I am creating a new type of photoacoustic measurement device, but I realized through doing said experiment that I need to correct for swings in temperature (for the Grunesian coefficient) due to the large quantity of air flow that is occurring in the laboratory I work in, which cannot be shut off due to safety regulations.
I would put the setup inside a sealed or insulated box but the setup is rather large (1/4 size of an optical table). As for measuring the temperature with a physical probe, I'm unsure where to place it since I cannot physically attach it to the piece I am irradiating since it would melt the probe, etc. and attaching it to a nearby location won't accurately read out the temperature of the material. Additionally, I do not have access to an accurate infrared thermal imaging diode.
If you can attach a thermocouple there are very high temperature devices in the Omega catalog. Get some advice from someone in your Mech Eng department on how to attach the TC to your sample - this can be critical to obtaining an accurate measurement. If needed you can insulate the wires from the TC using ceramic beads.
Otherwise IR imaging is your best solution.
You may want to consider using a digital temperature sensor such as the Burr-Brown TMP121 sensor.
I don't know anything about photoacoustics, but you could try taking temp measurements and including them as a covariate if youre doing an ANOVA analysis at the end (using TYPE2 Sum of Squares).
Many PA cells are enclosed in an environmental chamber. Some of the classic (read old) comercial cells for FTIR had temperature controllers. Temperature controllers for spectroscopy sample cells are commercially available. These are necessary for precise measurement because the sample temperature increases due to the average optical heating of modulated light sources. The sample does reach a steady state temperature and this is a function of both convective and diffusive heat transfer. So again, an environmental chamber is essential. If you are using pulsed periodic excitation, then sample heating is not as much of a problem.
Could you specify the times scales of your measurements and of the temperature changes (I assume you are actually observing the change in PA signal) you are observing? Have you checked the pulse-to-pulse variability in your laser energy output. Is it possible that you are mistaking fluence-related change in PA amplitude for large and rapid swings in temperature? Continued exposure to laser pulses, particularly those at high energies, also will elevate in situ temperature slightly.
Either way, you can get needle or wire thermocouples from Omega that can withstand relatively extreme temperatures.
If you do not want to insert probes in your sample, another method for tracking temperature fluctuation in real-time is by observing change in sound speed of your sample. I don't know what sample you are testing, but some polymers have a linear relationship between temperature and sound speed. Thermometry using sound speed also is well established in biomedical applications. You can use your photoacoustic sensor in pulse-echo mode (interlaced) and directly record time-of-flight of the acoustic pulse to infer sound speed as a function of time, or use another acoustic transducer to do this job.
You've described the problem quite undetailled. I understand that you don't want to share secrets but this way nobody can really help you.
To help you some more information is needed:
What is the desired temperature? of the cell? of the sample?
What is the volume of he PA cell and of the acoustic resonator?
Is the sample gas, fluid or solid? in case of gas or fluid is it flown through the cell continously or is it just encolsed inside? In case of flow at what speed?
How big is the setup? (in cm)
What is the Q factor of the PA cell?
In our PA measurements we use relatively low Q factor cells mounted on an aluminium plate, where the plate is equipped with a resistive heater and controlled by PWM algorythm with feedback of a pt100 temperature sensor. (Other sensors would be also great.)
Dear Benjamin Goldschmidt!
[The joke begins] Dear Gold … Ben … & Big Ben [A joke comes to an end]. For this purpose, to stabilize temperature in important experiments it is necessary to consider two parameters: 1) existence of the closed camera that in the camera didn't pass the streams of air created by fat research associates and employees when they go back and force in scientific laboratory 2) additional big and in a large number thermostatic elements which should be built the Chinese wall around precision photoacoustic measurements and experiments.
[The joke proceeds]. First of all for good thermostabilization, ask the wife of your research supervisor that she unscrewed the thermostat from the car of her husband and give it to you. It is known that automobile thermostats well stabilize temperature for acoustic experiments.
There is still the second, alternative option. Dear Benjamin Goldschmidt you go to a supermarket and there you buy 10 Coca Cola cans and 10 cans of Pepsi - Coca, however instead of Coca-Cola it is possible to take 10 cans light, and instead of Pepsi Cola of 10 cans of dark beer. All these purchases should be put in the plastic package, as big a possible. When you will come to laboratory please cover by a package from a supermarket your photoacoustic experiment, and also under a package put cans bought by you and temperature will be stabilized during 8 - 10 hours.
Sincerely yours,
Alexander Yurkin
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