G.R.A.S. Sound & Vibration
Sound-intensity Probe Type 50AI - Page 15
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).
4.5
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.
Fig. 4.3 Changing the spacer: Pull the two halves of the probe
apart, unscrew the spacer from the microphone grid,
screw another spacer on and push the two halves of the
probe
together
again.
Pull apart
Push together
