11. Chassis alarm architecture
The chassis provides seven alarms to assist you in monitoring the chassis. For example, you can set a temperature alarm threshold such that, if a chassis temperature sensor reports a temperature above the threshold, an alarm will be generated. Alarms can be set and monitored programmatically and using the SFP.
The following image describes the chassis alarm architecture, including identifying the functionality that is provided in hardware and the functionality that is provided in software. The figure also describes how alarms operate if multiple processes are using the same alarm.
In the following sections, the information provided by the front panel Power, Fan, and Temperature LEDs is described.
32 Keysight PXIe Chassis Family User Guide
Chassis Alarm Architecture
Alarm operation
The chassis has these eight alarms: 1. Fan speed alarm
2. Temperature alarm
3. 3.3V alarm
4. 5V alarm
5. 12V alarm
6. -12V alarm
7. 5Vaux alarm
8. 10 MHz reference clock changed alarm
Each alarm has an Alarm Set/Reset Latch (“latch”) – please see the figure below for an example of one latch . Each of the seven latches is set if its associated alarm threshold is exceeded. In the case of the fan speed alarm, exceeded means that at least one fan speed is lower than the Minimum Fan Speed Alarm
Threshold. Similarly, a power supply rail that has exceeded its alarm threshold means that its voltage is
outside of the range defined by the upper and lower voltage limits.
Interactions between programs using the chassis alarms
It is important to understand how your IVI.NET or IVI-C program interacts with the SFP alarms -- or, for that matter, with any program(s) that use the alarms. Programs that are operating simultaneously will need to share certain alarm resources. Each of the seven alarms has one instance of the tan-colored Set/Reset Latch and each alarm has the OR gate feeding into the latch – these tan elements represent hardware in the chassis. For discussion purposes, the Fan Speed Alarm Set/Reset Latch will be used as an example. The chassis contains one Fan Speed Alarm Set/Reset Latch, which all processes share.
The elements which provide inputs to the tan-colored hardware elements are also singular and shared. For example, there is only one Minimum Fan Speed Alarm Threshold. If the threshold is set using the SFP and is then set to a different value using the IVI.NET driver, the last-set threshold will be in effect.
Setting of the latches allows alarm conditions to be detected/captured in the absence of an operator. The latch OUT does not have a default value—if the SET input is true (for example, at power-on due to a fan speed being below the default Minimum Fan Speed Threshold of 1200 RPM), the fan alarm latch OUT will be set True at power-on.
Example of one alarm latch
Latch SET input example parameter value; for example, chassis temperature
A Clear Alarm IVI.NET or IVI-C call can be made from the application program to reset the latch. The SFP, in fact, implements its Clear
Alarm button by making an IVI.NET Clear Alarm call.
NOTE: To keep the SFP in sync with any changes that have been made programmatically to their shared resources, the SFP will poll the relevant chassis parameters every second and update its display accordingly. For example, if your program changes the Minimum Fan Speed Alarm Threshold, the new value will be reflected on the SFP Configure Alarms tab (if the
SFP is running, of course) within one second. If your application program is running in an environment where the SFP is also running and if chassis parameters are being changed using the SFP, your program can likewise poll the relevant parameters in order to detect if they have been changed by the SFP user.
Continuing with the fan alarm example, the two fan alarm resources that are not shared are Alarm Enabled and Alarm Occurred.
Each process, including the SFP, will have its own software version of these two properties as shown in the figure below. This allows a process that is interested in the fan alarm to enable its version of fan alarm while another, disinterested process can disable its version of fan alarm. In the example below, there are three Alarm Occurred properties, one for the SFP and two representing user applications. While they share the output of the Set/Reset Latch, they each have their own Alarm Enabled signal and their own Alarm Occurred signal.
Each latch can be reset (cleared) using its associated Clear Alarm button on the SFP. Reset on the SFP
Utility dropdown menu will reset all seven latches. However, if any alarm threshold is still exceeded when the latch is reset, the latch will be immediately set true again.
If the latch output is True and if the SFP Alarm Enabled is true, Alarm Occurred will be lit on the SFP.
Alarm Occurred is set false if Alarm Enabled is set false. However, setting Alarm Enabled false does not reset the latch—this can only be done using Clear Alarm or Reset. Likewise, changing the corresponding alarm threshold to a value such that the alarm limit is no longer being exceeded does not reset the latch. threshold
The SET input will be True if the associated alarm limit/threshold is exceeded.
Clear Alarm
IMPORTANT: Even though the Alarm Enabled and Alarm Occurred properties are separate for each process, all processes share the same latch as shown below. This can lead to the situation where one process detects that its version of Alarm
Occurred is true and then resets the shared latch (using the Clear Alarm call) before a second, also-interested process has read its version of Alarm Occurred. This can result in the second process missing its version of Alarm
Occurred. As recommended in the section PXIe chassis Software Architecture, application developers should establish policies for accessing shared resources to avoid this situation.
Application #1
Alarm Enabled AND
Application #1
Alarm Occurred
Application #2
Alarm Enabled
Alarm
Set/Reset Latch
AND
Application #2
Alarm Occurred
The Alarm Occurred signals need to be polled in software in order to detect their presence.
