Vibration meters are handheld instruments which are connected to and receive a signal from a vibration transducer and have a capability to process data so as to give an indication of vibration parameters. They are sometimes made specifically to meet certain standard, for example, ISO 2631 for Human Vibration or ISO 2372 for Vibration Severity of Rotating Machines. This blog article is focused on more general-purpose vibration meters.
A frequency range of 10 Hz to 10 kHz is desirable for vibration measurements on most rotating machinery. Hence most instruments are designed to be able to measure overall vibration levels in a range of 600 RPM to 600,000 RPM. It is possible to cover a total range of 10 Hz to 10 kHz with one accelerometer. If restriction to be made to one vibration parameter, then velocity is usually is the best choice, as most machine vibration signals have a roughly uniform velocity spectrum, so that an increase at any frequency has a roughly equal weight of influencing overall vibration levels.
It can be advantageous to be able to modify upper and lower limiting frequencies within the overall range. For example, restriction of the upper frequency does not allow measurements for gear mesh frequency and their harmonics in gearboxes, resonance frequencies typically excited by rolling element bearing faults, etc.
It is also desirable to be able to measure displacement and acceleration levels; changes at low frequency reflect themselves primarily in the displacement value, while changes at high frequency have the most effect on the acceleration value.
In addition to the measurement of rms levels in each of the vibration parameters, it can also be advantageous to be able to measure some parameter indicating the spikiness of the signal, such as peak values, crest factor and spike energy. Finally, it is useful if the meter has an ac output to allow the signal to be fed to headphones or a recorder. In the absence of data acquisition (DAQ), the human ear can perceive a great deal about the characteristics of a signal.