User's Manual

DOCU0093
CAS ToF Units & CAS Dual RF/ToF Units User Manual
Wabtec Proprietary Information 13
5.2. PRINCIPLE OF OPERATION
The CAS ToF units use a 2.4 GHz ISM band short range device radio transceiver for sending and receiving data
amongst the locally equipped fleet within radio range. CAS Dual RF/ToF units uses 433 MHz and 2.4 GHz ISM
band short range device radio transceiver for sending and receiving data amongst the locally equipped fleet
within radio range. For CAS ToF units the transmissions between units comprises a complex form of radio
frequency modulation. Figure 3 shows the basic sequence of events and resulting calculations between two
CAS ToF products when evaluating distance based on the Time of Flight signal interactions. The transmit and
response data sent between the two devices contains additional data information including vehicle identifiers,
processing times and correction factors.
Figure 3. Time of Flight Distance Measurement Algorithm
Multi-path reflections when measuring a ToF (Time of Flight) signal could introduce a measure of inaccuracy to
the principle operation of the device. To combat this anomaly each CAS ToF unit is equipped with dual
antennas operating in a diversity configuration for improved accuracy and design robustness in difficult
environments susceptible to radio signal multi-path reflections.
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