Stanford Research Systems SR830, Manual

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2-10
5. Press [Channel 1 Auto Offset]
Press [Channel 1 Offset Modify]
Use the knob to adjust the X offset to 40.0%
Press [Channel 1 Expand] to select x10.
X, Y and R may all be offset and expanded separ-
ately. Since Channel 1 is displaying X, the
OFFSET and [Expand] keys below the Channel 1
display set the X offset and expand. The display
determines which quantity (X or R) is offset and
expanded.
Auto Offset automatically adjusts the X offset (or Y
or R) such that X (or Y or R) becomes zero. In this
case, X is offset to zero. The offset should be
about 50%. Offsets are useful for making relative
measurements. In analog lock-ins, offsets were
generally used to remove DC output errors from
the lock-in itself. The SR830 has no DC output
errors and the offset is not required for most
measurements.
The offset affects both the displayed value of X
and any analog output proportional to X. The CH1
output voltage should be zero in this case.
The Offset indicator turns on at the bottom of the
Channel 1 display to indicate that the displayed
quantity is affected by an offset.
Show the Channel 1 (X) offset in the Reference
display.
Change the offset to 40% of full scale. The output
offsets are a percentage of full scale. The percent-
age does not change with the sensitivity. The dis-
played value of X should be 0.100 V (0.5 V - 40%
of full scale). The CH1 output voltage is
(X/Sensitivity - Offset)xExpandx10V.
CH1 Out = (0.5/1.0 - 0.4)x1x10V = 1 V
With an expand of 10, the display has one more
digit of resolution (100.00 mV full scale).
The Expand indicator turns on at the bottom of the
Channel 1 display to indicate that the displayed
quantity is affected by a non-unity expand.
The CH1 output is
(X/Sensitivity - Offset)xExpandx10V. In this case,
the output voltage is
CH1 Out = (0.5/1.0 - 0.4)x10x10V = 10V
The expand allows the output gain to be increased
by up to 100. The output voltage is limited to
10.9 V and any output which tries to be greater will
Outputs, Offsets and Expands