Stanford Research Systems SR865A Operation Manual page 98

80 Operation
terminated in a high impedance, the amplitude will be the specified value. If an output is
terminated in 50Ω, the amplitude will be half the specified value. The outputs are 180°
out of phase. If both outputs are used differentially, the amplitude will be twice the output
of a single BNC.
In general, if single output is used as the A input, the measured signal will be the
specified amplitude (a single output terminated in a high impedance).
Using differential signals can be helpful when the sine amplitude is very small.
When the reference source is Internal or Dual, this is the excitation source provided by
the SR865A. When an external reference is used (or in Chop mode), this sine output
provides a sine wave phase locked to the external reference.
The rear panel BlazeX BNC output can be configured in the System menu (hold
[Calc/system]) to provide a square wave sync at the reference frequency. This square
wave is generated by discriminating the zero crossings of the sine output. This signal can
provide a trigger or sync signal to the experiment when the internal reference source is
used. This signal is also available when the reference is externally provided. In this case,
the sync output is phase locked to the external reference.
<DC Level>
This knob adjusts the sine out dc level.
The dc level is shown in the info bar at the top of the screen. Touch the {DC} tile to show
the numeric entry screen.
The dc level has 3 digits or 0.1 mV resolution, whichever is larger. The dc level ranges
from −5.00 V to +5.00 V.
Press and hold this knob to set the dc level to zero.
The dc level adds an offset to the sine output. Each output BNC has the specified dc level
through a 50Ω output impedance. If an output is terminated in a high impedance, the dc
level will be the specified value. If an output is terminated in 50Ω, the dc level will be
half the specified value.
The dc level is added to the outputs in Difference mode (opposite sign dc level on each
BNC) or in Common mode (same sign dc level on both BNC's). Choose the mode with
the [Mode] key.
DC Level [Mode]
This key selects the dc level mode. The dc level is added to the sine outputs in Difference
mode (opposite sign dc level on each BNC) or in Common mode (same sign dc level on
both BNC's).
SR865A DSP Lock-in Amplifier
Chapter 3