Stanford Research Systems SR865A, Operation Manual

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Chapter 1 Getting Started 13
SR865A DSP Lock-in Amplifier
Using Displays
This measurement is designed to use the internal oscillator and an external signal source to explore some
of the display types. You will need a synthesized function generator capable of providing a 500 mVrms
sine wave at 100.000 kHz, BNC cables and a terminator appropriate for the generator function output.
Specifically, you will display the lock-in outputs when measuring a signal close to, but not equal to, the
internal reference frequency. This setup ensures changing outputs which are more illustrative than steady
outputs.
Do This Explanation
1. Disconnect all cables from the lock-in. Turn the
power on while holding down the [Local] key.
The power switch is on the power entry module
on the rear panel. When the power is turned on with [Local]
pressed, the lock-in returns to its standard
default settings. See the Standard Settings list in
the Operation section for a complete listing of
the settings.
2. Turn on the function generator, set the frequency
to 100.000 kHz (exactly) and the amplitude to
500 mVrms.
Connect the function output (sine wave) from
the synthesized function generator to the A input
using a BNC cable and appropriate terminator.
The input impedance of the lock-
in is 10 MΩ.
The generator may require a terminator. Many
generators have either
a 50Ω or 600Ω output
impedance. Use the appropriate feedthrough or
T termination if necessary. In general, not using
a terminator means that the function output
amplitude will not agree with the generator
setting.
The default screen is the Trend Graph. Four
data channels are displayed as values, bar and
trend graphs. The trend graph is the recent
history of each data channel with continuous
auto-scaling. In this case R (yellow) auto scales
to show the tiny amount of noise in the signal
magnitude. Trend graphs have no adjustments
and are most useful when adjusting an
experiment to find a maximum or minimum.
The lock-in defaults to the internal oscillator
reference set at 100.000 kHz. The reference
source is indicated by the
Internal
LED
.
The internal oscillator should be very close to
the actual generator frequency. The X (green)
and Y (blue) displays should read values which
change slowly. The lock-in and the generator
are not phase locked but they are at (nearly) the
same frequency with a sl
owly changing θ
(orange). The signal magnitude R (yellow) is
phase independent and does not change.