would have had to at the circuit anyway.
This is what Sphero meant by "stick the compensator down the tube", but he
was assuming you understood how thermocouple measuring circuits worked.


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2002\08\14@180049 by Brendan Moran

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> This is what Sphero meant by "stick the compensator down the tube",
> but he was assuming you understood how thermocouple measuring
> circuits worked.

I understand the principles of the thermocouple, but have never
looked at the functional circuitry.  I was going off of
manufacturer's specs without understanding the whole picture. (This
is one reason that I think it's good to know assembly before learning
a high level language)

I also seem to have been a bit out to lunch when I suggested that +/-
2 degrees C was a small error in the 10 to 30 range.  I think what I
was trying to say is that there are cheap complete solutions
available that do use thermocouples.  I think, though, that I sortof
didn't notice the lack of accuracy, and saw the 2% not the +/- 2
deg.C

Yes, the more I look at it, the more I think that the LM35 is a
pretty good solution.  Especially in a performance/cost evaluation.

- --Brendan

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2002\08\15@064151 by Roman Black

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> On Wed, 14 Aug 2002, Claudio Martin wrote:
>
> >Liquid is wine stored in tanks and the range of temp. is from 10 to 30
> >degrees. Regarding the response time isn't that important, because it's a
> >huge mass of liquid. I have to check the temperature at a point located at
> >the center of the mass of liquid. This point is about 3 meter from the top
> >cover of the tank. I guess one stainless steel tube could be a good
> >solution, but one point to work out is how to keep the sensor in contact
> >with the end of the tube, is there any kind of glue with a good thermal
> >conductive coeficient?.


Wine is acidic, so it's probably best not to use
a metal tube. Get plastic tube rated for the food
industry, and I would use a non-toxic heatsinking
grease like petroleum jelly in case of any leakage.
The thermal mass of the wine is very large and the
rate of temperature change will be slow, so the
thermal sensor does not need any special treatment,
ie anything buried in a 3 meter radius of water is
going to be at the average temp! :o)

I would also suspect that this being mainly water
with normal convection etc the temperature in the
middle probably won't be that much different than
near the edges of the tank. You may just be able to
put the probe near the tank wall (only about 30cm
in?) and be close enough in temp.

Be aware that there may be laws/standards related
to the materials you can immerse in a food product...
-Roman

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2002\08\15@075243 by Katinka Mills

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Hi Roman,
In WA (AU) we use stainless steel for all food stuff, I was involved in
manufacturing industrial mixers with heaters for making fudge (think a big
(8cubic') cement mixer made of stainless steel with a second layer of
stainless steel on the outside and oil inbetween so we can get even heating)
we have drop in stainless steel temp probes with PT 100 sensors (they were
thermally epoxied after the food end was weldeded closed (with tig (mig on
SS is not very good, tig is beter)) well the first two probes died after 2
weeks, seems the heating and cooling of the epoxy ended up cracking the
sensor. now they are just slid down the tube with a good supply of thermal
grease))

Regards,

Kat.

**********************************************
K.A.Q. Electronics.
Electronic and Software Engineering.
Perth, Western Australia.
Ph +61 (0) 419 923 731
**********************************************

> {Original Message removed}

2002\08\15@081409 by Roman Black

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face
Katinka Mills wrote:
>
> Hi Roman,
> In WA (AU) we use stainless steel for all food stuff, I was involved in
> manufacturing industrial mixers with heaters for making fudge (think a big
> (8cubic') cement mixer made of stainless steel with a second layer of
> stainless steel on the outside and oil inbetween so we can get even heating)
> we have drop in stainless steel temp probes with PT 100 sensors (they were
> thermally epoxied after the food end was weldeded closed (with tig (mig on
> SS is not very good, tig is beter)) well the first two probes died after 2
> weeks, seems the heating and cooling of the epoxy ended up cracking the
> sensor. now they are just slid down the tube with a good supply of thermal
> grease))


Hi Katinka. Yep stainless is pretty standard in
food production, but may not be best for use with
acidic liquids especially over long time periods.
I only mentioned it as a "just in case" scenario.
Cool fudge mixers! Interesting to hear about the
sensor failure.
-Roman

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2002\08\15@104333 by Katinka Mills

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> -----Original Message-----
> From: pic microcontroller discussion list
> [PICLISTspamBeGonespamMITVMA.MIT.EDU]On Behalf Of Roman Black
> Sent: Thursday, 15 August 2002 8:10 PM
> To: RemoveMEPICLIST@spam@spamspamBeGoneMITVMA.MIT.EDU
> Subject: Re: [EE]:Measure liquids temperature with 18S20
> Hi Katinka. Yep stainless is pretty standard in
> food production, but may not be best for use with
> acidic liquids especially over long time periods.
> I only mentioned it as a "just in case" scenario.
> Cool fudge mixers! Interesting to hear about the
> sensor failure.
> -Roman

Hmmmm should maybe speak to the local health department, I know with beer it
is SS used, as I used to repair PDL VFD's for a brewer in the hills (funny
how on site work always ended in a few samples of the differernt ale's ;o)

Regards,

Kat.

**********************************************
K.A.Q. Electronics.
Electronic and Software Engineering.
Perth, Western Australia.
Ph +61 (0) 419 923 731
**********************************************

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2002\08\15@153633 by Peter L. Peres

picon face
On Wed, 14 Aug 2002, Spehro Pefhany wrote:
...
>And doesn't have the somewhat dubious history that the 18S20's
>predecessor had with moisture ingress issues causing the reading
>to drift.

By the way moisture. In that tube below ambient temp. humidity will creep
up until it will reach 100% and stay there. It needs to be back filled
with something edible, or sealed with dry nitrogen. Maybe food grade
silicone under vacuum. This is easier than it sounds although a hole in
the floor is probably in order (or work on the stairways). 3m long tubes
are hard to maneouver ;-)

Peter

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2002\08\15@153646 by Peter L. Peres

picon face
On Wed, 14 Aug 2002, Brendan Moran wrote:

>-----BEGIN PGP SIGNED MESSAGE-----
>Hash: SHA1
>
>> This is what Sphero meant by "stick the compensator down the tube",
>> but he was assuming you understood how thermocouple measuring
>> circuits worked.
>
>I understand the principles of the thermocouple, but have never
>looked at the functional circuitry.  I was going off of
>manufacturer's specs without understanding the whole picture. (This
>is one reason that I think it's good to know assembly before learning
>a high level language)

Imho it's also good if you have a hard head if you do that. You're going
to need it to break down walls you'll be running into. (I learned this
from experience).

Peter

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