The rotation period has been measured for a turbine shaft in a thermal power station by an optoelectronic method. The electronic unit is screened from electromagnetic interference at line frequency, and the fiber-optic lines provide a measurement error of 5.10-4%.Metering and diagnosis for thermal power station turbines require elevated accuracy in measuring the shaft period. We have built a chronometric monitoring system whose block diagram is shown in Fig. 1.The primary optoelectronic converter is set up in the gap between the generator and the exciter of a T-250/300 turbine and includes light-emitting diodes, receiving lenses, connecting fiber guides with photocells, and a disk containing holes that modulates the light flux.To reduce the effects of electromagnetic fields and interference at 50 Hz, the electronic unit is shielded by a multilayer ferromagnetic screen, while the data-processing unit and personal computer are placed outside the area of strong external fields. The optical fibers transfer not only the modulated light flux but also the light pulses produced in the electronic unit.The monitoring system provides continuous recording of the rotation period and the time intervals corresponding to angles of rotation that are multiples of 1/12 of a complete rotation, and it has the following basic characteristics: monitoring system multichannel measuring time intervals in the range 13.5 to 10 -1 see, absolute error of measurement +1-10 -7 see, relative error 5-10-4%, limiting frequency of signals recorded in the RAM 120 kHz, and on hard disk 5 kHz.This accuracy enables one to record deviations in the rotation period T from the nominal value of 2-10 -2 see and to defect nonuniformity within a rotation.The software manages the data files, selects the processing algorithms (statistics, spectral analysis, filtration, and so on), and supports the graphical representation of the measurement and analysis results. A difference from other software is that it uses special data formats to provide the optimum combination with the hardware. The program works in a DOS environment in overlying mode and uses dynamic memory and free disk space for processing and storing the intermediate results. The software is implemented in Pascal.The accuracy is provided by protection recording of the instants of arrival of the video pulses in the system from the open input system. One recovers the envelope of the video pulse at the input to the primary transformer by simulation based on a Duhamel integral.Simulation shows that delay in the video signal envelope on passage through a low-pass filter is governed by the filter passband and by the variation in the triggering time for the entire front A in the relation ~t = 1/~0 + A. The random signal component is governed by the internal noise in the photodiode. A white thermal noise approximation was used.This gave the accuracy in envelope recovery in relation to the passband and the sensor noise, which enabled us to optimize the technical parameters in recording the pulse-modulated signal...
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