Norsonic nor140, Instructional Manual, Page: 34 / 220

16
Chapter 3
Calibration
Calibrating the
instrument
Calibration is the normal way of ensuring that the sound
level meter measures the level with sufficient accuracy.
To calibrate we need a sound calibrator.
The use of sound calibrators dates back to the days
when it was easier to design a stable sound calibrator
than a stable sound level meter. Today, sound
measuring instruments are, in general, as stable as
sound calibrators. However, measuring microphones
are very delicate devices designed to fulfil very rigid
specifications. This makes them vulnerable and
subject to damage unless proper care is taken.
One may therefore say that a sound calibrator is just
as much a verification of proper operation as it is a
device of adjusting the sensitivity of sound measuring
instruments.
The Nor140 is calibrated by means of menus and
key pushes – there is no need for a screwdriver to turn
a potentiometer!
When to calibrate
Calibration of the Nor140 should preferably take place
before a measurement session is commenced, or
whenever required by applicable standards. If you
know the microphone cartridge sensitivity, you may
key this in using the numerical keypad. However,
doing so will never replace calibration with a sound
calibrator, as the sensitivity adjustment procedure will
be unable to reveal possible microphone, preamplifier
or extension cable malfunctions.
No need to adjust the full scale setting
Since the Nor140 has a 120 dB dynamic range
(10–130 dB SPL), the 80 dB bar graph range is a
display limitation only. Hence, you won’t have to
bother with setting the full scale before you enter the
calibration menu.
Furthermore, since the Nor140 automatically enters
C-weighted mode, you won’t have to bother with the
calibrator frequency either.
However, you may have to adjust the display top
scale setting to see the top of the bar graph. Use
the
INC
and
DEC
keys for this before you enter the
calibration menu.
Carrying out the calibration
You will need a sound calibrator of sufficient accuracy,
i.e. a class 1 sound calibrator as defined by the
IEC 60 942 standard such as the Norsonic sound
calibrator Nor1251 or Nor1253. Do as follows: