User’s Manual
Model 407727
Digital Sound Level Meter
Introduction
Congratulations on your purchase of Extech’s Digital Sound Level Meter. This professional meter, with proper
care, will provide years of safe reliable service.
Specifications
Measurement ranges Auto range from 40 to 130dB ('A' Weighted)
Resolution 0.1 dB
Accuracy ±2 dB at 94 dB sound level
Display 3 1/2 digit LCD with analog bargraph
Display update rate 160ms (LCD), 40ms (bargraph)
Time weighting Fast / Slow Response (selectable)
Frequency weighting
Analog output
Microphone type Condenser Electret
Power Meter powered by 9V battery ;120 hour battery life
Dimensions/Weight 2.7x7.1x1.4" (68 x 180 x 36mm) / 5.1 oz. (160g)
Auto range from 45 to 130dB ('C' Weighted)
'A' and 'C' weighting (selectable)
AC: 0.707Vrms
Front Panel Description
1 Microphone
2 LCD Display
3 Analog Bargraph Display
4 ON/OFF key
5 Range key
6 A/C Weighting selection key
7 Min/Max Record key
8 Fast/Slow selection key
9 Maximum Hold activation key
Note: Battery compartment and Tripod mount are on the rear of the meter.
The Analog output jack is located on the left side of the meter.
Operation
LCD Display with Analog Bargraph
Sound levels are displayed both digitally and in bargraph format. When the ON/OFF key is pressed to
power the meter, the LCD will display all characters and then it will count down to zero. After countdown,
the meter dipslays sound pressure levels (SPL) in units of dB. Point the microphone toward the source of
the sound being measured, and read the measurement on the LCD.
Auto and Manual Ranging
The default mode of operation is Auto Range. To manually select a range, press the RANGE key (‘MANU’
will appear on the LCD). Press the RANGE key until the desired range is displayed. Note that the two-digit
number to the left of the bargraph changes to reflect the new range.
Tripod Mount
A threaded insert on the rear of the meter permits attachment to a tripod stand for increased stability and
accuracy (eliminates hand noise and minimizes the effects of sound reflected from the user's body).
Weighting A / C
Press the Weighting key to select A or C weighting. The LCD will reflect which weighting mode is currently
selected. Use ‘A’ weighting to have the meter respond as the human ear would with regard to frequency
response (the human ear boosts and cuts amplitude over the frequency spectrum therefore it is not ‘flat’
responding). ‘A’ weighting is used for environmental measurements, OSHA regulatory testing, law
enforcement, and workplace design. Select ‘C’ weighting for a flatter response measurement (especially
for lower frequencies). ‘C’ weighting is suitable for the sound level analysis of machines, engines, etc.
Fast (F) and Slow (S) Response
Press the Fast or Slow key to select the response. The LCD will reflect the currently selected mode.
Selection of Fast or Slow is determined by the application and any directives or standards related to that
application. For example, most hearing conservation or OSHA related testing is done using SLOW and A
weighting.
Maximum Hold
Press the Max Hold key to display the maximum reading during the measurement period. In the Max
position, the LCD will hold the highest reading measured and will update only if a higher reading is
measured. The bargraph will continue normal measurements. Press the key again to return to normal
operation.
Low Battery Indication
If the low battery icon ‘BAT’ appears on the display, replace the 9V battery as soon as possible. See the
battery replacement section for further information.
Analog Output
A 3.5mm phono output jack is provided on the meter for connection to external test equipment. An AC rms
voltage is provided (0.707V maximum) which is a linearized representation of the analog pointer reading.
Connect this output to a datalogger, chart recorder, etc. for datalogging purposes.
Data Recording
To begin recording the MIN and MAX sound level readings, press the RECORD key (REC will appear on
the LCD). To recall the stored minimum reading, press the RECORD key again (MIN will appear on the
LCD along with the recorded measurement data). To view the stored maximum reading, press RECORD
again. To resume normal meter operation, press RECORD key a final time. NOTE: The bargraph displays
continues to work while in the Data Recording mode.
Auto Power Off
The meter automatically shuts down after 20 minutes of non-use to preserve battery life. To override this
feature, press the ON/OFF and MAX HOLD keys simultaneously from a power off condition. When the
display appears release only the MAX HOLD key (a lower case ‘n’ will appear on the LCD). Now Release
the ON/OFF key. Note: The Auto Power Off feature will be re-activated the next time the meter is manually
powered down.
Battery replacement
Remove the battery compartment cover on the rear of the meter by removing the cover screw. Replace 9V
battery and compartment cover.
Typical A Weighted Sound Levels
50HP Siren (100’) 135db Speech (1’) 68dB
Jet Takeoff (200’) 120dB Large store 62dB
Riveting machine 110dB Large office 58dB
Chain saw 100dB Residence 48dB
Subway (20’) 90dB Night residential area 42dB
Freight train (100’) 80dB Whisper (5’) 32dB
Vacuum cleaner (10’) 72dB Sound studio 24dB
Warranty
EXTECH INSTRUMENTS CORPORATION warrants this instrument to be free of defects in parts and workmanship for one year
from date of shipment (a six month limited warranty applies on sensors and cables). If it should become necessary to return the
instrument for service during or beyond the warranty period, contact the Customer Service Department at (781) 890-7440 for
authorization. A Return Authorization (RA) number must be issued before any product is returned to Extech. The sender is
responsible for shipping charges, freight, insurance and proper packaging to prevent damage in transit.
This warranty does not apply to defects resulting from action of the user such as misuse, improper wiring, operation outside of
specification, improper maintenance or repair, or unauthorized modification. Extech specifically disclaims any implied warranties or
merchantability or fitness for a specific purpose and will not be liable for any direct, indirect, incidental or consequential damages.
Extech's total liability is limited to repair or replacement of the product. The warranty set forth above is inclusive and no other
warranty, whether written or oral, is expressed or implied
Copyright © 2000 Extech Instruments Corporation.
All rights reserved including the right of reproduction
in whole or in part in any form.
407727 V1.2 10/00
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