2009 年 3 巻 6 号 p. 999-1010
Differential pressure transmitter with an orifice is widely used as a major field flowmeter. A major drawback of this flowmeter used at operation sites is the blockage of an impulse line, which connects a differential pressure transmitter with an orifice tap. In our previous studies, experiments at a water line showed that the diagnostic method based on the pressure fluctuations in the impulse line can diagnose the blockage in the steady state. In this method, however, there was a possibility of making a wrong diagnosis in the transient state. This paper clarifies the applicable conditions of two diagnostic methods: the diagnostic method based on the pressure fluctuations and the diagnostic method based on the phase difference. In particular, the effectiveness of two diagnostic methods in both steady and transient states is investigated by comparing the experimental results at an air line with those obtained at the water line. Through experimental investigations, the following results are derived: (1) The line pressure change has a harmful effect on the blockage diagnosis with the pressure fluctuations. (2) The diagnostic method based on the phase difference can diagnose the blockage even in the transient state; however, this method cannot diagnose the blockage, where the pressure fluctuations are not transmitted at an air line. Therefore, the method based on phase differences remains to be improved in the future work.
