Inclination sensoring and magnetic signal transmission for trench wall constructions

Abstract

Abstract Trench walls find many applications in underground engineering, whereas the requirements on the verticality have been extensively extended in the last years. To obtain impervious 100 m deep sidewalls for waste deposits, powerplants, subway-tunnels or other underground constructions, a maximum deviation of 0.2% or 20 cm has to be guaranteed, at most. This corresponds to an average inclination angle of 170 millidegrees. To achieve this high accuracy, an on-line measurement system with a magnetic angler sensor is used. A NdFeB permanent magnet pendulum varies the output voltage of a semiconductor Hall-effect potentiometer. The angle dependent d.c. voltage is converted into a signal of variable frequency (2–15 kHz). The angle sensors, the electronic circuits, and batteries are mounted in waterproof (20 bar) and shock protected (100 g) cases on the gripper. It is operated by two steel cables which are used for the signal transmission by enclosing ring-core transformers of high initial permeability. The received angular information is decoded by a microprocessor and displayed together with the excavation depth on a screen in the operation cabin of the excavator. The depth is measured by counting the revolutions of the cable guiding wheel of the excavator with contactless magnetic proximity switches. The measurement system provides an angular resolution of 5×10 −3 degrees and an absolute accuracy of 7×10 −3 degrees at ±2° total range.