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The HD 2020 calibrator allows calibrating any sound level meter provided that it is equipped with a labora-
tory or wo
rking standard 1/2” microphone compliant with IEC 61094-01 and IEC 61094-4 standards.
Corrections depending on the microphone
The HD2020 calibrator generates a 94 dB (or 114 dB) sound pressure level referred to 20
μPa. Working
standard
½” microphones for sound level meters are manufactured to achieve flat frequency response in
free or diffuse field, i.e. in a field of progressive plane waves propagating in the same direction as the micro-
phone axis and in a field of sound waves coming from every direction, respectively. These propagation con-
ditions are different from those in the calibrator cavity.
In free field, reflections due to the microphone alter the sound level by increasing the high-frequency car-
tridge effective sensitivity. Microphones optimized for free field measurements exploit this phenomenon to
achieve flat frequency response even at very high frequencies. In these microphones, the sound level in-
crease at 1 kHz corresponds to approximately 0.05 dB ÷ 0.20 dB. Therefore, when you calibrate a free field
microphone, you must allow for this difference when you set a sound level 0.1 dB or 0.2 dB lower than the
calibrator nominal one.
Microphones optimized for diffuse field measurements
don’t require corrections when calibrated in a closed
cavity at 1 kHz instead.
L
OW BATTERY INDICATION AND REPLACEMENT
The HD 2020 calibrator is provided with two batteries: a 9V alkaline battery that can be replaced by the user
and a lithium buffer battery. The latter allows the date indicator and watch to work even without external bat-
tery: it must be replaced by a Delta Ohm authorized service centre.
The 9V battery power is constantly monitored:
•
If the battery is fully charged, its symbol is off;
•
If the battery is partially charged, its symbol blinks: please replace the battery as soon as possible;
•
If the battery is uncharged and the instrument cannot work properly, its symbol is constantly on. When the
battery is uncharged, the calibrator switches off in about 10 seconds.
To replace 9V batteries, switch off the instrument and open the lid at the bottom of the instrument. Replace
the battery. Close the lid.
Date, time and calibration interval are stored if the buffer battery is charged.
The average life of the buffer battery depends on the external battery: if you use it, the average life of the in-
ternal battery is about 5 years.
Battery tips
Remove the battery if the instrument is not to be used for an extended period. If the battery is low,
replace it as soon as possible.
Make sure that there is no loss of liquid.
Use good quality sealed batteries (alkaline if possible).
