Tilt Sensor Principles and Applications Introduction

    A tilt sensor principle

    The tilt sensor is often used for level measurement system, from the works can be divided into "solid swing style," liquid pendulum type, gas pendulum three tilt sensor, described below in respect of their works.

    1 "solid swing" inertial devices

    Solid pendulum force balanced servo system is widely used in the design shown in Figure 1 by Pendulum, cycloid, bracket, pendulum by gravity G and swing tension T, and its aggregate external force F is: (1 )

    Where, θ is the angle of the cycloid and vertical directions. When measured in a small angle range, can be considered a linear relationship between F and θ. The strain angle sensor based on this principle.

    2, liquid pendulum inertial devices

    Liquid pendulum principle of the structure built in the glass casing with a conductive liquid, and the three platinum electrode and the external connection, the three electrodes are mutually parallel and equally spaced, as shown in Figure 2. When the casing horizontal when the electrode is inserted into the same as the depth of the conductive liquid. Coupled with the equal amplitude of the AC voltage between two electrodes, forming an ion current between the electrodes, the liquid between the two electrodes is equivalent to two resistors RI and RIII. If the level of liquid pendulum, RI = RIII. When the glass housing is tilted, the conductive fluid between the electrodes is not equal, the three electrodes were immersed in the depth of the liquid also changes, but the intermediate electrode immersion depth essentially unchanged. Shown in Figure 3, the left electrode immersion depth is small, the decrease in the conductive fluid, conductive decrease in the number of ions, the resistance RI increases, the counter electrode conductive liquid increases, conductive increase in the number of ions, leaving the resistor RIII reduction, i.e. the RI> RIII. Conversely, if the inclination direction opposite RI <RIII.

    Also caused changes in the strain gage according to the changes in the position of a liquid, thereby causing the output signal changes and perception of changes in the inclination of the application of liquid pendulum. Addition type in practical, there is left in the electrolyte solution of a bubble, the movement of the bubble will be when the device is tilted so that the capacitance changes induced inclination liquid pendulum.

    3, "gas pendulum inertial devices

    Gas when heated by the buoyancy effect pendulum and liquid pendulum also has a sensitive mass, as a solid, hot air is always trying to maintain in the vertical direction, it also has the characteristics of the pendulum. "The gas pendulum" inertial components by the closed cavity, gas and hotline. When the plane of the cavity where the relative angle to the horizontal or cavity by the role of the acceleration, the hotline the resistance change, and a change in resistance of the hotline is the function of angle q, or the acceleration, and thus also has the effect of the pendulum. Wherein the hotline resistance change is caused by the exchange of energy between the gas and the hotline.

    Gas pendulum inertial devices sensitive mechanism is based on the energy of the closed cavity pass gas in a closed cavity and hotline, the hotline is the only heat source. When the device is energized, the gas is heated. Convection is the main form of the hotline energy exchange.

    Convective heat equation: (2)

    Wherein: H-heat transfer coefficient (W/m2 × k), s-hotline surface area (m2), the TH-hotline temperature (K), the TA-gas temperature (K).

    The heat transfer coefficient h, and the thermal conductivity of the fluid, dynamic viscosity, the fluid velocity and the hotline diameter, expressed as: (3)

    Wherein: Nu - the Nusselt (Nusselt) number, l-thermal conductivity (W / mK), the number of Re-RENAULT (Reynold), U-fluid velocity (m2 / s), the diameter of the D-hotline (m), n-the dynamics of the fluid viscosity.

    When the airflow is perpendicular to the velocity U through hotline, (4)

    (4) Substituting (3): (5)

    According to the heat balance equation can be obtained:

    Therefore: (6)

    Assumptions and s is constant, then: (7)

    From formula (7) can be seen, the dynamics of the fluid viscosity, density, and heat transfer characteristics, different from the velocity of the fluid around the hotline, the flow of current through the hotline also different, causing a hotline at both ends of the voltage is also generated corresponding changes. Gas pendulum inertia of the device is based on a principle developed.

    Core sensing element for the the gas pendulum detection devices hotline. The current flows through the hotline, the hotline produce heat, so the hotline to maintain a certain temperature. The hotline temperature higher than the temperature of the gas surrounding it, the kinetic energy increases, so the gas flows upward. In an equilibrium state, as shown in Fig 4 (a), hotline is in the same horizontal plane, rising airflow through the same speed as they are, i.e. V1 = V1 ', In this case, the impact of the stream on the hotline same, by the formula (7) shows that the current flowing through hotline is also the same, the bridge is balanced. Relatively horizontal plane when the hermetic chamber is tilted, the hotline height changes, shown in Figure 4 (b), because the flow of the gas in the sealed cavity is continuous, so the hot gas stream in the process of upward movement, passes through lower and the upper part of the hotline. Ignored gases rising process to overcome the gravity of energy loss, the airflow through the upper hotline lower hotline generator heat exchange, so that when the air velocity through the two hotline Then V2 ¢> V2, flows through The two hotlines current will change accordingly, so the bridge is out of balance, and outputs an electrical signal. The inclination angle is different from the electrical signal output is also different.

    Second, the solid, liquid, gas pendulum performance comparison

    Based on solid swing, liquid pendulum and gas pendulum tilt sensor developed by the principle, they have their own strengths. Sensitive mass in a gravitational field, the solid pendulum is a pendulum mass, liquid sensitive pendulum mass is the electrolyte, and the gas sensitive pendulum mass is a gas.

    Only the moving body of the gas is sealed inside the chamber, and its quality is small, a large impact or high overload of the inertial force is also small, and therefore have a strong anti-vibration or shock. Gas motion control is more complicated, affecting the movement of many factors, its accuracy is unable to meet the requirements of military weapon systems.

    Solid clear the length of the pendulum and pendulum heart pendulum tilt sensor, its mechanism is basically the same as the acceleration sensor. Practical Product Type more, such as electromagnetic pendulum, measuring range of its products, higher precision and resistance to overload, weapons systems more widely.

    Liquid pendulum tilt sensor in between, but the system is stable, high-precision systems, applied more widely, and in domestic and foreign products and more