Casella CEL CEL-296 - Manual (Page 13)

recording device.
The overall frequency response of the CEL-296/3 satisfies the
requirements of IEC 225 for octave and third octave filters, and ANSI
S1.11-1966 (R 1975) Class II for octave filters and Class III for third
octave filters (best classes). Figures 2 and 3 represent typical
response curves for octaves and third octaves respectively. These
curves were produced by using a CEL-493/2 Sound Level Meter to
measure the response for all bands, and then averaging the results.
3.1.2 Control System
The range, mode, and bandwidth of the instrument are set manually
by controls on the front panel. However, all internal and external
control functions are monitored by the built in microprocessor.
When the or nudge buttons are pressed, or band step control
signals are received from an external device such as a level recorder
via the bottom connector, the microprocessor controls the clock
oscillator to step the centre frequency of the filter band. The selected
band centre frequency will be identified on the digital display.
When used with a sound level meter equipped with the CEL low
power serial interface, the microprocessor can also perform several
additional functions. It controls the filter scanning by means of an
"autoscan" program, and receives digital data from the sound level
meter via the top connector.
This data can be stored in the CEL-296/3 under microprocessor
control as complete spectra that can be recalled for display at a later
time, or transmitted via the bottom connector for further processing.
3.2 Digital Display
The display fitted to the CEL-296/3 Autoscan Filter Set is a custom
designed LCD that has clear, easy to read digits (see Figure 4). As
in normal operation the instrument will be used close coupled to a
CEL Instruments Ltd CEL-296/3 Operator Handbook Page 13