Distance indicating devices

摘要

A distance indicating device comprises a probe having therein a light source and light sensitive element to receive light reflected from the surroundings of the probe. A reference point is movable relative to the probe. The light sensitive element gives rise to an electric signal. A first storage means stores a signal representing the maximum reflected light returned to the light sensitive element. A second storage means stores a signal representing the light returned to the light sensitive element representing the minimum reflected light. A selection means selects a signal level between the maximum and minimum stored signals' and a measuring element measures the distance between the reference point and a further reference point, associated with the probe, when the signal level reaches the selected signal level.