Diagnostics of Impulse Line Blockage with a Multi-sensing Differential Pressure Transmitter at the Air Line

A differential pressure transmitter with an orifice is widely used as a flowmeter. A major drawback of this type of flowmeter is blockage of the impulse line, which connects the differential pressure transmitter to the orifice tap. A diagnostic method based on the amplitude of pressure fluctuations in the impulse line can be used to diagnose a blockage in the steady state; however, there is the possibility of an incorrect diagnosis in the transient state. This paper investigates the causes of this problem by comparing experimental results obtained at an air line with those obtained at a water line. In addition, the effectiveness of a diagnostic method that is based on the phase difference between the orifice high-side and low-side pressures is clarified in the transient state. It was observed that (1) long-term line pressure changes have harmful effects on the diagnosis of a blockage and (2) the diagnostic method can diagnose the blockage even in the transient state. However, this method cannot be used to diagnose severe blockage at an air line. Therefore, further improvement of the method is necessary.