Maker Pro
Maker Pro

need a temperature sensor with .1 degree accuracy

I'm pretty new to thermal sensing and such, but I have a friend who
wishes me to make/aquire 3 types of temperature sensors, all with
greater than .1 degree celsius accuracy.

1) Ambient temperature
2) Contact temperature
3) Radiation temperature (a "directional" sensor of sorts which detects
IR radiation coming from a source). A further requirement is that if
this sensor (or array of sensors) can tell me the temperature /amount
of radiation in each Thermal IR band within 8.125 to 11.60 Micrometers
(total 5 bands within this bandwidth)(This should preferable correspond
to a satellite sensor band seperation, as he is doing some urban heat
phenomenon research).

I've done some experiments with NTC Thermistors before-I did some
interfacing to the PC joystick port. I thought maybe I can use the same
NTC thermistor for the above uses? Is the thermistor meant for "such"
sensitive work? (If I uses a better ADC)..and can I modify it in some
way to measure the radition temperature as well? (by adding some sort
of parabola?!)

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.

Many thanks
Suraj
 
D

Dan Hollands

Jan 1, 1970
0
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

--
Dan Hollands
1120 S Creek Dr
Webster NY 14580
585-872-2606
[email protected]
www.QuickScoreRace.com
 
S

Spehro Pefhany

Jan 1, 1970
0
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.


Best regards,
Spehro Pefhany
 
Are you sure you need 0.1 degree accuracy?

The WMO requirement for meteorological institutes on ambient
temperature measurement is +/- 0.3 degrees (WMO Guide on Meteorological
Measurements and Methods of Observation)

A Pt100 Class B (IEC-60751) has an accuracy of +/- 0.15 degree at 0
deg. C and a reasonable low error in temperature coefficient, so you
can have a sensor accuracy of let us say +/- 0.25 degree over a certain
temperature range

You need to add the inaccuracy that is introduced by the amplifier /
interface circuit / ADC. It requiers accurate (read: not so cheap)
components to build an interface circuit that does cause an error less
than 0.1 degree over a reasonable temperature range.

Since Pt100 elements are very stable over a long term, you can obtain a
higher accuracy from a Pt100 sensor if you can calibrate your sensor
against a high accuracy standard. This is one of the main questions in
this story: How are you going to calibrate your system ?

Note that any system that measures temperature with an accuracy of
better than 1 degree wll need serious calibration.

You will need to calibrate your sensor. How are you going to do that ?
 
R

redbelly

Jan 1, 1970
0
I'm pretty new to thermal sensing and such, but I have a friend who
wishes me to make/aquire 3 types of temperature sensors, all with
greater than .1 degree celsius accuracy.

1) Ambient temperature
2) Contact temperature
3) Radiation temperature (a "directional" sensor of sorts which detects
IR radiation coming from a source). A further requirement is that if
this sensor (or array of sensors) can tell me the temperature /amount
of radiation in each Thermal IR band within 8.125 to 11.60 Micrometers
(total 5 bands within this bandwidth)(This should preferable correspond
to a satellite sensor band seperation, as he is doing some urban heat
phenomenon research).

I don't see item (3) ever meeting your accuracy requirement, no matter
how much you are willing to spend. Even if you could measure the
radiated power accurately, uncertainty in the emissivity of the
measured objects would contribute too much error.

Mark
 
G

GregS

Jan 1, 1970
0
I don't see item (3) ever meeting your accuracy requirement, no matter
how much you are willing to spend. Even if you could measure the
radiated power accurately, uncertainty in the emissivity of the
measured objects would contribute too much error.

Mark

Never mentioned if he wanted absolute accuracy. Probably not.
Even if one can achieve having the instruments, there
is so much variation when actually taking measurments.
You could not find two places in a glass of water with the
same temperature.

greg
 
M

martin griffith

Jan 1, 1970
0
I don't see item (3) ever meeting your accuracy requirement, no matter
how much you are willing to spend. Even if you could measure the
radiated power accurately, uncertainty in the emissivity of the
measured objects would contribute too much error.

Mark

Never mentioned if he wanted absolute accuracy. Probably not.
Even if one can achieve having the instruments, there
is so much variation when actually taking measurments.
You could not find two places in a glass of water with the
same temperature.

greg[/QUOTE]
OT of course but
http://www.lsbu.ac.uk/water/anmlies.html


martin
 
P

Pooh Bear

Jan 1, 1970
0
I'm pretty new to thermal sensing and such, but I have a friend who
wishes me to make/aquire 3 types of temperature sensors, all with
greater than .1 degree celsius accuracy.

