ISO 5348:2021 pdf download – Mechanical vibration and shock — Mechanical mounting of accelerometers.
1 Scope This document specifies the important technical properties of the different methods for mounting vibration transducers and describes recommended practices. It also shows examples of how accelerometer mounting can influence frequency response and gives examples of how other influences can affect the fidelity of the representation of actual motion in the structure being observed. This document applies to the contacting type of accelerometer which is currently in wide use. It is applicable to both uniaxial and multi-axial transducers. This document can also be applied to velocity transducers. This document enables the user to estimate the limitations of a mounting and consequent potential measurement deviations. Transducer mounting issues are not the only problem that can affect the validity of acceleration measurement. Other such problems include, amongst others: transverse movements, alignment of the transducer, base bending, cable movement, temperature changes, electric and magnetic fields, cable whip and mounting torque. Issues other than mounting and their possible effects are outside the scope of this document.
2 Normative references The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 2041, Mechanical vibration, shock and condition monitoring — Vocabulary ISO 8042, Shock and vibration measurements — Characteristics to be specified for seismic pick-ups
3 Terms and definitions For the purposes of this document, the terms and definitions given in ISO 2041 apply. ISO and IEC maintain terminological databases for use in standardization at the following addresses: — ISO Online browsing platform: available at https://www.iso .org/obp — IEC Electropedia: available at http://www. electropedia .org/ 4 Basics A vibration transducer is mounted on the surface of a structure in motion, as illustrated in the simplified diagram shown in Figure 1. Under ideal conditions, the vibration transducer supplies an electric signal at its output which is proportional to the magnitude of the mechanical acceleration input vector, a N . The vector a N is normally directed to the transducer base and measures the projection of the structure vibration acceleration vector, a S , in the direction of the transducer nominal sensitive vectorial axis, a N (measurement direction).
Often, the transducer vibration acceleration vector with the largest sensitivity is not parallel to the accelerometer nominal axis, as a N is perpendicular to its coupling mounting area, as shown in Figure 1 . This forms a cross axis sensitivity of the transducer; see ISO 16063-31. Cross axis sensitivity is maximal in one direction and ideally zero in a direction perpendicular to this in the mounting area. In some transducers on the market, a red dot marks the minimal cross axis sensitive direction. Mounting the transducer in this direction minimizes the cross axis sensitive effects of the transducer during a measurement, if large lateral acceleration magnitudes occur by proper alignment of the transducer. Figure 2 illustrates the complex vectorial relationship between the structure vibration vector, a S , the accelerometer nominal axis vector, a N , the transducer vibration acceleration vector with largest sensitivity, a T , and the angles φ, α 1 and α 2 in between them. The elimination of these alignment deviations usually requires a coordinate transformation. In this consideration, the projection of the structure vibration acceleration vector, a S = (a X , a Y , a Z ), to the transducer vibration acceleration vector with largest sensitivity, a T = (a X , a Y , a Z ), forms the output signal, u, of the transducer. But it is the magnitude in the direction of the accelerometer nominal axis vector, a N = (a X , a Y , a Z ), which is of interest.