The IVI.NET and IVI-C drivers do not support an interrupt or event mechanism that can be used by software to detect the occurrence of an alarm.
SET
RESET
AND
SFP Alarm Occurred
Each of the seven alarms has a
Clear Alarm button and an Alarm
Enabled checkbox on the SFP. The
Fan Alarm Enabled check box is shown here.
Fan Alarm Enabled
OR
The SFP Reset will reset all seven alarm latches.
OUT
SFP thresholds: When the SFP is started, it will read and display the seven alarm thresholds from the chassis. Therefore, the SFP does not provide its own default thresholds – the thresholds it displays are based on the thresholds maintained by the chassis. The chassis thresholds will either be its power-on default values or the current value of any alarm threshold that has been changed – for example, if the user ran the SFP previously and changed the chassis minimum fan speed threshold. At SFP startup, the modified minimum fan speed threshold (which is maintained by the chassis) will be read and displayed by the SFP.
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Power-on default alarm thresholds
This section summarizes the power-on default values of the chassis alarm thresholds as well as the valid range over which the alarm thresholds can be set.
The phrase power-on default means that, regardless of how the thresholds are changed while power is applied, the thresholds return to factory-defined default values whenever the chassis is power cycled.
For example, if you use the SFP to set the Minimum Fan Speed Alarm Threshold to
500 RPM, this setting will not persist through a power cycle; the Minimum Fan
Speed Alarm Threshold will be restored to the power-on default value of 1200 RPM when the chassis is power cycled.
Both the SFP and the IVI drivers will error check the alarm values to ensure they are within the valid range. The SFP will prevent setting of alarm values outside the valid range while the IVI drivers will return an error for values outside the valid range.
Threshold Default
Threshold
Settable Range
1 to 10,000 RPM Minimum Fan Speed Alarm
Threshold
Maximum Temperature Alarm
Threshold
3.3V Rail
1200 RPM
70 °C
Upper Voltage Limit 3.630V
(3.3V + 10%)
5V Rail
Lower Voltage Limit 2.970V
(3.3V - 10%)
Upper Voltage Limit
5.25V
1
Lower Voltage Limit 4.75V
1 to 70°C nominal value +.01% up to nominal value + 20% nominal value -.01% down to nominal value
-20% nominal value +.01% up to nominal value + 20%
12V Rail
–12V Rail
Upper Voltage Limit 12.6V
Lower Voltage Limit 11.4V
Upper Voltage Limit -11.4V
Lower Voltage Limit -12.6V
nominal value -.01% down to nominal value -
20% nominal value +.01% up to nominal value +20% nominal value -.01% down to nominal value
-20% nominal value +.01% up to nominal value + 20% nominal value -.01% down to nominal value
-20%
Keysight PXIe Chassis Family User Guide
Threshold Default
Threshold
+5.0V
aux
Rail Upper Voltage Limit 5.25V
Lower Voltage Limit 4.75V
Settable Range
nominal value +.01% up to nominal value + 20% nominal value -.01% down to nominal value -
20%
1
Note that the 5V rail initially has voltage limits of ±5% around the nominal value. However, the IVI driver will expand the 5V limits to ±10%. Because the PXIe chassis SFP uses the IVI.NET driver, the SFP also expands the 5V limits to ±10%
Events which re-establish the power-on default thresholds
Power cycling is just one event that causes the chassis power-on default alarm thresholds to be re-established by the chassis. The complete list is:
Power cycling, as mentioned
Asserting a chassis reset using the SFP Utility > Reset menu
Asserting a programmatic chassis reset using the IVI.NET, IVI-C or
LabVIEW drivers
Relationship between alarm occurred and the front panel LEDs
The fans, temperature sensors, and voltage rails have front panel LEDs associated with them. This section describes the relationship between each LED and its associated Alarm Occurred indicator.
The following image shows one example of an alarm latch and an LED.
In this example, the Threshold Exceeded signal will be True if the chassis parameter being monitored exceeds its threshold. For example, if a temperature sensor reports a temperature greater than the temperature threshold. A True value of
Threshold Exceeded causes the following:
1.
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36
1.
The LED drive logic will flash the front panel LED, indicating that the parameter being monitored has exceeded its threshold.
2.
The Alarm Set/Reset Latch will be set. If, in addition, Alarm Enabled is True, the SFP Alarm Occurred indicator will be illuminated.
If the parameter being monitored then returns to below its threshold (for example, the room temperature is lowered, causing the chassis temperature sensors to report lower temperatures), Threshold Exceeded will go False. This will cause the
LED to cease flashing. However, the alarm latch will remain latched. This can lead to the situation where Alarm Occurred (based on the latched signal) will be indicating 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.
The SFP alarm thresholds
In Simulation Mode, the 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 will re-establish all default values. Continuing with the previous example, the chassis Minimum Fan Speed Alarm Threshold will be set back to its power-on default value of 1200 RPM by the power cycle. When the SFP next connects to the chassis, it will read this value from the chassis and display
1200 RPM as the Minimum Fan Speed Alarm Threshold.
Keysight PXIe Chassis Family User Guide
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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