I think your 'friend' is pulling your leg !

You would be doing well to get 1C accuracy.

Graham
 
J

John Perry

Jan 1, 1970
0
Pooh said:
I think your 'friend' is pulling your leg !
Right!


You would be doing well to get 1C accuracy.

Well, there are ways to measure temperature to millidegree accuracy, but
there are caveats.

First, if you use a physical sensor (RTD, diode, thermocouple, etc.) you
can never ever measure the temperature of anything but the sensor. You
have to then infer the temperature of your object or process from an
estimate of the thermal coupling to whatever you're trying to measure,
and an estimate of the self-heating due to your probe signal, and an
estimate of... (the list gets longer with increasing resolution and
accuracy :).

Second, as someone has already mentioned, it's very unlikely that
anything except a really tightly controlled material of high thermal
conductivity in a very tightly controlled environment will be uniform in
temperature to 1 degree, much less 0.1 degree. The larger it is, the
less likely it gets.

Third, the optical sensing technique can indeed measure to 0.1 degree
resolution and accuracy, but only at the specific location that is being
observed, and only if emissivities of the target, the sensitivities of
the receptor, and the details of the transmission medium and path are
very well known.

The upshot of all this is that you will be able to measure something
with 0.1 degree resolution, but it'll more than likely be irrelevant to
anything you want to do or observe, and you can only get that accuracy
of even the things you can truly measure (which will not include what
you mentioned in your original post) by spending lots and lots of bucks.

So, I agree with Graham, here. You're chasing an unattainable goal.

John Perry
 
R

Robert Baer

Jan 1, 1970
0
I'm pretty new to thermal sensing and such, but I have a friend who
wishes me to make/aquire 3 types of temperature sensors, all with
greater than .1 degree celsius accuracy.

1) Ambient temperature
2) Contact temperature
3) Radiation temperature (a "directional" sensor of sorts which detects
IR radiation coming from a source). A further requirement is that if
this sensor (or array of sensors) can tell me the temperature /amount
of radiation in each Thermal IR band within 8.125 to 11.60 Micrometers
(total 5 bands within this bandwidth)(This should preferable correspond
to a satellite sensor band seperation, as he is doing some urban heat
phenomenon research).

I've done some experiments with NTC Thermistors before-I did some
interfacing to the PC joystick port. I thought maybe I can use the same
NTC thermistor for the above uses? Is the thermistor meant for "such"
sensitive work? (If I uses a better ADC)..and can I modify it in some
way to measure the radition temperature as well? (by adding some sort
of parabola?!)

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.

Many thanks
Suraj
"Cheap" sensors are, by definition *cheap* and have poor accuracy; no
where near what you think you need.
 
R

riscy

Jan 1, 1970
0
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
 
R

Robert Baer

Jan 1, 1970
0
riscy said:
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.
 
P

PeteS

Jan 1, 1970
0
<< 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.
Most semiconductor temperature sensors are usually PN juntion types
where a differential current is pulsed. The best resolution on these is
1C in a limited range, with absolute accuracy of perhaps 3C across the
temperature range.

Once again, as noted, it is measuring the temperature of the sensor,
rather than overall ambient temperature. Even a slight air movement
will throw the readings out by far more than the OP wanted.

I agree with the previous posts that the OP is chasing an unattainable
goal.

Note that Maxim does have a nice sensor (minus the PN junction - supply
your own 2N3904 with base tied to collector for best results) that has
a parasitic reduction / elimination mode which is extremely useful for
measuring die termperatures when the transistor has been integrated on
chip..

That device has accuracy of 1C (but again, only across a limited
range).

Cheers

PeteS
 
M

mike

Jan 1, 1970
0
Robert said:
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

--
Wanted, Serial cable for Dell Axim X5 PDA.
Return address is VALID but some sites block emails
with links. Delete this sig when replying.
FS 500MHz Tek DSOscilloscope TDS540 Make Offer
Bunch of stuff For Sale and Wanted at the link below.
MAKE THE OBVIOUS CHANGES TO THE LINK
ht<removethis>tp://www.geocities.com/SiliconValley/Monitor/4710/
 
riscy said:
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.

