User`s manual

Page 22 · 4200-DR Series LaserSource User’s Manual
Using Limits
The 4200-DR provides several limit features for protection of the laser diode.
These include current, voltage, intermittent contact, photodiode current, and
photodiode power limits.
Both the laser current and voltage limits are implemented in hardware, providing
for fast response to changes in laser diode operation. When a voltage limit is
detected, the output is immediately shutdown. Because of the sensitivity of the
voltage limit, operating near the limit (within one to two hundred millivolts) is not
recommended. In general, you should set the voltage limit to 0.1V to 0.2V higher
than any anticipated operating point. The voltage limit is tested against the
voltage at the connector, unless in remote voltage sense mode. Any Laser
Cable R value is ignored, as Laser Cable R is a software only calculation, and
the voltage limit is implemented in hardware. See Using the Cable R Setting,
above, for more information on the Laser Cable R setting.
Unlike the voltage limit, the current limit simply prevents the 4200-DR from
delivering more current than the limit is set to. When the current limit engages,
the output will remain on, unless the
corresponding bit in the OUTOFF register was
set
.
The intermittent contact circuit is designed to protect against faulty connections
by detecting fast changes in voltages which can be caused by poor wiring or
faulty connectors. If false trigging of the intermittent contact circuit is frequently
occurring, it can be turned off from the menu.
The photodiode current and photodiode power limits are implemented in
software and may take up to one second to trigger when these conditions occur,
and therefore should not be relied on to provide fast protection of the laser
diode.