Extech Instruments 407740 User manual

User's Guide
Digital Sound Level Meter
Model 407740
Introduction
Congratulations on your purchase of the Extech 407740 Digital Sound Level Meter. This
device measures sound in decibels (dB). Useful features include A/C Weighting,
Fast/Slow Response Time, and Maximum Reading HOLD. Careful use of this meter will
provide years of reliable service.

Model 407740 version 1.6 8/05
2

Support Hotline [phone]
Tech support: Ext. 200; Email: [email protected]
Repair/Returns: Ext. 210; Email: [e-mail]
Website: www.extech.com
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 [phone] ext. 210 for authorization or visit our website at
www.extech.com (click on ‘Contact Extech’ and go to ‘Service Department’ to request an
RA number). 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.
Specifications
Display 2000 count multi-function LCD
Input Signal Range ‘A’ Weighting: 30 to 130dB
‘C’ Weighting: 30 to 130dB
Response Time Fast: Response = 125ms; Slow: Response = 1s
Resolution 0.1 dB
Standards Compliance ANSI and IEC Type 2
Accuracy (at 23o± 5 o C) ±1.5dB at 1KHz (94dB)
Frequency 31.5 to 8,000Hz
Microphone Electric condenser microphone, 0.5" (12.7mm)
Range Selector Switch 30 to 80dB, 50 to 100dB, 80 to 130dB
External Calibrator Use Extech model 407744 or 407766
Analog Output Signal AC: 0.5Vrms (full scale of selected range)
DC: 0.3 to 1.3VDC, 10mV/dB
Analog output impedance 600 ohms
Analog Output Terminal 3.5mm phone jack
Operating Temperature 32 °F to 122 °F (0 °C to 50 °C)
Operating Humidity Max. 90% RH (0° to 35°C)
Power Supply 9V battery
Dimensions / Weight 10 x 2.8 x 1.1” (255 x 70 x 28mm) / 10 oz. (280 g)

Model 407740 version 1.6 8/05
3
Meter Description
1. Microphone
2. LCD Display
3. Calibration potentiometer
Note: Adjust pot only while using an acoustic Calibrator
4. Selector Switches
5. Maximum Hold reset button
6. Analog output jack
The battery compartment and tripod mount are located
on the rear of the instrument
Operation
Powering the Meter and Configuring the Analog Output
Slide the POWER switch to the ON (DC) or ON (AC) position. The (AC) or (DC) determines
the type of signal present at the analog output jack.
Basic Measurements
Point the microphone toward the source of the sound to be measured. The meter can be
held in hand or mounted on a tripod (tripod mount on rear of instrument). The meter will
now display the sound level in dB.
Selecting ‘A’ or ‘C’ Weighting
Use the Weighting selector switch to select ‘A’ or ‘C’ frequency weighting. Use ‘A’
weighting to have the meter simulate the response of the human ear (the human ear
boosts and cuts sound levels at specific points over the frequency spectrum). ‘A’ weighting
is used for environmental measurements, OSHA regulatory testing, law enforcement, and
workplace design. Select ‘C’ weighting for flat response measurements (the readout does
not boost or dampen the measurement across the frequency spectrum). ‘C’ weighting is
suitable for the operational maintenance and analysis of machinery, motors, pumps,
engines, etc.
Selecting FAST or SLOW response
Use the RESPONSE switch to select Fast or Slow. The setting is determined by the
application and any directives or standards related to the application. For example, most
hearing conservation or OSHA related testing is done using the SLOW setting (with ‘A’
weighting). To capture quick sound peaks, however, use the FAST setting.
Selecting the Measurement Range
Select the measuring range using the ‘dB’ selector switch. If the high (▲) or low (▼)
indicators appear on the display, select a lower range (for ▲) or higher range (for ▼).
Maximum Hold Function
Select MAX HOLD using the RESPONSE selector switch to capture the maximum dB
level. The meter response will be set to FAST. The display will only display the highest
reading in this mode. To reset the Maximum Hold display, press the black reset button on
the bottom of the meter next to the analog output jack.
Calibration
Frequent calibration using an acoustic calibrator is recommended. Follow the instruction
provided with the calibrator.
1
2
3
4
5
6

Model 407740 version 1.6 8/05
4
Battery Replacement
The low battery indication (BAT) appears on the LCD when the 9V battery is nearing
depletion. Reliable readings can be obtained for several hours after the first appearance of
the low battery indication. To replace the battery, slide the battery compartment cover off
the rear of the instrument and replace the 9V battery. Secure the cover before use.
Reference Information
Frequency Weighting Characteristics
Frequency (Hz) A Weighting C Weighting Tolerance (IEC 651 Type 2)
31.5 -39.4dB -3dB ±3dB
63 -26.2dB -0.8dB ±2dB
125 -16.1dB -0.2dB ±1.5dB
250 -8.6dB 0dB ±1.5dB
500 -3.2dB 0dB ±1.5dB
1 k 0dB 0dB ±1.5dB
2 k +1.2dB -0.2dB ±2dB
4 k +1dB -0.8dB ±3dB
8 k -1.1dB -3dB ±5dB
Typical A-Weighted Sound Levels
Calibration and Repair Services
Extech offers repair and calibration services for the products we sell. Extech also provides
NIST certification for most products. Call the Customer Service Department for information
on calibration services available for this product. Extech recommends that annual
calibrations be performed to verify meter performance and accuracy.
Copyright ©2003 Extech Instruments Corporation
All rights reserved including the right of reproduction in whole or in part in any form.
50HP Siren (100')
130
120
110
100
90
80
70
60
50
40
30
20
10
140
0
Jet takeoff (200')
dB
Riveting machine
Chain saw
Subway (20') Boiler room
Pneumatic drill (50') Freight train (100')
Vacuum cleaner (10') Speech (1')
Large store Large Office
Small office Residence
Night residential area
Whisper (5'0) Sound studio
Threshold of hearing