What Sample Rate Do I Use To Measure Whole Body Vibration?

What sample rate should I use if I am measuring whole body vibration?

Strict ISO8041 compliance imposes a minimum sample rate of 900 samples per second. This ensures the amplitude and phase characteristics of the applied weightings meet the required criteria. To take account of the anti alias hardware filter we would recommend 1200 samples/second. If non-strict compliance is used the minimum sample rate is 300 samples/second.

ISO2631-1 recommends a minimum data duration of 227 seconds. However, for greater reliability, 600 seconds is now considered essential. That is, a 600 second or longer signal will be more representative and will provide better quality results.

Relative signal levels of a sinusoid with and without background noise

In the process of looking at some order data, a question about the accuracy of the measurement of the signal level of discrete frequency signals which were close to the general noise level.  To answer this question, a small DATS worksheet was created which generated 2 signals.  The first signal was a 35 Hz sinusoid which, by itself the spectrum level was measured to be approximately -9 dB (ref 1 V) as seen in Figure 1.

Spectrum level of 35Hz sinusoid
Fig 1: Spectrum level of 35Hz sinusoid

Continue reading Relative signal levels of a sinusoid with and without background noise

What sensors are required to perform a Rotor Runout Measurement?

The DATS Rotor Runout Measurement package can be used on any shaft where the following probes are available…

  1. A LVDT (Linear Variable Differential Transformer) probe. This is basically a contact probe. This will allow the measurement of the shaft total runout*.
  2. If an electrical runout measurement is also required then an additional eddy current probe (also known as a proximity probe) is needed. This is a non contact probe and can be used in conjunction with the LVDT to measure the electrical runout only.
  3. A once per revolution tachometer is also required. This could be optical, proximity, magnetic and so on.

With these three sensors it is possible using the DATS Rotor Runout Measurement package to find both electrical and mechanical runout.

* Total runout is a composite tolerance including the effects of cylindricity and concentricity, co-axiality, straightness and parallelism along the axis.

How do I balance a shaft?

“How do I balance a shaft?” seems like a fairly straightforward question, but there are a number of things that we need to understand first. Here we look at a number of key concepts that need to be understood in order perform balancing.

What does balance mean?

Well broadly speaking to balance a shaft, mass must be added or removed at certain angles. The concept being that the centre of gravity and rotational centre of the shaft will be equal when the shaft is balanced. Continue reading How do I balance a shaft?