Casella CEL CEL-393 - Manual (Page 47)

Having gained an appreciation of the function of the controls, operation
of the filter is quite straightforward.
Introduction
Prior to commencing an analysis the instrument measurement range
should be set, preferably to the Lin frequency weighting, to give a signal
in the upper 5 to15dB of the chosen measurement span. The range
should not then be changed during the analysis. It should be noted that
the filter circuits are in series with the broad band weighting network,
hence A-weighted bands can be produced if required and the
mnemonic therefore refers to the setting of the Off - 1:1 - 1:3 switch, and
not to the convention for Linear weighting.
With the filters active the mnemonic indicator will signal the band
selected, while the bar graph and main digital display both show the
instantaneous sound level in that band.
Automatic Operation
The CEL-393B will perform any one of four automatic frequency sweeps,
and the codes used to initiate these are given in Table 3. The algorithm
used for automatic sweeps calculates the energy equivalent band level
L
eq , and shows this on the main digital display whilst the bar graph shows
the instantaneous sound pressure level.
The filter dwells in each band until the averaged band result is changing
at a rate less than approximately 0.2dB/s. The average result is then
written to memory, the filter switched to the next band, and the current
averaging register automatically reset ready to perform a new average.
This arrangement optimises the filter performance, and it will be seen
that automatic analyses of signals that vary over a wide range of levels
will take longer to complete.
When automatic sweeps are being used, it should be noted that the
memory must be configured in the analyser mode after the filter has been
selected. This is achieved by the key sequence 0C. This operation will
393 Handbook /43.