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Setting Enhanced Monitor Limits
Temperature Limits
Current and Power
Limits
36 Getting Started
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The Agilent E840x Enhanced Monitor has several limits that affect when it
will issue warnings. Each limit should be selected based on the VXI modules
installed in the mainframe.
The Enhanced Monitor monitors two types of temperature limits. First are
the "Delta slot temperature limits" whose primary function is to pass your
specified temperature limits to the Fan Controller (refer to "Enhanced
Monitor Fan Control" on page 35). If these limits are not maintained, a
warning is issued. The default value is 15 °C rise above ambient; this is a
compromise between cooling and noise. Check the specifications of your
installed VXI modules to determine sensitivity to temperature variation. You
may need to specify a smaller delta slot temperature for some modules.
Second are the absolute temperature limits, for both individual slots and the
ambient temperature. These guard the top end of the acceptable temperature
spectrum and generate warnings if exceeded. The default values are
generally acceptable to most VXI modules; but you should verify the
temperature ratings for all VXI modules installed in the mainframe and set
the slot's absolute temperature limit accordingly. For example, many
modules are specified for a temperature range of 0 to 55 °C and assume a
10 °C rise to occur in operation. Therefore, their absolute temperature is
safely 65 °C (the default). But, if a VXI module is only rated to 45 °C (and
assumes a 10 °C rise) then its slot should have an absolute temperature limit
of 55 °C. You might set the limit lower for earlier warning.
Use the
STATus:QUEStionable:TEMPerature:LIMit?
to set temperature limits, both ambient and delta slot temperatures. Use the
STATus:QUESTionable:TEMPerature:LEVEL?
actual threshold when an over-temperature warning will sound.
By default, the Enhanced Monitor provides power supply current and power
limit warnings only when the power supply is exceeding its capacity. But it
is unlikely that all seven supplies will be used at maximum capacity.
Consequently, this warning is generally too late for most applications. For
example, the +5V supply in the Agilent E8404 is capable of providing up to
90A (peak current, refer to Appendix A). It is therefore capable of delivering
the regulated voltage into nearly a dead short -- 0.06Ω. For this reason, you
should specify current and power limits to reflect the actual needs of the VXI
modules installed in the mainframe. Then a warning is generated in
sufficient time to correct a problem.
To set current limits, calculate the worst case current needed on each supply
for your application, add 10%, and set your current limit to this value.
Alternately, allow your system to operate normally for a time, query the
maximum values measured by the Enhanced Monitor's history subsystem,
and set the current limit to a comfortable margin above this maximum. Do
this for each of the seven VXI supplies and for the total power value. In this
way, the Enhanced Monitor can issue a warning when a module begins using
more power than normal. Use the
command (page 105) to set current limits, and STAT:QUES:POW:LIM to
command (page 114)
(page 113) to determine the
STATus:QUEStionable:CURRent:LIMit
Chapter 2
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