Infrared Thermometer

Overview

An infrared thermometer measures how hot something is without touching it. Every object above absolute zero radiates infrared energy, and the warmer it is the more it radiates; this instrument collects that radiation through a lens, turns it into a small electrical signal, and reports the surface temperature in well under a second. The gun shape lets a user point, pull a trigger, and read a number, which is why these are used for checking cooking surfaces, electrical panels, HVAC ducts, and machinery from a safe distance.

Radiation from the target passes through the IR Optics, which focus it onto a heat-sensing detector. The faint signal is amplified and converted to a temperature by the Signal Board, then shown on the Display. So the user knows exactly what is being measured, the Laser Aiming Module paints a visible dot at the center of the spot. The whole instrument is powered by an Li-ion Cell, 18650 cell, started by the Trigger Switch, and packaged in a molded Housing.

How it works

The IR Optics act like a camera lens for heat. An infrared-transmitting lens gathers radiation from a circular patch of the target and concentrates it onto a thermopile, a cluster of tiny thermocouples in series whose hot junctions sit on a blackened membrane. As that membrane warms relative to a built-in cold-junction reference, the thermopile puts out a voltage of just a few microvolts per degree. A field stop sets the distance-to-spot ratio, fixing how large the measured patch is at any range.

That microvolt signal would be lost in noise without conditioning, so the Signal Board amplifies it with a low-offset preamplifier and digitizes it. The microcontroller then applies two corrections: it adds back the ambient temperature read at the cold junction, and it divides out the target's emissivity, the fraction of a perfect blackbody's radiation that a real surface emits, to recover the true temperature. The result drives the Display.

Because the spot is invisible, the Laser Aiming Module collimates a visible diode into a dot that marks the patch being read. Pulling the Trigger Switch wakes the board, fires the laser, and holds the last reading when released.