The GM90 microphone disc was developed in cooperation with the BMU-funded RENEBAT research projects and represents the successor to the microphone disc FG-DT90 of Avisoft Bioacoustics. The disc features an ultrasonic microphone capsule Knowles FG -23629-P16, which fulfills all the requirements in terms of sensitivity, frequency response and directionality for a successful bat monitoring in nacelle heigth at wind turbines. A built-in preamplifier enables low noise levels of the microphone signals and thus allows cable lengths of 50 m and more between the bat monitoring system BATmode S/S+ or BATmode 2S/2S+ and the microphone disc. To avoid weather-related condensation on the microphone capsule, an electric heater is installed in the disc. With it, a constant microphone sensitivity is achieved over the entire monitoring period and guarantees consistently high data quality. This sensitivity can be monitored and logged with the help of the integrated test signal speaker. Consequently, bat activity data collected with this microphone disc is fully compatible with the BMU guidelines and the sofware tool ProBat, which can calculate wind turbine operating algorithms from the acoustic data of the nacelle monitoring.
To protect against weather and environmental influences, all electronic components are encapsulated splash-proof in the aluminum made microphone disc. For installation in the floor of the nacelle of wind turbines a 100mm mounting hole is required (Drilling plan - GM90).