Stanford Research Systems SR810 Manual page 20

Outputs, Offsets and Expands
Press [Channel 1 Offset Modify]
Use the knob to adjust the X offset to 40.0%
Press [Channel 1 Expand] to select x10.
6. Connect the DVM to the X output on the
Auto Offset automatically adjusts the X offset (or R)
such that X (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 SR810 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 percentage
does not change with the sensitivity. The displayed
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 turn on the
OVLD indicator in the Channel 1 display.
With offset and expand, the output voltage gain and
offset can be programmed to provide control of
feedback signals with the proper bias and gain for a
variety of situations.
Offsets add and subtract from the displayed values
while expand increases the resolution of the display.
The X and Y outputs on the rear panel always provide
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