General DSM8925 Manuel utilisateur

DIGITAL SOUND

METER WITH

JUMBO DISPLAY

USER’S MANUAL

DSM8925

Please read this manual carefully and thoroughly

before using this product.

TABLE OF CONTENTS

Introduction . . . . . . . . . . . . . . . . . . . . . . 3

Key Features . . . . . . . . . . . . . . . . . . . . . 4

What’s in the Box . . . . . . . . . . . . . . . . . 5

Product Overview . . . . . . . . . . . . . . 5 – 7

Setup Instructions . . . . . . . . . . . . . . . . . 8

Install Batteries . . . . . . . . . . . . . . . . 8

Operating Instructions . . . . . . . . . 8 – 15

Making Basic Measurements . . 8 – 9

Autoranging vs.

Manual Ranging . . . . . . . . . . . 9 – 11

Time and Frequency

Weighting Options . . . . . . . . . 11 – 12

Storing and Recalling

MIN and MAX Readings . . . . 12 – 13

Operating in

MAX HOLD mode . . . . . . . . . . 13 – 14

Disabling Auto Power Off . . . . . . . 14

Calibrating the Meter . . . . . . . . . . 15

Specifications . . . . . . . . . . . . . . . . . . . 16

Maintenance Tips . . . . . . . . . . . . . . . . 17

Warranty Information . . . . . . . . . .17 – 18

Return for Repair Policy . . . . . . . . . . . 18

INTRODUCTION

Thank you for purchasing General Tools &

Instruments’ DSM8925 Digital Sound Meter

with Jumbo Display. Please read this user’s

manual carefully and thoroughly before using

the instrument.

The DSM8925 uses an integrated condenser

microphone to measure the noise level of an

environment or the loudness of a machine,

typically in order to comply with health and/or

safety rules. The meter has a range of 30 to

130 dB and an accuracy of ±2 dB. Real-time

measurements are shown within a backlit

liquid-crystal display window in two forms: as

a three- or four-digit number, and as a line on

an analog bar graph.

Several features improve the meter’s

versatility. Among them are two user-

selectable operating modes: “A” or “C”

frequency weighting, and fast or slow time

response. Users also can override autoranging

(the default mode) and manually select a fixed

measurement range, improving the meter’s

response time and measurement resolution.

The meter can display the minimum and

maximum sound levels measured during a

recording session, as well as hold a maximum

level on-screen until it is exceeded.

Physical features of the DSM8925 include an

analog output jack for connecting to a data

logger or chart recorder, a tripod mounting

socket, and an adjustment screw for

calibrating the meter to a standard 94 dB

input.

The DSM8925 includes a wind shield ball

and is powered by four “AAA” batteries

(also included).

KEY FEATURES

• Measures sound level of a machine

or an environment

• Jumbo LCD is easy to read

• “A” or “C” frequency weighting

• Fast or slow time weighting

• Autoranging or manual ranging

• Displays maximum and minimum readings

• Max reading can be held until exceeded

• Auto power off

• Analog output for data logging

• Calibrates to standard 94dB signal

• Tripod mount socket on back

• Includes wind shield ball

• Powered by four “AAA” batteries

WHAT’S IN THE BOX

The DSM8925 comes fully assembled in a box

along with a wind shield ball, four “AAA”

batteries and this user’s manual.

PRODUCT OVERVIEW

Figure 1 shows all of the controls, indicators

and connectors on the front and right side of

the DSM8925. Familiarize yourself with their

positions and functions before moving on to

the setup procedure.

1. The DSM8925’s controls, indicators

and connectors

A. Wind shield ball

B. Microphone

C. Liquid-crystal display

D. Power on/off button

E. A/C—Selects “A” or “C” frequency

weighting

FRONT RIGHT SIDE

F. REC—Enters/exits Recording mode

G. RNG—Selects autoranging or manual

ranging

H. F/S—Selects fast or slow time response

I. MAX HOLD button

J. Calibration adjustment screw

K. Analog output jack

Figure 2 shows all text and icons that could

appear in the display window at various times.

2. All possible display indications and their

meanings

REC Meter is in Recording mode, tracking

maximum and minimum sound level

measurements

MAX Digital readout is highest level

recorded since entering Recording

mode

MIN Digital readout is lowest level

recorded since entering Recording

mode

MAX HOLD Meter is in Max Hold mode. Digital

readout is highest level measured

since entering this mode

FAST Meter is applying fast time weighting

to inputs

SLOW Meter is applying slow time weighting

to inputs

AUTO Meter is automatically choosing

measurement range with best

resolution

MANU Meter is using user-selected

measurement range

BA Reserved for future use

SPL Abbreviation of sound pressure level

(the parameter measured)

Meter’s battery is very low on charge

and should be replaced

AMeter is applying “A” frequency

weighting to inputs

CMeter is applying “C” frequency

weighting to inputs

dB Sound level unit (accompanies

reading at its left)

40 Range Baseline (low end of current

measurement range, in dB). “40”

indicates 40 to 70 dB range; other

possible numbers in this display

position are 60 (for 60 to 90 dB

range), 80 (for 80 to 110 dB range)

and 100 (for 100 to 130 dB range)

+0, +10, Labels of analog bar graph scale.

Indicate amplitude of input (in dB)

relative to Range Baseline above left

end of graph

+20, +30

SETUP INSTRUCTIONS

INSTALL FOUR BATTERIES

The meter’s battery compartment is

accessible from the back of the unit. Use a

Philips-head screwdriver to remove the one

screw holding the cover in place. Then install

the four included “AAA” batteries so their +

and – ends match the images stenciled inside

the compartment. Finally, replace the cover

and secure it with the Philips-head screw.

OPERATING

INSTRUCTIONS

MAKING BASIC MEASUREMENTS

To begin, press the button to power on the

meter. The display will take a few seconds to

stabilize and then begin reading out real-time

sound level measurements.

Note how the digital numbers and the

readings from the analog bar graph track each

other. At times, the two displays may seem

slightly out of sync—and they are, because

they refresh at different rates.

Also note how the number above the left end

of the bar graph—the Range Baseline—

changes each time a much louder or softer

sound is heard. Each change confirms that the

meter is operating in Autoranging mode. To

demonstrate that autoranging is on in a quiet

environment, rub the windscreen with your

hand (to simulate a loud noise) and watch the

Range Baseline change to 100.

To measure the loudness of a sound

source, point the microphone at it.

The meter’s default settings are autoranging

on (enabling measurements from 30 to 130

dB), fast time weighting and “A” frequency

weighting. When the meter is powered on,

AUTO will appear on the left side of the

display, with FAST on the top line and Aon

the right side. Following are procedures for

changing each of these settings to suit the

application.

AUTORANGING VS.

MANUAL RANGING

The DSM8925 has four measurement ranges:

40 to 70 dB, 60 to 90 dB, 80 to 110 dB, and

100 to 130 dB. When the meter is powered

on, it automatically enters Autoranging mode.

In this mode, it automatically switches to the

range that displays the input with the finest

resolution. For example, the meter could

display a sound level of 65 dB using either the

40 to 70 dB or the 60 to 90 dB range. In

autoranging mode, it would choose the lower

of the two ranges (40 to 70 dB) because on

this scale 65 dB has a better (finer)

measurement resolution.

If you already know the loudness range of the

machine or environment you wish to measure,

and that range is limited, consider exiting

autoranging mode and operating the meter in

only one of those four fixed ranges. The

benefit of operating the meter in this mode—

called Manual Ranging mode—is speed.

The meter can display its results more quickly

because it does not have to first determine

which range to use.

To exit Autoranging Mode and enter

Manual Ranging mode, briefly press the RNG

button on the front panel. Note that when you

press the button, the text MANU replaces

AUTO on the left side of the display. Also note

that the Range Baseline above the left end of

the bar graph no longer changes in response

to louder or softer sounds, as in did in

Autoranging mode.

When the RNG button is pressed, the meter

randomly chooses one of the four ranges.

Accordingly, the first Range Baseline number

displayed could be 40, 60, 80 or 100. For the

highest display resolution, the low end of the

range you choose should be just below the

quietest sound you expect to hear. For

example, if your target normally produces

sound levels between 85 and 105 dB, you

should manually choose the 80 to 110 dB

range.

To manually select a specific measurement

range, briefly press the RNG button as many

times as necessary until its Range Baseline

number appears above the left end of the

analog bar graph. Each press of the RNG

button advances the Range Baseline number

by 20 dB; after 100, it returns to 40.

Note that in Manual Ranging mode, whenever

a sound level is outside the chosen range the

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