SRS Labs SR850 - Manual (Page 49)

2-37
Press <Return> twice.
8. Press <Smooth>
Press <17 point>
Press [CURSOR]
Use the knob to move the cursor past the left
edge of the graph. The data will scroll to the
right to display unsmoothed portions of the
trace.
Press <Return>
8. Press <Calc>
Press <Operation>
Use the knob to select x
2
.
Press <Do Calc.>
Press [AUTO SCALE]
Use the knob to select
√
.
and right edge of the graph display. In this case,
50 seconds of data (800 data points at 16 Hz
sample rate).
The results are displayed at the bottom of the
screen. The standard deviation (
σ
)should be about
6 nV or so. This is the rms noise of the input in a
noise equivalent bandwidth of 1.2 Hz (100 ms, 12
dB/oct time constant). The input noise (in Volts/
√
Hz) is thus the standard deviation divided by the
square root of 1.2 Hz.
The lock-in can measure noise directly in V/
√
Hz,
this measurement is meant to illustrate the statisti-
cal functions.
Return to the main Math menu.
Choose the Smoothing menu.
Perform 17 point smoothing on the noisy data. The
data should become less noisy and smoother.
Smoothing reduces narrow variations in the data.
Let the knob move the cursor.
The smoothing operation changed the data within
the time window of the graph. Data which was not
displayed was not smoothed. This trace now con-
tains a region which has been smoothed and a
region which is untouched.
Smoothing changes the data in the buffer and the
original unsmoothed points are lost.
Return to the main Math menu.
Choose the Calculator menu.
Highlight the operation.
Let's square the data.
Calculations are performed on all of the data
within the time window of the graph. Let the calcu-
lation finish.
X squared is a positive quantity. The magnitude of
the data is now 10
-18
so auto scale is required to
view the data.
Select square root.
Trace Math