A measuring device for measuring a hole in the ground having at least one measuring probe having at least one measurement signal transmitter to transmit a measurement signal, at least one measurement signal receiver to receive the measurement signal reflected on a wall area of the hole, and an evaluation unit for determining a wall distance between the measurement signal transmitter and the wall area of the hole, wherein a measuring distance based on an assignment rule can be assigned to the received, reflected measurement signal. A calibrating device having at least one calibration element. The measurement signal transmitter transmits a calibration signal, which can be reflected on the calibration element, wherein the measurement signal receiver receives the calibration signal reflected on the calibration element. The evaluation unit changes and calibrates the assignment rule based on the calibration signal reflected and received by the calibration element.

A system has an actuator with a first surface and a second surface, the first surface being offset a step dimension from the second surface. A sensor is configured to measure a distance between the sensor and both the first surface and the second surface via a signal received by the sensor after having reflected off the first surface or the second surface. The step dimension is greater than a minimum dimension, which is defined in view of a medium through which the actuator moves and a frequency of the signal.

A device for monitoring the local orientation or position of an object by sound waves, with a sensor part positioned at a distance from the object with at least one sound wave emitter, at least one sound wave receiver, and a computing unit. The computing unit controls the at sound wave emitter and the sound wave receiver and determines the distance between the sensor part and the object, based on the echoes of a sound wave emitted by the sound wave emitter in the direction of the object. An identification reflector separate from the sensor part comprises a three-dimensional pattern. The sensor part has an array of sound wave receivers and sound wave emitters, wherein for identifying the identification reflector and for measuring the distance between the sensor part and the identification reflector, a plurality of echoes between different emitter/receiver-combinations is evaluated.

A sensor and a method for detecting a position of the sensor relative to a guide surface, comprising a housing and an electronic analysis device which outputs measurement values for the position of the guide surface on the basis of the measurement signals. The sensor contains an ultrasonic transducer array, each of the two outer ends of which is additionally equipped with a respective reference ultrasonic transducer and a respective reflector surface flush with the reference piezo disc at a distance from the base side, said ultrasonic transducers and reflector surfaces being inclined by 45? relative to the base side and pointing towards one another, thus forming a reference measurement path with a known length between the two reference ultrasonic transducers. In the method for detecting the relative position, the measurement values are corrected with respect to environmental influences by measurements in a reference path.