发烧预测(1)

Sticking a thermometer into an armpit, mouth, ear or other body cavity is the most accurate way to take someone's temperature. Understandably, though, this cannot be done at airports or checkpoints set up elsewhere to screen the masses for feverish victims of covid-19. So, in a bid to detect the warmth produced by a fever without touching any bodies, officials have opted for alternatives.
The hand-held "thermometer guns" now ubiquitous in China, among other places, are one option. These instruments, known technically as spot pyrometers, use a device called a bolometer to estimate an object's temperature.
A bolometer's electrical resistance depends on how hot it is. That, in turn, depends on the amount of infrared radiation fllig on it from whatever it is pointing at.
Spot pyrometers are used widely in industry to check equipment for signs of overheating, but the infrared signals they rely on can be muddled by dust, moisture, smoke, a change in ambient temperature,
a smudge on the device's lens or even by radio signals. Beyond all this, an official checking a stream of foreheads may, for reasons of personal safety,
be reluctant to hold the gun close enough to obtain an accurate reading. An alternative technology, the thermal camera, is costlier. But it can operate from farther away.
Instead of a single bolometer, it has an array of them. These form the pixels which generate the camera's image, thus building up a heat map of whatever that camera is looking at.
One popular thermal camera, the A320, made by FLIR Systems, an American firm, can detect variations in radiation which correspond to temperature differences within an image of just 0.02"C.
But this merely shows whether one part of the object being examined is warmer or cooler than another. When measuring the object's actual temperature, the A320 is accurate only to about 2°C, says Giovanni Scaglia, FLIR's head of sales in Italy.
For a single reading, this is enough to mistake normal body temperature for a raging fever. In practice, however, the camera's software looks for deviations from the average temperature of passers-by.
Those noticeably hotter than their fllows can then be selected for closer investigation.