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Chapter 5, FRONT PANEL OPERATION
5-82
RELOCK EXT. REFERENCE
The 7124 includes frequency-dependent calibration parameters. When operating in
Internal reference mode the correct parameters can be chosen because the reference
frequency is equal to the specified oscillator frequency. In External reference mode
the applied frequency is measured, and the measured value is used to select the
correct parameters. If , however, the external reference frequency drifts or changes
with time then the lock-in amplifier may need to use different calibration parameters.
It therefore includes an automatic algorithm that detects significant changes in
reference frequency, and if these occur, updates all the frequency-dependent
calibration values.
Pressing this key has the effect of manually updating these calibration parameters.
This should be done when operating in External reference mode after each
intentional change to the applied reference frequency.
AUTO MEASURE1 and AUTO MEASURE1
These functions only operates when the corresponding harmonic frequency is greater
than 1 Hz, and perform the following operations:
The instrument is set to AC-coupled and input FLOAT mode. If the reference
frequency is more than 10 Hz the output time constant is set to 10 ms, otherwise it is
set to the lowest synchronous value, the filter slope is set to 12 dB/octave, output
expand is switched off, the reference harmonic mode is set to 1, the X offset and Y
offset functions are switched off and the Auto-Sensitivity and Auto-Phase functions
are called. The Auto-Sensitivity function also adjusts the AC Gain if required.
AUX DAC 1, AUX DAC 2, AUX DAC 3, and AUX DAC 4
These four controls set the voltage appearing at the DAC1, DAC2, DAC3, and
DAC4 output connectors on the rear panel to any value between +10 V and -10 V
with a resolution of 1 mV, assuming that the corresponding output is set to the
USER DAC mode on the DAC Menu - see section. Adjustment is faster using the
Keypad or Active Cursor controls - see section 4.1.04.
OSC FREQUENCY
The frequency of the instrument's internal oscillator may be set, using this control, to
any value between 0.5 Hz and 150.0 kHz with a 1 mHz resolution. Adjustment is
faster using the Keypad or Active Cursor controls - see section 4.1.04.
RCU OSC AMPLITUDE
This control sets the amplitude of the signal at the 7124 RCU's OSC OUT connector
to any value between 1 mV and 5 V rms. Adjustment is faster using the Keypad or
Active Cursor controls - see section 4.1.04.
OSC AMPLITUDE
This control sets the amplitude of the signal at the 7124's main console OSC OUT
connector to any value between 1 mV and 5 V rms. Adjustment is faster using the
Keypad or Active Cursor controls - see section 4.1.04.
NOTE: Only one of the two controls RCU OSC AMPLITUDE and OSC AMPLITUDE will
be available, depending on the whether the RCU oscillator in enabled on the
Oscillator menu - see section 5.3.09
Since the instrument is now generating two sets of outputs (one for each harmonic of
the reference) there are more output display choices in this mode than in single
reference mode, and these are listed in table 5-4. The outputs corresponding to the
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