Verotec (Derry, NH) recently custom designed intelligent fan trays for a major defence project. The 19-inch rackmounted 1U trays have six fans, strategically located within the tray to maximise the cooling of critical elements of the electronic system located above the fan tray. Key issues for the fan tray design were noise levels, current consumption and reliability. A custom control board sequentially powers up each of the fans in order of importance to minimise initial inrush current. An embedded microprocessor controls fan speed using PWM technology.
Reliability is critical, so three separate events will trigger a warning signal: if power is lost to the fan tray, if the controller board itself develops a fault or if the speed of any fan falls below 20% of maximum. The fan cooling the main processor board is deemed to be a critical component, so if its speed falls below 20% the relay latches into the alarm position. If triggered by any of the other five fans, the alarm relay will re-energise when the speed increases above the 20% threshold.
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