Contacta Loop-FSM Manuale d'uso - Pagina 4

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Background Noise Level Test

After turning the meter on it comes up in the Background

Noise "A weighted" measurement mode. The display will indicate

the RMS reading on the first line and the MAX reading on the second

line. Pressing button "B" resets the MAX reading.

How to test for background noise:

When testing a new facility for background noise first turn on

all lights, fans, sound system and other electrical equipment which

is normally on when the facility is in use. Usually the loop system has

not been installed yet, however if you are certifying an installation

this test is done without the hearing loop system turned on.

Walk throughout the seating area where the loop system will

be used, holding the meter in a vertical position at the listening

plane height. The important reading will be the MAX reading, Howev-

er it is important to watch the RMS reading. If the MAX reading ex-

ceeds –32dBA (readings above –32dBA will have a lower negative

number ex. –30dBA means there is more background noise than

–35dBA), you will need to document the areas where those higher

noise levels are found.

IEC 60118-4 Notes and Requirements

The standard as revised in 2004 notes that any background

noise level lower than –47dBA will result in a excellent signal to

noise ratio, however levels below –32dBA are acceptable and do

meet the requirements of the standard. If the background noise lev-

el is above –32dBA, then the facility management should be notified

and the source of the interference found and repaired.

Method II - Pink noise signal Cont.

Record the RMS level readings for each of the frequencies`.

As in method I if the level does not vary by more than ±3dB the sys-

tem as installed will meet the IEC specification. This method was

requested by the field engineer so they could run the test with one

instrument without continually adjusting the frequency source. It

also makes it easy to conduct the test in more than one location.

Headphone / Full Spectrum Output

The headphone output jack serves two purposes: First it can

be used to monitor the loop program and gives you an "A Weighted"

output signal that can be listened to with standard 1/8" stereo head-

phones. To change the headphone volume slide the Use/Menu

switch to Menu and use the Mode button to advance to Headphone

Volume. Pressing the Select button advances to the volume adjust

screen where the top button raises the volume and the bottom but-

ton lowers it. Once adjusted sliding the switch back to Use will save

the setting.

A full (flat) spectrum output can be sent from this same con-

nector which could then feed a spectrum analyzer. This would show

the signal level at the various frequencies and help to both confirm

proper operation and asses the frequency and level of any interfer-

ences.

To switch from "A-Weighted" to Flat: With the meter turned

on slide the Use/Menu switch over to Menu. Press the Mode button

"A" once and you will advance to the Headphone Jack setup screen.

Then pressing the Select button "B" you can choose either A-

Weighted or Flat Spectrum.

Menu Adjustments

In the Menu mode, selected by the slide switch, the following items

can be adjusted: Backlight level, Headphone output type, Head-

phone volume, Display units (dB, mG, uT) and Power timeout (5 to

30, or none.