Casella CEL CEL-393 - Manual (Page 38)

An analogue maximum arrangement is employed that is read by the
processor on each 15ms duty cycle, and is operative on all four time
constants. When L
max is used in conjunction with the peak time constant,
the combination of these two systems can result, in the worst case, in
an uncertainty of up to 2.3dB on any single impulse, dependant upon the
relative phase of the peak, and the computer read cycle.
However, it must be born in mind that for a signal with repetitive peaks,
the true peak will almost certainly be captured. On all other settings,
these considerations do not apply, and the maximum value is always
captured. Once captured, the result is stored digitally with a resolution
of 0.1dB, and will not decay with time. It will be updated when a new
higher maximum is logged.
Period Memories
When the instrument is in profile or environmental modes, results are
calculated automatically, and transferred to the memories at the end of
each period based on the data accumulated so far. On completion of this
process, the current period memories are reset and a new period
commenced. The latching overload memory is also stored and reset by
this procedure. Results above full scale or below minimum scale deflec-
tion are both stored as a minimum value. It is good practice to accept
minimum scale deflection plus 1dB as the first valid answer, which in
practice could apply only to the L
90 value.
Event Memories
Events are defined as signals that have an excursion 20dB above the
measurement range datum. Crossing this level starts the event routine,
which will be terminated when the signal falls below this threshold and
stays there for more than 4 seconds.
Event mode is selected by setting the period time with the sequence 0C.
As this setting is also used for the analyser mode, the event system is
disabled on the B (and D) version once the Off - 1:1 - 1:3 switch has been
moved to one of the filter positions (1:1 or 1:3). This is to prevent events
from being registered during a frequency sweep.
/34. 393 Handbook