Rotating machinery analysis is primarily concerned with signals relating to the rotational speed and its harmonics. Orders are harmonics of the rotational speed, and therefore evaluating orders can be critically important on many types of rotating machines. Typically order tracking and analysis is done on non-stationary data, such as a run-up or coast-down of a machine.
Basic order analysis, or vibration order analysis, is performed using a fixed sample rate and generating waterfall plots of frequency data versus speed. Speed is most often measured with tachometer inputs that sample at very high sample rates. Measurements are taken realtime, and cursors or user inputs allow users to easily pick out waterfalls, frequency slices, or the overall level of the measurement. It is common to record the raw time signal and perform post processing on this measurement also.
Order tracking is another method to evaluate orders. Order tracking synchronizes the sampling of input signals to the instantaneous angular position of the machine shaft using a resampling technique. Rather than a constant number of samples per time, this results in a constant number of samples per revolution and transforms the analysis to the order domain rather than the frequency domain.
Order tracking has a number of advantages. First, because the orders lie on spectral lines, leakage problems can be avoided. Because of this, order tracking allows for better data with higher speed run-ups. Additionally, order tracking can visually pick out orders easier and to higher order numbers.
Filtered orders provide another method for evaluating rotational speed harmonics. Filtered orders apply a bandpass tracking filter to the signal and filter out everything not related the order of interest. This method is similar to the tracking filters used in sine testing or rotor dynamics analysis. Filtered orders are useful when the user does not want to see the “big picture” of the waterfall plot and only wants the order data versus speed without effort. Applications such as bench testing often use this technique.
Order analysis is used in a variety of applications from basic plant machinery testing to complex automotive engine testing. In the case of automotive engines, the order analysis is often combined with acoustic measurements to understand the noise, vibration, and harshness (NVH) qualities of the engine or vehicle as a whole. Automotive engineers often use order tracking methods for product evaluation and development, design validation, production testing and quality evaluation, and trouble shooting.
Whether performing basic order analysis, order tracking, or order filtering, SignalCalc Dynamic Signal Analyzers offer the best in capability available for these applications. For more information explore SignalCalc Dynamic Signal Analyzers.