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2.3 Navigating the front panel
2.2.4.2 AC Volt mode
2.3 Navigating the front panel
Stanford Research Systems
SENSITIVITY
OVLD
200
100
500
µV
50
1
2
20
10
5
5
10
knob
mV
2
20
1
50
INPUT FILTER
100
500
200
200
10
5
nV
100
500
2
SIGNAL INPUT
knob
1
A
OVLD
A–B
Q-factor
6
I (10
)
AC
Float
8
I (10
)
DC
Ground
Band Pass
High Pass
Input
Couple
Ground
Low Pass
Notch
A/I
B
Flat
Type
BNC
BNC
10 MΩ
10 MΩ
SR124 Analog Lock-In Amplifier
When phase-sensitive detection is not possible, the SR124 can be
configured for AC Volt mode. In this setting, the reference oscillator
is unused and the phase-sensitive detector (square wave mixer) is
controlled directly by the polarity of the amplified AC input signal.
The instrument now acts as an averaging AC voltmeter, where the
detection element is an absolute value detector.
For most applications using AC Volt mode, the Reserve setting
should be set to Low Noise, since there is no reserve benefit from
the mixer in this configuration. If the input signal is not already rel-
atively clean with high signal-to-noise, the input filter may be used
to define the frequency band for measurement.
The front panel of the SR124 is organized into distinct functional
sections. Knowing this organization will help you to become familiar
with its operation. A diagram of the entire front panel is in Figure 2.2,
below.
kHz
Hz
f trim
depth
Push to select
Hold to
null
20
OUTPUT
knob
50
100
10% ENBW
6dB/oct.
RESERVE
ms
100
300
12 dB/oct.
30
10
Slope
High Res.
3
Signal
Normal
Monitor
1
Low Noise
knob
min
Reserve
BNC
Time Constant
600 Ω
In Figure 2.2, the two large rectangular blocks above "INPUT FIL-
TER" and "REFERENCE" are static numeric displays. The larger
white rectangle in the upper center of the drawing is the jewel bear-
ing analog panel meter.
The two large knobs each have a push-button secondary function;
in addition to adjusting the parameter currently "in focus" (more
about that later), briefly pressing the knob inward has a secondary
function. Also, holding the knob in for several seconds has a tertiary
function—clearing or nulling the parameter in focus.
AUTO
Gain
Phase
OVLD
O set
Lock
Assist
SETUP
Local
Save
Recall
CONTROL INHIBIT
OUTPUT
OFFSET
INHIBITED
OVLD
Lock-In
All CPU clocks, panel
1
On
AC Volt
3
controls, and remote
s
10
commands disabled
On/O
Mode
30
switch
100
300
Modify
BNC
CPU Activity
Remote Activity
600 Ω
Figure 2.2: The SR124 front panel.
2 – 11
Model SR124 Analog Lock-In Ampli er
kHz
V
Hz
mV
deg
%
coarse
REM
PHASE
FREQ
AMPL
BIAS
OFFSET
REFERENCE
Push to select
Quadrant
270
360
Phase
Freq
Ampl
180
270
knob
90
180
0
90
Mode
Push for
3f
Ext. In TTL
2f External
knob
DC Bias
Ref. Out
f
knob
Square
Internal
On
Sine
Rear VCO
Ext. In
On/O
Shape
TTL
Range (Hz)
Unlocked
2.0k
210k
200
21k
Modify
20
2.1k
BNC
knob
BNC
2.0
210
0.2
21
50 Ω
ne
Hold to
null
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