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In ISO 10816-8 for reciprocating compressors, there are some plots that show the allowable RMS vs. frequency for every part of a compressor.

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However, in the text of the standard, it is mentioned that overall RMS should be calculated in a range of 2 to 1000 Hz. The question is here, overall RMS in the range of 2 to 1000 Hz will be a single number, so how can we use these plots that show RMS for every frequency?

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The text below is excerpted from the standard that may answer your question:

4.2 Measuring instrumentation and measured quantities

Criteria for classifying vibration values for reciprocating compressor systems are specified in Clause 5. It is recognized that the main excitation frequencies for reciprocating compressor systems are generally found in the range 2 Hz to 300 Hz. However, when considering the complete compressor system, including auxiliary equipment that is a functional part of the compressor, a typical range of 2 Hz to 1 000 Hz is applied to characterize the overall vibration. For the purposes of this document, the overall RMS vibration value shall represent vibration across the frequency range from 2 Hz to 1 000 Hz. For special purposes, a different range can be agreed between the vendor and purchaser.

Since the overall vibration signal usually contains many frequency components, there is no simple mathematical relationship between the RMS, peak or peak-to-peak overall vibration measurements; see Annex D.

The measuring system should provide the RMS values of displacement, velocity and acceleration with an accuracy of ±10 % over the range 10 Hz to 1 000 Hz and with an accuracy of +10 % and –20 % over the range 2 Hz to 10 Hz. These values can be obtained from a single transducer whose signal is processed to derive the quantities not directly measured, preferably an accelerometer whose output is integrated once for velocity and twice for displacement. ISO 2954 gives requirements for instruments for measuring vibration severity. Guidelines on applying methods of signal rocessing and display, e.g. time and frequency domain, windowing and averaging, are covered in ISO 13373-2 and ISO 18431-1 and common examples are given in ISO 18431-2.

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