Stanford Research Systems SR865A, Operation Manual

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Chapter 1 Getting Started 23
SR865A DSP Lock-in Amplifier
percentage of the Sensitivity up to 999% (10×).
Offsets are useful for making relative
measurements.
Offsets can also be set using the keypad or
<Offset> knob.
The offset affects the value of X and any
outputs or displays of X. The DVM voltage
should be zero in this case.
The Offset indicator turns on next to the <CH1
Offset> knob. The X display on the screen has
an ‘Ofst’ indication that the displayed quantity
is affected by an offset. In this case, the bar
graph and numeric value are both zero.
11. Touch {9}{0}{Enter} to set the offset to 90%. The X output (10 mV) is now 10% of the
sensitivity (100 mV). The bar graph is at 10%
and the DVM reads 1 V.
Notice that the trace of X (green) is a line
10 mV above zero (center). This is because the
offset affects the value of X (unlike the
sensitivity).
12. Press the <CH1 Offset> knob briefly once to
turn the X offset off.
The offset for CH1 can be turned on and off
without changing the offset value. Notice how
the trace of X changes when the offset is turned
off.
Press it again to turn it back on. Leave the X offset on for now.
13. Press [CH1 Expand] once to select ×10. Expand ×10 effectively decreases the sensitivity
by 10 after the offset is applied.
10V Expand Offset
y Sensitivit
X
CH1
u u
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·
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Now, X = 100 mV, Sensitivity = 100 mV, the
offset is 90% and the expand is ×10. Thus the
DVM reads 10 V.
The X bar graph is now at 100% and the
numeric readout has added resolution. The X
display has an ‘Expd’ indication that the
displayed quantity is affected by a non-unity
expand.
Expand increases the resolution of the X
display and CH1 output. Note that the trace of
X is unaffected by expand. This is because
expand does not change the value of X.