Stanford Research Systems SR124 Operation And Service Manual page 41

2.3 Navigating the front panel
2.3.4.1 Quadrant
2.3.4.2 Ext. In
SR124 Analog Lock-In Amplifier
of the parameters, turning the large REFERENCE knob allows that
parameter to be adjusted.
Pressing the REFERENCE knob inward toggles between coarse and
fine scrolling speeds for adjusting parameters. Holding the knob in
for approximately 2 seconds will cause the parameter to be nulled
(other than frequency and amplitude, which do not allow zero set-
tings).
Within the REFERENCE section, pressing [Phase] brings the refer-
ence phase shift into focus. Note that in AC Volt mode, phase is
unused (but may still be adjusted). (PHAS, 4 – 9 )
Pressing [Freq] brings frequency into focus. When operating in In-
ternal mode, frequency can be adjusted across the 2 decades range
selected by the Range block. (FREQ, 4 – 9 )
Pressing [Freq] when operating either in Rear VCO mode or one of
the External modes causes the SR124 to perform a frequency mea-
surement on the actual reference oscillator frequency. That frequency
is then displayed on the numeric display.
If the focus is already on FREQ when the instrument changes mode
into either Rear VCO or External, the display will show "- - - - -
"; pressing [Freq] again will cause a frequency measurement to be
performed and displayed. Each successive press of [Freq] initiates a
new measurement.
Pressing [Ampl] brings the reference output amplitude into focus.
Turning REFERENCE adjusts the output amplitude (in Vrms).
(SLVL, 4 – 10 )
Turning the Quadrant knob adds or subtracts 90 from the current
value of the reference phase shift. One of the four quadrant indicators
is always illuminated to show which quadrant the current value of
phase lies in. (QUAD, 4 – 9 )
The Ext. In BNC input is used for locking the SR124 to an external
reference; this input is unused when in Internal or Rear VCO mode.
The Ext. In circuit can be configured for either sine inputs or TTL
inputs; when in TTL mode, the TTL indicator is illuminated in this
section. The user can toggle between sine and TTL mode by pressing
the Mode knob (see below).
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