Stanford Research Systems SR844, User Manual

Page: 18 / 246

1-8 The Basic Lock-In
SR844 RF Lock-In Amplifier
19 Reconnect the cable to SIGNAL IN. The bargraph rises slowly. In fact, with a filter slope
of 12 dB/oct, it takes about 5 time constants to get
to within 1% of the final reading. In this case, this
takes more than 15 s.
20
Press Slope/Oct DOWN until 24 dB is
selected.
The filter slope is adjusted using the right hand pair
of keys in the Time Constant area. The filter rolloff
can be 6, 12, 18 or 24 dB/oct.
With 24 dB/oct rolloff, it takes about 12 time
constants to get within 1% of the final reading.
Remember, both the time constant and filter slope
affect the output settling time.
21
Press Slope/Oct UP until NO FILTER is
selected.
No filtering is also available. In this case, the
demodulator outputs are amplified but not filtered.
The high output bandwidth in this case requires that
the outputs be taken from the CH1
or CH2
OUTPUT from the front panel and not from the
displays.
22
Press
Slope/Oct DOWN
until
12 dB
is
selected.
12 dB/oct works well in most situations.