【正文】 1 附錄 C Liquid Level Measurement Chemical industry with the progress of science and technology got rapid development, in order to make the equipment safe and reliable operation, and can be utmost to improve product quantity and quality, to effectively operate automatically and process adjustment, realize the scientific management for the enterprise to provide the necessary material and energy of accurate data, must be in production in the process of pressure, flow, level, temperature, chemical position of various parameters such as timely, accurate measurement. Generally the process of containers, tanks, towers, tank of liquid surface position level, slot bucket, cans, and warehouse ChuFa solid block, the accumulation of particles, powder height and surface position is called a material level。 Two not fluid boundary between the height and the liquid and solid separation height is called interface position, the position of assembly level, material level, liquid level interface. Material level measurement to correctly measure the container storage capacity or quality, know container level of high and low and adjust at any time, in the material level to maintain the required height. Material level measurement in chemical process, not only under normal temperature, atmospheric pressure and ordinary medium, material level, liquid level measurement of the interface, but also often meet high temperature, low temperature, high pressure, inflammable and explosive (negative temperature). Viscosity and foam, boiling dielectric material level measurement problems. In order to adapt to the characteristics of chemical objects, to meet the requirements of the chemical process material level measurement, there are many material level measurement and instrumentation. 1. Ultrasonic liquid level meter and radar material level meter (1) ultrasonic liquid level meter Material level measurement process, the ultrasonic signal, issued by the ultrasonic probe, the liquid or solid material surface after launch back, by the same sensor receiving, ultrasonic measurement of the whole running time, so as to realize the measurement of material level, 2 acoustic velocity transmission of the ultrasonic pulse, from transmitting to receiving to ultrasonic pulse need time interval and the transducer to the surface of the measured medium is proportional to the distance. Emit ultrasonic level meter pulse, not the echo of detection at the same time. Due to the launch of the ultrasonic pulse width has a certain time, and after launch the ultrasonic sensor and aftershocks, during cannot detect the echo, so from the start down the surface of the probe a short distance can39。t normal inspection, this distance is called blind spots. Was the highest level such as into the blind area, detect instrument will not be able to correctly, there will be error, if necessary, heightened level meter can be installed. Ultrasonic liquid level meter also has shortings, the ultrasonic transmission by gas interference, level surface bubbles, corrugated, etc, the ultrasonic transmission by gas interference, level surface bubbles, corrugated, etc., the ultrasonic reflection effect. Material is volatile, liquid gas entrapment, the container by vibration (., motors) are installed on the container can39。t use ultrasonic liquid level meter. (2) radar material level meter Radar level gauge USES launch reflection receive work mode. Radar level meter antenna emit electromagic wave, the wave reflected by the measured object surface, again by the antenna, the electromagic wave from transmitting to receiving time is proportional to the distance to the liquid surface. In practice, there are two kinds of radar level gauge means the frequency modulation continuous wave and pulse wave. Liquid level meter adopts frequency modulation wave technology, power consumption is big, the four wire system, should be used in electronic circuit is plicated. And the radar pulse wave technology level gauge, low power consumption, easy to implement essential safety, high precision, wider application scope. Radar level gauge measuring the electromagic waves can pass through a vacuum, don39。t need a transmission medium, is not affected by air, steam, groove volatile fog effect, can be used for such as coarse benzene volatile medium level measurement. Rad