，物位的定义：“物位”一词统指各种设备和敞开或密闭的容器中液体或固体物料的表面位置。 Ultrasonic level gauge , definition of level: The term "level" refers to the surface position of liquid or solid materials in various equipment and open or closed containers. There are the following definitions for materials of different properties:
1. The liquid level refers to the height of the surface of the liquid medium in the equipment and the container. 2. The material level refers to the stacking height of solid, granular or powdery solid materials stored in the equipment and the container. 3. The boundary level refers to the position of the phase interface: container The two immiscible liquids in the medium form the interface due to their different severity, which is the liquid-liquid phase interface; the interface between the immiscible liquids and solids in the container is the liquid-solid phase interface. The position of the -liquid, liquid-solid phase interface is referred to as the boundary level.
Level is the general term of liquid level, material level and boundary level. The instrument for measuring, indicating and controlling the level is called the level detection instrument. Classification of level detection instruments: Because there are many types of objects to be measured, and the conditions and environments for detection are also very different, there are a variety of methods for level detection to meet the measurement requirements of different production processes. Level detection instruments are based on measurement The method can be divided into two categories: continuous measurement and fixed-point measurement. Continuous measurement can continuously measure the level change (continuous quantity, output standard continuous quantity signal). Fixed-point measurement method only detects whether the material level reaches the upper limit, lower limit, or a specific Position, fixed-point measuring instruments are generally called level switches (point, output switching signal) are classified according to the working principle, level detection instruments have direct reading type, static pressure type, buoyancy type, mechanical type, electrical type, etc. This is divided into two types of contact type and non-contact type according to our application habits. The currently used contact level instruments mainly include: hammer type, capacitive type, differential pressure type, floating ball type, etc. Non-contact type mainly includes : Ray type, ultrasonic type, radar type, etc. Due to the length of the space, we will focus on the working principle and classification application of ultrasonic material / level gauge.
，物位计的原理及选型 2. Principle and selection of ultrasonic level gauge and level gauge
In many industrial productions, such as chemical, petroleum, metallurgy, power, water treatment and other industries, the position detection and control of materials stored in containers, storage tanks, and warehouses during the production process are often performed, and the accuracy of material level detection Timeliness is of great significance for achieving safe and efficient industrial production. The accuracy of the measurement will affect the correct calculation and credibility of the enterprise's cost accounting, energy consumption and other indicators. At the same time, the scope of application and maintenance of the detection components are also related to the normal and stable production. As mentioned above: The general methods of measuring level include differential pressure, heavy hammer, ultrasonic, radar and so on. With the continuous development of science and technology, the degree of production automation is getting higher and higher, and the requirements for level measurement accuracy, reliability and continuity are becoming higher and higher. Ultrasonic level measurement has been widely used at home and abroad due to its non-contact method and its advantages of corrosion resistance, non-toxicity, maintenance-free, long service life and high cost performance. 1. Measuring principle of ultrasonic material / level gauge We generally call sound waves with a sound wave frequency exceeding 20kHz as ultrasonic waves. Ultrasonic waves are a type of mechanical waves, that is, a propagation process of mechanical vibration in elastic media. Its characteristic is frequency High, short wavelength, small diffraction phenomenon, and good directivity, can be directional propagation. Ultrasonic waves have very low attenuation in liquids and solids, and therefore have strong penetrating power. Especially in solids that are opaque to light, ultrasonic waves can penetrate tens of meters in length, and there will be significant reflection when they encounter impurities or interfaces. Ultrasonic measurement Level is the use of this feature. In the ultrasonic detection technology, no matter what kind of ultrasonic instrument, it is necessary to transmit the electric energy converted ultrasonic wave, and then receive it back and convert it into electrical signals. The device that accomplishes this function is called an ultrasonic transducer, also called a probe. The ultrasonic transducer is placed above the liquid to be tested, and the ultrasonic wave is transmitted downward. The ultrasonic wave passes through the air medium and is reflected back when it encounters the water surface. It is received by the transducer and converted into an electrical signal. The electronic detection part detects This signal will be turned into a liquid level signal for display and output. From the principle of ultrasonic wave propagation in a medium, it can be known that if the medium pressure, temperature, density, humidity and other conditions are constant, the propagation speed of the ultrasonic wave in the medium is a constant. Therefore, when the time required for the ultrasonic wave to be received from the reflection of the liquid surface is measured, the distance through which the ultrasonic wave passes can be converted, and the liquid level data is obtained. 2. Selection and application of ultrasonic level / level gauges At present, various types of ultrasonic level detectors at home and abroad are widely used. The application of CKY series ultrasonic level gauges (separate or integrated) in sewage treatment plants introduces it. Selection and use.
