The Non-Contact Blade Vibrtion Measurment Of Axial Fan

Fan has a great effect on mining industry. It can continuously provide fresh air for underground workers and reduce gas density. Therefore, fan is called "the lung of the mine".In recent years, more and more fans with little hub ratio are used in order to meet the requirements of low negative pressure and large flow. But when the blade becomes relatively longer, which is easy to cause fatigue failure. Great attention should be paid to the problem of fan blade vibration. In order to monitor the fan blade vibration, it is essential to develop a set of the fan blade vibration monitoring system. The problems caused by fan blade vibration can be found timely by the monitoring system, and measures can be taken timely. The safety and reliability of the fan operation can be improved.The blades are rotating in high speed, so the blade vibration should be measured using non-contact measurement method. The non-contact blade vibration meaurement technology has developed in aviation turbine engine and steam turbine. The two above are similar with axial fan on the overall structure, but they are different on concrete structure. Measurement technique can't applied directly.Based on the analysis of domestic and international non-contact blade vibration measurement technology and combined with the fan's structure and working environment, a non-contact measurement method of axial fan blade vibration was put forward. Then several key problems were studied as follows:Acquiring tip-timing time is one of the key techniques for the method of non-contact blade vibration measurement. There are two methods about acquiring tip-timing time:data analysising method based on date aqusition card and direct measurement method based on the rational combination of processing chip and logic divices. The fromer has sampling error caused by discrete sampling points, the latter is complex and has a long development cycle. For the purpose of overcoming the shortcomings, a method called pulse-width measurement used for axail fan was proposed. Data acquisition programe was writen by LabVIEW. A experiment was designed using PCI-6601 date acquisition card, homemade signal source XHY3A-HFD and DSO-25216A oscilloscope. The feasibility of pulse-width measurement method was verified with the experiment. In order to prove the algorithm of getting blade vibration frequency from the data collected by tip-timing sensors, nonuniform sampling signal of tip-timing sensors was simulated by Lab VIEW, then the amplitude and dynamic frequency was calculated by LabVIEW program. The result was analyzed and the relative error was within engineering ranges allowed. It is illustrated that mathematical algorithm is accurate and the program is correct.To sum up, exploratory study is done in the theory and key technology of non-contact blade vibration measurement. LabVIEW simulation and experiment verification is done. A solid foundation is laid in field application.