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FIGURE-1A: TACH FAN WAVEFORM
FIGURE-1B: ROTOR-LOCKED WAVEFORM
Fans with tachometer sensors are commonly used in computers as it’s a simple matter for the
computer’s processor to monitor and compute fan speed. For unattended equipment, RotorLocked fans are popular as they integrate easily into alarm systems due to their simpler 2-state
outputs. Unfortunately, Rotor-Locked fans generally cost more, are not as common as
Tachometer fans, and are even harder to find in sizes over 92mm making the noise reduction
technique of getting a bigger fan tougher to realize. So the Tachometer-Rotor Adapter (TRA)
was born and given the power of the MCU, additional features were added which are described
below.
FEATURES
The TRA PLUS provides the following 3 functions:
1. Speed Sensing, Display, and Sound
2. Fault Indication
3. Rotor-Locked Conversion
Speed Sensing, Display, and Sound:
In the same way a computer calculates fan speed; the MCU in the TRA PLUS calculates fan
speed and illuminates an RGB (red-green-blue) LED to a color indicating which one of four RPM
ranges, or bands, the fan is operating. User fan speed can be verified against the DEFAULT RPM
Band Colors and Ranges or the TRA PLUS can be programmed by the user to allow all four
colors to span the range of speeds using the fan controller. DEFAULT RPM Ranges can be
restored at any time.
TRA PLUS Manual 2.5
Page 2