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Summary of Contents for G.R.A.S. 50AI
- Page 1 Instruction Manual Sound Intensity Probe Type 50AI G.R.A.S. Sound & Vibration Skovlytoften 33, 2840 Holte, Denmark www.gras.dk...
- Page 2 Sound-intensity Probe Type 50AI Revision 6 June.2014...
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Page 3: Table Of Contents
G.R.A.S. Sound & Vibration CONTENTS Introduction and Description........3 Main Components . -
Page 4: Introduction And Description
G.R.A.S. Sound & Vibration Introduction and Description The Sound-intensity Probe Type 50AI (Fig. 1.1) is a two-microphone sound intensity probe. It has a pair of G.R.A.S. phase-matched ½″ microphones Type 40AI (Fig. 1.2), two G.R.A.S. ¼″ microphone preamplifiers Type 26AA, solid spacers, remote control handle and connection cable. The probe is adjustable, durable and fully complies with the following requirements: • IEC 61043, Electroacoustics - Instruments for the Measurement of Sound Intensity - Meas- urements with Pairs of Pressure Sensing Microphones, 1993 for Class 1 Sound-intensity probes. Fig. 1.1 The Sound-intensity Probe Type 50AI Sound-intensity Probe Type 50AI - Page 4... -
Page 5: Main Components
The main components of the Sound-intensity Probe Type 50AI are: • Sound Intensity Microphone Pair Type 40AK • Two Microphone Preamplifiers Type 26AA • Four solid spacers of various lengths and a spacer cup (see Fig. 1.5) • Remote-control handle with (where applicable) up to two push buttons for controlling meas- urements See also Fig. 1.8. The Type 50AI is delivered in a carrying case similar to the one shown in Fig. 1.2, complete with microphones, preamplifiers, standard accessories and a remote-control handle. Fig. 1.2 The type of carrying case delivered with the Type 50AI 1.1.1 Microphones The microphones (Fig. 1.3) are high sensitivity, free-field ½″ condenser microphones with a uniquely-designed pressure equalization system that ensures extremely well defined phase characteristics. The microphones and preamplifiers are mounted on the end of the telescopic arm of the Remote-control handle. To cover the full frequency range from 50 Hz to 10 kHz, the Type 50AI is delivered with four solid interchangeable spacers for spacing the microphones at 12 mm, 25 mm, 50 mm and 100 mm. Sound-intensity Probe Type 50AI - Page 5... -
Page 6: Preamplifiers
RA0266 RA0265 RA0264 RA0263 Spacer cup 12 mm spacer 25 mm spacer 50 mm spacer 100 mm spacer Fig. 1.5 Showing the various spacers and the spacer cup supplied with the Type 50AI Sound-intensity Probe Type 50AI - Page 6... -
Page 7: Available Versions
Use with the Type 12AB enables direct use with 01dB Sound Intensity systems. Type 50AI Type 50AI Type 50AI version B version HP version C version D version LD Fig. 1.6 Showing the markings and external features on the remote-control handles of the various versions of the Type 50AI Sound-intensity Probe Type 50AI - Page 7... - Page 8 Slide cover back Fig. 1.7 Access to the 9 -V battery located inside the remote-control handle of the Type 50AI version D. The battery should be disconnected / reconnected while inside the remote-control handle Sound-intensity Probe Type 50AI - Page 8...
- Page 9 G.R.A.S. Sound & Vibration Sound-intensity Probe Type 50AI - Page 9...
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Page 10: Input Channels
Sound-intensity Axis Fig. 2.2 illustrates the origin and direction of positive sound-intensity vectors. This positive direction is always from microphones A to B. The origin of the sound-intensity axis lies on the geometric centre of the pair of probe micro- phones. Markings for chan- nels A and B Fig. 2.1 Showing the inputs and markings for the two preamplifier inputs Sound-intensity Probe Type 50AI - Page 10... - Page 11 Origin of intensity axis Fig. 2.2 Showing the microphones ‘A’ and ‘B’ which correspond with channels A and B respectively. ‘A’ is the leading microphone and is struck first by a sound wave Sound-intensity Probe Type 50AI - Page 11...
