Outdoor Microphone System Type 41AM Product Data and Spcifications Typical applications ■ Permanent outdoor-noise monitoring ■ Airport-noise monitoring ■ IEC 60651 Type 1 noise measurements The Outdoor Microphone System Type 41AM (Fig. 1) is for outdoor use whenever trouble-free acoustic measurements and, in particular, noise monitoring around airports are required. It complies with IEC 651 Type 1 and ANSI S1.4 1983 Type 1 requirements and can be used with any suitable electronic sound or vibration measurement system. It is PTB approved as part of an IEC 651 Type 1 system. A '/2-inch precision condenser microphone and thick-film preamplifier ensure maximum stability and performance. Both microphone and casing are made of stainless steel. Precise in-situ calibration checks at 1000 Hz are ena-bled any time via a built-in electrostatic actuator and test oscillator. The Type 41AM is itted with anti-bird spikes, a windscreen, and a rain cap which is an integral part of its acoustic omnidirectional characteristics. The rain cap, which contains the electrostatic actua-tor, remains in position while calibrating the micro魭phone with a pistonphone. The large dynamic range of the Type 41AM is obtained via a twin circuit board with a DC con-verter for supplying 200 V for microphone polariza-tion as well as a 120 V supply for the preamplifier. The sensitivity of the amplifier can be adjusted by 12 dB and the gain changed by ± 20 dB (via a pair of circuit-board jumpers) to give optimum signal-to-noise ratios on long cables. The gain is normally set to 0 dB on leaving the factory. Fig. 1 Outdoor Microphone System Type 41AM. Inset shows reference direction An A-weighting ilter for increased dynamic capa-bility is included in the Type 41AM. A circuit-board jumper is used to select either the A-weighting or linear frequency response. A-weighting or linear response can be speciied when ordering, otherwise Lin-weighting will be active on delivery. The built-in calibration oscillator can be switched on or off by short-circuiting a pin to ground in the output socket of the Type 41AM. The electrostatic actuator is factory set to a calibration level of 90 dB re. 20 (i Pa at 1000 Hz. A calibration level of 94 dB can be speciied when ordering. The electrostatic actuator and microphone assembly is electrically isolated from the casing of the Type 41AM; thus eliminating EMC and ground loops. A silica-gel desiccator is located inside the lower half of the casing and a humidity-indicator window Ci C t G.R.A.S. Sound&Vibration Skovlytoften 33 2840 Holte, Denmark Tel +45 45 66 40 46 Fax +45 45 66 40 47 e-mail: [email protected] www.gras.dk