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Difference between revisions of "NVGate Synchronous Order Analysis"
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NVGate Synchronous Order Analysis (view source)
Revision as of 09:14, 30 April 2020
, 09:14, 30 April 2020→What is Order Tracking?
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To make order measurements, you must use a proper tach signal which is synchronized with the rotational speed of the machine. | To make order measurements, you must use a proper tach signal which is synchronized with the rotational speed of the machine. | ||
==Outlines== | |||
===What is Order Tracking?=== | ===What is Order Tracking?=== | ||
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The classical way uses a tracking ratio synthesizer based on phased locked loop oscillator which generates a constant number of sampling pulses during one shaft revolution. This synthesizer also controls variable cut off frequency of analog anti-aliasing filters. they are adapted to the variable sampling frequency that is itself depending on the frequency bandwidth. | The classical way uses a tracking ratio synthesizer based on phased locked loop oscillator which generates a constant number of sampling pulses during one shaft revolution. This synthesizer also controls variable cut off frequency of analog anti-aliasing filters. they are adapted to the variable sampling frequency that is itself depending on the frequency bandwidth. | ||
===How the OROS Analyzer Works?=== | |||
====Basics==== | |||
The OROS analyzer is based on a variable digital resampling technique implemented as software in a digital signal processor chip. | The OROS analyzer is based on a variable digital resampling technique implemented as software in a digital signal processor chip. | ||
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The tach signal is sampled and processed in order to compute sampling rate of tach revolution pulses. The arrival time of a tach pulse is computed using interpolation between 2 samples. This tach processing also computes instantaneous speed in order to adjust the cut off frequency of the low pass digital filter used in resampling. | The tach signal is sampled and processed in order to compute sampling rate of tach revolution pulses. The arrival time of a tach pulse is computed using interpolation between 2 samples. This tach processing also computes instantaneous speed in order to adjust the cut off frequency of the low pass digital filter used in resampling. | ||
[[Image:Order_analysis_01_1024.png|800px|none]] | [[Image:Order_analysis_01_1024.png|800px|none]] | ||
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After low pass digital filtering, the analyzed signals are resampled and a standard FFT analysis is done. | After low pass digital filtering, the analyzed signals are resampled and a standard FFT analysis is done. | ||
====Resampling date computation==== | |||
The tach processing first measures date arrival of tach pulses and next computes resampling dates as shown in the figure below: | The tach processing first measures date arrival of tach pulses and next computes resampling dates as shown in the figure below: | ||
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[[Image:SOA_02.png|framed|none]] | [[Image:SOA_02.png|framed|none]] | ||
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So in case of a large speed variation in a revolution, the analyzer can always deliver valuable spectrums. During implementation the operator can adjust the speed variation threshold over which measurements are automatically rejected. | So in case of a large speed variation in a revolution, the analyzer can always deliver valuable spectrums. During implementation the operator can adjust the speed variation threshold over which measurements are automatically rejected. | ||
====Signal resampling==== | |||
The digital resampling of analyzed signals needs a complementary antialiasing filter whose cut off is continuously adjusted to a frequency equal to the product of the maximum analyzed order by instantaneous shaft speed. | The digital resampling of analyzed signals needs a complementary antialiasing filter whose cut off is continuously adjusted to a frequency equal to the product of the maximum analyzed order by instantaneous shaft speed. | ||
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Compared to other methods, the OROS one has the main advantage to be able to work with the full available frequency range of the original sampled signal, so the OROS order tracking analyzer is able to work with signals up to 40 kHz with initial sampling at 102.4 kHz. | Compared to other methods, the OROS one has the main advantage to be able to work with the full available frequency range of the original sampled signal, so the OROS order tracking analyzer is able to work with signals up to 40 kHz with initial sampling at 102.4 kHz. | ||
====Signal analysis==== | |||
The signal analyzer does FFT processing on resampled signal. | The signal analyzer does FFT processing on resampled signal. | ||