48 Keysight PXIe Chassis Family User Guide
Chassis Alarm Architecture Relationship Between Alarm Occurred and the Front Panel LEDs
can lead to the situation where Alarm Occurred (based on the latched signal)
indicates an alarm condition, while the associated LED is not likewise indicating
an alarm condition.
This situation simply means that the condition that caused the alarm is no longer
present. While the alarm can be easily cleared by pressing the SFP Clear button,
it is suggested that the cause of the alarm be explored. Although it can be
difficult to determine the cause of a prior alarm, the SFP will often provide
information regarding what might have caused the alarm. For example, the
temperature threshold may be set too close to the temperature being reported by
one of the chassis temperature sensors, which could cause intermittent setting
of the temperature alarm latch. Possible next steps include determining if a
module is running excessively hot, or adjusting the temperature threshold higher
to provide additional margin.
Note that, while the front panel Temperature LED is off when temperatures are
normal, the Fan and Power LEDs are on when their associated parameters are
normal. In all cases, a flashing LED indicates that the associated parameter has
exceeded its alarm threshold.
Soft Front Panel Alarm Thresholds
In Simulation Mode, the Soft Front Panel (SFP) default alarm thresholds are
identical to the chassis alarm thresholds. However, in Simulation Mode, the
alarms are not active. In Hardware Mode, however, the SFP reads and displays
the chassis thresholds. In other words, the SFP does not provide its own default
thresholds in Hardware Mode.
For example, assume that the SFP has been used to change the Minimum Fan
Speed Threshold from 1200 RPM to 500 RPM followed by closing the SFP. When
the SFP is started next, it will read the value of Minimum Fan Speed Threshold
from the chassis (500 RPM, in this example), and display this value on the SFP as
the Minimum Fan Speed Alarm Threshold.
Power cycling the chassis re-establishes all default values. Continuing with the
previous example, the chassis Minimum Fan Speed Alarm Threshold is set back
to its power-on default limit RPM by the power cycle. When the SFP next
connects to the chassis, it will read this value from the chassis and display the
default limit RPM as the Minimum Fan Speed Alarm Threshold. The default for
the M9010A is 900 RPM. The default for the M9018B and M9019A is 1200 RPM.
In the description of each SFP alarm capability, the SFP alarm
diagrams will show the chassis default alarm thresholds. This is
because, as described above, the SFP reads and displays the
chassis alarm thresholds. As long as the particular chassis alarm
has not been changed earlier (for example, during a prior SFP
session), the chassis power-on default alarm threshold will still be
in effect and will be read and displayed by the SFP.
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