Outputs, Offsets And Expands - Stanford Research Systems SR810 Manual

OUTPUTS, OFFSETS and EXPANDS

This measurement is designed to use the internal oscillator to explore some of the basic lock-in outputs. You
will need BNC cables and a digital voltmeter (DVM).
Specifically, you will measure the amplitude of the Sine Out and provide analog outputs proportional to the
measurement. The effect of offsets and expands on the displayed values and the analog outputs will be
explored.
1. Disconnect all cables from the lock-in. Turn
the power on while holding down the [Setup]
key. Wait until the power-on tests are
completed.
2. Connect the Sine Out on the front panel to
the A input using a BNC cable.
3. Connect the CH1 OUPTUT on the front
panel to the DVM. Set the DVM to read DC
Volts.
4. Press [Ampl]
Use the knob to adjust the sine amplitude to
0.5 V.
5. Press [Channel 1 Auto Offset]
Outputs, Offsets and Expands
When the power is turned on with the [Setup] key
pressed, the lock-in returns to its standard settings.
See the Standard Settings list in the Operation section
for a complete listing of the settings.
The Channel 1 display shows X.
The lock-in defaults to the internal oscillator reference
set at 1.000 kHz. The reference mode is indicated by
the INTERNAL led. In this mode, the lock-in generates
a synchronous sine output at the internal reference
frequency.
The input impedance of the lock-in is 10 MΩ. The Sine
Out has an output impedance of 50Ω. Since the Sine
Output amplitude is specified into a high impedance
load, the output impedance does not affect the
amplitude.
The sine amplitude is 1.000 Vrms and the sensitivity is
1 V(rms). Since the phase shift of the sine output is
very close to zero, Channel 1 (X) should read close to
1.000 V.
The CH1 output defaults to X. The output voltage is
simply (X/Sensitivity - Offset)xExpandx10V. In this
case, X = 1.000 V, the sensitivity = 1 V, the offset is
zero percent and the expand is 1. The output should
thus be 10 V or 100 % of full scale.
Display the sine output amplitude.
Set the amplitude to 0.5 V. The Channel 1 display
should show X=0.5 V and the CH1 output voltage
should be 5 V on the DVM (½ of full scale).
X and R may all be offset and expanded separately. (Y
via the interface only). 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.
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