是一系列非接触，高可靠、低价格、免维护的物位仪，它彻底解决了由压力变送器、电容式浮子式等测量方式带来的缠绕、泄露、接触介质、昂贵的维护等麻烦，它不必要接触工业介质就满足大多数密闭／敞开容器里的物位测量要求。 The ultrasonic level gauge is a series of non-contact, high reliability, low price, and maintenance-free level gauges. It completely solves the entanglement, leakage, and contact with media caused by pressure transmitters, capacitive floats, and other measurement methods. Costly maintenance and other troubles, it does not need to touch industrial media to meet most level measurement requirements in closed / open containers. Today, with the development of electronic technology, ultrasonic level measuring instruments can measure level ranges from a few centimeters to tens of centimeters, showing extraordinary capabilities under many harsh conditions. The internal principle of ultrasonic level gauge measurement is very simple. The ultrasonic probe is located on the top of the container. It transmits pulse waves to the surface of the measured medium, and at the same time receives echoes reflected from the surface of the measured object. , Which is the round-trip travel time of sound waves in space to measure the distance of the probe from the surface of the measured medium.
The effect of speed:
The frequency of the ultrasonic level gauge in industrial applications is 5KHZ-5MHZ, and the level measurement technology is 5HZ-40HZ. The calculation formula for the distance from the ultrasonic probe to the surface of the medium is as follows:
D = t1 × C / 2
D: the distance from the probe to the surface of the medium
t1: propagation time of sound waves
C: It can be known from this that in addition to the measurement accuracy of the propagation time of the acoustic wave, the propagation speed of the acoustic wave plays a decisive role.
The speed of sound varies depending on the media. In practical applications, various factors affect the propagation medium and the speed of sound. Today, in order to obtain more accurate measurement results, the ultrasonic level meter can set the sound speed of different media by the degree.
Effect of temperature:
The change in temperature affects the change in speed of sound. In normal environments, the change in temperature brings about a change in speed of sound of 0.17% ° C. In actual measurement, a variety of natural factors can cause errors, and Baxter's advanced measurement system, including temperature sensors and software functions, can automatically compensate for the effects of temperature. 传播媒介的温度以及被测介质的温度不尽相同。 In practical applications, due to the surrounding environment of the probe, the temperature of the ultrasonic level gauge propagation medium and the temperature of the measured medium are different. The measurement system should select the built-in temperature sensor combined with the probe and the external temperature sensor separated from the probe according to the actual requirements. A more accurate measurement system can place an echo reflection reference object at a specific position from the probe to generate a reference echo to compensate for temperature effects. The effectiveness of this method depends on the accuracy with which the echo-reflected reference is placed.
Effects of stress:
Relationship between temperature changes caused by pressure changes: LnT1 / T2 = 1.4LnP1 / P2
Although the change in pressure affects the working state of the probe, the change in pressure does not directly change the speed of sound. Because of the relationship between pressure and temperature: T = KP (K is constant), the change in pressure affects the change in temperature. This in turn affects changes in the speed of sound.
Emission and propagation of sound waves:
There are one or more piezoelectric ceramic crystals inside the probe, which are used to generate and receive acoustic wave signals. When the piezoelectric ceramic crystals obtain electrical signals, they generate small mechanical vibrations to emit acoustic waves. Similarly, the echo causes the piezoelectric ceramic crystal to generate small mechanical vibrations to emit electromagnetic signals. The practical method is that a probe plays the dual role of transmitting and receiving.
When the piezoelectric ceramic crystal is excited by an electric pulse, it will resonate for a period of time. The initial resonance amplitude is large. As the vibration energy of the probe weakens, the amplitude will tend to zero. During the resonance period, the resonance covers the echo, making the probe inaccurately determine the echo. This period of time is a few milliseconds, and the corresponding distance range becomes: "blind zone". The relative dead zone of 10mS is 1.7m.
In order to ensure the accuracy of the time difference between the transmitted wave and the echo, the echo signal must have sufficient strength to generate and convert into electrical pulses. The strength of the echo signal depends on the strength of the transmitted signal, the characteristics of the propagation medium, the distance traveled and the distance The measurement medium reflects the characteristics of the surface.
The attenuation of the intensity during the propagation of sound waves is due to its absorption by the air, which is determined by the viscosity and heat conduction of the air and the behavioral characteristics of the air molecules.
Impact of dust The impact of dust environment on the speed of sound is very small, but the attenuation of ultrasonic waves is obvious, which is the main factor hindering the implementation of ultrasonic solutions. In practice, the use of low-frequency probes with special foamed plastic surfaces in dusty environments is very successful.
Influence of airflow In an open environment, air acts as a carrier of ultrasonic waves. The lateral airflow will make the propagation path of sound waves bend and become longer. The actual impact is not great.
Influence of the surface of the measured medium
回波强度比率取决于被测介质的特性，所有的介质对超声波都是部分的反射，部分的吸收以及部分的传输。 The echo intensity ratio of the ultrasonic level gauge depends on the characteristics of the measured medium. All media are partially reflected by ultrasonic waves, partially absorbed, and partially transmitted. A dense medium will produce a strong echo, and vice versa. In actual measurements, the echo at the liquid interface is much better than the solid. When echoes are generated on the surface of a fixed particle, their angle directions are different and they have a time difference with each other, causing different phases to reduce the intensity of the echo directly reflected back to the probe.
In principle, there are many factors that affect the measurement. Many manufacturers' ultrasonic level meters have software functions such as temperature compensation and echo tracking identification, which make the meter one of the most successful industrial measurement solutions, including liquid level. , Solid material level, various storage materials, open channel flow, etc., have become the most widely accepted non-contact measurement technology today.