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

(more…)

Continue ReadingRelative signal levels of a sinusoid with and without background noise

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. (more…)

Continue ReadingHow do I balance a shaft?

What is the difference between microphone types?

I’m often asked what is the difference between free field microphones, diffuse field microphones and pressure microphones.

For a run-of-the-mill ½ inch microphone the short answer is nothing.

However the long answer is a bit more involved.

Basically if the frequency range is below 16 kHz and an accuracy of ±2dB is acceptable then there is no real difference between the types.

So what is the difference between these types of microphone?

(more…)

Continue ReadingWhat is the difference between microphone types?