407790 Datasheet, PDF (9/18 Pages) Extech Instruments Corporation. – Real Time Octave Band Analyzer

Setting the Calendar Clock
Date and time information is stored with each record saved. Set the date and time as follows:
1. Press the 2nd button once and then press the MEAS TIME button to enter the date and
time mode. The display screen in the second function location will flicker.
2. Press the LEVEL button to increment/decrement the values.
3. Use the Cursor button to scroll through year/month/day/hour/minute/second
setting locations (location will flash when it is ready to be programmed).
4. Press the LEVEL button to set the value.
5. When the settings are correct, press the ENTER button to exit this mode. The calendar
clock will start running.
Note: When no changes are made to the date and time or the ENTER button is not
pressed within one minute, the date and time settings will not change and the unit
returns to normal operating mode automatically.
Sound Pressure Level
Technical notes
1. The decibel (dB)
The range over which the human ear responds to sound pressure (noise) is extremely
large; in Pascals (Pa) it is 20μPa (the threshold of hearing) to 100 Pa (the threshold of
pain). The measurement of sound pressure has been made more convenient by the
use of the decibel, which is logarithmic. However, decibels are non-linear and
therefore cannot be added together. A simple rule is that doubling the amplitude of the
noise under test causes the level to rise by 3dB.
2. SLM-sound level meter: Instantaneous sound pressure level (SPL) is used for spot
checks to establish instantaneous noise levels. SPL is defined by the logarithmic
equation:
P
P ^{SPL (in dB): 20 log10}
0
Where P = rms measured sound pressure level
P0 = rms reference sound pressure level (20μ Pa)
3. Leq-level equivalent (continuous): Leq is used to assess the rms average noise level
over a preset period of time, often the starting point of a noise assessment. To take a
Leq measurement the period of time over which it is to be made must be selected.
The longer the period of measurement time, the more accurate the Leq reading will be,
a typical period is 8 hours (the length of a working day).
4. LE – Sound exposure level
LE measurements are almost identical to Leq measurements but normalized or
compressed to 1 second. This allows the total sound energy of an event, such as train
passing a platform, to be evaluated. Another event, such as the next train, which lasts
for a different amount of time, can be measured in the same way. The two readings
can be compared to assess how much total noise the passengers standing at the
platform were exposed to by each train. To make an LE measurement either a preset
time period must be selected on the instrument, or the PAUST/CONT key must be
used to stop and start the measurement of a specific event.
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Model 407790 Ver. 2.1 9/07