This is getting, confusing, complex and interesting!

In the same line as the Omega hint, and in the same cole palmer
catalog, I saw a Digi-sense Digital Handheld thermistor thermometer,
which has range of -40 to +125 Degree C and claims accuracy of +- 0.2
Degree C. Also offers an optional probe. Now is there any fine print
here?

It appears to me till now, that the process of measuring "true"
temeperature is more complex than measuring temperature of the sensor
accurately?
I mean this friend person just wants to go outdoors (with the sun
shining and all) and go to a spot (a longitude/latitude that he
identified from his satellite thermal IR image) and take/sample the
temeperature there. and then he wishes to relate the satellite thermal
imagery with the on-ground samples that he thus takes, and come to some
conclusion about this urban heat phenomenon..and sometimes he cannot go
INTO dense vegetation, or a brick kiln, so he infers the temeprature at
THAT site by pointing the IR thermometer at it.

so what I mean is, Can he use this 30$ Digi-sense thermometer at the
site and just take a sample and note it and claim that AT THAT POINT ON
EARTH AT THAT TIME the temperature was X degree C +- 0.2 deg C? or it
just dosen't work like this?

But I shall, at least in my spare time and slowly, wish to interface
and calibrate the sensor, because he takes PDA computer, and it has a
RS 232 port, and I'd love it if he just pressed a button and the
temperature was directly logged with the time and the GPS position (yes
the GPS is fairly inaccurate!)

It also occurs to me that I need to better understand this
"temeprature" term!

Many thanks,
Suraj

P.S. As a bonus, I experimented with my digital camera and used my TV
remote to illumate a target, and gave a 5 second manual exposure and
the image came rather decently bright! this leads me to making a BIG IR
torch and do some "stealth" photography!




wrote:
In sci.electronics.design wrote:
It would be best if I can get cheap sensor(s) which I can interface
myself (to the PC), but worst comes I can buy one/seperate standalone
devices which preferable have some sort of computer connectivity and
some memory.

Look at Omega, http://www.omega.com . They have stuff in all kinds of
accuracies and price ranges; some of it is expensive, but it's handy if
you have a credit card and want it tomorrow. You might use their prices
to set an upper bound on how much you should spend trying to do it
yourself. Or, you might find that it's cheaper to buy than build. For
instance, for US$150 (HH12A + CAL-3-HH), you can fulfill 1) and 2) at
a basic level with NIST-traceable 0.1 C resolution (but read the spec
sheet).

Standard disclaimers apply; I don't get money from Omega.

Matt Roberds

On 15 Oct 2005 00:36:49 -0700, wrote:

This is getting, confusing, complex and interesting!

In the same line as the Omega hint, and in the same cole palmer
catalog, I saw a Digi-sense Digital Handheld thermistor thermometer,
which has range of -40 to +125 Degree C and claims accuracy of +- 0.2
Degree C. Also offers an optional probe. Now is there any fine print
here?

Don't assume that marketing copy writers understand the differences
between "digits displayed to the right of the decimal point" and
"precision" and "accuracy."

As a minimum, read the manufacturer's datasheet, not a blurb on a web
page. If they are indeed making an assertion with respect to absolute
accuracy then I would expect to see:

A number for the instrument's accuracy as a standard deviation or a
statement that the stated accuracy is +/- so many std devs. There should
be a statement regarding operating and/or environmental limits.

AND a statement that the instrument calibration is traceable to a
standard maintained by NIST or an equivalent national standards bureau.

AND a signed and dated seal on the instrument (preferred), or a
similarly signed and dated document with the instrument's serial number,
stating by whom and when it was last calibrated and including a graph or
table showing the residuals between the measurements of that instrument
and a maintained standard throughout the instrument's range.

Absent all three of those, any claimed "accuracy" is, at best, a dumb
mistake by the English major who wrote the blurb and, at worst, a
deliberate attempt to mislead the customer.

--
Rich Webb Norfolk, VA

wrote in message
oups.com...
This is getting, confusing, complex and interesting!

In the same line as the Omega hint, and in the same cole palmer
catalog, I saw a Digi-sense Digital Handheld thermistor thermometer,
which has range of -40 to +125 Degree C and claims accuracy of +- 0.2
Degree C. Also offers an optional probe. Now is there any fine print
here?


