Introduction

Today's electronic systems are in a continuing, evolving design cycle where more smaller, and hotter components are being crammed inot tight enclosures. These expensive systems need to remain dependable and reliable. A fan failure may result in other delicate and expensive components failing, causing costly repairs and delays. The best way to deal with fan failures is to know exactly when a fan fails and moderate the system until repairs can be made.

Comair Rotron currently offers two ways to monitor the fans performance. A Tachometer Output is an easy and inexpensive way to monitor the speed at which the fan is running. The customer will need to develop circuitry to read the tachometer signal and determine when the fan has failed to provide adequate cooling. A Fan Performance Sensor (FPS) has the circuitry internally in the fan to read the tachometer signal and determine if the fan has failed. Both options are further described below.

Tachometer Output

The Tachometer Output is derived from a hall cell that senses the rotating magnetic fields generated by the rotating motor. The hall cell emits a square wave pulse train as shown in Figure 1.

The square wave has a 50% duty cycle with an amplitude of Vout On most fan models, the tachometer will have 2 pulses per revolution. A few others will have 1 pulse per revolution.

Signal Output
The standard amplitude, shown as Vout is 5V. This voltage level is set internal to the fan. (See Figure 2). The customer will need to develop electronic circuitry to monitor the output and detect failure. The customer may desire a Vout of a different amplitude. Comair Rotron can provide that output up to the value of the input voltage. (i.e. a 24 VDC fan would generate up to 24V square wave on the sensor lead.)

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