Principle and application precautions of ultrasonic level gauge

Ultrasonic level gauge is a non-contact, highly reliable, cost-effective, easy-to-install and maintain level measuring instrument. It is a device that can emit energy waves (usually pulse signals) to emit energy waves. The obstacle is reflected, and the reflected signal is received by a receiver. The change of the material level is determined according to the time difference of the movement process of the measured energy wave. The microwave signal is processed by the electronic device and finally converted into an electrical signal related to the material level. The ultrasonic level gauge consists of three parts: ultrasonic transducer, processing unit, and output unit. The structure and working principle of the ultrasonic level gauge The ultrasonic sensor is mainly composed of piezoelectric chips, which can not only transmit ultrasonic waves, but also receive ultrasonic waves. Low-power ultrasonic probes are mostly used for detection. It has many different structures, which can be divided into straight probe (longitudinal wave), oblique probe (transverse wave), surface wave probe (surface wave), Lamb wave probe (Lamb wave), dual probe (one probe transmitting, one probe receiving) Wait. The core of an ultrasonic sensor is a piezoelectric wafer in its plastic or metal jacket. The materials that make up the wafer can be of many kinds. The size of the wafer, such as diameter and thickness, is also different, so the performance of each sensor is different. The working principle of the ultrasonic level gauge: the ultrasonic level gauge is installed on the upper part of the container, and the probe emits to the measured medium under the control of the electronic unit. A beam of ultrasonic pulses. The sound wave is reflected by the surface of the medium, and part of the reflected echo is received by the probe and converted into an electrical signal (such as a 4-20mA signal). The electronic unit detects the time and calculates the measured distance according to the known speed of sound, and the level value can be obtained by subtraction. Ultrasonic waves have very little attenuation in liquids and solids, so they have strong penetrating ability, especially in solids that are opaque to light. Ultrasonic waves can penetrate a length of tens of meters. The bit meter works on this principle. Since the temperature has an effect on the speed of sound, the instrument should measure the temperature to correct the speed of sound, which is often referred to as temperature compensation. The types and applications of ultrasonic level gauges are divided according to the use environment. Ultrasonic level gauges can be divided into ordinary ultrasonic level gauges and anti-corrosion ultrasonic level gauges. The material of the ordinary ultrasonic level gauge transducer is PC, which can be used in the measurement of most non-corrosion environments. The anti-corrosion ultrasonic level gauge transducer is made of PTFE, which can be used in the measurement of strong corrosive environments in industrial sites, such as the measurement of sulfuric acid and hydrochloric acid. According to the structure, the ultrasonic level gauge can be divided into two types: integrated type and split type. The integrated ultrasonic level gauge is the instrument head and the transducer as a whole. This integrated ultrasonic level gauge has high protection level and strong anti-interference ability, and can adapt to most industrial environments. The split ultrasonic level gauge is installed separately from the meter head and the transducer, and the head and the transducer are connected by wires. The split ultrasonic liquid level gauge is suitable for complex environments such as inconvenient maintenance and debugging, and the functions of bus communication and switch output on the meter head can be used for transmission and remote control. According to the requirements of GB 50093-2013 'Code for Construction and Quality Acceptance of Automation Instrumentation Engineering' 12.2.11, the tank level gauge and material level gauge can be calibrated directly by simulating the material level after the installation is completed. We don't need to calibrate it before installation, and to put it bluntly, we can't think of a good way to calibrate it. But before installation, we can conduct power-on test on it, and use the Hart475 handheld communicator to plan parameters such as range, bit number, unit, and display. The purpose of this is to reduce the workload of the back loop test, and to check whether the watch has been damaged by bumps in transit. In the initial stage of construction of the factory, the conditions were relatively poor, and 24VDC MEAN WELL power supply was generally used to power the instrument for stand-alone testing. In this way, the circuit of the wiring instrument has no resistance, so a 250Ω resistance must be connected in series in the circuit, or an adjustable resistance box can be used to supply the resistance value, otherwise it cannot communicate with the instrument. When wiring the two-wire system, pay attention that the positive and negative poles of the instrument terminal and the power cord cannot be reversed, otherwise the transmitter will not display data. When wiring the four-wire system, pay attention to the fact that the power terminals and display terminals cannot be wrongly connected, and must be connected to the instrument terminals in sequence. Temperature has an impact on the speed of sound. In fact, the speed of sound is not only affected by temperature, but also related to factors such as gas density, humidity, air pressure, noise, and suspended matter in the air. Therefore, in practical applications, only using the method of measuring temperature to compensate has many shortcomings, and there will be some errors in the process of temperature measurement. Therefore, the temperature compensation method is only suitable for general applications, and cannot satisfy high-precision measurement. It is precisely because of this,In the petrochemical industry, ultrasonic level gauges are usually used in equipment that does not require high-precision liquid level measurement, such as open containers or pools.

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