6.9
How the Genius Derives the Temperature of an Infrared Target
1. Genius uses an infrared sensing device called a "thermopile detector" to measure infrared emissions from a
target such as the tympanic membrane in the ear.
2. The thermopile is best described as a series of thermocouples, arranged around a blackened, "heat collecting"
surface. The thermopile operates by outputting a voltage level, which is a function of the difference in
temperature between the thermocouple "cold junctions" and the hot or "sensing junctions."
3. When the thermopile is pointed at a radiating target, energy strikes the blackened area inside the detector,
causing a temperature differential between the sensing area and the cold junctions.
4. If we know the sensitivity of the thermopile, in terms of change of voltage output per degree of differential
temperature (t. sensing junc. - t. cold junc.), and the temperature of the cold junction is known, then a
formula can be derived to calculate target temperature.
6.10 Equivalence
If a patient's temperature were measured at four sites simultaneously: oral, rectal, arterial, and an infrared
reading of the ear canal, you would get four separate but correlated readings.
There are two reasons an infrared reading in the ear canal is lower than core (arterial) temperature:
1. The ear is not a perfect "black body". In a perfect "black body", one hundred percent of the energy from a
radiating object is emitted. In the ear canal, this is not so.
2. There is some heat loss down the ear canal due to thermal gradients.
By adding linear corrections, Genius is able to compensate for the two conditions described above. These linear
corrections were based on extensive, non-biased, clinical study. By calibrating these corrections to ambient
temperature, the problem described in condition 2 is minimized.
6.11 Pre-Scan Buffer
Because the probe tip of the Genius is not heated as in the First Temp Model 2000A, a new factor presents
itself. Since heat energy will always travel from a warmer object to a colder object, the cold probe tip will act as
a "heat-sink" to the ear canal, thus lowering the temperature in the outer portions of the ear canal. When the
Genius probe is inserted into the ear, the infrared detector sees a peak temperature in a matter of milliseconds.
Then, the peak rapidly drops off because of the heat-sinking effect of the cold probe. We call this "draw-down."
Normally, this effect of draw-down would make it very difficult to get an accurate infrared reading of the ear
canal without missing the peak.
However, this condition is remedied by use of a unique "Look-Ahead" feature in the Genius software:
1. When the user installs a disposable probe cover on the Genius probe tip, if the unit is set to "TYMPANIC"
mode, it will immediately start to scan for a peak temperature, before the probe is actually inserted into the
ear canal.
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