Casella CEL CEL-193 User Manual
Page 11
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Amherst, NH 03031 USA
L
eq
(cumulative) = 10 log x 1/T[t1 x antilog (Leq1/10) + t2 x antilog (Leq2/10)]
where
Leq1
=
L
eq
for the first period
t
1
=
Duration of first period
Leq2
=
Leq for second period
t
2
=
Duration of second period
T = (t1+t2)
The expression may of course be extended for n terms.
The Leq
value will be calculated on any of the weightings and also in each of the frequency bands selected
on the CEL-196 or CEL-178 analysers. This later function will eliminate the need for taking visual averages
of the band level and enable an accurate repeatable answer to be obtained thereby greatly simplifying the
correct prescription of hearing protectors and the specification of attenuating partitions, etc.
During the first few seconds of the L
eq
calculation the L
eq
may be seen slowly increasing when high noises
are present and falling back during quiet periods. After a longer time even large sound inputs will not have
much effect on the L
eq
unless they are present for a considerable period of time. The lack of movement of
the L
eq
level is to be expected, therefore, and does not indicate a failure of the instrument.
6 LTm ‘Takt-Max' Integrating Mode
This method of measurement originated in Germany and is extensively used in DIN, VDI and other
regulations. L
Tm
is the L
eq
of the highest, Fast RMS level that occurred in preselectable 3 or 5 second periods
assuming that this level is present for the whole of the next period. It is therefore a method of peak
weighting the average level and the result is, therefore, always higher than an L
eq
reading of the same noise
in proportion to the peak content. LTm is selected by operating switch (a) to L
Tm
instead of L
eq
and the time
constant selector to FAST. All other operating procedures are as for L
eq
.
When in this mode the CEL-193 does not pass any data to the calculating circuits for one period (3 or 5
seconds) and during this first period the answer is entirely random and should be ignored. After the first
period the answer is correct and will be seen to update every period. The Tm period is set by the switch
located just above the battery compartment and this is accessible when the rear cover has been removed.
(Earlier production units were manufacturer preset.)
7 LAX Noise Event Mode
The single event noise exposure level, SEL or L
AX
,
is defined as the L
eq
of an event normalised to 1 second.
This is achieved in the CEL-193 by fixing the elapsed time counter to 1 second and, in other respects,
operation is similar to the L
eq
mode. The system is primarily intended for the measurement of 'events' and it
is, therefore, necessary to define these events, this is done by means of the RESET (f) and PAUSE (j)
controls, i.e. the RESET control should be depressed and released at the beginning of the noise event. The
instrument will then log data and calculate the L
AX
value and at the end of the event the answer can be held
by depressing the PAUSE control. It will be found more convenient if the CEL-3300/ SLM handset is used to
remotely control the PAUSE function.
8 Alternative Microphones
The CEL-186 0.5 inch Precision Measurement Microphone is provided as standard. This is a 150V polarized
high, sensitivity type enabling measurements to be made up to 20kHz. Levels as low as 23dB(A) may be
measured with this microphone and it is, therefore, suitable for most applications. For special applications
the extra high sensitivity 1 inch microphone type CEL-190 may be used. This enables measurements to be
Page 11 of 20
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www.casellausa.com
2 Mar 2009
Fax: (603) 672-8053