Innovation meets tradition – News from Gefell for wind turbine noise
The Boundary-Layer Microphone - GF 1 and the weatherproof power supply unit WN 1
Microtech Gefell: The boundary layer and the weatherproof power supply unit are specifically developed extensions in order to record the sound emission of wind power stations with measuring microphones pursuant to DIN EN 61400-11.
Additionally, the GF 1 is suitable for determining emission-relevant sound power levels in open spaces, e.g. measurements at power stations, construction sites, filtration and cooling plants among others.
Due to the operation near the ground, unwanted influences of the measurement results by reflections of the ground are avoided. The low wind speed near the ground also has the effect of reducing the wind noise at the microphone.
Together with the impregnated secondary windscreen, the primary windscreen of the GF 1 ensures a broadband reduction of the induced wind noise at the microphone by 40dB.
Due to the acoustic effect of the sound-reflecting boundary layer, the microphone sensitivity increases by 6 dB as inherent to its functional principle. Thus, an overall improvement of the signal-to-noise ratio of approx. 46 dB can be achieved.
As measuring microphone element, class 1 measuring microphones are suitable, which consist of measuring microphone cartridges with a frequency range from 20 Hz to a minimum of 10 kHz, a dehumidifier adaptor and a measuring microphone preamplifier with 200 V or IEPE supply.
The WN1 is a weatherproof power supply unit with the measuring microphone power supply unit MN921. It provides an operating voltage for conventional measuring microphones (7-pol.LEMO®), as well as for IEPE measuring microphones. It can be operated with accumulators, batteries or mains voltage. The amplification of the microphone signal can be set using a rotary switch. The integrated line driver allows a transmission of the microphone signals over a cable length sufficient for measurements on wind power stations.
The structural design of the GF1 allows a simple calibration with a sound calibrator. With the divisible ground plate and the secondary windscreen reduced to an optimum for function and handling, transportation in a compact transport case is possible. With the impregnated secondary windscreen, the ground plate coated with varnish and the weatherproof power supply unit, GF1 and WN1 form a weatherproof system for the standard-conforming sound emission measurement of wind power stations.