MTS SWIFT 10 MC Sensor - Manual (Page 78)

SWIFT 10 MC Sensors 78
Road and Track Vehicles
Installing the Transducer
Effect of zero
reference on SWIFT
output
When the SWIFT sensor is used in spinning applications, it is important that a
correct absolute zero of each strain gage bridge is used to ensure the proper
computation and transformation of the transducer outputs to a non-rotating
vehicle coordinate system. An error in the absolute zero of each bridge will
produce a one-time-per-revolution modulation error in the output signals. To
achieve absolute zero of each bridge, the zeroing process must account for the
tare weight acting on the transducer.
When the vehicle is lifted and the tire and wheel assembly are suspended, the
mass of the tire, rim, outer diameter fasteners, and outer ring of the transducer are
all reacted through the beams of the transducer. With gravity acting on this outer
tire/rim assembly, the SWIFT sensor measures a vertical force pulling down on
the transducer.
The SWIFT output cannot be zero, because it is not possible to set the vehicle on
the ground precisely enough that the ground supports only the outer tire/rim
weight.
As the vehicle is set completely on the ground, the output from the SWIFT sensor
will read the corner weight of the vehicle from the reference point of the
transducer. The output of the SWIFT sensor will be slightly less than the total
corner weight of the vehicle, because the SWIFT sensor is inboard of the outer
tire and rim assembly, and will therefore not measure the weight of the outer tire
and rim assembly.