Ametek 7280 Instruction Manual page 106

Chapter 5, FRONT PANEL OPERATION
5-60
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
REF1 HARMONIC
This control sets the harmonic of the applied external reference frequency at which
the lock-in amplifier's reference 1 channel operates, in the range 1 st (fundamental
mode) to 32 nd.
RELOCK EXT. REFERENCE
The 7280 includes frequency-dependent calibration parameters. In Dual reference
mode the correct parameters can be chosen for the internal reference channel because
its frequency is equal to the specified oscillator frequency. The parameters for the
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.
REF2 HARMONIC
This control sets the harmonic of the internal reference frequency at which the lock-
in amplifier's reference 2 channel operates, in the range 1 st (fundamental mode) to
32 nd.
For example, if Ref1 Harmonic is set to 3rd, Ref2 Harmonic is set to 1st, an external
reference signal of 1 kHz is applied and the internal oscillator set to 12 kHz, the
instrument will measure signals at its input at frequencies of both 3 kHz and 12 kHz.
AUX DAC 1 and AUX DAC 2
These two controls set the voltage appearing at the DAC1 and DAC2 output
connectors on the rear panel to any value between +10 V and -10 V with a resolution
of 1 mV. 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, used for the reference 2
detection channel, may be set using this control to any value between 0.5 Hz and
2.000 MHz with a 1 mHz resolution. Adjustment is faster using the Keypad or Active
Cursor controls - see section 4.1.04.