SRS Labs SR850 - Manual (Page 17)

2-5
9. Press <Sensitivity>
Use the knob to change the sensitivity to
50 mV.
Change the sensitivity back to 20 mV.
10. Press <Time Constant>
Use the knob to change the time constant to
300 µs.
Change the time constant to 3 ms.
11. Press the <Filter db/oct.> softkey until 6 dB/oct
is selected.
Press <Filter db/oct.> again to select
12 dB/oct.
Press <Filter db/oct.> twice to select
24 db/oct.
Press <Filter db/oct> again to select 6 db/oct.
12. Press [REF/PHASE]
Press <Ref. Frequency>
Press [5] [0] [ENTER]
that the measured magnitude (R) is a sizable per-
centage of full scale.
Highlight the full scale sensitivity.
Parameters which are discrete values, such as
sensitivity and time constant, can only be changed
with the knob. Numeric entry is not allowed for
these parameters.
Highlight the time constant.
The values of X and Y become noisy. This is
because the 2f component of the output (at 2 kHz)
is no longer attenuated completely by the low pass
filters.
Let's leave the time constant short and change the
filter slope.
Parameters which have their available options dis-
played within the menu box are selected by press-
ing the corresponding softkey until the desired
option is chosen.
The X and Y outputs are somewhat noisy at this
short time constant and only 1 pole of low pass
filtering.
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 rea-
sonably well and provides steady readings.
Let's leave the filtering short and the outputs noisy
for now.
Display the Reference and Phase menu.
Highlight the internal reference frequency.
Enter 50 Hz for the reference frequency. With a
3 ms time constant and only 6 db/oct of filtering,
the output is totally dominated by the 2f compo-
nent at 50 Hz.
The Basic Lock-in