Will the working principle of the liquid level switch change

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Liquid level switch

As a key device for monitoring and controlling liquid levels, it plays an indispensable role. From liquid level monitoring in chemical storage tanks to liquid level control in spacecraft fuel tanks, liquid level switches can provide real-time feedback on liquid level information to ensure safe and stable operation of the equipment. However, when the liquid level switch is transferred from a conventional atmospheric environment to a vacuum environment, its working conditions change dramatically. There is no atmospheric pressure in a vacuum environment, and the physical and chemical properties of the substance will also be affected, which raises the question: Will the working principle of the liquid level switch change in a vacuum environment?

1. Working principle of common liquid level switch

1. Float type liquid level switch

The float type liquid level switch is a common liquid level monitoring device. It is mainly composed of a float, a connecting rod and a switch contact. Its working principle is based on the Archimedean principle. When the liquid level in the container changes, the float moves up and down with the rise and fall of the liquid level. When the liquid level rises to the set height, the rise of the float drives the connecting rod to move, so that the switch contacts are closed or disconnected, thereby outputting a liquid level signal. For example, in the water level control of a water tank, when the water level rises to the set value, the float type liquid level switch is activated, triggering the water pump to stop filling water; when the water level drops to a certain level, the switch is activated again, starting the water pump to replenish water.

2. Capacitive liquid level switch

The working principle of the capacitive level switch is based on the change of capacitance. It consists of a capacitive detection electrode and a circuit. The capacitive detection electrode is placed in the liquid to be measured and forms a capacitor with the container wall (or another electrode). When the liquid level changes, the capacitance value of the capacitor will change accordingly because the dielectric constant of the liquid is different from that of air. The change in capacitance value is detected by the circuit and compared with the set value. When the set threshold is reached, the switch outputs a signal. This level switch is suitable for level measurement of a variety of liquids and has the characteristics of high sensitivity and fast response.

3. Ultrasonic level switch

The ultrasonic level switch works on the principle of ultrasonic reflection. It transmits ultrasonic waves, which are reflected when they encounter the surface of the liquid, and the reflected waves are received by the sensor. The liquid level can be calculated based on the time difference between the transmitted wave and the reflected wave, combined with the propagation speed of the ultrasonic wave in the medium. When the liquid level reaches the set height, the switch outputs a corresponding signal. The ultrasonic level switch does not need to be in direct contact with the liquid, and is suitable for level monitoring of special liquids such as corrosive and high-viscosity liquids.

4. Tuning fork liquid level switch

The tuning fork level switch is based on the vibration characteristics of the tuning fork. The tuning fork is excited by a piezoelectric crystal to produce vibrations. In the air, the tuning fork vibrates at a specific frequency. When the liquid covers the tuning fork, the vibration frequency of the tuning fork will change due to the damping effect of the liquid. By detecting the change in the tuning fork vibration frequency, when the set conditions are met, the switch outputs a signal to indicate that the liquid level has reached a predetermined height. The tuning fork level switch has high reliability and is often used for fixed-point monitoring of liquid levels.

2. Characteristics of vacuum environment and its influence on liquid level switch

1. Basic characteristics of vacuum environment

The salient feature of a vacuum environment is that the gas pressure is extremely low, and there is almost no collision and convection of gas molecules. In a high vacuum environment (pressure below 10?3 Pa), the mean free path of gas molecules is much larger than the container size, and the physical properties of the gas are very different from those in a conventional atmospheric environment. In addition, there is no atmospheric pressure in a vacuum environment, the boiling point of the liquid will decrease, and the physical properties of the liquid, such as surface tension and density, may also change. These characteristics will affect the operation of the liquid level switch.

2. Impact on float type liquid level switch

In a vacuum environment, the working principle of the float type liquid level switch will not change in essence, and it still relies on the change in the buoyancy of the float to trigger the switch action. However, since there is no atmospheric pressure in a vacuum environment, the surface tension of the liquid will increase relatively, which may cause the liquid to adhere to the container wall more strongly, affecting the normal rise and fall of the float. In addition, the density of the liquid in a vacuum environment may change due to factors such as temperature and pressure changes, which in turn affects the buoyancy of the float, affecting the accuracy of liquid level monitoring.

