Page 183 - Intro Predictive Maintenance

174 An Introduction to Predictive Maintenance

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E = A = .7 R = .3 T = 0

Figure 8–3 Graybody emissions. All bodies that are not
blackbodies will emit some amount of infrared energy. The
emissivity of each machine must be known before implementing
a thermographic program. A = Absorbed energy. R = Reflected
energy. T = Transmitted energy. E = Emitted energy.

ables in the surrounding atmosphere can distort measured infrared radiation. Because
the atmospheric environment is constantly changing, using thermographic techniques
requires extreme care each time infrared data are acquired.

8.2 TYPES OF INFRARED INSTRUMENTS
Most infrared-monitoring systems or instruments provide special filters that can be
used to avoid the negative effects of atmospheric attenuation of infrared data; however,
the plant user must recognize the specific factors that will affect the accuracy of the
infrared data and apply the correct filters or other signal conditioning required to
negate that specific attenuating factor or factors.

Collecting optics, radiation detectors, and some form of indicator are the basic ele-
ments of an industrial infrared instrument. The optical system collects radiant energy
and focuses it on a detector, which converts it into an electrical signal. The instru-
ment’s electronics amplifies the output signal and processes it into a form that can be
displayed. Three general types of instruments can be used for predictive maintenance:
infrared thermometers or spot radiometers, line scanners, and imaging systems.

8.2.1 Infrared Thermometers
Infrared thermometers or spot radiometers are designed to provide the actual surface
temperature at a single, relatively small point on a machine or surface. Within a pre-
dictive maintenance program, the point-of-use infrared thermometer can be used in
conjunction with many of the microprocessor-based vibration instruments to monitor
the temperature at critical points on plant machinery or equipment. This technique
is typically used to monitor bearing cap temperatures, motor winding temperatures, spot