In rotordynamics, order tracking is a family of signal processing tools aimed at transforming a measured signal from time domain to angular (or order) domain.
In some cases the outcome of the Order Tracking is directly the Fourier transform of such angular domain signal, whose frequency counterpart is defined as "order".
Each order represents a fraction of the angular velocity of the reference shaft.
Order tracking is based on a velocity measurement, generally obtained by means of a tachometer or encoder, needed to estimate the instantaneous velocity and/or the angular position of the shaft.
Three main families of computed order tracking techniques have been developed in the past: Computed Order Tracking (COT), Vold-Kalman Filter (VKF) and Order Tracking Transforms.
Order tracking refers to a signal processing technique used to extract the periodic content of a signal and track its frequency variations over time.
This technique is often used in vibration analysis and monitoring of rotating machinery, such as engines, turbines, and pumps.
In order to track the order of a signal, the signal is first transformed into the frequency domain using techniques such as the Fourier transform.
Computed order tracking[1] is a resampling technique based on interpolation.
The procedure begins by estimating the time instants
corresponding to integer rotations of the shaft (i.e. angle equal to
A corresponding vector of time instants is obtained by means of a first interpolation step
A second interpolation step is then applied to obtain the angular resampled signal
Vold-Kalman[2] filter is a particular formulation of Kalman filter, able to estimate both instantaneous speed and amplitude of a series of harmonics of the shaft rotational velocity.
Order tracking transforms are mathematical transforms which perform in a single step both the order tracking (synchronization of the signal domain with the reference shaft) and the Fourier transform to assess amplitude and phase of each order of the so obtained spectrum.
With such transforms it is possible to directly assess the amplitude of a synchronous, sub-synchronous or super-synchronous shaft-locked harmonics, without an additional resampling step.
is the total angular rotation of the shaft in the acquisition window,
are respectively the instantaneous angular rotation and velocity of the reference shaft.