BRUEL & KJAER 2225 User Manual

Introduction
Noise, as the cause of annoyance
and hearing loss, is now a generally
accepted problem, causing many
countries and local communities to
adopt anti - noise legislation of var-
ious type and severity . The responsi-
bility for measuring noise and en-
forcing the limits often falls to the
police, health officers, and other pu-
blic officials who are not . them -
selves noise experts . The Types
2225 and 2226 have been de-
signed with these users particularly
in mind . They fulfil the need for a sim -
ply operated, rugged meter which
newcomers to noise measurement
can approach without apprehension
and use effectively and confidently
with only a minimum of training .
Nevertheless, they have a wide
range of facilities hitherto available
only on more comprehensive and ex -
pensive instruments .
The damaging and annoying ef -
fects of noise are basically depend -
ent on 3 parameters, the level, the
frequency content and the duration.
The concept of Leq combines these
parameters into one unit .
The Types 2225 and 2226 are
not only normal A - weighted Sound
Level Meters with "Fast" and
" Slow" time constants but also Leq
meters which integrate automati -
cally for a period of 1 minute. They
differ in only one respect. The
2225 has a "peak" hold with
30J.Lsec rise time , necessary to eval-
uate the damaging effects of impul -
sive noise. The 2226 has an inter -
nationally standardised "impulse"
detector, and a " Max . hold" mode
on all functions .
The "thermometer" type display
is by means of a row of 41 LEOs
giving a 40 dB dynamic range with
0,5 dB resolution . This is achieved
by lighting two adjacent diodes to in-
dicate the half - value between. Dis -
play brightness is controlled auto -
matically with respect to ambient
light conditions via a photo-transis-
tor and enables the display to be
read
easily , even in direct sunlight .
Range changes automatically
bring the correct values into view in
the windows which enumerate the
display scale , and the chosen meas -
urement mode is also displayed in a
2
window. This ensures simple, error-
free read-out.
Operating "Reset. Batt." displays
the battery condition and resets the
instrument, returning the display to
the lowest point on the scale. Any
subsequent measurement starts
from this point, thus preventing
false readings. Measurement re-
starts 200m sec. after the switch is
released so that local noise from
the click (which is less than 1 00
ms long) does not interfere with
measurement . Especially important
at low sound levels and in the
"Peak" mode. In addition, operation
of any switch initiates the reset pro-
cess as an insurance against unin -
tentional false readings.
The meter is powered by 3 easily
obtained 1 ,5 V alkaline cells (IEC
Type LR 6) giving approximately 30
hours continuous operation under
normal use . Their condition is easily
checked on the display by operating
"Reset. Batt . ".
An internal timer turns the instru-
ment off two minutes after the last
reset occurs. This also has the ad-
vantage that the batteries are not
run down if the i nstrument is accid-
entally switched on while being
transported .
With a level recorder connected
to the DC output, the automatic
switch - off is disabled and on the
2226 the "Max . hold" facility is
overridden so that sound levels can
be
recorded continuously. When in
"60s Leq" mode the instrument is
reset every 60s, the maximum re-
corded value being the 60s L• eq .
In
the max. hold "Peak" mode the
peak is held for 0,3 seconds while
it is recorded. Examples of all possi-
ble output functions are shown in
Fig.1.
Short-term Leq Measurements
Leq is based on the equal energy
principle and can be considered as
the continuous steady noise which
would have the same A-weighted
acoustic energy as the real fluctuat-
ing noise measured over the same
period of time.
This calculation is carried out auto-
matically when measuring in the
"60s Leq" mode, the rising value of
the currently accummulated Leq
DDODDOOODOOOOOODDDDDDDDC
Bruel & Kj oo r
=dB (Al -- "Siow" -- Paper Speed
0,3 mm /s :=
~ 70
~ 60
~ 50
:::= 40
1== 30
OP 01 02
100
200
Time is) 7 8084 2
Fig. 1. The Portable Level Recorder Type 2306, and examples of recordings made with 2225
and 2226 in the various measurement modes

BRUEL & KJAER 2225 Specifications

General

Brand	BRUEL & KJAER
Model	2225
Category	Measuring Instruments
Language	English