Order Analysis ​​​​​​​​​​​​​​for Rotating Machinery

Order analysis is a technique for analyzing noise and vibration signals in rotating or reciprocating machinery (engines, compressors, turbines, and pumps). These machines have a variety of parts, each of which contributes unique noise and vibration patterns to those of the whole machine.

The common application, often referred to as Run Up/Run Down, is used to survey a machine’s dynamic response when the operating RPM is varied across the entire operating span. In this case, the RPM can range from a few RPM to 10,000 RPMs. Such tests are performed on automotive or aircraft engines and when commissioning new or refurbished stationary processing equipment. The measurements can be any physical quantities such as sound, displacement, velocity, acceleration, torque, etc. The analysis measure can be the amplitude or the power of an order, the energy over a fixed frequency band, a bin of octave filter, etc. The most important result for this type of measurement is the magnitude of the response versus RPM. 

Another common application is monitoring measured machine displacement, velocity, acceleration, pressure, current or sound while the machine is performing its normal duty. The data acquisition system measures the amplitudes of specific orders and their phase relative to a reference tachometer input signal. The phase is calculated relative to the tachometer input or a separate reference input. This application is common for machine diagnosis and balancing. In this case, the operating RPM is relatively stable. Order tracking technology is useful to increase the accuracy of the estimation of orders.

Order Track signals with phase are useful in the study of rotating machines during Run Up/Run Down. This is often presented as a Bode Plot, useful in characterizing resonance/excitation intersections. The Bode Plot is a concept borrowed from control theory. It provides simultaneous Amplitude and Phase data over a changing speed range. 

To perform an order tracking analysis on rotating machinery you will need one vibration sensor (usually accelerometer sensor, a microphone or a pressure sensor) mounted on the chassis of the device and a counter/encoder sensor to read RPM of the rotating shaft.

Both senors will need to be time-synchronized and connected to the data acquisition (DAQ) system for reading. Once data is read you will need data analysis software to perform order tracking analysis.

Dewesoft offers turnkey order tracking analysis solution from sensors, data acquisition system, and software for real-time visualization, analysis, and reporting.

Dewesoft allows performing order tracking analysis only with an accelerometer sensor. To get the rotational frequency of the motor, the exact frequency math is used, with the option to track the first harmonic.

This math calculates the frequency of the highest peak in FFT and this can be used further in the order tracking analysis instead of the reading from external RPM sensor. For more details see this guide.

We refer to Engine orders or harmonics of vibration when we describe multiples of the fundamental frequency. So again using the engine as an example, a 4 cylinder 4 stroke engine generates 2 combustion events per engine revolution.