Study On Capacitively-coupled Electromagnetic Flowmeter

Electromagnetic flowmeter is a volumetric flowrate flowmeter which based on the Faraday's law of induction. Due to its simple structure, no pressure loss and wide measurement range, electromagnetic flowmeter becomes one of the most popular flowmeters in industry. Capacitively-coupled electromagnetic flowmeter is a relatively new electromagnetic flowmeter and is still in developing. The capacitively-coulped electromagnetic flowmeter can measure low-conductivity fluids, high-concentration slurry fluids and adhesive fluids, which are difficult to be measured by the conventional electromagnetic flowmeters. Thus the capacitively-coupled electromagnetic flowmeter extends the application of electromagnetic flowmeter and become one of the important research content of the electromagnetic flowmeter in recent years.After reviewing the related literatures, research in this work focuses on the sensor and signal conversion circuit (the key parts of the capacitively-coupled electromagnetic flowmeter). A prototype flowmeter is developed and has been tested on the flow loop in lab. The main works are listed as follows:(1) The cross-correlation detection theory is introduced to the design of the signal converter and the rotating capacitor filter technology is applied to solve the problem of detecting the weak flow-related signal from the background with high level noise under the low signal-to-noise ratio condition.(2) For processing the signal come from the rotating capacitor filter, a synchronous rectification and sampling circuit is designed. Experimental results indicated that the circuit can reduce the noise and provide steady voltage signal.(3) A prototype of the capacitively-coupled electromagnetic flowmeter is developed and the measurement test is carried out on the experimental system. Experimental results indicated that the method is effective and the design of the prototype is applicable.