I looked at the Cole-Parmer web site and tried to find the specific unit you
saw. I'm looking at their model 93210-00 thermistor thermometer. And there
is fine print.
If you took the time to download and read the instruction manual for that
model, you would see that it uses a YSI 400 series calibrated thermistor.
These thermistors are manufactured and specified to very close tolerances,
and can be used to good advantage in temperature measuring equipment. The
model 93210-00 thermometer is specified to have an accuracy specification of
+/- 0.2 deg C, but look at the specs a bit further. This accuracy is only
valid over the temperature range of 18 to 28 deg C. The "useful range", or
the range of temps that are deemed to be "in the ballpark", is a bit larger
at 0 to 40 deg C. Everything else is meaningless.
This same method of specification of themometers applies to most other
consumer-level (cheap) instruments. You have to read the complete spec..
not just the one that the marketing folks use to catch your eye.


so what I mean is, Can he use this 30$ Digi-sense thermometer at the
site and just take a sample and note it and claim that AT THAT POINT ON
EARTH AT THAT TIME the temperature was X degree C +- 0.2 deg C? or it
just dosen't work like this?


I couldn't find any of the Cole-Parmer models for $30 US... Which model
did you see for that price?


But I shall, at least in my spare time and slowly, wish to interface
and calibrate the sensor, because he takes PDA computer, and it has a
RS 232 port, and I'd love it if he just pressed a button and the
temperature was directly logged with the time and the GPS position (yes
the GPS is fairly inaccurate!)

I did see a model EW-93210-50 logging thermometer that boasts much better
accuracy, but it's also twice the price of the other unit. It offers you an
RS-232 port for connection to your laptop or handheld computer. These units
can offer the higher accuracy because of the tightly specified thermistors
used in the probes, and by use of a microprocessor-based measuring system.
The processor uses a lookup table that was created at the time of
calibration to compare the thermistor reading to the table of temperature
values. The temperature from the lookup table is the value displayed. When
these units are calibrated, they have to be calibrated as a probe-instrument
set. In order to maintain the stated accuracy, they have to be used as a
set.


It also occurs to me that I need to better understand this "temeprature"
term!

I'm not sure that "temperature" is your problem. I think you might need to
understand how to read and interpret manufacturers specs, which should be a
required course toward an engineering degree. {:) Just be sure that you
look at the complete spec before you buy (or recommend) an instrument.

Cheers!!!
--
Dave M
MasonDG44 at comcast dot net (Just substitute the appropriate characters in
the address)

Never take a laxative and a sleeping pill at the same time!!

DaveM wrote:
wrote in message
oups.com...
...

It also occurs to me that I need to better understand this "temeprature"
term!


I'm not sure that "temperature" is your problem. I think you might need to
understand how to read and interpret manufacturers specs, which should be a
required course toward an engineering degree. {:) Just be sure that you
look at the complete spec before you buy (or recommend) an instrument.


Not to disagree too strongly with your comments, Dave, but "temperature"
is his big problem -- or at least understanding the principles of
temperature measurement.

Go back, Suraj, and reread my other post on this subject. There are
fundamental matters that you have to understand and take care of before
you even start reading manufacturers' data sheets. Keep in mind that
all these devices maintain their specifications only under certain
definitely specified conditions, and if you don't use the equipment
under these conditions, you don't get the accuracy in your measurement,
even if the equipment meets its specifications perfectly!

I haven't looked closely at the satellite measurements' techniques and
specifications, but I do know that they get their fractional degree data
by averaging many, many readings over rather wide areas. There is no
such thing as a city with a temperature of 22.7C. There will be a city
whose average temperature at a particular time is 22.7C, with a range of
individual measurements at that time maybe +-5C or more.

The satellite measurements can quote this kind of resolution and
accuracy because their sensors are stable and known to this kind of
resolution and accuracy. So if yesterday's temperature for Rome is
22.7C, and today's is 23.2C, you can be sure that the average of the
readings of many places in Rome is 0.5C higher today than that average
was yesterday. That's all. Your friend is not going to verify the
satellite readings with a handheld, or IR, or any other kind of
ground-based measurement. I doubt seriously he could get an equivalent
measurement with the satellite's own equipment from a balloon!

The best he could do is verify that his location is some temperature
near the satellite's reading. But then, maybe his location is in one of
the extreme places :-). If he had dozens or hundreds of sensors spread
all around the city, he still might not be able to couple his sensors to
their surroundings well enough to get an equivalent reading (remember,
you can never measure the temperature of an object -- only the
temperature of the sensor). IR readings won't help, either, since they
are made from different angles at different distances over different
areas.

Now, if your friend has access to a satellite that he can use to
rendezvous with the weather satellite, and take the same kind of
measurement at the same time, from the same location in orbit, with
sensors calibrated to the same specifications under the same conditions,
then he might have a case for saying reasonably that he's verified or
disputed the satellite's measurement.

John Perry

On Thu, 13 Oct 2005 12:30:44 -0400, Spehro Pefhany
wrote:

On Thu, 13 Oct 2005 16:10:37 GMT, the renowned "Dan Hollands"
wrote:

To know how difficult it is to get 0.1 degree accuracy one must know the
temperature range to be measured and the ambient temperature range for the
equipment doing the measuring. This also determines the resolution required
of the ADC.

