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

6:1 and 12:1, with various distances. (Note:

The ratio is calculated in millimeters, so the

standard inch measurements only approxi-

mate the ratio.)

Generally you will want to measure the

temperature of a small target, such as an elec-

trical termination, so a larger distance-to-spot

ratio is better, providing you with the flexibility

to take accurate measurements from a greater

distance.

In practice, I have found a 6:1 ratio to be

satisfactory for boat work. (The Extech unit

shown in this chapter has a 6:1 ratio, which

limits its useful distance to a maximum of

about 4 feet/1.2 m; otherwise the sample area

gets too large.) I’ve found this distance to be

quite satisfactory for anything I’ve ever needed

around boats. As I’m typically checking the

temperatures at wire and cable termination

points or along the length of a conductor,

I don’t need a long range, nor do I want to

cover a very large area in my measured sample.

62 electrical systems troubleshooting

S

29 mm @

150 mm

38 mm @

300 mm

57 mm @

600 mm

1.1“

@ 6”

1.5“

@ 12”

2.3“

@ 24”

D

S

25 mm @

150 mm

50 mm @

300 mm

100 mm @

600 mm

1“

@ 6”

2“

@ 12”

4“

@ 24”

D

infrared

heat sensor gun

infrared

heat sensor gun

__D

S

__^6

1

• – __D
  S
  
  
  • – __^12
    1
  
  
  
  

D = distance S = spot size D = distance S = spot size

area of coverage area of coverage

Infrared distance-to-spot ratios for both a 6:1 and 12:1 configuration.

Using an Infrared Heat Gun

Learning to operate an infrared heat-sensing

gun is relatively easy. However, knowing how

to use it and interpret the results is a bit more

complicated. Here are some important points

to keep in mind:

• As noted earlier, electrical resistance pro-
  duces heat. An electrical problem often
  results in increased resistance, and thus
  increased heat. So we are looking for
  abnormal heat readings, not necessarily
  high temperatures, because as we all
  know, some electrical devices normally
  run hot during operation.


• A change in temperature (for example,
  from one point in the circuit to another)
  is more important than the temperature
  reading on the heat gun. In other words,
  we are looking for a temperature differen-
  tial. (The actual average temperature will
  vary depending upon ambient temperature