Patent ID: 8392139

Claim:
A multi-point calibration method for the depth of a horizontal directional drilling guiding instrument, comprising the steps of: (1) maintaining a constant power output of a power transmitter in a specific power supply condition; (2) selecting at least two depth calibrations; (3) receiving a signal transmitted from a transmitter and an intensity of a signal at a depth calibration position by a receiving instrument; (4) performing a signal shaping and an analog/digital conversion to the signal received by a signal receiving instrument; and (5) entering the signal into a central digital signal processor, and performing a depth calibration by any compensation method to obtain a required measuring depth; wherein the compensation method includes a linear compensation method, the linear compensation method is implemented by the equation of: r =( M 0 /s ) 1/3 +[( M 0 /s ) 1/3 −5]× k where, r is the measuring depth, and M 0 is the measured value, and s is the intensity k of the signal transmitted from the transmitter and received by the receiving instrument, and the value of k is obtained by the equation of: k=[ 10−( M 0 /s 2 ) 1/3 ]/[( M 0 /s 2 ) 1/3 −5 ] where, M 0 is the measured value, and s 2 is the intensity of a signal occurred at the second calibration point and received by the receiving instrument.