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Title: Environmental Tests Of Gap Discharge Emitter For Use In Ultrasonic Gas Flow Measurements
Author: Emil Martinson And Jerker Delsing
Source: 2009 International Symposium on Fluid Flow Measurement
Year Published: 2009
Abstract: In some situations, the ability to measure gas flows can be very limited due to difficult environmental conditions. Examples of such conditions identified in real situations include very high temperatures of up to 1200C, low pressure gas, high humidity, dust, heavy surface contamination and large dimensions (1-5m pipe diameters). In this paper, we investigate the performance of the only ultrasound emitter type we expect to be able to handle the mentioned conditions. The transmitter has been developed for harsh condition gas flow measurement using the approach of transit time or sing around technology for flow metering. Tests have been performed in a real environment in the iron ore process industry. The testing environment includes gas flows with condensing moisture, moderate temperatures and heavy surface contamination. The device investigated for the emission of ultrasound uses the principle of electric gap discharge to obtain acoustic pressure waves. Since all exposed parts of the emitter can be made using high quality metal and ceramics if necessary, it can be designed for very high temperatures, with a goal of reaching around 1200C. The tests performed here are divided into two categories: the effects of long term exposure in a bad environment and the sonic performance in the same environment. The first test revealed that both emitters were capable of surviving the contamination problem and could still work after almost 1.5 months in the environment. The signal amplitude difference before and after the test was less than 5%. In some cases the signal was stronger after the test than before. The second test showed that sound signals feasible for flow measurement under high dust content and high humidity were obtained. This was shown under realistic operation conditions in an iron ore pelletizing plant. The sound path varied from 1.9 - 3m, and the temperatures were moderate, around 30-80C. From the results in these two tests it can be stated that the idea of using a gap discharge emitter in the above mentioned conditions is a promising way to generate ultrasonic pulses for flow measurements in difficult and unfriendly environments.

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