Extech Instruments 407750 Manual de usuario

User's Guide

Digital Sound Level Meter

Model 407750

Model 407750 Version 2.1 February 2004

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 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.

Introduction

Congratulations on your purchase of the Extech 407750. This device measures sound

level in dB and the measurement range can be set automatically or manually. The

407750 offers selectable frequency weighting (‘A’ and ‘C’) and Time Response (Fast and

Slow). The built-in RS-232 PC interface allows the user to record readings onto a PC in

real-time. Careful use of this meter will provide years of reliable service.

Specifications

Display Backlit 2000 count LCD with analog bargraph

Display update rate Main LCD digits: 0.5 seconds; Bargraph: 50mS

Analog Bargraph 1dB steps with 50dB display range

Microphone Electret condensor (0.5” diameter)

Measurement Bandwidth 31.5Hz to 8KHz

Measurement Range A weighting: 30 to 130dB; C weighting: 35 to 130dB

6 ranges in 10 dB steps: 30 to 80dB, 40 to 90dB, 50 to

100dB, 60 to 110dB, 70 to 120dB, 80 to 130dB

Accuracy / Resolution ± 1.5dB / 0.1dB

Time response selections Fast (125ms) and Slow (1 second)

AC and DC Analog outputs 0.707VAC rms at full scale; 10mVDC / dB;

3.5mm output jacks

Standards Meets ANSI and IEC Type 2

External Calibrator Extech models 407766 or 407744

Power 9V Battery; 20 hour battery life (typical) with low battery

indication

Dimensions/weight 3.2 x 10.1 x 1.5” (80 x 256 x 38mm) / 8.5 oz. (240g)

Model 407750 Version 2.1 February 2004

Meter Description

1. LCD Display

2. Microphone

3. ON/OFF key

4. REC (Record) key

5. MAXHLD (Max Hold) key

6. C/A Weighting Select key

7. BA (Background Absorber) key

8. F/S Fast / Slow Response select key

9. DOWN

10. Backlit (LCD backlighting) key

11. UPPER

12. AC adaptor jack

13. Calibration screw adjust

14. AC analog output jack

15. DC analog output jack

16. RS-232 output jack

Note: The Battery Compartment and the Threaded Tripod mount access are located on

the back of the instrument (not pictured)

Model 407750 Version 2.1 February 2004

Operation

Quick Start

1. Power the meter by pressing the ON/OFF key.

2. The meter’s LCD will count down to zero (99.9, 88.8, 77.7, etc.) and then begin

measuring sound levels. If the LCD does not switch on after pressing the ON/KEY

check the 9V battery.

3. Point the microphone toward the source of the sound level to be measured and view

the reading on the meter’s LCD.

‘A’ and ‘C’ Frequency Weighting

Select ‘A’ or ‘C’ weighting via the C/A key. The LCD will reflect the currently selected

frequency weighting. 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). ‘A’ weighting is used for environmental measurements, OSHA

regulatory testing, law enforcement, and workplace design. Select ‘C’ weighting for flat

responding measurements (less amplitude boost or cut across the frequency spectrum).

‘C’ weighting is used in applications where hearing conservation is not an issue; for

example, in the diagnosis of malfunctions in electrical, electronic and mechanical devices.

FAST/SLOW Response Time

Select either FAST (125ms response) or SLOW (1 second response) measurements by

pressing the F/S key. 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.

MAX HOLD

The meter is capable of taking continuous measurements and only updating the LCD when

a higher reading (than the one presently on the display) is detected. The bargraph display

continues to change while the main LCD waits for a higher reading. Press the MAXHLD

key to activate the MAX HOLD mode. The LCD will reflect the MAX HOLD function. Press

the MAXHLD key again to return to normal operation.

Record (REC) Function

To Record the Maximum and Minimum sound level measurements over a programmable

period of time, press the REC key. The REC indicator will appear on the LCD. Once the

REC key is pressed, the meter begins tracking the highest (MAX) and lowest (MIN)

readings. Press the REC again and the MIN indicator will appear on the LCD along with

the lowest sound level reading since the REC key was pressed. Press the REC again and

the MAX indicator will appear along with the highest reading the meter has encountered

since the REC key was first pressed. Press and hold the REC until the REC indicator

extinguishes to exit the RECORD mode.

Model 407750 Version 2.1 February 2004

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.

Model 407750 Version 2.1 February 2004

Analog Outputs

The meter includes an AC and a DC analog output. These outputs are proportional to the

displayed sound level and are ideal for use with chart recorders and dataloggers. The AC

output is 0.707V rms full scale and the DC output is 10mV per dB. The labeled 3.5mm

output mini-plugs are located on the bottom of the instrument.

RS-232 Output

The meter includes an RS-232 PC interface jack. This PC interface allows the meter to

store and display readings on a PC as they are recorded. The interface cable and software

for data acquisition are sold separately. Detailed instructions are provided with the

software.

Model 407750 Version 2.1 February 2004

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

50HP Siren (100')

130

120

110

100

140

Jet takeoff (200')

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

Model 407750 Version 2.1 February 2004



Support Hotline (781) 890-7440

Tech support: Ext. 200; Email: [email protected]

Repair/Returns: Ext. 210; Email: repair@extech.com

Website: www.extech.com

Battery Replacement

When the low battery message appears on the LCD, the 9V battery has fallen to a critically

low voltage level and should be replaced as soon as possible. The battery compartment

cover resides at the rear of the meter. Remove the rear battery compartment screw and

remove the battery compartment cover, change the battery, and replace the compartment

cover.

Calibration and Repair

The meter includes a Calibration adjustment on the bottom of the meter. A sound level

calibrator must be used to complete a calibration. Extech can supply a calibrator for this

purpose. Once the Calibrator is affixed on the microphone, adjust the calibration screw so

that the LCD sound level display matches the calibrator’s output signal.

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.

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