Stanford Research Systems SR844, User Manual

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The Basic Lock-In 1-5
SR844 RF Lock-In Amplifier
The Basic Lock-In
This measurement is designed to use the internal oscillator to explore some of the basic lock-in
operations. You should already be familiar with the fundamentals of lock-in detection. See Chapter 2 for a
discussion of the basics of lock-in measurements.
Specifically, you will measure the amplitude of the reference oscillator at various frequencies,
sensitivities, time constants and phases. You will need a BNC cable for this section.
1 Disconnect all cables from the SR844.
If the power is off, turn it on. Wait for self-
tests to complete.
Turn on the unit.
2 Press Shift then Recall (PRESET) to restore
factory presets.
We will start with the unit in its factory preset
configuration.
The factory preset configuration is Internal
Reference mode (shown by the
INTERNAL
LED)
at 1.00 MHz, shown on the Reference display.
The time constant is 100 ms (shown by the time
constant indicators
1
,
××××
100
and
ms
above the Time
Constant Up/Down keys) and the sensitivity is 1 V
rms (the indicators are below the Sensitivity
Up/Down keys).
3 Connect REF OUT on the front panel to the
SIGNAL IN with the BNC cable.
The SR844 reference output (1.0 Vpp nominal
square wave into 50
Ω
) is within the unit’s
measurement range (1 Vrms) so we can connect it
directly to the input. The SR844 input impedance is
set to 50
Ω
(shown by the 50
Ω
Ω Ω
Ω
indicator) which is
appropriate for the REF OUT.
The BNC cable has a small phase shift at 1 MHz
(the free-space wavelength is 300 m), so the input
signal should be mostly X (in-phase) with a small Y
(quadrature) component.
The CH1 Display is set to X and should show
something close to 0.54 V. The CH2 display is set
to Y and should show less than
±
0.05 V.