Abstract: A guidance module for an underground horizontal boring assembly. The module determines the pitch angle of the boring tool independent of roll using a single accelerometer sensor. The accelerometer sensor has a single sensitive axis which is aligned parallel to, and preferably coaxial with, the longitudinal axis of the boring tool. The accelerometer sensor is calibrated to obtain a temperature offset and a gain compensating gain factor. Data samples are read from the accelerometer sensor while the boring tool is rotating. The temperature is read from the temperature sensor. The data samples from the accelerometer sensor and the temperature from the temperature sensor are transmitted to a processor. The processor applies simple average filtering to the accelerometer data samples to get an average result, and adjusts the average result for gain. The average result is adjusted for the temperature offset and for the gain compensating gain factor.

Abstract: An electronic compass (10) for use in a boring tool (12) which will provide an orientation of the boring tool relative to the earth's magnetic field. In addition, a more straightforward left or right deviation from an initial bearing can be determined. The invention can correct for pitch angle and roll angle variation as well. The magnetic field is sensed by an axial magnetic field (12), a radial magnetic field sensor (18) and a plane-normal magnetic sensor (24) which are preferably magnetoresistive sensors.

Abstract: The pitch sensor of the invention includes a sealed container filled about half full with a magnetic liquid. A pair of coils are wound around the container and produce inductances corresponding to the amount of magnetic liquid disposed within the opening of the coils. As the angle of inclination of the pitch sensor changes, the volume of magnetic liquid becomes greater in one coil, as compared to the other coil, thereby providing a differential inductance. A pulsing circuit pulses the inductances and produces an analog voltage corresponding to the absolute angle of pitch, and a polarity voltage corresponding to the angle quadrant.