Stanford Research Systems SR810 Manual page 36

for a signal which is 10 µV greater than the 0.9 mV
nominal. (Offset = 0.9 and expand =10).
The X and Y offset and expand functions in the
SR810 are output functions, They do NOT
affect the calculation of R or θ. R has its own
output offset and expand.
The X and R offsets and expands may be set from
the front panel. The Y offset and expand may
only be set from the interface.
CH1 Display
The CH1 display can show X, R, X Noise, Aux
Input 1 or 2, or any of these quantities divided by
Aux Input 1 or 2.
Output offsets ARE reflected in the display. For
example, if CH1 is displaying X, it is affected by
the X offset. When the X output is offset to zero,
the displayed value will drop to zero also. Any
display which is showing a quantity which is
affected by a non-zero offset will display a
highlighted Offset indicator below the display.
Output expands do NOT increase the displayed
values of X or R. Expand increases the resolution
of the X or R value used to calculate the displayed
value. For example, CH1 when displaying X does
not increase its displayed value when X is
expanded. This is because the expand function
increases the resolution with which the signal is
measured, not the size of the input signal. The
displayed value will show an increased resolution
but will continue to display the original value of X
minus the X offset. Any display which is showing a
quantity which is affected by a non-unity expand
will display a highlighted Expand indicator below
the display.
Ratio displays are displayed as percentages. The
displayed percentage for X/Aux 1 would be
Display % = (signal/sensitivity-offset)xExpandx100
where offset is a fraction of 1 (50 %-0.5), expand
is 1, 10 or 100, and the display can not exceed
100 %.
For example, if the sensitivity is 1V and CH1
display is showing X/Aux 1. If X= 500 mV and Aux
1= 2.34 V, then
(0.5/1.0)x100/2.34 or 21.37 %. This value is
affected by the sensitivity, offset and X expand.
The Ratio indicator below the display is on
whenever a display is showing a ratio quantity.
Display output scaling
What about CH1 outputs proportional to ratio
displays? The output voltage will simply be the
displayed percentage times 10V full scale.
In the above example, the displayed ratio of
21.37 % will output 2.137 V from the CH1 output.
3-11
SR810 Basics
Aux In 1 (in Volts)
the display value is