Advanced Marine Electrics and Electronics Troubleshooting A Manual for Boatowners and Marine Technicians

61

Infrared Heat-Sensing Gun

So what should you look for when choosing a
heat-sensing gun? Two specifications are
important: temperature range, and distance-
to-spot ratio.

Temperature Range

The most important specification is the heat
gun’s temperature range. Some inexpensive

temperature monitoring

units have a range from slightly below 0°F to

500°F or so (–18°C to 260°C), which is fine

for electrical troubleshooting and work on air-

conditioning and refrigeration systems. How-

ever, if you intend to use the gun for other

areas of troubleshooting as well, such as look-

ing for temperature variations between cylin-

ders on engines or tracing coolant flow

through the engine’s cooling system, you may

want to spend a little more and get a unit that

can read up to 1,000°F (538°C) or even

higher. (Typical operating temperatures of

cylinders and exhaust systems can exceed

1,000°F.) It’s also useful if the unit displays

results both in degrees Fahrenheit andCelsius

(outside the United States, Celsius is the

temperature-measuring unit of choice, and

equipment manufacturers may list perfor-

mancespecifications in either units).

The RadioShack model listed in the sidebar

will work fine for electrical troubleshooting, but

its measurement scale (0°F to 400°F/–18°C

to 204°C) may not be sufficient for the entire

range of applications discussed here. For

engine work, exhaust systems, and other high-

temperature applications, look for a unit with a

range of approximately 5°F to 1,000°F (–15°C

to 538°C).

Distance-to-Spot Ratio

The second specification to consider is the

device’s distance-to-spot ratio, which is the ratio

of the distance to the object (D) to the diameter

of the infrared beam (S), or D:S. Simply put, as

the infrared beam moves farther away from the

gun, the diameter of the beam widens. Conse-

quently, as the effective width of the infrared

beam increases, the device measures tempera-

tures across a larger area. For example, with a

12:1 ratio, if you aim at a spot 24 inches away,

the diameter of the beam at the spot will be

roughly 2 inches; with a 6:1 ratio, if the meter

is 12 inches from the target, the diameter will

be 2 inches. The illustration shows two ratios,

The Extech #42520 infrared heat-sensing gun. (Note: This
model was recently replaced by model #42500.)