GRAS 40SC CCP Probe Microphone

Typical applications and use

• Acoustic-impedance measurements
• Exhaust-system measurements
• Near-field measurements
• Measurements at high temperatures
• Pressure-distribution measurements in small enclosures

Design

The GRAS 40SC is constructed with detachable stainless-steel probes tubes which guide the acoustic signal to a prepolarised microphone inside the housing of the 40SC. After being sensed by the microphone, the acoustic signal is passed on to an impedance-matching wave guide which eliminates unwanted internal reflections. The result is a smooth frequency-response ranging from 2 Hz up to 20 kHz. The internal microphone is connectedto an CCP preamplifier with a high dynamic range; ensuring a measurement range from approximately 40 dB to 160 dB re. 20 μ Pa.

The integrated BNC socket is for drawing power from, and delivering the signal to, a constant-current power supply, e.g. the GRAS 12AL CCP Supply, or any other compatible constant-current power supply.

The CCP Probe Microphone 40SC is internally compensated to equalize the internal pressure of the microphone with the static pressure at the probe’s tip . The static pressure within the 40SC will therefore adjust itself to the static pressure existing at the probe’s tip; which it does with a time constant of approximately 0.1 s.

The 40SC can be used with various probe lengths and is delivered with four standard probe lengths, i.e.: 20 mm, 40 mm, 80 mm and 160 mm. Intermediate lengths can be made by cutting these standard lengths. Also, the stainless steel tubes can be bent to a radius as low as 5 mm without downgrading the system’s acoustics. A flexible probe tube is also provided for use in measurements where stiff stainless-steel tubes are not practical. This does, however, slightly downgrade the system’s acoustic performance.

The right angled design of the 40SC makes it particularly well suited for measurements on exhaust-gas systems and other machinery in general as well as for scanning vibrating surfaces such as loudspeaker diaphragms and cabinets.

The compact size, low weight and all-stainless-steel construction of the 40SC make it robust, easy to handle and easy to mount.