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Page 12: Output Socket
Use with Power Module Type 12AB If the Type 50AI is used with a G.R.A.S. Power Module Type 12AB, pins 9, 10, 11 and 12 (Fig. 3.1) automatically have an outlet via the RS232 port of the Type 12AB (see Fig. 3.2) for further connection to an analyser/computer. Fig. 3.2 9-pin female D-sub connector socket of the Power Module Type 12AB for connecting directly to an RS232 computer port (external view) Sound-intensity Probe Type 50AI - Page 12... -
Page 13: Handling And Assembling The Probe
The distances between microphones and preamplifiers have been kept to a minimum in order to avoid problems with any stray capacitance and sensitivity to vibration. While amplitude characteristics are little influenced, the phase characteristics of a Sound-intensity Probe can be critically affected by even very small vibrations in the conductors carrying the raw signals from the microphones. Therefore, the ¼″ preamplifiers are mounted in rigid contact with the ½″ microphones via short adapters (right-angled and/or straight). This also eliminates problems with non-matching capacitances between microphones and preamplifiers, which could give rise to phase problems. Physical Strength From a physical point of view, a Sound-intensity Probe should be robust and easy to assemble and dismantle. Typically, there are two points in a Sound-intensity Probe which can be identi- fied as critical for physical strength and are the most likely to suffer damage and are the most difficult to repair. These points are the threads on microphones and preamplifiers as well as on the microphones’ protection grids. The connections between microphones and preamplifiers are very delicate and carry both microphone signals and microphone polarisation voltages. There- fore, the preamplifier threads of the Type 50AI are supported by stainless steel ½″ to ¼″ adapt- ers. There is also a protective guard within the ¼″ housing of each preamplifier. In addition, the microphones’ protection grids are made of stainless steel to withstand rough physical treatment since a buckled or damaged protection grid will almost invariably damage a microphone’s dia- phragm beyond repair. Assembling the Probe The Sound-intensity Probe can be assembled in either a straight configuration or a symmetri- cal configuration The straight configuration (Fig. 4.1), is for intensity measurements close to surfaces and general source location measurements. The symmetrical configuration (Fig. 4.2), is ideal for sound power measurements, for example according to international standard ISO 9614-2 “Acoustics - Determination of sound power levels of noise sources using sound inten- sity” where a rotation test is required. The probe on the Type 50AI consists of the parts shown in Fig. 4.4. Assemble as follows. Sound-intensity Probe Type 50AI - Page 13... - Page 14 The frequency range of intensity measure- ments may therefore be extended to frequencies up to 10kHz using ½″ probes with a 12 mm spacer. Sound-intensity Probe Type 50AI - Page 14...
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Page 15: Using The Windscreen
2. Now assemble the probe head by pressing the free end of the spacer (mounted on the one microphone) into the spacer cup mounted on the other microphone. To change the spacer, in order to cover a different frequency range, dismantle the probe head by pulling the spacer out of the spacer cup, unscrew the spacer and replace it with another one (see Fig. 4.3). 3. Mount the probe head by sliding one of the preamplifiers into the clamp (which can be locked at angles of 0 °, 45 °, 90 °, 135 ° and 180 °) at the top of the telescopic arm and tighten the finger screw (see the examples in Figs. 4.1 and 4.2). Connect the two preamplifiers to the input connectors at the top of the tubes shown in Fig. 2.1. The left input connector is labelled as channel A on the probe handle and the other input is labelled channel B. For the correct sign of the intensity vector, the front, or leading microphone should be connected to input channel A (see section 2.1). 4. Connect the probe to the analyser via the appropriate adapter cable (depending on the specific type of analyser). The functions of the operating buttons and indicating LEDs on the control handle are determined by the analyser in use and information about these should be found in the instruction manual of the given analyser (see also sections 1.2 and 3.1). Using the Windscreen The Sound-intensity Probe Type 50AI includes an elliptical windscreen (AI0001) which can be used whenever making outdoor measurements or when making indoor measurements in the presence of bulk air movements. Use it only when measurements are influenced by wind. It gives good protection at wind speeds greater than 0.5 m/s and can reduce pressure fluctuations caused by turbulence by as much as 20 dB with this technique of intensity measurements. Sound-intensity Probe Type 50AI - Page 15... - Page 16 RA0266 Spacer Type 40AI Matched pair of GR0040 microphones Spacer cup RA0001 Right-angled adapter Type 26AA ¼″ Preamplifier Fig. 4.4 Exploded view of probe assembly. On the left: straight setup. On the right the branch for a symmetrical setup Sound-intensity Probe Type 50AI - Page 16...
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Page 17: Specifications
0.4 kg (0.9lbs) Version B Accessories included: Windscreen AI0001 Version B Remote-control handle: Built-in remote control functions for 01dB analysers. Two buttons for averaging control and two LEDs for status indication and overload indication. Accessories included: 5 m cable AA0021 Adapter cable AC0002 (12-pin LEMO to 2 x 7-pin LEMO, plus remote- control male 6-pin mini DIN plug) Version C Remote-control handle: General-purpose intensity handle with two 7-pin LEMO 1B output connectors. Accessories included: 5 m cable AA0021 Adapter cable AC0003 (12-pin LEMO to 2 x 7-pin LEMO) Sound-intensity Probe Type 50AI - Page 17... -
Page 18: Version D
AC0005 (12-pin LEMO to 2 x 7-pin LEMO, plus remote- control female 9-pin D-sub plug) Version HP Remote-control handle: Built-in remote control functions for Hewlett-Pakard analysers. One button for measurement control. LEDs for status indication and overload indication. Accessories included: 3 m cable AA0040 Adapter cable AC0006 (12-pin LEMO to 2 x 7-pin LEMO, plus remote- control male 15-pin D-sub plug) Version LD Remote-control handle: Built-in remote control functions for Larson Davies analysers (LD3000 or LD2900). One button for measurement control. LEDs for status indication and overload indication. Accessories included: 5 m cable AA0021 Adapter box AC0007 (for LD3000) AC0004 (for LD2900) Sound-intensity Probe Type 50AI - Page 18... - Page 19 Fig. 5.1 Working frequency ranges covered by the various spacer lengths. The top bar is for the case when a Type 50AI is equipped with a pair of ¼″ intensity microphones (Type 40BI) and a 6 mm spacer (note the extend- ed high-frequency range).
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