Keysight E8402A, E8404A C-Size Mainframes User and Service Guide 35Enhanced Monitor Fan Control Using the Enhanced MonitorEnhanced Monitor Fan ControlWith the front panel fan switch in the VAR position, the Enhancedmonitor controls the fan speed based on slot temperature limits youspecify. With the fan switch in the FULL position, the fan operates atfull speed.Essentially, the Enhanced Monitor’s fan control has two contrastingfunctions: 1) keep the VXI modules installed in the cardcage cool and2) operate as quietly as possible. These are somewhat conflictinggoals because to operate at its quietest, the fan would have to be offand hence not keep the modules cool. Alternately, at its coolest, thefans would have to be full on and the airflow is not quiet. Therefore,the fan control algorithm is to keep the mainframe as quiet as possiblewhile cooling the VXI modules adequately.What is adequate cooling? You specify it through your selection of slottemperatures. For example, if you specify slot 7 temperature to bemaintained within 15 °C of the ambient temperature, the fan controlleradjusts fan speed until the cooling air coming off slot 7 is just under15 °C above ambient. And it will keep it there, adjusting the fan speedas needed to maintain that temperature rise no matter what theambient temperature might do. That way, the fan noise is at its lowestwhile maintaining appropriate cooling.Each slot is monitored and compared to the specified slot temperaturelimits every two seconds. The slot closest to its limit is allowed toapproach the limit in order to keep the fan speed as low as possible.If you want a cooler mainframe, lower the slot temperature limits. Ifyou want a quieter mainframe, raise the temperature limits. Justremember that the Enhanced Monitor Fan Controller is very accurate;if you specified30 °C rise above ambient, the controller will maintain a limit just below30 °C.There is one exception. The power supply cooling overrides all othercooling requirements. For example, you may specify a 30 °C limit forall slots, but as you monitor the slot temperatures you notice that noslot is approaching the limit. It is likely that the Enhanced Monitor isworking to keep the power supply adequately cooled. Power supplycooling requirements are primarily driven by the load placed on thepower supply. It needs more cooling if it is significantly loaded. So, ifthe fan controller stops dropping the fan speed even though the slottemperatures are not close to the specified limits, it is probablybecause the power supply cooling requirements are dominating.Software Control of Fan SpeedThe SYSTem:BLOWer:STATe command can change the state of thefans from VARiable to FULL at any time. When software control hasset the fans to FULL, the front panel fan switch can be set to variable
