407750 Datasheet, PDF (5/8 Pages) Extech Instruments Corporation. – Digital Sound Level Meter

BA (Background Noise Absorber) Mode
The Background Noise Absorber allows the user to accurately measure equipment noise
by “eliminating” background noise. The Sound Level Meter first stores the background
noise as a reference level. From there, when a sound is measured, the display will show
the sound level measurement minus the background noise. To operate the meter in BA
mode, follow these steps:
1. Power the meter.
2. Press the MAXHLD key (the MAX HOLD icon will appear on the LCD).
3. Press the BA key (‘F” will appear to the left of the SPL display icon).
4. Press the MAX HOLD key again (the MAX HOLD icon will reappear on the LCD).
5. The meter is now displaying the background, reference noise.
6. Power the device under test and note the new sound level meter reading.
7. If the reading changes, the new reading is the sound level of the device. If the reading
does not change, the noise produced from the device is either equal to or less than the
background noise.
8. Press the BA key again to return to the normal mode of operation.
Auto and Manual Ranging
The meter powers up in the Automatic Range mode. In automatic mode the meter
automatically finds the correct range in order to produce the best accuracy. However, if it is
desired to set the range manually, follow these steps:
1. Power the meter
2. Notice the two (2) digit number to the immediate left of the analog bargraph. This
number is the low end of the presently selected range (see the specifications for the
ranges).
3. To change the range, press the UP key to raise the range or press the DOWN key to
lower the range. The two digit number on the left of the bargraph will change with each
key-press.
4. An advantage of Manual mode is that it takes less time for the meter to take a reading.
In Auto Range mode the meter must first locate the correct range before displaying a
measurement.
LCD Backlighting
Press the BACKLIT key to illuminate the LCD. The backlight will remain on for 5 seconds
and then automatically switch off to preserve battery life.
Auto Power Off
To preserve battery life, this meter has an automatic power off feature. If the unit is not
used for approximately 20 minutes, the meter shuts off. To override this function, follow
these steps:
1. From a power OFF condition, press and hold the ON/OFF and MIN/MAX keys
simultaneously.
2. When ‘n’ appears on the display, release the MIN/MAX and then the ON/OFF key.
3. The Auto Power Off feature is now disabled. Note that the Auto Power Off feature is re-
activated the next time the meter is powered down.
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Model 407750 Version 2.1 February 2004