Inventory|Principle of commonly used tilt sensor

Inventory|Principle of commonly used tilt sensor
Inclination sensors are also called inclinometers, inclinometers, levels, and inclinometers. They are often used to measure the horizontal angle of the system. This type of sensor used to be a simple bubble level. With the development of automation and electronic measurement technology, the inclination The types of sensors are gradually increasing. From the working principle, they can be divided into three types of inclination sensors: 'solid pendulum

1. Solid pendulum tilt angle sensor

The solid pendulum is widely used in the design of a force-balanced servo system. As shown in the figure, it is composed of a pendulum, a cycloid, and a bracket. Under the action of gravity G and pendulum pulling force T, the resultant external force F u003dG sinθu003dmg sinθ. Among them, θ is the angle between the cycloid and the vertical. When measuring in a small angle range, F and θ can be considered to have a linear relationship, and the strain-type inclination sensor is based on this principle.

2. Liquid pendulum tilt sensor

The structure principle of the liquid pendulum is that a conductive liquid is installed in a glass shell, and there are three platinum electrodes connected to the outside, and the three electrodes are parallel and spaced apart. Equal, as shown in the figure. When the housing is horizontal, the electrode is inserted into the conductive liquid to the same depth. If an alternating voltage of equal amplitude is applied between two electrodes, an ionic current will be formed between the electrodes, and the liquid between the two electrodes is equivalent to two resistors RI and RIII. If the liquid swings horizontally, then RIu003dRIII.

When the glass shell is tilted, the conductive liquid between the electrodes is not equal, and the depth of the three electrodes immersed in the liquid also changes, but the immersion depth of the middle electrode remains basically unchanged. If the immersion depth of the left electrode is small, the conductive liquid will decrease, the number of conductive ions will decrease, and the resistance RI will increase. On the opposite pole, the conductive liquid will increase, the number of conductive ions will increase, and the resistance RIII will decrease, that is, RI>RIII. Conversely, if the tilt direction is opposite, RI

In the application of liquid pendulum, there is also a change in the strain gauge according to the change of the liquid position, which causes the change of the output electrical signal and the change of the inclination angle. In practice, in addition to this type, there is also a 'liquid pendulum' that leaves a bubble in the electrolyte solution. When the device is tilted, the bubble will move to change the capacitance and induce a 'liquid pendulum'.

3. Gas pendulum type inertial sensor

'Gas pendulum' type inertial element is composed of a closed cavity, gas and hot wire. When the plane of the cavity is inclined relative to the horizontal plane or the cavity is subjected to acceleration, the hot wire The resistance of the heating wire changes, and the change of the resistance of the hot wire is a function of the angle q or acceleration, so it also has a pendulum effect. The change in the resistance of the hot wire is caused by the energy exchange between the gas and the hot wire.

The sensitive mechanism of the 'gas pendulum' type inertial device is based on the energy transfer in a closed cavity. There are gas and a hot wire in the closed cavity, and the hot wire is the only heat source. When the device is energized, it heats the gas. Convection is the main form of heat exchange energy.

The core sensitive element of the gas pendulum detection device is the hot wire. Electric current flows through the hot wire, and the hot wire generates heat to keep the hot wire at a certain temperature. The temperature of the hot wire is higher than the temperature of the gas around it, and the kinetic energy increases, so the gas flows upward. In the equilibrium state, as shown in Figure 4(a), the hot wires are on the same horizontal plane, and the ascending air flows through them at the same speed, that is, V1u003dV1'. At this time, the airflow has the same effect on the hot wires, as shown in equation (7) It can be seen that the current flowing through the hot wire is also the same, and the bridge is balanced. When the enclosed cavity is inclined, the height of the hot wire relative to the horizontal plane changes, as shown in Figure 4(b), because the flow of gas in the enclosed cavity is continuous, the hot air flow passes through the lower part in sequence during the upward movement. And the upper hotline. If we neglect the energy loss of overcoming gravity during the ascent of the gas, the airflow passing through the upper hot wire has already exchanged heat with that of the lower hot wire, so that the airflow velocity when passing through the two hot wires is different. At this time, V2¢>V2, so it flows through The currents of the two hot wires also change accordingly, so the bridge loses balance and outputs an electrical signal. The electrical signal output is different when the tilt angle is different.

Comparison of the performance of solid, liquid and gas pendulums

As far as the inclination sensors based on the principles of solid, liquid and gas pendulums are concerned, they have their own advantages. In the gravity field, the sensitive mass of a solid pendulum is the mass of the pendulum, the sensitive mass of a liquid pendulum is electrolyte, and the sensitive mass of a gas pendulum is gas.

Gas is the only moving body in the sealed cavity. Its mass is small, and the inertial force generated in the event of a large impact or high overload is also small, so it has a strong ability to resist vibration or impact. However, gas motion control is more complicated, and there are many factors that affect its motion, and its accuracy cannot meet the requirements of military weapon systems.

The solid pendulum inclination sensor has a clear pendulum length and center, and its mechanism is basically the same as that of an acceleration sensor. In practical applications, there are many types of products such as electromagnetic pendulums, which have high measurement range, accuracy and anti-overload capability, and are also widely used in weapon systems.

The liquid tilt sensor is somewhere in between, but the system is stable, and it is widely used in high-precision systems, and most of the domestic and foreign products are of this type.

At present, the inclination sensor has become an indispensable and important measurement tool in the fields of bridge erection, railway laying, civil engineering, oil drilling, aviation and navigation, industrial automation, intelligent platforms, and mechanical processing.

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