• How is an order track calculated?

Answer: The order track and frequency track extraction functions provide the same basic capabilities. In the case of order tracks, the tracked "frequency" is actually a frequency value that is proportional to the fundamental tracked gate (i.e. engine RPM, etc.). In the case of the frequency tracking, the tracked value is fixed independent of any of the fundamental gate parameters. For purposes of description, the order tracked option is described in the following explanations. The order plot function extracts the specified order value from the data records. The order value is that value which can be found (for example) in the spectral data by extracting the frequency information corresponding to the equation: Freq = Order# x Fundamental Where the "Fundamental" is the reference gate used to specify the basic fundamental order property (such as the system RPM, etc.). Note that there are implied conversions between frequency (1/sec) and rpm (1/min) which are automatically performed. The Order# is a floating point entry provided by the user. There are several ways to extract the order data from the associated record's spectrum. The options are: Line, Peak and Filter FFT. All of these options operate using the Fourier domain (FFT) data. Due to the nature of using a finite FFT, certain restrictions may be placed on order resolution and consequential results. Line: The line extraction method calculates the nearest spectral line corresponding to the order frequency for the data record. The value is extracted as an rms based result. Errors and other data biases can be attributed to smearing and effects of order frequency truncation due to the finite resolution of the FFT process. The use of this option should generally be accompanied by use of a spectral window (unless the data is synchronously sampled) to try to minimize the leakage effects. Peak: The peak extraction method is similar to the line method with the exception that a range of spectral lines are examined and the maximum value within the range is extracted. This method is slightly less tolerant to leakage effects but a spectral window is still recommended. The range utilized for the maximal scan is established by the dialog "Filter" selection type. The filter employed is a proportional bandwidth filter. The filter settings use the "Width(%)" dialog entry to establish the scanning width by taking the entered % and determining the half width of the bandpass frequency by the equation: Half_Width (Hz) = Order_Freq * Width(%)/200 The Half_Width value is converted to a spectral line count. This line count is used to scan above and below the approximate Order frequency position. Filter FFT: This extraction method utilizes an integration process. All spectral data within a range of spectral lines is (power) summed. The derivation for the range of spectral lines utilized is exactly as described for the Peak extraction method. The Filter FFT method is slightly less tolerant to leakage effects and is useful when a spectral window is not utilized on the data. In both the Peak and Filter FFT methods, the results are based on a proportionally defined tracking filter. This means that the filter bandwidth varies proportionally to the tracked center frequency of the filter. In both cases, the width/accuracy of the filter is predicated on the basic FFT resolution established under the acquisition parameters dialog.

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• I’ve recently changed some of my graphics settings and some of my spread sheets in the dialogs don’t look the same as they did.

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