THORLABS MNA601/IR, Руководство пользователя

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Appendix E
54 HA0118T Rev 6 Oct 2014
The loop gain can also effect system stability. If the gain is too high, the circle moves
erratically, whereas too low a setting results in the circle ‘floating’ around the edge of
the screen. Loop gain can be configured from the Controller GUI.
Both circle size and loop gain effect the system amplification. As a guide to manual
settings, if the scan circle moves erratically round the screen, the amplification should
be reduced, and conversely, if the scan circle movement is sluggish, the amplification
should be increased. As with any phase locked control loop, it may be necessary to
perform application-specific adjustments to optimize the speed of response and
stability.
E.1.4 Phase Offset
Theoretically, if the NanoTrak were to read the power and respond by moving the fiber
instantaneously, the power signal read in would be in phase with the modulating
signal. In reality, the various electronic and electromechanical components (e.g.
power meters, piezo actuators) within the control loop can introduce delays which
means that the NanoTrak is always reacting to a power reading which was taken in
the past. This, in turn, can cause a phase shift and in extreme cases can lead to
instability.
A phase offset can be introduced to compensate for any phase shifts. In the APT
system, a different phase offset can be specified for each axis of motion. This is
particularly useful in those mechanical systems that exhibit different delays in different
directions.
E.1.5 Latch, Track and Tracking modes
The purpose of the latch is to disable scanning and hold the drive outputs at the
present position. With the latch released, the NanoTrak is in track mode. However, to
minimise the risk of detecting a false peak, tracking should be activated only after a
threshold power has been located, which is sufficiently above the background noise
level. See table below for details of the three modes of operation.
Mode Description
Button
LED
Tracking
indicator
Latch Drive outputs held in constant
position
Latch ON OFF
Track mode,
not yet tracking
The drive outputs wander and the
circle drifts around the display
Track ON OFF (i.e. below
threshold power)
Track mode
and tracking
The drive outputs seek and
maintain maximum power settings
Track ON ON (i.e. above
threshold power)