It helps if you use AC - or at the very least, reversing DC excitation.

You can only put a limited amount of current through a Pt resistance
sesnsor before self-heating becomes a problem - 1mA through 100R is
typical, giving you a voltage drop of 100mV. As the resistance of a Pt
resistor changes by about 0.4% per degree Celcius, measuring to 0.1C
involves resolving a voltage difference of 40uV.

You can buy interchangeable thermistors from Yellow Springs Instruments
(YSI) which are good to +/-0.05C from the YSI 4604x series (where x can
be 0,1,3,4,6 or 7).

Newark stock the 46046 as part number 52F9276 - and want $187.20 for
each part. they are sold out at the moment and the lead time is
currently 74 days. This part has a resistance of 10k at 25C.

The power you can dissipate in a thermistor is limited, both by
self-heating, and - usually more important - by the nasty tendency
thermistors have of giving unstable resistance values when they are
dissipating too much power. I usually limit the dissipation to 10
microwatts, but people using thermistor as sensors in microdegree
controllers have chosen to hold this as low as 2uW (to get measured a
stability of +/-15uC).

10uW in in 10k is a voltage drop of 316mV, and since thermistors
typically have a temperature ocefficient of 4% per degree Celcius, your
0.1 degree change corresponds to a change of 1.25mV in this voltage -
not too difficult to measure.

A cheaper, lower tolerance thermistor can be calibrated to +/-0.1C
accuracy with a single point calibration in a well-stirred ice bath,
where the thermistor is completely immersed in crushed ice (made from
distilled water) through which distilled water is being foced to
circulate. When you set up one of these baths correctly, you get a
stability and accuracy of the order of a few milli-degrees.
 
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
 
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
 
S

Spehro Pefhany

Jan 1, 1970
0
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?

You'll be lucky to get within several degrees C in boiling water, let
alone 0.1°C. That's almost two orders of magnitude off.
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?

You can also buy a "Class A" RTD sensor. It will be within +/-0.15°C
at 0°C and +/- 0.35°C at +/- 100°C. You can calibrate your instrument
to much better than that with ordinary precision electronic equipment.
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?

It's difficult. The glass thermometer requires immersion to a certain
depth in liquid in order to read correctly. You could conceivably (and
with significant care) use that for calibration.
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" ?

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


Best regards,
Spehro Pefhany
 
B

Bob Masta

Jan 1, 1970
0
I'm pretty new to thermal sensing and such, but I have a friend who
wishes me to make/aquire 3 types of temperature sensors, all with
greater than .1 degree celsius accuracy.

1) Ambient temperature
2) Contact temperature
3) Radiation temperature (a "directional" sensor of sorts which detects
IR radiation coming from a source). A further requirement is that if
this sensor (or array of sensors) can tell me the temperature /amount
of radiation in each Thermal IR band within 8.125 to 11.60 Micrometers
(total 5 bands within this bandwidth)(This should preferable correspond
to a satellite sensor band seperation, as he is doing some urban heat
phenomenon research).

I've done some experiments with NTC Thermistors before-I did some
interfacing to the PC joystick port. I thought maybe I can use the same
NTC thermistor for the above uses? Is the thermistor meant for "such"
sensitive work? (If I uses a better ADC)..and can I modify it in some
way to measure the radition temperature as well? (by adding some sort
of parabola?!)

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.

Forget thermistors. If you want cheap and accurate, the best
thing is a plain old PN junction. Apply a constant current, and
measure the voltage. Calibrate in ice water and boiling water.
This approach is extremely linear, but like all approaches
at this kind of accuracy requires extreme care. For instance,
it will be no more accurate than the constant current source,
and those tend to drift. The current can cause self-heating.
And it is not as simple as it sounds to do a good ice water
and boiling water calibration, since there will be impurities
in the water that change the temperatures, etc.

The modern solid state approach uses a switched current
through the junction, where the ratio of the higher current
and lower current are well characterized (precision resistors
controlling the current source, etc). This method is used
to provide absolute as well as relative accuracy, so you
don't typically need to calibrate. But you could probably
use one of these chips and supply your own calibration
to get the desired accuracy.

Best regards,


Bob Masta
dqatechATdaqartaDOTcom

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Home of DaqGen, the FREEWARE signal generator
 
Top