Noise insulation the easy way – Part 2
The first part imparted the basics about noise insulation. Now the second part concentrates on the area of measurement and test systems.
A noise-related examination of the building is advisable if the building site requirements are not met by the building’s technical installations. Based on experience, in the event of disagreements between lift companies and clients (employers/operators), only the noise pressure in areas that deserve protection is measured. Checking the building sound reduction index with a dodecahedron loudspeaker and whether there are sound bridges between the lift shaft and areas that deserve protection is seldom carried out. It is possible to carry out a fast and reliable check whether structure-borne noise transmission occurs between areas that deserve protection and the lift shaft using a Gösele small tapping machine system.
Special measuring and testing devices
With regard to the lift it is necessary to determine what air-borne sound is emitted in the shaft and what accelerations and structure-borne sound is transmitted by the lift and its components to the shaft wall. In the case of lifts without a machine-room, structure-borne sound is a significant factor in generating air-borne sound in areas that deserve protection.
There are special measuring and testing devices for lifts on the market: systems for determining travel quality, energy requirements, network quality, suspension media tension, pressure measurement and the measurement of air-borne and structure-borne sound. Apart from special measuring systems specially developed or adjusted for lift building, there are measuring systems used above all in industry – also in the field of lift technology. Energy measurement technology, network quality, air-borne and structure-borne sound are not special measuring systems for lifts, but are needed to determine quality and for troubleshooting.
Measured values are reproducible
Measuring and testing equipment and its software must comply with the relevant standards and be calibrated or adjusted at set intervals. When measuring air-borne sound the complete measurement system consisting of microphone, connection cable and evaluation unit must be checked before and after each measurement cycle with an adjusted sound calibrator.
Measurements with calibrated or adjusted measuring and testing equipment guarantee that measured values are reproducible and correspond to the measurement tolerances specified in the standards. The proper handling of the measuring and testing equipment and their use under comparable environmental conditions guarantee that the measured results are comparable and reproducible.
Measuring and testing equipment for data determination
A noise level meter is a combination of a microphone with a preamplifier, signal processor and display device. The determination of characteristics made in the standard DIN EN 61672-1 applies to all versions of microphones and preamplifiers suitable for sound level meters.
A microphone is an electroacoustic transducer, which converts acoustic vibrations into electric signals. DIN EN 61094-6, Measurement microphones – part 6: electrostatic actuators for determination of frequency response.
Sound calibrator must be adjustable
The measuring system must be checked with a measurement system consisting of noise level meter and microphone with a sound calibrator before and after every measurement cycle. A class 1 sound calibrator according to IEC 60942 must be used for checking the complete measurement system. The sound calibrator must be adjustable with a corresponding adjustment certificate.
Dodecahedron loudspeakers must meet the following standards: ISO 140-3 Annex C (laboratory measurements), ISO 140-4 Annex A (field measurements) and ISO Annex C (reverberation time measurements). Dodecahedron loudspeakers are needed to determine the sound reduction index of a wall / shaft wall.
Acceleration sensor is nessessary
The Gösele small hammer tapping machine system, like the standard hammer tapping system, is based on the periodic impact of a moved mass. Unlike the standard hammer system, it is primarily intended as an impetus for other components, namely walls, drive frame, rail brackets and in the mechanical engineering industry. While gravity is used to accelerate the impact hammer in the standard hammer system, in the Gösele small hammer system this is electrodynamic force generated by periodic direct current impulses.
An acceleration sensor is nessessary as well. The most common measurement factor for mechanical vibrations is vibration acceleration. It has the SI unit m/s². Gravity acceleration (g) is also frequently used. 1 g corresponds to about 9.81 m/s². Vibration velocity (mm/s) or vibration amplitude (µm, mm) are suitable for several applications, e.g. in machine monitoring.