Chapter 5, WEB CONTROL PANEL OPERATION
5-23
Source
This control allows selection of the source of reference signal used to drive the
reference 2 circuitry, and has three settings. The corresponding control in the
Reference 1 section also offers the same choices when in dual mode:-
Internal
The lock-in amplifier's reference is taken from the instrument's internal
oscillator. Note that this setting gives the best phase and gain measurement
accuracy under all operating conditions, and it is always to be preferred, if
possible, to design the experiment so that the lock-in amplifier acts as the source
of the reference signal.
External digital
In this setting the reference channel is configured to accept a TTL reference
source applied to the front panel REF IN input connector, except if the
Reference 1 input selection is set to External Analog, in which case a TTL
reference at a frequency no greater than 3.0 kHz should be applied to the rear
panel TRIG IN connector.
External analog
In this setting the reference channel is configured to accept an analog reference
source applied to the front panel REF IN input connector
Note that it is not possible to use virtual reference mode when the instrument is in
dual mode, so there is no selection to allow this.
Frequency
This indicator shows the current frequency at which the Reference 2 channel is
operating.
Harmonic
This control allows selection of the harmonic of the reference frequency at which the
reference 2 channel of the lock-in amplifier operates. It can be set to any value
between 1F and 127F, but most commonly is set to 1F.
Phase
This control allows the reference phase for the second set of demodulators to be
adjusted over the range -180° to +180° in 1 m° steps.
+90 Deg
Each click of this button adds 90° to the reference 2 phase setting.
Auto Phase
Clicking this button initiates an Auto-Phase operation, where the value of the signal
phase with respect to the reference is computed and an appropriate phase-shift is
then introduced into the reference 2 channel so as to bring the difference between
them to zero. The intended result is to null the output of the Y channel while
maximizing the output of the X channel.
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