Norsonic NOR150, Instruction Manual

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41 Norsonic Nor150
Instruction Manual
NOTE that frequency compensations, such as
windscreen and or diffuse field, are disabled in the
calibration menu in order to simplify the calibration.
All you have to do is to compensate -0.2 dB for the
difference between the pressure and free field if you
are calibrating a free field microphone using a
1000 Hz calibrator. The frequency corrections are
enabled again when leaving the calibration mode.
Hence, you may therefore obtain a different level
when entering back to the measurement mode from
what you obtained in the calibration mode if you have
a correction switched on.
2 Enter calibration mode . Press the
CAL
key to
gain access to the
Calibration
menu (Figure 8.1).
Nor150 offers two different ways to perform an
acoustical calibration,
Manual or Auto . The third
option
Mic. Check
is an electrical verification of
outdoor microphones.
3 Know the output level of your sound calibrator.
Some sound calibrators have an output level
of 94 dB, while others (like the Nor1255 which
is used in the example below) have an output
level of 114 dB. Some have an output of 124 dB
(like the Nor1253). Unless you know the output
level of your sound calibrator you won’t be able
to know what level the measuring instrument is
supposed to show. The output level is normally
printed on the sound calibrator or stated in its
accompanying user documentation.
4 Free-field microphones require lower settings.
Be aware of the fact that instruments using free-
field microphones shall be adjusted to a value
slightly lower than the output level of the sound
calibrator. For a half-inch cartridge this will
typically amount to 0.2 dB lower for calibrators
producing a 1000 Hz calibration signal (e.g. the
sound level meter should then be set to 113.8 dB
when using a 114 dB @ 1000 Hz sound calibrator).
Other frequencies will require different correction
values.
5 Set the sensitivity. Select either
Manual
or
Auto
.
Do not use Mic. Check . See separate chapter for
description of this feature.
In Manual mode (Figure 8.2) you simply use the
+
and
-
to adjust the sensitivity until you read correct
level. New values are set with the √ . The old value
is preserved with the button.
In Auto (Figure 8.3) you select the calibrator level
and frequency and push the
Calibrate
soft key
button. The instrument will automatically perform a
calibration. The level is displayed in the L(t) trace in
the calibration menu. New values are set with the √ .
The old value is preserved with the button.
Calibrating outdoor microphone Nor1214,
Nor1216, Nor1217 or Nor1218! Please note that
the frequency correction is turned off, when entering
into the calibration menu. Perform calibration and
calibrate the microphone as a normal free field
microphone. I.e.-0.2
dB if using a 1000 Hz calibrator.
When leaving the calibration menu, you will observe
that the level measured with the calibrator on, is
different from what obtained in the calibration mode.
This is correct, and is due to the frequency correction
added. If Horizontal position is selected the signal
will be about 0.1 dB higher than the calibrated signal,
in vertical position the signal will be 0.3 dB lower
than the calibrated level.