Stanford Research Systems SR844 User Manual page 75

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In addition, changing the Reference Phase will modify the values of Xoffset and
Yoffset. Think of (Xoffset, Yoffset) as a signal vector relative to the Reference
(internal or external) which cancels an actual signal at the input. This cancellation is
preserved even when the detection phase (Reference Phase) is changed. This is done
by circularly rotating the values of Xoffset and Yoffset by minus the Reference
Phase. This preserves the phase relationship between (Xoffset, Yoffset) and the signal
input.
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Since the vector (Xoffset, Yoffset) is used to cancel a real signal at the input, Xoffset
and Yoffset are always turned on and off together. Turning either offset on turns on
both offsets. Auto offsetting either X or Y performs auto offset on both quantities.
These statements are true even if only one of the quantities X or Y is currently being
displayed.
On/Off
This key turns the Offset On or Off for the current CH1 display quantity. As indicated in
the table above, X, R[V] and R[dBm] may be offset, while Xnoise and AUX IN 1 may
not. This key has no effect if the currently displayed quantity is Xnoise or AUX IN 1.
When Offset is turned On, the offset value last used for the current display quantity is
applied.
Turning Xoffset on and off also turns on and off Yoffset. The XYOffs indicator in the
display indicates that the displayed quantity is affected by X and Y offsets.
Xoffset and Yoffset are applied before R and
indicator will be on if the display is showing R and XY offsets are on.
R Offsets (V or dBm) are simply added to the displayed quantities. The displayed value
of R is simply R(display) = R(computed from offset X and Y) + Roffset. The ROffs
indicator in the display indicates that the displayed value of R has an Roffset applied. The
R[dBm] offset simply adds or subtracts a number of dB from the display.
The Offsets can be set by pressing the Modify key and then using the knob, or using the
Auto key. The Offsets can also be set from the remote interface.
Auto
This key sets the Offset for the displayed quantity equal to the negative of its current
displayed value, so that the display, with offset applied, is equal to zero. The Offset is
turned On if it is not already On. This key has no effect for quantities that may not be
offset.
Important!
If the display is X, Auto performs Auto Offset for both X and Y and turns on both X and
Y offsets. This is true even if the CH2 display is not displaying Y at the time.
Modify When Modify is pressed, the Offset of the currently displayed quantity appears on the
Reference Display (above the knob), even if the Offset is Off. Press Phase, Freq or
AuxOut to return the Reference Display to its previous state.
The Offset is displayed as a percentage of Full Scale. For R[dBm] full scale is 200 dBm
regardless of the sensitivity. The knob may be used to modify the offset. Turn the Offset
on to apply the displayed offset.
CH1 Display and Output 3-17
θ
are calculated. Thus, the XYOffs
SR844 RF Lock-In Amplifier