What is the Structure of a Gyro Theodolite?

High Accuracy Gyro Theodolite

Gyro theodolite is an instrument used to measure true north azimuth by combining gyroscope and theodolite through connecting mechanism. It uses the physical characteristics of the gyroscope itself (fixed axis and precession), the sensitive part of the gyroscope with the center of gravity moved down is used to sensitive the horizontal component of the earth’s rotation angular velocity, and under the action of gravity, a northward precession moment is generated, so that the gyroscope spindle swings around the Earth’s meridian plane, so as to determine the true north azimuth. Gyro theodolite is widely used in mine survey, engineering survey and military surveying, and is also an important supporting equipment for radar antenna orientation, UAV flight orientation, artillery and long-range weapon launching orientation.


The gyro theodolite consists of a gyroscope, a theodolite and a tripod.

(1) gyroscope

The gyroscope is the core of the system, which is mainly composed of gyroscope sensitive part, electromagnetic shielding mechanism, hanging wire and guide wire, azimuth rotary servo drive device, damping device, inertial sensitive part locking device, supporting and leveling device, photoelectric Angle sensor, power supply, control and display part.

A gyro motor rotating at a constant speed is provided in the gyro sensitive department. The gyro motor is suspended from the gyro frame by the hanging wire and powered by the guide wire.

The gyro sensitive part locking device is to ensure the gyro sensitive part safety in the transportation state, and the inertial sensitive part and the frame are fixed.

The damping device is designed to attenuate the swing amplitude of gyro sensitive part after release, make its swing state meet the requirement of north search, and finally overcome the north precessional moment, so that the gyro sensitive part is relatively stable in a fixed position in inertial space.Damping friction damping, liquid damping and electromagnetic damping and other ways.

The azimuthal indentations servo drive system can realize azimuthal rotation of the gyroscope and provide rotation torque and stable transmission.

The support and leveling device can realize the mechanical and optical docking between the theodolite and the gyroscope, the leveling of the whole instrument and the installation and fixation of each component.

The photoelectric Angle sensor includes a photoelectric Angle sensor for detecting the swing Angle of the inertial sensing part and a grating code disk system for detecting the azimuth rotation Angle of the gyroscope.

Electromagnetic shielding is mainly used to shield the interference of internal and external magnetic fields to gyro north finding.

The control and display part collects the signal through the sensor, and processes it, and completes the lock and release of the gyroscope sensitive part, damping control, azimuth follow up, communication, calculation, sending and display true north azimuth and other functions.

(2) the theodolite

The theodolite is the bearing extraction device of the system. It can also measure the target’s geographic azimuth or coordinate azimuth by aiming at the target.The theodolite has the function of self-collimation for easy measurement and calibration.Usually, the theodolite has serial communication interface, which can realize serial data communication with the gyroscope and the command system.

(3) the tripod

The tripod provides support for the gyro theodolite.

Principle of gyrotheodolite

The gyroscope rotating around its symmetry axis at high speed has two important characteristics: first, it is fixed axis,without the action of external torque, the direction of the gyroscope axis always points to the initial constant direction; Second, it is precession, under the action of the external torque, the gyroscope axis produces precession, and moves close to the vertical plane where the rotation axis of the external torque is located along the shortest path until the two axes are in the same vertical plane.

The true meridian is the intersection between the plane of the Earth’s axis of rotation (the meridian plane) and the Earth’s surface, so that the true meridian of the ground (true north direction) is in the same plumb plane as the Earth’s axis of rotation. When the gyroscope gyro rotates at a high speed and its axis is not in the plumb plane of the true meridian on the ground, the gyroscope axis generates precession under the action of the earth’s rotation torque and is close to the plumb plane where the true meridian and the earth’s rotation axis are located, so the gyroscope axis can automatically indicate the true north direction.

Under the action of inertia, the axis of the free gyroscope rotating at high speed does not rest in the true north direction, but swings left and right in the true north direction. The maximum amplitude of the east-west oscillation of the gyro axis is called the reversal point. Therefore, the gyroscope is combined with the theodolite, and the theodolite is used to track the east-west reversal point of the cursor, read the level dial and take its average value, so as to obtain the true north direction.

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