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Ultrafast Temperature Measurement

Hello all,

for medical research purposes we are desperately looking for a good method to measure temperature very quickly. The most important thing is the time constant of the measuring system; it should be as low as possible. Microbead thermistors appear to be one possible solution but they have some problems, mostly mechanical ones.

We want to measure temperature in breath air, for example in ventilated patients. So there are flow and water vapour that will be dangerous for microbead sensors. Encapsulated ones are not suitable since their time constant is too high due to the encapsulation.

So there are two questions:

Is there an alternative to microbead thermistors for an ultrafast temperature measurement?

How can microbeads be protected against mechanical and chemical influences without prolonging the time constant by some encapsulation or things like that?

Any hint would be greatly appreciated.

Thank you very much for your efforts in advance and best regards

Gerd

Reply to
Gerd Roethig
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The time constant should be as low as possible. There are Thermometrics microbead sensors that are supposed to have a time constant of 10 ms in still air. Seems that this is the lowest possible value. They achieve this time constant by using a very low amount of material for the thermistor itself which makes that microbeads somewhat sensitive to environmental influences.

You're partially right - we really want to measure temperature changes caused by certain factors. But the system must react very fast to these changes - that's the problem.

Cheers,

Gerd

Reply to
Gerd Roethig

Wouldn't a thin platina wire be useful? Corrosion resistant and easy to warm up if there is any appreciable flow.

It is big, but you have the mass to be measured - and it will react quickly. How thin platina wire can one get? How wind resistant is it?

Thomas

Reply to
Zak

[snip]

In one of the Omega temperature measuring books there is a reference to: "The Measurement of Respiratory Air Temperature", by P Webb. Rev Sci Instrumentation, Vol 23, pp 232-234, May 1952.

He appears to have constructed a fine copper-constantan micro-thermocouple for use in nasal passages. Claimed results were 0.1C resolution, with the response time being 50% down at 200 milliseconds.

The Omega book is "Temperature Measurement in Engineering", Vol 2. Might be worth obtaining, because it describes various resistive, thermoelectric, and velocity of sound techniques that have claimed responses down to 1uS.

--
Tony Williams.
Reply to
Tony Williams

I suspect it could be done with IR spectroscopy to work out the water/CO2 content, then measuring the speed of sound. You would need also to measure the Oxygen in the incoming air. Measuring Argon and Nitrogen would be nice, but you could probably skip it, and go with just pressure.

This could have response times in the microseconds, but may not be very accurate.

The patient can't change temperature in 10ms, or even 1s significantly, unless they are on fire.

Are you trying to measure peak exhalation temperature, or pick up faults in the equipment?

Very fine platinum wires can be obtained, and you can accurately measure the resistance of these. This is somewhat complicated as you can't have significant current flowing through them due to self-heating causing large errors.

Condensation on the sensing element may also be a problem, depending on where it is.

--
http://inquisitor.i.am/    |  mailto:inquisitor@i.am |             Ian Stirling.
---------------------------+-------------------------+--------------------------
"The device every conquerer, yes, every altruistic liberator should be required
to wear on his shield... is a little girl and her kitten, at ground zero"
      -  Sir Dominic Flandry in Poul Andersons 'A Knight of Ghosts and Shadows'
Reply to
Ian Stirling

You could use two, and extrapolate the temperature of a currentless one from one with I and the other with 2I current.

Condensation... hmm. If the wire heats up a bit as above...

Thomas

Reply to
Zak

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