Casella CEL CEL-63X - Manual (Page 49)

CEL-63x Environmental & Occupational Noise Meter
49 Casella CEL
L
Avg
threshold
The L
Avg
threshold can be set in the range 0 dB or 70 dB to 90 dB.
This threshold is used in the calculation of the average sound level (L
Avg
) over
the measurement period (equivalent to L
eq
). L
Avg
is a function used in OSHA
measurements.
Normally, the term L
Avg
is used when the exchange rate Q is some value other
than 3, for example when making measurements for the OSHA Hearing
Conservation Amendment with Q = 5. The threshold value is used during
calculation of L
Avg
, where any levels below the threshold are not included.
Example:
Assume the threshold level is set to 80 dB and the exchange rate is 5 dB (Q = 5).
In this case, if you made a one-hour measurement in an environment where the
noise levels varied between 50 dB and 70 dB, the sound level would never
exceed the threshold so the instrument would record no value for the L
Avg
.
However, if the sound level exceeds the 80 dB threshold for only a few seconds,
only these seconds contribute to the L
Avg
, producing a result of approximately
40 dB. This result is much lower than the actual ambient sound levels in the
measured environment.
Octave weighting
The setting options are for A, C or Z weighting
This is the octave weighting used to display octave or ⅓-octave band results.
A weighting is the usual method of adjusting the measured sound
pressure level so that the measurements represent the frequency
response of the human ear.
C weighting applies only a relatively small correction to very high and
low frequencies. C weighting represents how the human ear responds at
very high noise levels.
Z weighting does not include any frequency correction to the sound
pressure levels, so that the response is effectively „flat‟.
NOTE
Whichever setting you use for octave weighting, the CEL-63x instrument only stores
Z-weighted measurements. This allows you to transfer measurements to a PC for post-
processing to A or C weighting
using the Casella „insight‟ software.
Refer to “
Mini B USB port ” on page 55 for information about connecting the instrument
to a PC.