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12
Getting Started
14. Press [Slope] to select 12 dB/oct.
Press [Slope] twice more to select 24 dB/oct.
Press [Slope] again to select 6 dB/oct.
15. Press [Sync] to turn on synchronous filtering.
SR865A DSP Lock-in Amplifier
The output values become noisy. This is
because the 2f component of the output (at
2 kHz) is no longer attenuated completely by
the low pass filter.
The red Output
Overload
light indicating that the output voltage is
clipping. The 50 mV signal outputs 10 V when
the sensitivity is 50 mV. The large additional 2f
component will cause the output to try and
exceed 10 V and results in an output overload.
Output overload does not affect the actual
displayed value, it just indicates that the CH1
(or CH2) output is not following the measured
value.
Parameters which have only a few values, such
as Filter Slope and External Source, have only a
single key which cycles through all available
options. Press the key until the desired option is
indicated by an LED.
The outputs are less noisy with 2 poles of
filtering.
With 4 poles of low pass filtering, even this
short time constant attenuates the 2f component
reasonably well and provides steady readings.
Let's leave the filtering short and the outputs
noisy for now.
This turns on synchronous filtering whenever
the detection frequency is below 4.8 kHz.
Synchronous filtering effectively removes
output components at multiples of the detection
frequency. At low frequencies, this filter is a
very effective way to remove 2f without using
extremely long time constants.
The outputs are now quiet and steady, even
though the time constant is very short. The
response time of the synchronous filter is equal
to the period of the detection frequency (1 ms in
this case).
This concludes this measurement example. You
should have a feeling for the basic operation of
the front panel. Basic lock-in parameters have
been introduced and you should be able to
perform simple measurements.
Chapter 1
LED for CH1 will
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