2 Fan FTF Systems

All the necessary circuitry for a 2-fan FTF system can be provided internal to most of our DC fans. We simply use our Therma Pro-V programmable feature and a Fan Performance Sensor, then cross-wire them together. The cross wiring allows the Fan Performance Sensor (FPS) signal of fan #1 to program the speed of fan #2 (see Figure 1). The program lead uses the output transistor of the alarm as its path to the common ground. In normal operation, both fans are running at reduced speed (the program lead is shortened to the common ground). If fan #1 fails, then its FPS output transistor will allow the programming lead of #2 fan to open and increase to full speed. The end result is an uninterrupted supply of airflow.

Figure 1

3 or more Fan FTF systems

3 fan FTF systems use circuitry similar to the 2 fan FTF systems, but have special circuitry internal to the fan motor to account for the additional alarm transistors. This system wires all of the alarm outputs together as well as the program leads together. The base fan speed is predetermined by a resistor network internal to the fan. If a failure occurs in one or more of the fans, the remaining fans will program up to a high-speed condition.

Conclusion

Uninterrupted cooling is a significant concern for companies who offer products for On-Line Transaction Processing or other high reliability systems. The effectiveness of high-reliability systems is that they are always on-line. Since a system shutdown would lead to a loss of transactions, not being able to accept an order is very costly for immediate maintenance, etc. An FTF system, as described above, will provide continuous cooling and help avoid nuisance shutdowns due to loss of airflow. Expensive and elaborate external controller cards can be used, but the idea behind the FTF system is to keep it simple and take advantage of the fans existing abilities. To further integrate the fans, the additional FPS alarm can alert the system of a failure and to call for field service.

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