Page 23 - 810 Trianing Book Extract

FFT resolution: automatically set at 800 lines. The resolution that the 810 provides is optimized to serve
the 810’s target applications. The 810 collects data in 2 ranges, both in low frequency range (1-10X) and high
frequency (1-100X) which provides the Tester with better resolution and data accuracy than 1600 lines in just

one frequency range.

Since the 810 is designed to diagnose the most common machine faults and not troubleshooting resonances,

800 lines in two ranges is more than enough. Higher resolution increases the measurement time and does not
give any better diagnostic capability.

Example: On a motor running at 1800 RPM, compare two ranges of 800 Lines, or one range of
1600 Lines

• Two Range method

Low Range: 10X1800=18000/800=22.5 RPM/bin

High Range: 100X1800=180,000/800=225 RPM/bin

• One range method

Mid Range: 50x1800=90000/1600=56.25 RPM/bin

Note: Two ranges gives better resolution in the low range where it is needed and collection time is much faster.

(High resolution not needed in the high range to diagnose the common faults)

Windowing: automatically selected as Hanning window. This is typical for diagnosing rotating machines.

High-pass ilter: automatically set at 2 Hz. The Tester was designed for use on the most common machine
drivetrains, which excludes machines with very low and very high rotational rates. Vibrations on low speed
applications (1 Hz, for example) are generally dificult to see, and not needed for diagnosing common faults. There

are a few factors that make the signal from low speed applications unusable:

1. Vibration signals are very small and show up at very low amplitudes (if they show up at all)

2. Tester’s high pass ilter rolls off at 2 Hz (rolls off at 6 dB per octave ➔ @ 1Hz the signal is reduced by 50 %)

3. The integration of acceleration to velocity can add noise to low frequency signal (noise is higher than peaks)

Anti-alias ilter, decimation, overlapping, and averaging: automatically set for the optimum setting.

MEASURE

How do I know that I am getting good data?

Using a vibration analyzer, an experienced analyst would select each machine test location based on knowledge
gained over many years. A single channel sensor is often used by the expert and they will manually analyze the
data by comparing it to the last data collected. When diagnosing machine faults, the change in the data is more

important than the absolute value. Using a triaxial sensor is better suited for the automated diagnostic software
in the vibration tester because it is faster, more complete, and easier to use by a technician who is not a vibration
expert. Instead of having to ind three good locations per bearing with a single channel sensor, the technician

needs to ind just one location per bearing with the triaxial sensor. The baselines were designed by experts who
compared data measured with a triaxial sensor: looking for the amount of change in each of the three directions.

The tester was designed to be easy to use, but it also needs to be able to provide accurate and reliable results. In
order to get a valid diagnosis, the user needs both accurate and complete data. There are two areas of accuracy
that will be discussed: measurement accuracy and triaxial sensor accuracy.

Chapter 6: Advanced topics 143