Stanford Research Systems SR865A, Operation Manual

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70 Operation Chapter 3
SR865A DSP Lock-in Amplifier
The Sensitivity should be chosen to conveniently and accurately display the measurement
results on the output BNC, the bar graph and the numerical readout. The Sync filter also
uses the Sensitivity as an indicator of the signal range it needs to accommodate. An
output overload does not necessarily mean a Sync filter overload, but a ‘Sync’ error
indicated in the X, Y, R or θ displays does signify a Sync filter overload.
θ ranges from − 180° to +180° regardless of the scale or range. When CH2 outputs a
voltage proportional to θ, the output scale is 18°/Volt or 180°=10
V. The phase bar graph
and numeric readout scales are also unaffected by the Sensitivity.
Synchronous Filters and Noise Calculations
Synchronous filtering and calculation of X
noise
and Y
noise
are performed on the output
scaled values of X and Y. Thus, their accuracy is affected by a poor choice of Sensitivity.
If the Sensitivity is set too large, the values of X and Y (in the numeric displays) will lack
the necessary resolution. If the Sensitivity is set too low, the values will be overloaded
(pinned) and no noise will be measured. In general, setting the Sensitivity to display a
reasonable amount of bar graph is sufficient.