Reference - Stanford Research Systems SR810 Manual

Reference

UNLOCK
TRIG
[Phase]
The UNLOCK indicator turns on if the SR810 can not lock to the external
reference.
The TRIG indicator flashes whenever a trigger is received at the rear
panel trigger input AND internal data storage is triggered.
Pressing this key displays the reference phase shift in the Reference
display. The knob may be used to adjust the phase. The phase shift
ranges from -180° to +180° with 0.01° resolution.
When using an external reference, the reference phase shift is the phase
between the external reference and the digital sine wave which is
multiplying 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
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Front Panel