westinghouse air brake tech locomotive products Odometer

The odometer is a non-resettable, electronic device to count and display the total number of miles accumulated (in either direction) by the vehicle. The odometer registers miles to the nearest mile and has eight digits. The odometer receives an electrical signal from a passive speed sensor. The number of teeth on the sensing gear determines the number of pulses per revolution (PPR). The pulse count is accumulated to determine the number of wheel revolutions. The average wheel diameter, 34.5”, is used to calculate the distance. The distance is displayed to the nearest mile. The current input count is saved using FLASH memory to conserve the data when the system is not powered. The Odometer uses the average (or mid-worn) wheel diameter in its distance calculations. The measurement error introduced with a new wheel (maximum 36”) is compensated by the error with a worn-out wheel (33”). The net result is an accurate mileage total over the life of the sensing wheel.