(1)
This sensor is to measure the distance from center position of sensor to chain link that is the nearest to the center position of sensor in the direction of sensor and in the range of sensor.
(1)
where, 
is the position of the closest part
of chain link on the direction and in the range of the sensor and 
is the position of sensor center.
is the specified direction of the
sensor.
Figure 1 Distance Sensor