Ch1 And Ch2 Outputs: Offset, Ratio And Expand - Stanford Research Systems SR865 Operation Manual

Chapter 3

CH1 and CH2 Outputs: Offset, Ratio and Expand

Analog Outputs
Analog voltages proportional to X, Y, R and θ can be output from the SR865. The X and
Y rear panel outputs always output X and Y. The CH1 output voltage is proportional to
either X or R. The CH2 output voltage is proportional to either Y or θ. The output
voltages are determined by
The output is normally 10 V for an input signal equal to the sensitivity. The offset
subtracts a percentage of full scale (up to ±999%) from the output. Expand multiplies the
difference by a factor of 1, 10 or 100. This result may be divided by a ratio input (Aux
Input voltage). An Aux Input voltage of 1.000 V corresponds to unity.
Outputs which would exceed ±10 V generate an Output Overload and the red output
Overload
indicate 'Scale' in the display. The actual measurement is unaffected since it is done in
floating point and has no overload. Data displayed in the strip chart will still be accurate.
The X and Y offset, expand and ratio functions in the SR865 are output functions, they
do not affect the calculation of R or θ. R has its own output offset, expand and ratio.
Phase ranges from −180° to +180° regardless of the sensitivity. When CH2 outputs a
voltage proportional to θ, the output scale is 18°/Volt or 180° = 10 V. The phase bar
graph and numeric readout scales are also unaffected by the Sensitivity. Phase has no
offset, ratio or expand capability. To offset phase, simply use Auto Phase. To expand
phase, expand the value of Y in quadrature.

X, Y or R

Sensitivit y

=
Output


Ratio




1.000
LED will light. Any corresponding displayed numeric value/bar graph will

−
Offset


× ×
Expand 10


In




V
Operation
V
SR865 DSP Lock-in Amplifier
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