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HA0373T Rev Ck May 2017
Chapter 4
4.5.2
Open Loop Mode
When in ‘Open Loop’ mode, the signa ls on th e rear pan el XDIFF and YDIFF
connectors now represent the XOut a nd YOut position demand signals, used to
position the beam steering element. These signals are either fixed at zero (0V), or
held at the last Closed Loop value (depending on the ‘
Position Demands In Open
Loop Mode
’ parameter in the Settings panel - see Section 6.2.) - see Fig. 4.7 This is
useful when the system is being adjusted manually, to position the light beam within
the detector array.
Fig. 4.7 OPEN LOOP and CLOSED LOOP Schematic Diagram
PDQ80A
Quad Detector
A/D
A/D
DAC
DAC
A/D
DSP
XDIFF
YDIFF
SUM
USB
LV OUT XDIFF
LV OUT YDIFF
SUM
OPEN LOOP MODE: The XDIFF and YDIFF signals are routed to the DSP.
The DSP either sets the outputs to zero, or holds them at their last closed loop
voltage (dependent on the setting of the '
Position Demand In Open Loop
Mode
' parameter in the Settings panel).
CLOSED LOOP MODE: The XDIFF and YDIFF signals are routed to the DSP.
The DSP implements a PID control loop for each axis. The resulting position
demand signals (XPos YPos) are routed, via the rear panel SMA connectors,
to the positioning elements to drive the spot to the center of the detector.
X + 0 . 0 9 + 0 . 0 0 O
Y
- 0 . 1 6 + 0 . 0 0
