a gyroscopic sighting device used in orienting tunnels and mine shafts and topographical surveys. It is used to determine the azimuth (bearing) of the direction of orientation. It is widely used in mine surveying and in geodetic, topographical, and other work. By its principle of operation, a gyroscopic theodolite is a terrestrial gyrocompass. Some gyroscopic theodolites are based on the naval gyrocompass. Several designs follow the principle of the Foucault gyrocompass—that is, they utilize an astatic, one-axis gyroscope. To reduce the friction moment and other disturbing influences, gyroscopic theodolites of this type have an air, liquid, or torsional suspension. In addition to a gyroscopic sensing element, a gyroscopic theodolite contains an angle-measuring device, whose readings show the location of the sensing element; the same device also determines the azimuth (bearing) of the direction being located. The angle-measuring device consists of a theodolite and an autocollimation tube that is rigidly connected to the alidade of the theodolite. Since the axis of the gyroscope oscillates with respect to the plane of the meridian, the true meridian in a gyroscopic theodolite is found by observing through the autocollimation tube the reversion points of the sensing element (the maximum deflections of the gyroscope’s axis from the true meridian). The readings for the reversion points are then averaged. These observations are made with the aid of a line projected on a mirror that is fastened to the sensing element. In this case the line of sight of the autocollimation tube is located parallel to the axis of the gyroscope. A scale connected to the theodolite is used in finding the azimuth (bearing) of the direction to be oriented with the aid of the theodolite. Gyroscopic theodolites are highly accurate—the error ranges from less than ten minutes to less than ten seconds of angle.
A. IU. ISHLINSKII and S. S. RIVKIN