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Chapter 5, FRONT PANEL OPERATION
5-80
100 ks in a 1-2-5 sequence. Settings of 1 ms and below restrict the choice of
instrument outputs to X, Y and Magnitude.
HARMONIC 1 PHASE and HARMONIC 2 PHASE
These controls allows the reference phase of each detection channel to be adjusted
over the range -180° to +180° in 1 m° steps. Adjustment is faster using the Keypad
or Active Cursor controls - see section 4.1.04.
HARMONIC 1 PHASE ±90° and HARMONIC 2 PHASE ±90°
These controls allow the relevant reference phase to be adjusted in steps of ±90°.
X1 OFFSET, Y1 OFFSET, X2 OFFSET and Y2 OFFSET
These are the manual X1/X2 channel and Y1/Y2 channel output offset controls. The
offset levels set by these controls, which can be any value between -300% and
+300% in 0.01% steps, are added to the X1, X2, Y1 or Y2 channel outputs when the
relevant channel offsets are switched on using the Output Channels menu.
Adjustment is faster using the Keypad or Active Cursor controls - see section 4.1.04.
The values are set automatically by the Auto-Offset function. Note that the Auto-
Offset function automatically switches on all output offsets
HARMONIC 1 and HARMONIC 2
These controls set the harmonic of the applied reference frequency, either internal or
external, at which the lock-in amplifier's two reference channels operate, in the range
1 st (fundamental mode) to 127 th. For example, if a reference frequency of 1 kHz is
applied, Harmonic 1 is set to 3 and Harmonic 2 to 5, the instrument will measure
signals at both 3 kHz and 5 kHz.
RELOCK EXT. REFERENCE
The 7270 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 MEASURE 1 and AUTO MEASURE 2
These controls allows an auto-measure cycle for harmonic 1 or 2 to be initiated
directly from the main display.
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
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