It is also important to monitor the wheel/rail contact to
detect skidding and wear. Matsumoto et al. [84] applied a
multifaceted approach. They fitted noncontact gap sensors on
nonrotating parts of a bogie to measure the bending deflection
(distortion) of the wheel by the lateral contact force. They
also used magnetostrictive displacement sensors to measure the
deflection of the primary suspension by the vertical contact
force. These two measurement combined give the wheel/rail
contact forces. Matsumoto et al. [84] used the same derailment
coefficient as [10] and [71] (discussed in the fixed monitoring
section): the ratio between the lateral and the vertical force (L/V
ratio). Balas and Jain [9] fused data from speed sensors and
piezoelectric accelerometers attached to train wheels. Using
data modeling, they were able to detect skidding if the integral
of the acceleration (speed of the wheel) measured by the
accelerometer differed from the speed of the carriage. They also
calculated the wheel adherence as a function of the carriage
weight, carriage velocity, brake cylinder pressure, and the skid
amount from the skid model.