Larson Davis System 824, Technical Reference Manual

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13-16 824 Reference Manual 9/29/09
manually lock to the current frequency; a lock icon will
appear as shown below.
Press the left arrow key once to activate the automatic lock
mode, a diamond shaped icon will appear. The lock mode
will step in sequence from unlocked to manual locked to
automatic and back to unlock with the right arrow. The left
arrow will sequence through the modes in the reverse order.
Manual Lock
For manual operation select unlock while at a high
amplitude (70dB HL or above) where the highest amplitude
filter can be detected easily. When the correct frequency is
displayed press the right arrow to manually lock the filter so
that it does not change when measuring low amplitudes.
AGC is not active in the manual unlock or lock modes.
Automatic Lock
For automatic operations select the auto mode by pressing
the left (or right) arrow key until the diamond icon appears.
A trigger level setting is found on the check menu that
defines the amplitude below which the lock is set. When
above the trigger level the filter frequency will track the
highest amplitude signal. When the level of that filter drops
below the trigger level the lock is activated and the filter
frequency is unchanged. The icons will show this condition
with the lock and diamond icons.
Note: To change to another filter in auto mode, just increase
the amplitude until the level is above the trigger level.
When in automatic mode the Automatic Gain Control will
be activated. When the gain is set to 0dB, it will be changed
to +30dB when the signal is more than 45dB below the
overload level for 1.5 seconds. When the gain is set to
Lock Icon