Stanford Research Systems SR865A, Operation Manual

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Chapter 3 Operation 79
SR865A DSP Lock-in Amplifier
The internal frequency has 6 digits or 0.1 mHz resolution, whichever is larger. The
frequency can range from 1.0 mHz to 4.0 MHz. The upper limit is decreased if the
harmonic number is greater than 1. In this case, the upper limit is 4 MHz/N where N is
the harmonic number.
Press and hold this knob to set the harmonic detect to 1 (fundamental).
Frequency [Harm Up] and [Harm Down]
Pressing these keys increments and decrements the harmonic detect number from 1 to 99.
The harmonic number is shown in the info bar at the top of the screen. Touch this
{Harm} tile to show the numeric entry screen.
The SR865A can detect signals at harmonics of the reference frequency. The SR865A
multiplies the input signal with digital sine waves at N×f
ref
. Only signals at this harmonic
will be detected. Signals at the original reference frequency are not detected and are
attenuated as if they were noise. Always check the harmonic detect number before
making any measurements.
The Sine Out is not affected by the harmonic detection. Its frequency is always the
fundamental reference frequency.
Internal and Chop Reference
When the reference mode is Internal or Chop, these keys change the internal harmonic
number N
int
and detection is at N
int
×f
int
and the internal reference frequency is limited to 4
MHz/N
int
.
External Reference
When the reference mode is External, these keys change the external harmonic number
N
ext
and detection is at N
ext
×f
ext
. The SR865A will always track the external reference.
Dual Reference
When the reference mode is Dual, detection is at f
dual
= | N
int
×f
int
−
N
ext
×f
ext
|. Use the
harmonic numeric entry screen to adjust either harmonic number. The limits described
above apply. The Sine Out will still be at f
int
.
<Amplitude>
This knob adjusts the sine out amplitude.
The amplitude is shown in the info bar at the top of the screen. Touch the {Ampl} tile to
show the numeric entry screen.
The amplitude has 3 digits or 1 nV resolution, whichever is larger. The amplitude can
range from 1 nVrms to 2.00 Vrms.
Press and hold this knob to set the amplitude to zero.
The Sine Out amplitude is specified for differential output (Sine+) − (Sine−). Each output
BNC has the specified rms amplitude through a 50Ω output impedance. If an output is