Feedback Controlyzer DigiLock 110
Page 20
Status: 5.12.17
automatically selected to be the input of the frequency modulation
module. Since the auto setting (see below) relies on the fact that the FM
signal also carries the DC part, it is possible to manually select a different
spectrum input
2
.
Treat as LI/PDH: Advanced Function
The intelligence of the AutoLock feature can also be used together with
external equipment providing PDH or LI error signals. In this case select
the appropriate Input channel to which this signal is fed (Main in, Aux in)
and enable this option by checking the box.
NOTE ! This option is not available when selecting LI out or PDH out as
input source.
Auto: Advanced Function
Uncheck the auto checkbox to select the spectrum channel manually.
Controllers checkboxes: Select the controllers to be combined for the Autolock mode. Once
selected for AutoLock, the input channels of the controllers are set to
the selected common input (see above) and can, hence, no longer be
modified in the corresponding controller tabs. The same holds true for
the setpoint.
Gen (General):
Setpoint: Since all PID controllers selected share a common error input signal, they
also share a common setpoint.
Mode: Displays the operating mode of the AutoLock. If the AutoLock module is
configured such that the feature to lock to (slope, peak, valley) may be
chosen manually (see Advanced|Smart Assistance|Engage) this con-
trol can be changed.
Hold: Sets the controller on hold.
Wnd (Window):
Use Window: Activates a window comparator to determine the lock state: The
selected input channel is compared to the window defined by four
parameters. This option specifies boundaries for the selected channel. If
the signal leaves the outer bounds (Level out Max/Min), the controllers
associated with the AutoLock module are on hold. They are reactivated
when the signal is back in the selected range specified by the inner
bounds (Level in Max/Min).For further details please see section 9.5).
Channel: Input signal to be compared to the window.
Delay: Time to wait between detecting the unlocked state (signal outside win-
dow) and initialization of a reset/relock procedure. This Delay allows for
an immediate relock, e.g. after the system was subject to a temporary
disturbance.
Level out Max/Min: Upper/lower bound of the comparator window. Leaving this window
stops the PID controller(s).
Level in Max/Min: Upper/lower bound of comparator window for reactivating the PID con-
troller(s).
Rst (Reset):
PID1/PID2: Enables the corresponding PID reset.
Rate: Slope in Volt/second when resetting the outputs of PID 1 and PID 2,
respectively. Finite rates restrict the reset speed of the PID outputs to
avoid destabilization due to rapid changes, e.g. creep of piezos after a
sudden voltage step
2. This is, e.g., the case when locking to a cavity using an AC coupled photodiode for the Pound-Drever error signal in reflec-
tion and a DC-coupled photodiode for the spectrum in transmission (cp. section 10.3).
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