Casella CEL CEL-414 - Manual (Page 30)

6.8Measurement of 3 & 5s
Cumulative Average - L Tm3
& L Tm5 (A, B & CEL-493/3)
To comply with the West German require-
ment for measuring L
Tm values, the fast
time weighting and A-weighting are used
to obtain maximum weighted results in a
similar way to equivalent continuous level.
Note: Certain applications may require the
impulse maximum weighted average
L
AITm to be measured by using the
impulse time weighting.
1. Use the FUNCTION buttons to step
the arrow marker until it points to
whichever of LT3 (3 s), or LT5 (5 s)
is to be determined.
Maximum weighted results are pro-
duced by including a maximum hold
function that captures the highest
level measured during the three or
five second period.
The levels are then averaged over the
following period as if they had been
present for the whole time (so no
results are available during the first
measuring period), after which they
are updated once each period.
The average values are shown on the
digital display with a resolution of
0.1 dB.
The analog bar graph continues to
show the instantaneous sound
pressure level.
6.9Measurement of L OSHA
& L DOD (C & D not
CEL-414/3)
To comply with the U.S.A. Health and
Safety at Work Act (OSHA) requirements
for measuring L OSHA and Department of
Defense requirements for measuring
L
DOD parameters which are used to
asses the risk of hearing damage, slow
time weighting with A-weighting is used.
Normally the 80 dB default threshold
level will also be used, but this may be
set by the Operator to any value be-
tween 75 and 90 dB following the instruc-
tions in Section 6.9.1.
Note: The threshold level set will apply for both
L
OSHA and L DOD measurements.
6.9.1 Setting the Threshold
Level
When the instrument is switched ON,
the threshold level defaults to 80 dB.This
threshold level can be set to any dB value
in the range from 75 to 90 dB, so that cal-
culation starts as soon as the level is
equalled or exceeded. However, if the
threshold has been set to a value below
80 dB, then subsequently the instrument
range changed to 80 dB, a threshold of
80 dB will be used until such time as a
lower range is selected again.
With the instrument in any measurement
mode, set the threshold level as follows.
1. Slide the ON-BAT-OFF switch to the
“BAT” position.
2. Press the reset button once to bring
the threshold level to the display in
the format “xx d”.
3. Use the FUNCTION buttons to change
the display to any required threshold
level.
Each press of a FUNCTION button
changes the indicated level by 1 dB.
Page 26 - General CEL Sound Level Meters Handbook