Casella CEL CEL-193 User Manual
Page 9
Casella USA
17 Old Nashua Rd #15
Amherst, NH 03031 USA
3.3 Frequency Weighting Selection
This should be selected by the operator to suit the application in question. Generally speaking the 'A'
weighting is required when measurements are being made to ascertain the effect of the noise on humans.
However, for some more specialized measurements the B, C or D weightings are called for and these are
available in the companion CEL-178 Octave Filter Set. Because of the dual overload system employed in
these instruments it is not necessary to refer to the LIN (Flat) response range setting prior to selecting the
required frequency weighting.
4 Using the CEL-193 in the Maximum Hold Mode
The maximum hold circuits remember the highest sound pressure level that is experienced during a
measurement sequence. They continuously update the old maximum level when a new level exceeds it and
this process is continuing all the time irrespective of which made the function switch (b) is placed in.
Selecting MAX merely displays the stored maximum on the meter. The result is stored digitally and will,
therefore, be retained as long as the instrument is switched on without any decay.
In order to clear switch-on transients or a previously unwanted maximum level the RESET button (f) should
be pressed. This is operative on positions L
eq
or MAX but not on SPL. The measurement range and
frequency weightings are selected as applicable, but taking extra care to ensure that the range selected is
high enough to ensure that the maximum level does not exceed the displayable range, i.e. 55dB above the
range indicator. If the FAST, SLOW or IMPULSE time constant is selected the maximum level stored will be
the maximum RMS level attained with either of these averaging time constants in circuit. The SLOW time
constant will, therefore, always give consistently lower maximum levels than when FAST is selected. The
selection of either of these two may be dictated by relevant noise regulations. IMPULSE may be used in
conjunction with the maximum hold arrangement in order to obtain the 35msec maximum; however, this is.
rarely required. PEAK time constant is less than 50µsec and is hence very fast and it is used to detect
absolute peaks of impulse or impacts rather than their RMS level. This time constant should only be used in
conjunction with the maximum memory as the inertia of the meter movement will prevent it rising to the
correct level if PEAK and SPL modes are used together. However, the digital hold arrangement is more than
fast enough to capture even the fastest transient which may then be applied to the meter via the MAX
facility. Should the range be changed during the detection of maximum levels the old answer will then be
incorrect as the memory will still be holding data relevant to the previous range. The old maximum should
therefore be noted, the adjustments made, the instrument reset, and a new measurement sequence
commenced.
Extrapolation of maximum levels that are either off the top or bottom of the meter scale should be avoided
as they may be more considerably off the range than the meter appears to indicate.
5 The CEL-193 as an Leq Meter
The CEL-193 is continuously calculating L
eq
irrespective of the position of function switch (b) but the result is
displayed on the meter only when L
eq
is selected on this switch. The L
eq
is calculated three times every
second from samples taken every 10 msec as the average back to when the RESET button (f) was last
depressed. A slight wavering of the needle can just be detected as each new calculation is performed. A
continual display of L
eq
is therefore available for periods from 1 second to about 30 hours depending upon
the life left in the batteries.
Page 9 of 20
Tel: (800) 366-2966
www.casellausa.com
2 Mar 2009
Fax: (603) 672-8053