Position Sensor Operating Principles: Notes

The sensor determines current vehicle location by calculating the previously sensed position, the distance traveled from this position, and the directional changes occurring during this travel.

1. Distance traveled

   The distance traveled is calculated using signals received from the vehicle speed sensor. The sensor automatically compensates for the slightly reduced wheel and tire diameter resulting from tire wear.

2. Forward movement (Direction)

   Changes in the direction of forward movement are calculated by the gyro (angular velocity sensor) and the GPS antenna (GPS data). Each of these functions has its advantage and disadvantages. Depending upon conditions, one function takes precedence over the other to accurately determine the direction of forward movement.

   Fig 1: Identifying Position Sensor Operating Principles

   
   ADVANTAGE AND DISADVANTAGE
   
   

   Function type	Advantage	Disadvantage
   Gyro (Angular velocity sensor)	Able to accurately detect minute changes in steering angle and direction.	Calculation errors may accumulate over a long period of continuous vehicle travel.
   GPS antenna (GPS data)	Able to sense vehicle travel in four general directions (North, South, East, and West)	Unable to detect direction of vehicle travel at low vehicle speeds.