Stanford Research Systems SR830 Manual page 41

SR830 Basics
The analog output with offset and expand is
Output = (signal/sensitivity - offset) x Expand x10V
where offset is a fraction of 1 (50%=0.5), expand
is 1, 10 or 100, and the output can not exceed 10
V. In the above example,
Output = (0.91mV/1mV - 0.9) x 10 x 10V = 1V
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
SR830 are output functions, they do NOT affect
the calculation of R or θ. R has its own output
offset and expand.
CH1 and CH2 Displays
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. The CH2 display can show Y, θ,
Y Noise, Aux Input 3 or 4, or any of these quanti-
ties divided by Aux Input 3 or 4.
Output offsets ARE reflected in the displays. 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 dis-
play 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, Y or R. Expand increases the resolu-
tion of the X, Y or R value used to calculate the
displayed value. For example, CH1 when display-
ing X does not increase its displayed value when
X is expanded. This is because the expand func-
tion 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
Aux In 1 (in Volts)
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 dis-
play 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 affect-
ed by the sensitivity, offset and X expand.
In the case of θ, the full scale sensitivity is always
180°.
The Ratio indicator below the display is on when-
ever a display is showing a ratio quantity.
Display output scaling
What about CH1 or CH2 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 2.137V from the CH1 output.
3-14
the display value is