1. PRINCIPLE

On a 3D APS of a vibration reading as a function of the rotational speed of the electrical machine, we note the presence of:

• harmonics directly related to the rotational speed (blue arrows),
• as well as those related to the PWM (orange arrows).

We want to extract the different types of harmonics and to compare them to the global level over the frequency range, in order to be able to estimate their level of contribution.

This feature is compatible with PAK's dynamic links and cursors management.

2. USE

When displaying a 3D APS (depending on the rpm), there is the option “Use order freq. offs”, to be able to manage the offset of the order cursor:

It can be configured in several ways:

• Fixed value = constant PWM frequency
• User defined = graphic adjustment of points Frequency Offset [Hz] / Time [s]
• RPM dependent Offset = RPM / Frequency Offset [Hz] correspondence table
• Measured frequency channel = when we have a recorded frequency signal (which corresponds to the frequency of the PWM)

In this way, the order cursor will be shifted to this new reference.

It can then be combined with an order extraction (from an APS stored on measurement or by synchronous resampling with the PAK license “P_ORDER” streaming from the Throughput):

We can also combine this functionality with an order sum calculation:

You can also easily ask to be set on the second harmonic of the PWM, by modifying “Offset Factor”, without changing the setting of the “Frequency Offset type”: