General DSM8925 User manual

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
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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.
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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
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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
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B
C
D
E
F
G
H
I
J
K
A
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
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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
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+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.
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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.
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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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