2.1. Features of CKY series ultrasonic level / level meter HLT series ultrasonic level / level meter is a kind of intelligent instrument. It can be remotely connected with the appropriate type of transducer through a cable, which can measure the level in different ranges. Its unique intelligent software makes it have the following characteristics:
(1) The D value requirement of the liquid level gauge is the smallest and the measurement dead zone is the shortest under the same measurement range; (2) The applicable ambient temperature range is -40 ~ + 95C, with automatic temperature compensation; (3) The performance is reliable and maintenance free. It uses intelligent software to effectively identify true and false echoes, which can meet many non-contact measurement applications. (4) Unaffected by the agitator. The unique echo processing function ensures that when the agitator and other liquid surface surges are serious or It can still work reliably and provide stability when there is a lot of foam. (5) Simple installation and easy operation.
2.2 Selection According to the needs and working conditions, selecting the appropriate model is an important condition to ensure accurate and reliable measurement results.
(1) Maximum measurement range CKY series ultrasonic material level gauge (separate or integrated) can be configured with 4, 6, 8, 10, 20, 30m and other types of transducers. When selecting a transducer, you need to consider the characteristics of the material being tested, the nature of the media on the interface, environmental conditions, and the operating conditions of the production system. The degree of attenuation and reflection characteristics of the interface after ultrasonic emission have a great influence on the measurement range. When the ultrasonic attenuation is fast and the interface reflection is poor, in order to avoid that the ultrasonic signal received by the ultrasonic probe is too weak to be distinguished from the noise signal, it is necessary to increase the transmission power of the transducer. (2) The temperature-compensated ultrasonic probe is made of materials with acoustic and electrical effects. When the temperature is higher than a certain temperature, the piezoelectric element will lose its effect and cannot be used. Generally, the ultrasonic transducer is more suitable under the working condition of -20-80 ° C. In addition, because the ultrasonic measurement level is based on the constant sound velocity C in the medium transmitting the ultrasonic waves on the interface of the measured material, in actual applications, the sound velocity of the medium is affected by the temperature in addition to the composition of the medium. With the change of the season, the ambient temperature changes greatly. In order to ensure the measurement accuracy, an ultrasonic substance / level gauge with temperature compensation should be selected. (3) Sound velocity correction The material properties and components of the sound velocity transmitted on the material interface affect the measurement results. In order to adapt to different measurement media, the HLT series ultrasonic material / level gauge is equipped with a sound velocity correction system to correct the changes caused by the composition of the medium The error.
2.3. Whether the installation and testing of the transducer can obtain accurate measurement data is not only related to the accuracy of the meter itself, but also to the installation and commissioning of the meter. In addition to obtaining more accurate test data, correct installation can also ensure that the instrument works stably and is easy to maintain. Pay attention to the following points when installing the ultrasonic level detector:
1. The ultrasonic transducer should be installed in a place that can only “see” the surface of the measured medium, so that the sound waves will not encounter interference from objects such as baffles, agitators, and walls when transmitting in containers, storage tanks and silos. , Resulting in measurement errors; 2. Between the pulses transmitted and received by the ultrasonic transducer, there is a blind zone that cannot be recognized by itself. In order to measure reliably, the highest level of the measurement object should be outside the blind zone; 3. Measurement bin When the internal solid material level is taken into consideration, the solid material is uneven at the interface. Usually, the material at the inlet is higher than the periphery of the storage bin. Therefore, the transducer should be installed at a position that reflects the average height of the material; 4. Another important point when installing a transducer is to avoid zero reflections. When the ultrasonic transducer is aimed at the bottom of the tank or the inclined wall of the discharge port, ultrasonic pulses are emitted but no echo is received. The detector issues an alarm or is adjusted to the maximum. Moreover, the interference echo is used as the material level. Danger of echo reception. An effective way to solve this problem is to place a small reflective plate on the bottom of the liquid storage tank or install the transducer near the tank centerline. 5. The shielded cable should be connected between the ultrasonic transducer and the detector, and both ends of the shielded wire should be grounded to avoid the interference of electrical noise.
的非接触测量原理 3.Because of the non-contact measurement principle of CKY series ultrasonic level gauge
In theory, it is suitable for level measurement in various processes, but in applications, it will be affected by various factors such as installation position, temperature, pressure, humidity, and foam, surge, etc. on the surface of the measured medium. influences. In addition, the transmission distance and directivity of ultrasonic waves are related to the frequency of sound waves and are mutually restricted. Therefore, this measurement method is not suitable for long-distance measurement. In practical applications, appropriate instruments should be selected according to measurement requirements and working conditions to achieve the best measurement results.