Patent ID: 7417919

Claim:
An apparatus to enable a determination of a distance, R 1 , of a range sensor from a reference plane, the range sensor transmitting pulses and detecting echoes along a pulse-echo path, the reference plane being normal to the pulse-echo path, the apparatus comprising: i) a reference plate with pulse-reflective surface; ii) positioning means to locate the reference plate in the reference plane at a first position on the pulse-echo path, there to reflect pulses back to the range sensor; iii) positioning means to locate the reference plate at a second position on the pulse-echo path at a known distance D from the first position, there to reflect pulses back to the range sensor; and the range sensor incorporating: iv) timing means to determine a time interval, dt 1 , between sending a pulse and receiving its echo from the reference plate at the first position; v) timing means to determine a time interval, dt 2 , between sending a pulse and receiving its echo from the reference plate at the second position; and vi) computing means to calculate the distance, R 1 , of the sensor from the reference plane from, R 1= D |( dt 1/( dt 2 −dt 1))|.