STC SmartScanIS, User Manual

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14 January 2021, SmartScanIS User’s Guide for Union Pacific, EUD-2016026-00 Rev.2
When a bearing passes through the field of view of the scanner, a rapid change in temperature
is presented to the internal lithium tantalite crystal. This causes the signal level from the
pyrometer to increase proportionally to the amount of exposed infrared energy. When an axle
is between the gating transducers, the pyrometer signal is sampled at every 1/2 inch
(1.27 centimeters) of wheel movement for a total of 48 samples and the maximum signal level
is stored. This signal level, measured in volts, is converted to a digital value and expressed in
degrees Fahrenheit above ambient temperature. This value is the basis for the alarm analysis
done by the system.
10.7.3 Pyrometer Linearity
The output of the pyrometers is linear across most of the operating speed range of the system.
However, the output of the pyrometers is nonlinear at either end of the operating speed range.
To compensate for this nonlinear output, the firmware applies a correction factor to the
sampled heat value. The correction factor applied to each bearing sample is based on the
speed of the bearing (axle's on time) as it passed through the gate and on the actual value
read by the pyrometer. The correction factor is derived from a table that is keyed by the axle's
on time and heat value. Due to the fast nature of this lookup table, linearity compensation is
done real-time so that detected alarms reflect the heat value after the linearity step has been
done.
10.8 Hotwheel Alarms
When used, wheel scanners are mounted in the center of the crib of two ties spaced at least
14 inches (35.6 centimeters) apart. Both wheel scanners are mounted in the crib between the
two gating transducers. They are mounted directly opposite each other, one on each rail of
the track. The hole on the top of the scanner covers faces the center of the track.