The usual spatial dimension consists of three dimensions: length, width and height, and the inclination sensor can measure the inclination angle of these three dimensions. Therefore, the inclination sensor can be divided into single-axis, double-axis and three-axis according to the axial direction. Literally, the single-axis inclination sensor can only measure the angle in one direction, the dual-axis inclination sensor can measure the angle in two directions that are perpendicular to each other, and the three-axis can measure the change of any axis in three directions in three-dimensional space.
 The theoretical basis of the single-axis inclination sensor is Newton's second law. According to basic physics, inside a system, velocity cannot be measured, but its acceleration can be measured. If the initial velocity is known, the linear velocity can be calculated by integrating, and then the linear displacement can be calculated. So it is actually an acceleration sensor that uses the principle of inertia.
 The dual-axis inclination sensor is a measurement tool designed for the angle between two directions on the basis of a single axis and combined with specific practical requirements.
The dual-axis inclination sensor directly measures the acceleration of the measured object, and can obtain the linear velocity of the object through integral operation, and then further obtain the displacement of the object. Fundamentally, the inclination sensor is still an inertial sensor, which follows the inertial law and integral calculation method of object motion. The dual-axis sensor is designed based on this basic principle.
 Dual-axis tilt sensors share two sensitive axes, counted as X-axis and Y-axis. When the sensitive axis is perpendicular to the direction of gravity, the output change value caused by one degree of inclination is larger; when the sensitive axis is at an angle of 45 degrees to the direction of gravity, the change value caused by each time is small; when the two are close to parallel, each time the change value is small. The secondary offset almost no longer causes output changes. According to this principle, the dual-axis inclination sensor can measure more types of objects and measure more types of angles, greatly improving the measurement efficiency.

 In general, the dual-axis inclination sensor has the measurement advantages of the single-axis inclination sensor, and at the same time has the measurement effect that the single-axis cannot achieve, and has a wider measurement range. However, the accuracy of the dual-axis inclination sensor is not as good as that of the single-axis, and it should be noted that the dual-axis inclination sensor can measure the angles in both directions of the X-axis and the Y-axis, but cannot measure the X-axis and the Y-axis at the same time. Measure the angle of one axis, X-axis or Y-axis, if it is measured at the same time, it will cause horizontal axis error, and its value cannot be determined.
 Depending on the data to be measured, we can choose from different inclination sensors. In theory, if there are three-dimensional angle changes, a three-axis inclination sensor needs to be used, but in fact, in practical applications, the three-axis inclination sensor does not exist. More precisely, the dual-axis inclination sensor can measure the three-dimensional angle. change without the use of a so-called "triaxial tilt sensor".
 As shown in the figure, taking the X-axis single-axis inclination sensor as an example, the measurement surface of the sensor can only have an included angle with the X-axis, and the inclined surface is fixed on one axis (Y-axis) for rotation. Similarly, the Y-axis single-axis inclination sensor rotates with the X-axis as the fixed axis. The inclined surface of the dual-axis inclination sensor can have an included angle with the X and Y axes, or only with one of the axes. The right side of the figure below shows the general situation of the inclined surface of the dual-axis inclination sensor.

 From the comparative analysis of the single-axis and dual-axis inclination sensors above, we can see that the active part of the inclined surface of the dual-axis inclination sensor is a point or line, while the single-axis can only be a line. For example, the inclination of a vertical wall is based on the joint line of the wall and the foundation as the active part, and a single axis can be used at this time; and the process of a vertical rod toppling slowly is based on the contact point as the active part, so it is necessary to use double Axle inclination sensor for measurement.
In fact, in the process of tilting the vertical rod, no matter which direction it is tilted, one thing is certain, that is, the angle between the tilted position and the original position is the angle between the inclined plane and the horizontal plane, and this angle may only be a single X or Y axis Inclination, and possibly both, which is why it can only be measured with a dual-axis inclination sensor. As for why there is no three-axis inclination sensor, this is because when the inclination angle between an inclined plane and the X and Y axes is determined, the inclined plane is fixed, and there is no possibility of change, that is, the angle of the Z axis is also determined. value.