Various Technics of Liquids and Solids Level （液体和固体的各种工艺水平）.pdf

Various Technics of Liquids and Solids Level Measurements (Part 3) In part one of this series of articles, level measurement using a floating system was discusses and the instruments were recommended for each application. In the second part of these articles, level measurement with the aid of pressure instruments was discussed. Inthe third part of this series of articles, radar level measurement basics and parameters affecting its efficiency will be explained. RADAR LEVEL MEASUREMENT BASICS Radar level measurement is based on the principle of measuring the time required for the microwave pulse and its reflected echo to make a complete return trip between the non-contacting transducer and the sensed material level. Then, the transceiver converts this signal electrically into distance/level and presents it as an analogue and/or digital signal. The transducer’s output can be selected by the user to be directly or inversely proportional to the span. Pulse radar has been used widely for distance measurement since the very beginnings of radar technology. The basic form of pulse radar is a pure time of flight measurement. Short pulses, typically of millisecond or nanosecond duration, are transmitted and the transit time to and from the target is measured. The pulses of a pulse radar are not discrete monopulses with a single peak of electromagnetic energy, but are in fact a short wave packet (Fig. 13). The number of waves and the length of the pulse depend upon the pulse duration and the carrier frequency used. These regularly repeating pulses have a relatively long time delay between them to allow the return echo to be received before the next pulse is transmitted. Ifwe consider that the speed of light is approximately 300,000 kilometres per second. Then the time taken