STC SmartScanIS, User Manual

Page: 66 / 391

66
14 January 2021, SmartScanIS User’s Guide for Union Pacific, EUD-2016026-00 Rev.2
4.6.1.18 Jumper J6
On the System Interface board, jumper J6 isn't for use by the customer. Rather, it is used at
the factory along with plug P7 to test the system. Therefore, do not short jumper J6.
4.6.1.19 Jumpers J-TO1 and J-TO2
On the System Interface board, the jumpers J-TO1 and J-TO2 set the sensitivity of the gating
transducers. Jumper J-TO1 is used to select the sensitivity value for gating transducer
TO1 .
TO1 is the first gating transducer going north or east from the bearing scanner. It is the gating
transducer closest to the bearing scanner. Jumper J-TO2 is used to select the sensitivity
value for gating transducer
TO2 . TO2 is the second gating transducer going north or east
from the bearing scanner. It is the gating transducer farthest from the bearing scanner.
Each jumper setting selects a different loading. From top to bottom, the selections are high
(470 ohms), medium (220 ohms), and low (100 ohms) sensitivity. High is the most sensitive.
Low is the least sensitive. Medium is somewhat between these sensitivities.
Transducer loading is the application of a parallel resistance to the magnetic wheel transducer
for controlling sensitivity. The SmartScanIS uses jumpers on the circuit board to select a
loading resistor for each gating transducer. The transducer's sensitivity lowers as the loading
resistance value lowers. It becomes more sensitive as the loading resistance value increases.
Too much sensitivity can make the transducer susceptible to interference from external
sources, such as radio transmitters and locomotive traction motors. In this case, the detector
can misinterpret this noise as extra wheel pulses. Not enough sensitivity will result in missed
wheel pulses.
Once the transducers are optimally loaded, the SmartScanIS operates over a relatively wide
range of transducer signal strengths. This wide range is necessary because the signal level
can vary greatly from one wheel to the next. This variation is largely due to wheel wear. For
example, a newer wheel tends to generate a weaker transducer pulse than a worn wheel,
which has a deeper flange that comes closer to the transducer. Track gauges that are out of
tolerance also cause variations in signal strength allowing the wheel flange to wander out near
the lateral operating limitations of the transducer.
A relatively high sensitivity setting, in the 470-ohm range, works well at most sites, but not
necessarily for all. It is difficult to define a value that works with 100% accuracy for all
installations due to external variables unique to a given site. Many sites produce very little if
any external interference, which allows a higher sensitivity setting resulting in the ability to
scan slightly slower trains than normal. Others have various issues that require a lesser
resistance value than the standard 470 ohms.
Generally, start with 470 ohms for maximum sensitivity. If you observe too many wheel pulses
for a given train, reduce the loading to the center position of 220 ohms. If the SmartScanIS
still counts too many pulses, reduce the loading to the bottom position.