Crystal Instruments Spider - Order Tracking; Introduction; Capabilities of the Spider

Spider DSA User’s Manual
261
Order Tracking
Introduction
Order Tracking is a general term describing a collection of measurement
functions used for analyzing the dynamic behavior of rotating or reciprocating
machinery for which the rotational speed can change over time. Unlike the power
spectrum and other frequency-domain analysis functions where the independent
variable is frequency, Order Tracking functions present the data against multiples
(Orders) of the variable shaft running speed.
The most useful measurements are Order Spectra and Order Tracks. An Order
Spectrum displays the amplitude of the signal as a function of harmonic orders of
the reference shaft’s rotation frequency. This means that a harmonic or sub-
harmonic order component remains in the same analysis line (at the same
horizontal position) regardless of the speed of the machine.
The technique that observes the changes of a measured quantity at a given order
vs. RPM is called tracking, as the rotation frequency is being tracked and used
for analysis. Most of the dynamic forces exciting a machine occur at multiples of
the rotation frequency, so interpretation and diagnosis is greatly simplified by use
of order analysis.
An Order Track is simply the history of measured amplitude at a single order
versus the machine shaft speed (in RPM). There are other types of tracking
functions. For example, you can track the FFT-based PSD spectra, a fixed band or
an octave band versus RPM; these are all tracking functions.
Capabilities of the Spider
The processing repertoire of Crystal Instruments’ Spider includes performing
Order Tracking functions. With the CI Order Tracking package, the Spider can:
◼ Measure and optionally record up to two (analog or digital)
tachometer pulse signals simultaneously.
◼ Measure and optionally record 1 to 8 analog dynamic response signals
simultaneously.
◼ Process both tachometer signals to yield high fidelity RPM versus time
speed signals (Tach Ch1 and Tach Ch 2) which can in turn be
recorded.
◼ Measure the constant frequency spectrum, also called as the FFT
spectrum for up to 128 channels (requires multiple Spider modules).
◼ Measure the Order Spectra for up to 128 channels
◼ Measure the Order Tracks with phase for up to 128 channels (Can
include multiple orders, including fractional orders for each channel).
Measure the energy in fixed frequency bands vs. RPM for up to 128
channels