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Author Topic: Help requested for temperature sensor calibration  (Read 5303 times)

Offline s3370389

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Help requested for temperature sensor calibration
« on: December 28, 2014, 05:11:11 AM »
Hi all,

My university did not provide any metrology courses as part of my degree, and our lab experiment sessions are not very hands on, unfortunately. Thus, I am a bit out of my depth. I need to calibrate some temperature sensors as part of my mechanical engineering internship.

I have an 8 channel data acquisition unit with 8 assorted sensors attached: SMDs, RTDs, and general purpose probes. I submerged these sensors into a bath of ice water, and later a bath of boiling water in order to set baselines for zero degrees and one hundred degrees Celsius. I will be redoing the ice water bath and the boiling water bath as I am not satisfied that I did these properly the first time around. I have confirmed that all sensors are working by monitoring their real-time temperature readings as I held them between my fingers.

Shown below in Figure 1 is the data output for the ice water submersion. I will ignore the boiling water for the time being.

Figure 1: Logged temperature data from ice water bath.

[figure1.jpg][/figure1.jpg]

This is what I think I need to do next: select a time slice near the beginning of the submersion so that I know that the water is still as close to zero degrees as possible (the time slice that I am proposing to use is shown below in Figure 2), and find the mean value of each of the temperature sensors for the example time slice.

Figure 2: Proposed time slice for determining mean values for each sensor. I feel that this time slice is too larger, however. A slice from the 200 second mark to the 300 second mark may be more appropriate?

[figure2.jpg][/figure2.jpg]

The mean value will then be an offset that I will need to subtract from my measured data (my measured data being logged temperature measurements after the calibration has been completed). For example: if I measure 20 degrees Celsius on sensor 3 (and the mean value during calibration for the ice water was 3 degrees Celsius) then I would need to do 20 – 3 Celsius to determine the actual temperature is 17 degrees Celsius.

I am pretty uncertain of most of the things that I have proposed above, so I would greatly appreciate any input.

[I seem to be having trouble posting the images to the appropriate place in the text. I've searched through the online help but cannot find a method to doing this.]

Best regards,
s3370389

Free Energy | searching for free energy and discussing free energy


Offline MarkE

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Re: Help requested for temperature sensor calibration
« Reply #1 on: December 28, 2014, 05:15:00 AM »
For every ice bath calibration there is an equilibrium:  Turn, turn, turn.

Offline s3370389

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Re: Help requested for temperature sensor calibration
« Reply #2 on: December 28, 2014, 06:18:32 AM »
For every ice bath calibration there is an equilibrium:  Turn, turn, turn.

Okay, thanks MarkE. I will ensure to stir the ice bath when I redo the calibration after the Christmas break. Can you give any suggestions as to the rest?

Thanks.

Free Energy | searching for free energy and discussing free energy

Re: Help requested for temperature sensor calibration
« Reply #2 on: December 28, 2014, 06:18:32 AM »
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Offline MarkE

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Re: Help requested for temperature sensor calibration
« Reply #3 on: December 28, 2014, 06:26:17 AM »
There are plenty of college tutorials on basic temperature calibrations.  If there is some solid ice in a well stirred water bath, then the bath is at 0C.  Keeping the bath stirred is the important part.

Offline s3370389

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Re: Help requested for temperature sensor calibration
« Reply #4 on: December 28, 2014, 07:42:34 AM »
There are plenty of college tutorials on basic temperature calibrations.  If there is some solid ice in a well stirred water bath, then the bath is at 0C.  Keeping the bath stirred is the important part.

Thanks, MarkE. What about my proposed method of finding the mean offset for each temperature sensor and then subtracting from any measurements to determine the actual temperature? Or is that incorrect?

Regards,
s3370389

Free Energy | searching for free energy and discussing free energy

Re: Help requested for temperature sensor calibration
« Reply #4 on: December 28, 2014, 07:42:34 AM »
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Offline MarkE

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Re: Help requested for temperature sensor calibration
« Reply #5 on: December 28, 2014, 08:24:59 AM »
A two point calibration gives you slope and offset for each sensor.

The reliability of the values depends on how repeatable the raw calibration values are.  Measure carefully, measure often, hold conditions as pristine as possible.  To the extent that you have truly random noise, averaging more measurements will help remove the noise from the calibration.  Ditto for live measurements.  A problem that is often encountered is that things that are not random seem random because they are not recognized as being associated with something else going on.  Averaging lots of measurements do not reliably attenuate noise from deterministic sources.  When measuring temperature in a room, air currents of all kinds can disturb measurements, (ventilation on/off, doors opening and closing, people walking by ... ) as can the sun shining through a window, etc.

Offline s3370389

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Re: Help requested for temperature sensor calibration
« Reply #6 on: December 29, 2014, 03:12:17 AM »
A two point calibration gives you slope and offset for each sensor.

The reliability of the values depends on how repeatable the raw calibration values are.  Measure carefully, measure often, hold conditions as pristine as possible.  To the extent that you have truly random noise, averaging more measurements will help remove the noise from the calibration.  Ditto for live measurements.  A problem that is often encountered is that things that are not random seem random because they are not recognized as being associated with something else going on.  Averaging lots of measurements do not reliably attenuate noise from deterministic sources.  When measuring temperature in a room, air currents of all kinds can disturb measurements, (ventilation on/off, doors opening and closing, people walking by ... ) as can the sun shining through a window, etc.

This calibration will be done in a clean room. But I will give this some thought.

After I have redone the ice-bath I will post the graph to show the effects of stirring, if anybody else is interested.

Thanks MarkE for taking the time.

Regards,
s3370389

Free Energy | searching for free energy and discussing free energy

Re: Help requested for temperature sensor calibration
« Reply #6 on: December 29, 2014, 03:12:17 AM »
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