The gyro theodolite is an instrument for measuring the true north angle by combining the gyroscope and the theodolite through a connecting mechanism. It utilizes the physical characteristics (fixed axis and precessibility) of the gyroscope itself, and uses the metal belt to suspend the gyro sensitive part of the center of gravity to sense the horizontal component of the angular velocity of the earth's rotation, and generates a northward thrust under the action of gravity. The gyroscope main shaft reciprocates around the meridian plane of the earth to determine the true north angle. The gyro theodolite is widely used in mine surveying, engineering surveying and military surveying. It is also an important supporting equipment for radar antenna orientation, drone flight orientation, artillery and long-range weapon launching.
The gyro theodolite consists of two parts: a gyroscope and a theodolite. The theodolite was invented by the British in 1730. After a long process of metal theodolites, it developed into an optical theodolite in the 1920s. It has entered the stage of electronic theodolite since the 1960s and is now quite advanced, moving towards intelligent direction. The gyroscope is the main body of the gyro theodolite, which dominates the development process of the whole machine.
The gyro theodolite can be classified into engineering grade (outside direction accuracy of 10'') and precision grade (direction accuracy within 10'' according to the orientation accuracy. The orientation principle is generally pendulum except for the speed type that has been used in the United States and the United States. The gyroscope and the theodolite are used as a whole, and the combination is of the following types: under-hanging and on-shelf. Under-mounted instruments were developed in the 1950s, and almost all precision instruments and instruments with a high degree of automation belong to this category.
The use of the gyro theodolite is related to the structural characteristics. Generally, the overhead type instruments use manual measurement methods, and the down-mounted instruments use automatic measurement methods. The automatic measuring instrument mainly adopts the automatic tracking method, the multi-point photoelectric timing method and the photoelectric integral method to observe. Among them, the photoelectric integration method is the most advanced. The manual measurement method mainly uses the tracking reversal point method, the Zhongtian time method, the chrono-swing method and the multi-point chronograph method.
Gyro theodolite and north seeker (or north finder) belong to similar Azimuth measuring tools and have very wide application field, mainly used in Subway engineering survey, Mine through surveying, College survey teaching, Radar precision orientation, Setting up the azimuth datum, Navigation equipment calibration, Missile testing fields, but Gyro theodolite also uses in following special applications.
1.Tunnel centerline measurement
In tunnels and other excavation projects, the center line measurement in the pit generally adopts the long distance traverse which is difficult to ensure the accuracy, especially in the case of shield excavation. Starting from the short reference center line of the vertical pit, the accuracy of Angle measurement and station shifting must be very high. In the measurement, the corresponding inspection of ground and underground should be carried out frequently to ensure the accuracy of measurement. Especially in dense urban areas, inspection conditions are difficult and it is impossible to conduct excessive inspection operations. If the gyro theodolite can be used to obtain the absolute high accuracy of the bearing datum, and can reduce the cost of high detection operations (minimum checkpoint), it is a high efficiency of the center line measurement method.
2.Azimuth Angle acquisition through visual obstruction
When the directional Angle cannot be obtained from a known point due to the obstruction of sight, it can be obtained by means of astronomical survey or gyro theodolite survey. Compared with astronomical measurement, the gyro theodolite measurement method has many advantages: less dependence on weather, no complicated astronomical calculation, can be obtained in the field of any measurement line direction Angle and easy to calculate the closure difference.
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