TMP006 heating affect

Sheng Luo

Other Parts Discussed in Thread: TMP006

Hi,

I have set up a box embedded a TMP006 sensor. The box has a hole which is in front of TMP006. The hole size is 40mm of diameter.
The distance from hole to TMP006 is about 13mm.
My application is to measure water temperature in the cup. I put a cup of hot water on the hole (the cup is bigger than the hole).
Although I have posted data measured in this forum before, I intend to post it in new thread because I have new questions.
Below are some TMP006 data read from registers. A complete spreadsheet can also be found here
3858.TMP006 Calibration(luo).xls

T_water   V_object(00)   T_ambient(01)
(degree)
67       0x01CA         0x0ACC
60       0x0143         0x0A82
55       0x00BF         0x0A6A
49       0x0058         0x0A47
42       0xFFEB         0x09F1
37       0xFFCB         0x09DD
31       0xFF5D         0x0A0C

I have done S0 calibration and found it did not converge. Especially, Tdie was affected by hot water. The room temperature is 14 degree.
But I noticed that Tdie was about 20 degree. Furthermore, the calculated result changed gradually as TMP006 was warmed by the hot water.
It would spend about several minutes to be steady until heat stability was established. So, it seemed that TMP006 was slow from customer point of view.

To eliminate warming effects, I tried to introduce Fresnel lens between the cup and TMP006. Vobject became smaller than before. My questions are
1) I have problem with S0 calibration. I think something wrong with my test platform. Did you have any video to describe each S0 calibration steps that you have done in your lab?
2) How to make TMP006 calculation result stable and fast? Compensating result from heating or isolating heat from hot water?
3) Is it feasible to add Fresnel lens? If yes, how to install TMP006, Fresnel lens and measured object?

Best regards,

Luo Sheng

over 12 years ago

0 John Caldwell over 12 years ago

TI__Genius 12325 points

Sheng,

I'll start with your last question first, a Fresnel lens is feasible if the material that the lens is made out of transmits IR in the 4-8 micron wavelengths. See this thread for in-depth discussion of lens materials: http://e2e.ti.com/support/other_analog/temperature_sensors/f/243/t/117229.aspx Polypropylene is the most commonly recommended material as it offers a good compromise between price and transmission performance. An additional consideration is that the TMP006 must be placed at the focal point of the lens, as is true for all lenses. Either improper positioning or the transmission characteristics of the lens material could be responsible for the reduced object temperature that you experienced.

The S0 calculation spreadsheet that Ian posted to your other thread is really the best method to perform the calculation. Because it takes your measurement several minutes to reach a stable state, that indicates that you are measuring something being heated by the water instead of the water itself. Remember that any barrier between the TMP006 and the measurement object must be transparent to IR energy, in this case is the cup transparent to IR?

0 Sheng Luo over 12 years ago in reply to John Caldwell

Intellectual 430 points

Hi Caldwell,

Thanks for your clarifications.

I think question (2) is still open. Let me describe it in detail. When hot object is placed in front of TMP006 for several minutes, Tambient will grow higher gradually, for example, from 12 degree to 24 degree. This is issue. It may have big impact on calculation result. Does SBOU107 take into account heating affect? What is impact on calculation result?

Best regards,

Luo Sheng

0 John Caldwell over 12 years ago in reply to Sheng Luo

TI__Genius 12325 points

Sheng,

Yes, local heating will affect the calculation result. One method to improve the accuracy is to use a transient correction calculation as described in the attached document, created by my colleague Ian Williams.

Transient Correction.pdf