tailieunhanh - GasTurbine Engineering HandbookSecond Edition phần 8

Nhiệt độ tối đa đạt được trong các khu vực trọng điểm stoichiometric 4040 F (2230 C) và sau khi pha trộn của quá trình đốt cháy với không khí làm mát nhiệt độ giảm xuống mức thấp F (1370 C). Cơ sở để phòng chống NOx. Phát thải từ tua-bin là một hàm của nhiệt độ và do đó | Spectrum Analysis 559 For example 6db 2 10db 20 db 10 40 db 100 If the S N ratio is less than 10 db it becomes difficult to differentiate the periodic part of the spectrum from noise. Several types of analyzers exist today that allow a time-domain signal to be converted to a frequency-domain spectrum. The resulting spectrum of all spectrum analyzers is equivalent to the amplitude frequency plot which is obtained by passing the given signal across a set of constant bandwidth filters and noting the output of each filter at its center frequency. Unfortunately such a simple procedure cannot be used because for adequate resolution each filter can cover only a very narrow frequency band and because of the cost involved. In the so-called wave analyzer or tracking filter one filter is utilized by manually incrementing the filter across the time input to determine which frequencies exhibit a large amplitude. In time-compression real-time analyzers RTA the filter is swept electronically across the input. The term real time as applied here means the instrument takes the time-domain signal and converts it to a frequency domain while the event is actually taking place. In technical terms real time is viewed when the rate of sampling is equal to or greater than the bandwidth of the filters taking the measurements. RTAs use an analog-to-digital converter and digital circuits to speed up the data signal effectively and improve the sweeping filter scan rate thus creating an apparent time compression. Both of the previous analyzers are basically analog instruments and because of the characteristics of analog filtering may be quite slow at lower frequencies. The Fourier analyzer is a digital device based on the conversion of timedomain data to a frequency domain by the use of the fast Fourier transform. The fast Fourier transform FFT analyzers employ a minicomputer to solve a set of simultaneous equations by matrix methods. Time domains and frequency domains are related through