4.1. Recommendations for correct performing of measurements
Fasten the instrument (or its microphone) to its supporting stand and ensure you are located at
a distance (from the instrument or its microphone) assuring to avoid sound field disturbance.
The measurement range should be chosen so that the meter does not indicate over-range or
under-range condition of the measurement circuit. If the indicated value is less than the lower
limit of the meter's linearity range the correction should be subtracted from the measurement
result. This correction is calculated on the basis of the self-generated noise level read from
calibration certificate using the formula:
(
)
Ls
Lw
L
⋅
⋅
−
⋅
=
1
.
0
1
.
0
10
10
log
10
where:
L
corrected sound level
Lw
sound level read from the meter
Ls
self-generated noise level
Do not perform measurements if the ambient temperature and humidity combination can lead
to vapor condensation in the microphone
4.2. Internal battery
The instrument is normally operated with internal battery supply. To charge the battery, connect
the charger. Attaching the charger is indicated by lighting LED located near charger connector
and displaying icon on results screen, also there is a battery gauge displayed on results screen.
Battery charging in progress is indicated by pulsing LED. If the LED continuously lit, it means that
battery is fully charged.
As far as possible, before charging, the internal battery have to be fully discharged (to
automatically switch off the instrument) - avoid the situation when the battery is often
recharged a little bit, beacause it reduces its durability. Continuous operation with connected
charger is possible.
WARNING! If the instrument is not used for more than two months, the battery should be
recharged. This is necessary because of self-discharge of the battery.
WARNING! The battery is charged regardless of whether the instrument is turned on or off.
4.3. Calibration of the instrument
Correct measurement can be performed only when calibrated instrument is used.
Recommended sound calibrator for DLM-101 sound level meter is SONOPAN KA-50 acoustic
calibrator. This device produces calibrated sound signal of 94 dB nominal sound pressure level
and 1000 Hz nominal frequency. Another sound calibrator of class 1 or better, producing signal
of nominal sound pressure level and frequency equivalent to KA-50 sound calibrator, can be also
used for calibration.
To perform calibration of the instrument correctly:
•
enter calibration mode (see chapter 3),
•
calculate and set reference level:
L
ref
= L
cal
+
∆
L
ff
L
cal
acoustic calibrator sound pressure level, read from its calibration certificate,
∆
L
ff
free field correction, for ½” microphone equal to –0.15dB,
•
couple calibrator with the microphone and turn it on,
•
start the calibration procedure,
•
calibration will be conducted automatically, after a moment you will get the result to
accept,
