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Asia-Pacific Forum on Science
Learning and Teaching, Volume 5, Issue 2, Article 5 (Aug., 2004) Isaac Pak Hoi TSE, Winston Kwok Kuen LEUNG and Shing Yi CHAN Science, Technology and Society - An authentic exploration on IR thermometers application in schools
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Our Sequence of Investigations
With any artificial electronic device, the first thing scientists trained was to learn about zero adjustment and calibration. We demand the device to be consistent in its reading within a known range of detection. If it functions but fails to be consistent, or if its readings drop consistently, we check battery voltage input. The simplest remedy is to change for new batteries. If these were not good enough, we suspect consistency of user in applying these handheld devices.
With these tentative hypotheses in mind, we tackled suspected reasons of fluctuations, which include:
(1) Battery voltage drop after current consumption has reached a certain level
(2) Low quality and/or poor stability of the device
(3) Ambient temperature fluctuations where the device is being used
(4) Skill of the operators holding these handheld devices
(5) Specifications requirement of the device not observed when being usedWe put forward our study in the report in web html format in order to be as reader friendly as we could. Web browsers offer a convenient "PREVIOUS" button within the "Standard Buttons" tool bar at the top left corner of the current window for quick return to where the reader clicks a hyper-link. Press this button instead of scrolling up and down with mouse keys. We anticipate including senior secondary students as our potential readers too. We falsified hypotheses 1 and 2 using the Data-Logger.
Using a 3Kg cast iron block as proxy of a human head, our results (Fig. 1-3) confirmed that the IR non-contact thermometer devices were calibrated to acceptable standard, which is the linear readings displayed between 20°C and 55°C (Section 1 of the html report).
In Section 2 of the html report, we proved that there is no significant difference in performance by using a fresh battery or a spent one. Voltage drop was not a burning issue.
In Section 3 of the html report, we disproved the possibility of internal warming of the thermometer or any other internal fault that might cause declining stability of the device while operating a prolonged time beyond the session it was originally designed.
The repeated tests in Section 4 of the html report confirmed that cool air blowing towards the target of temperature measurement (Fig. 4) or even blowing hot warm air towards the target (Fig. 5-7) do not significantly affect the performance of the IR non-contact thermometer.
Investigation on the physical dimension of the artificial device comes to a temporary end. The next target of suspect would be human factors, namely, the handgrip and attitudinal variations (Fig. 8).
Our results in Section 5 provide clues for possible source of deviations, focused aiming and casual targeting of the hand held device make some difference despite an undetectable tilt of 9 degree in perspectives (Fig. 9). The print on the hand-held device (Pic C) then arrested our attention. The invisible IR emission should obey the Inverse Square Law, but not the visible laser beam for focusing.
The operation manual stipulated that a "Distance to Spot Ratio" requirement should be observed; and that the detection area must be larger than the required spot size stipulated in order to get correct readings. This has been ignored. Biologists among us then recalled that surface temperature distribution of the forehead is not uniform as shown in the thermographic image (Fig. 11). The reading shown on display offers the AVERAGE temperature of the detected region. If the object to be measured cannot fill up the Field of View for the detection spot (Positions S2, S3, S4 and S5 of Fig. 9), unpredictable errors easily occur (Pic D). For example, if the diameter of the spot with consistent body temperature on human forehead was only about 40mm, the device should thus be placed at about 320mm away from the detected region all the time in accordance with the specification requirement of the model used.
By inspecting another similar product in the market, we learned further that we could easily be fooled by our own mindset towards known range of output. Product capability claimed by the advertisers and local sales agents could be totally different from the technical advice of the manufacturers. Maybe we have discovered the need for a purpose built, speedy, handy and portable technical device to measure human forehead temperature as a marketable health protection product for a contagious disease conscious society.
Copyright (C) 2004 HKIEd APFSLT. Volume 5, Issue 2, Article 5 (Aug., 2004). All Rights Reserved.