In my experience achieving this accuracy is not easy and not cheap.

Dan

Yes. Getting 0.1°C *resolution* is easy and cheap (even with a
relatively low-level sensor like a thermocouple).

Getting 0.1°C accuracy is not easy and not cheap, and it only gets
worse the further you move from the ideal
fully-immersed-in-benign-liquid "CSTR" type of situation.

When i was an apprentice so long ago, I remember the company i worked
for using one junction of a transistor for doing 0.1degC. Accuracy was
actually a lot better, but thats all they could claim becasue of the
equipment used for calibration.

I remember that everytime they got a new batch of transistors, i would
have to spend days with an old 4wire thermistor and meter to make
readings every 0.05degC. Sitting with an ice bath waiting for the ice
to melt and trying to zero that meter was a right pain in the arse.
Calibrating the standard device was the same, and that had to be done
every three months.

mike wrote:

Robert Baer wrote:

riscy wrote:

I believe there is semiconductor device from analog device or national
or maxim or similar that is capable of 1C accuracy within temperature
range. It worth looking into this as it very easy to use.

All you have to do is to connects to ADC and that it(!).

Some recent device has build ADC which includes all accuarcy of the ADC
and temperature sensor.

Failing that, you can get PT100 type calibrated probe and then select
the semi temp IC to match the accuracy and reject those do not.

If commiting to PT100 solution, you need precision constant current
source involving precision voltage reference (which interface to op-amp
that provides regulated current output). Some care on circuit is
needed.

Good luck

Riscy

Yes, i have found that the LM35Z is not only within 1C but that it
does not get too far off even up to 185C (3-4C higher).
Not too bad for around a dollar.


Within 1C of What???
Describe your reference and measurement technique.
Thanks, mike

Lemme see....will two different types of thermocouples and a glass
thermometer, all agreeing with each other within 1C worst case be good
enough?

wrote:

Seeing all the posts, I'm not sure! if he's gonna get this fabeled
accuracy. I think this is a pretty complex (!) topic, and I better be
spending some more time reading up on calibration and such..

Calibration? Last time I calibrated my NTC thermistor I did in Ice (0
degree C) and boiling water etc. etc. It was a 10K NTC
and there was also a reference sheet with it, I remember. But nobody
tells me how Accurate I can go with this 10K NTC FENWAL thermistor I
have with me already?

Lets say I want As much accuracy as possible with a *decently low cost
solution* (200 $ ?) To top it up, I'm in India, but I think getting
electronic components is not much of a problem.

This PT100 class B appeals to me certainly.. I'll work on it.. But how
do I go about calibration? can I use distilled water Ice etc. as one
poster mentions?

I got hold of a Cole-Palmer scientfic catalog and they have this .1
Degree accuracy on their SAMA glass thermometers. cost around
90$..should I go in for this manual solution? but how about measuring
contact temperature?

Further reading this book, and as some other posters point out, it is
clear how vain a pursuit the radiation temperature measurement at this
accuracy shall be. The best models I see in this catalog give me around
2 Degree C, and they are pretty expensive..

Just curious, But I remember reading that CCDs have similar response to
IR as to light.. is this so? if so, can there be this remote
possibility that I turn a 5 Mega pixel Digital camera as a thermal
imager of sorts? maybe with appropriate "IR filters" ?

Also, Can I ever use IR diodes (like those in a TV) for any kind of
temperature measurement?
Many thanks
Suraj

I understand that digital camera constructionhas been changed to
include an IR blocking filter.
Why?
So you cannot use it to take tittie pictures thru (transparent)
tshirts....

On Sun, 16 Oct 2005 09:31:05 +0000, Robert Baer wrote:

I understand that digital camera constructionhas been changed to
include an IR blocking filter.
Why?
So you cannot use it to take tittie pictures thru (transparent)
tshirts....

I really don't think that they're all that "transparent" - as far as
I know, the clothing simply warms up to a temperature close to whatever
area of skin it's over - you're not really seeing titties, only their
heat signature. :-/

Thanks,
Rich

I couldn't find any of the Cole-Parmer models for $30 US... Which model
did you see for that price?

Oops! It was the price of the vinyl carrying case that I saw! the
thermometer is around 180$

Suraj

wrote in message
oups.com...

I couldn't find any of the Cole-Parmer models for $30 US... Which model
did you see for that price?

Oops! It was the price of the vinyl carrying case that I saw! the
thermometer is around 180$

Suraj


Wow!!!! For 30 bucks, you'd think it would be gold gilded eelskin

--
Dave M
MasonDG44 at comcast dot net (Just substitute the appropriate characters in
the address)

Never take a laxative and a sleeping pill at the same time!!