Norsonic nor1251, User Documentation

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ON button is released. However, you may still use the type
1251 for calibration by keeping the ON button depressed while
you calibrate, provided that the LED is illuminated.
Background Noise Considerations
The high sound pressure level generated in the coupler makes
the calibrator virtually insensitive to external noise. Neverthe-
less, care should always be taken when calibration is made in
places with high extraneous noise levels.
It is always good practice to verify that the background noise
level measured with the microphone mounted in the calibra-
tor—but prior to switching it on—is sufficiently below the cali-
bration level (20dB or more below).
Due to the power-cords, you will not be able to mount the
rear cover while at the same time having the calibrator con-
nected to an external power source.
Without the rear cover, the stated calibrator output level and
the frequency will be altered slightly. The sound from the rear
side of the loudspeaker will be less attenuated and the calibra-
tion process will also be more sensitive to extraneous noise. We
therefore recommend that you always cover the rear side or
compensate for the variation in level and frequency whenever
the rear cover is removed
Battery Replacement
Remove the battery as soon as it is discharged or if the Sound
Calibrator is stored for a prolonged period of time. Leakage from
the battery may otherwise destroy the electronic components.
To change the battery:
1. Remove the rear cover by pulling it straight backwards
2. Pull out the battery from the battery compartment and unclip
the battery connector
3. Replace the battery with a fully charged battery of the type
IEC type 6LR61 (nine-volt alkaline)
4. Alternatively, a nine-volt lithium battery of identical physical
dimensions may be used
5. Install the battery and the rear cover
See also the Fig. on the previous page for details.
Consider Locking the On Button
If the application requires excitation signal for longer periods of
time, you may apply adhesive tape to lock the ON button in its
on position. In this case no indication of proper power supply
voltage will be given as the battery comparator will not be able to
switch the calibrator off.
External Supply of Power
For some applications it may be required to power the calibrator
from an external voltage in the range 8–15V to the battery con-
nector.
Due to the power-cords, you will not be able to mount the
rear cover while at the same time having the calibrator con-
nected to an external power source. See also
Noise Considerations
on the previous page spread for more on this.
The calibrator’s aluminium casing is connected to a voltage
between the positive and negative battery terminals. An exter-
nal supply must therefore be electrically floating relative to the
casing of calibrator.
Recalibration
At regular intervals – at least once per year – proper operation
of the sound calibrator should be verified, preferably by an ac-
credited acoustic calibration laboratory or the Norsonic factory.
The calibration should be carried out at room temperature and
should cover:
• Frequency accuracy
• Level accuracy
• Harmonic distortion
• Level stability