history of walkover locating technology - Digital Control Inc.

moved. The ability to get roll information would eliminate thewrap-up problem, and the ability to determine pitch wouldgreatly reduce the operator training. Although the intent was onthe mark, the implementation was not practical, so it did notbecome commercialized.In 1991 competition grew with new manufacturers enteringthe industry. Several significant advancements were madeto walkover tracking systems. Both Ditch Witch ® and DigitalControl introduced new systems. The Ditch Witch Subsite system was a combined cable locator and tracking system. Thissystem was based on digital signal processing and could operateon several frequencies. It also included a gravitational rollsensor that provided an absolute roll orientation, whichcompletely eliminated wrap-up steering errors. At the same timeDigital Control introduced the DigiTrak System. The DigiTrakSystem was designed from the beginning to be a boring toollocator and departed from the conventional cable locatortechnology. It used a pair of orthogonal antennas to measure thetotal magnetic field in the plane of the locator. This techniqueeliminated one of the locating challenges mentioned above, thatDitch Witchof ghosts. There are no ghosts with this method. Also, the unit® Subsite 80 Rdeparted from the cable locator scheme of determining depth.Instead it employed a calibration procedure based on the fact that the transmitter in the drillheadhousing is designed to produce a uniform, constant signal. The depth was displayed continuously,unlike prior systems which required the operator to push a button and wait a few seconds. Whennot over the transmitter, the display showed the approximate slant distance to the tool head. Thecompact design employed internal ultrasonic measurement of the locator height above the groundsurface to accommodate operators of different heights. This feature additionally providedseparation of the locator’s antennas from the ground to greatly reduce the adverse influence ofrebar in streets.At its introduction, the DigiTrak was the firstwalkover system to display both the roll and pitchorientation of the tool head as well as the first toprovide a warning for a weak battery condition in thetransmitter. The pitch orientation covered a range of-100% to +100% grade in 1% grade increments andwas not influenced by roll orientation. The roll andpitch orientation for the DigiTrak were based on gravityand therefore independent of where the operatorwas standing relative to the tool head. Knowledge ofthe pitch orientation greatly increased the speed ofdrilling since fewer locate points were needed tocontrol depth. Also, this knowledge improveddrilling accuracy particularly on uneven terrain. AtDigital Control DigiTrak Receiver6