Reference and phase menu, Reference and phase – SRS Labs SR850 User Manual

Page 113

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REFERENCE AND PHASE MENU

Sine Output

Harmonic

12.345 deg.

Rotate

90 deg.

Internal

Ref Frequency

50.000 Hz

#

1

0.100 V rms

Ref. Source

Ref. Phase

Sine Output

Harmonic

Reference Source

90° Shift

Phase Shift

REFERENCE

PHASE

Internal

Internal Sweep

External

Reference

Frequency

Sweep Menu

Reference

Slope

Sweep Type

Sweep Limits

Return

Reference and Phase

The Reference and Phase menu sets the reference source, phase shift,
and detection harmonic. The internal oscillator frequency , sweeps, and
amplitude are also specified in this menu.

Reference Phase

Pressing the Reference Phase key (top soft key) selects the reference
phase shift as the active entry field. A new phase shift may be entered
from the numeric keypad or the knob may be used to adjust the phase.
The phase shift ranges from -180° to +180° with 0.001° resolution. A
numerically entered phase is rounded to the nearest 0.001°.

Pressing the Rotate 90 Degrees soft key will add 90.000° to the present
value of the phase shift.

When using an external reference, the reference phase shift is the phase
between the external reference and the digital sine wave which is multi-
plying the signal in the PSD. This is also the phase between the sine
output and the digital sine wave used by the PSD in either internal or
external reference mode. Changing this phase shift only shifts internal
sine waves. The effect of this phase shift can only be seen at the lock-in
outputs X, Y and

θ

. R is phase independent.

Auto Phase

Pressing [AUTO PHASE] will adjust the reference phase shift so that the
measured signal phase is 0°. This is done by subtracting the present
measured value of

θ

from the reference phase shift. It will take several

time constants for the outputs to reach their new values. Auto Phase may
not result in a zero phase if the measurement is noisy or changing.

5-3

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