Engineering

Taking a peek inside an infrared thermometer



Back in September, within the introduction to my teardown of a pulse oximeter, I wrote:

One upside, for lack of a better word, to my health setback [editor note: a recent, and to the best of my knowledge first-time, COVID infection over the July 4th holidays] is that it finally prompted me to put into motion a longstanding plan to do a few pandemic-themed teardowns.

That pulse oximeter piece was the kickoff to the series; this one, a dissection of an infrared thermometer, is the second (and the wrap-up, unless I subsequently think of something else!). These devices gained pervasive use during the peak period of the COVID-19 pandemic, courtesy of their non-contact subject measurement capabilities. As Wikipedia puts it:

At times of epidemics of diseases causing fever…infrared thermometers have been used to check arriving travelers for fever without causing harmful transmissions among the tested. In 2020 when [the] COVID-19 pandemic hit the world, infrared thermometers were used to measure people’s temperature and deny them entry to potential transmission sites if they showed signs of fever. Public health authorities such as the FDA in United States published rules to assure accuracy and consistency among the infrared thermometers.

And how do they work? Wikipedia again, with an introductory summary:

An infrared thermometer is a thermometer which infers temperature from a portion of the thermal radiation sometimes called black-body radiation emitted by the object being measured. They are sometimes called laser thermometers as a laser is used to help aim the thermometer, or non-contact thermometers or temperature guns, to describe the device’s ability to measure temperature from a distance. By knowing the amount of infrared energy emitted by the object and its emissivity, the object’s temperature can often be determined within a certain range of its actual temperature. Infrared thermometers are a subset of devices known as “thermal radiation thermometers”.

 Sometimes, especially near ambient temperatures, readings may be subject to error due to the reflection of radiation from a hotter body—even the person holding the instrument—rather than radiated by the object being measured, and to an incorrectly assumed emissivity. The design essentially consists of a lens to focus the infrared thermal radiation on to a detector, which converts the radiant power to an electrical signal that can be displayed in units of temperature after being compensated for ambient temperature. This permits temperature measurement from a distance without contact with the object to be measured. A non-contact infrared thermometer is useful for measuring temperature under circumstances where thermocouples or other probe-type sensors cannot be used or do not produce accurate data for a variety of reasons.

Today’s victim, like my replacement for the precursor pulse oximeter teardown subject, came to me via a May 2024 Meh promotion. A two-pack had set me back only $10, believe it or not (I wonder what they would have cost me in 2020?). One entered our home health care gear stable, while the other will be disassembled here. I’ll start with some stock photos:

Now for some as-usual teardown-opening box shots:

Speaking of opening:

The contents include our patient (of course), a set of AA batteries (which I’ll press into reuse service elsewhere):

and a couple of slivers of literature:

Now for the star of the show, as usual accompanied by a 0.75″ (19.1 mm) diameter U.S. penny for size comparison purposes (the Meh product page claims that the infrared thermometer is “small” and “lightweight” but isn’t any more specific than that). Front:

They really don’t think that sticker’s going to deter me, do they?

Back:

A closeup of the “LCD Backlit display with 32 record memory”, with a translucent usage-caution sticker from-factory stuck on top of it:

Right (as defined from the user’s perspective) side, showcasing the three UI control buttons:

Left:

revealing the product name (Safe-Mate LX-26E, also sold under the Visiomed brand name) and operating range (2-5 cm). The label also taught me something new; the batteries commonly referred to as “AAs” are officially known as “LR6s”:

Top:

Another sticker closeup:

And bottom, showcasing the aforementioned-batteries compartment “door”:

Flipping it open reveals a promising screw-head pathway inside:

although initial subsequent left-and-right half separation attempts were incomplete in results:

That said, they did prompt the battery-compartment door to fall out:

I decided to pause my unhelpful curses and search for other screw heads. Nothing here:

or here:

Here either, although I did gain a fuller look at the switches (complete with intriguing connections-to-insides traces) and their rubberized cover:

A-ha!

That’s more like it (complete with a trigger fly-away):

I was now able to remove the cap surrounding the infrared receiver module:

Followed by the module itself, along with the PCB it was (at the moment) connected to:

Some standalone shots of the module and its now-separated ribbon cable:

And of the other now-disconnected ribbon cable, this one leading to the trifecta of switches on the outside:

Here’s the front of the PCB, both in with-battery-compartment overview:

and closeup perspectives, the latter more clearly revealing its constituent components, such as the trigger switch toward the bottom, an IC from Chipsea Technologies labeled “2012p1a” toward the top, and another labeled:

CHIPSEA
18M88-LQ
2020C1A

at the top (reader insights into the identities of either/both of these ICs is greatly appreciated):

And here’s the piezo buzzer-dominant, comparatively bland (at least at first glance) backside:

which became much more interesting after I lifted away the “LCD Backlit display with 32 record memory”, revealing a more complex-PCB underside than I’d originally expected:

That’s all I’ve got for today. What did you find surprising, interesting and/or potentially underwhelming about the design? Let me (and your fellow readers) know in the comments!

—Brian Dipert is the Editor-in-Chief of the Edge AI and Vision Alliance, and a Senior Analyst at BDTI and Editor-in-Chief of InsideDSP, the company’s online newsletter.

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