3. Impact on capacitive liquid level switch

The core working principle of capacitive level switch based on capacitance change remains unchanged in vacuum environment. However, the change of gas medium in vacuum environment (almost no gas molecules) will change the capacitance characteristics of capacitance detection electrode and surrounding environment. At the same time, due to the change of physical properties of liquid in vacuum environment, such as the change of dielectric constant due to the interaction between liquid molecules, the change law of capacitance value will be different from that in atmospheric environment, thus affecting the accuracy of liquid level measurement and the reliability of switch action.

4. Impact on ultrasonic level switch

Ultrasonic level switches will be greatly affected in a vacuum environment. Because the propagation of ultrasound requires a medium, and there is almost no gas medium in a vacuum environment, ultrasound cannot propagate like in the atmosphere. Therefore, the liquid level switch based on the ultrasonic reflection principle cannot work properly in a vacuum environment, and its working principle is no longer applicable. Other methods must be used to achieve liquid level monitoring.

5. Impact on tuning fork level switch

The basic working principle of the tuning fork liquid level switch in a vacuum environment is still to determine the liquid level by detecting the change in the tuning fork vibration frequency. However, since there is no gas damping in a vacuum environment, the vibration frequency of the tuning fork in the air will be higher and more stable than in the atmospheric environment. When the liquid contacts the tuning fork, the damping effect of the liquid is relatively more obvious, and the trigger threshold of the switch may need to be readjusted to adapt to the changes in the tuning fork vibration characteristics in a vacuum environment to ensure the accuracy of liquid level monitoring.

3. Improvement and countermeasures of liquid level switch in vacuum environment

1. Structural optimization and material selection

In view of the influence of vacuum environment on liquid level switch, its structure can be optimized. For example, for float type liquid level switch, the shape and material of float can be improved to reduce the influence of liquid surface tension on the rise and fall of float; for capacitive liquid level switch, special insulating materials and electrode structures can be used to reduce the interference of vacuum environment on capacitance characteristics. At the same time, materials with stable performance in vacuum environment, such as corrosion-resistant, high and low temperature resistant materials, can be selected to ensure the reliability of liquid level switch.

2. Calibration and algorithm adjustment

Because the working characteristics of the liquid level switch change in a vacuum environment, it needs to be recalibrated. By measuring and analyzing the switch output signals at different liquid levels in a vacuum environment simulation experiment, a new liquid level-signal relationship model is established. For switches that rely on algorithms to calculate liquid levels, such as capacitive and ultrasonic liquid level switches, the algorithm parameters need to be adjusted to adapt to the measurement requirements in a vacuum environment.

3. Adopt new liquid level monitoring technology

In a vacuum environment, the operation of some traditional liquid level switches is limited, so new liquid level monitoring technologies can be considered. For example, liquid level monitoring technologies based on optical principles determine liquid levels by detecting the refraction, reflection or absorption characteristics of light by liquids. Such technologies do not rely on gas media and have good application prospects in vacuum environments. In addition, liquid level monitoring technologies based on radioactive isotopes use the attenuation of rays when they pass through liquids to determine liquid levels, and can also be used for liquid level measurement in vacuum environments.

In a vacuum environment, the working principles of different types of liquid level switches are affected differently. The core working principles of some liquid level switches remain unchanged, but the working characteristics have changed, resulting in reduced measurement accuracy and reliability; and devices such as ultrasonic liquid level switches that rely on gas media to transmit signals, their working principles are no longer applicable in a vacuum environment. In order for the liquid level switch to work properly in a vacuum environment, it is necessary to respond through structural optimization, calibration adjustment, and the use of new technologies. With the continuous development of science and technology, it is expected that more liquid level switches that can adapt to vacuum environments will be developed in the future to meet the growing needs of aerospace, vacuum experiments and other fields, and promote technological progress in related industries.