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Chapter 5, FRONT PANEL OPERATION
5-64
external reference channel are selected by measuring the applied frequency. 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 Dual reference mode after each intentional
change to the external reference frequency.
AUTO MEASURE1 and AUTO MEASURE1
These functions only operates when the corresponding reference 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.
REF2 HARMONIC
This control sets the harmonic of the reference frequency at which the lock-in
amplifier's reference 2 channel operates, in the range 1 st (fundamental mode) to
127 th.
For example, if Ref1 Harmonic is set to 3rd, Ref2 Harmonic is set to 1st, Reference 1
is set to External, an external reference signal of 12 kHz is applied and the internal
oscillator set to 1 kHz, the instrument will measure signals at its input at frequencies
of both 3 kHz and 12 kHz.
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 5.3.31. 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
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