Casella CEL CEL-224 - Manual (Page 3)

Casella USA
17 Old Nashua Road #15
Amherst, NH 03031-2839
Controls and Indicators Technical Description
The instrument covers the range 40 - 130dB(A)
and is equipped with the 'A' frequency
characteristics as this is now universally used in
the types of noise measurement for which the
instrument is intended. The standard FAST and
SLOW time constants are also provided to
enable both general background levels and
more rapidly changing levels, such as motor
vehicles drive-past noise, to be measured. The
instrument employs a robust piezoelectric
microphone that has a proven record of
calibration stability in respect of both its
amplitude and frequency characteristics. Signals
from the microphone are passed through the
preamplifier stages onto the calibrated range
attenuators and frequency weighting circuits.
OFF/BATT/ON
In the OFF position no functions are performed
and the instrument draws no power. In the
BATTERY position the meter indicates the on
load voltage of the lower of the two batteries
with the end of useful battery life shown as the
lower mark on the scale; hence, when end of life
is indicated both batteries must be changed.
When in the ON position the instrument carries
out its selected functions.
FAST/SLOW
This switch selects the time constants employed
in the RMS detector and these are as defined in
the International Standards - 125msec for FAST
and 1 second for SLOW.
After additional amplification a discrete RMS
detector that employs a logarithmic amplifier in
order to provide an output that is linear in
decibels over a 40 dB range processes the
signals. This wide dynamic range considerably
improves the interpretation of the readings given
on the meter as it eliminates the need for the
frequent range changing that is necessary when
the older type of instruments having logarithmic
scales are used. The instrument is powered by
two 9V radio batteries and is equipped with a
battery check function.
40/70/100
This control selects the measurement range by
setting the meter scale zero to the value
selected; hence, the answer is given by reading
the appropriate scale on the switch plus the
meter. Measurement ranges provided are,
therefore, 40-80, 70-110 and 100-140.
www.casellausa.com Page 3 of 4 tel: ( 800) 366-2966
[email protected] 25 Jan 2006 fax: (603) 672-8053