Precor GEN06 Series C952 Service Manual page 112

8 Theory of Operation
Treadmill Base Operation
speed of an AC motor is controlled by frequency, there is no need for a speed sensor.
The 3 phase AC motor generates enough torque to provide continuous duty run time. The 3
phase voltage amplitude of all three input AC sine waves is the same at any given time which
allows the torque to be applied smoothly throughout the rotation of the motor. Increasing the
input voltage/current amplitude increases the torque and decreasing the input amplitude
decreases the torque.
The lower electronics module (IFT drive) is responsible for sending the proper frequency to
control speed and the amplitude (same on all 3 phases) to control torque. The motor must then
be balanced both mechanically and electrically in order to translate the frequency and amp-
litude into fluid motion. Mechanical balance is achieved by balancing the weight of the fly-
wheel, and electrical balance is achieved by having the same winding resistance on all 3
phase windings.
Other AC drive motor controller features include "Dynamic Braking" and "Power Factor Cor-
rection". Dynamic Braking addresses an issue where an over-speed condition could occur. If a
heavy user runs at a high incline, the weight of the user has the potential to push the running
belt to go faster than the commanded motor controller speed (generates excess current). The
dynamic brake circuit senses the load variations and applies a braking force within the motor.
The system utilizes an external power resistor (Dynamic Brake resistor) to absorb the excess
generated current and determine applied braking force. Power Factor Correction is a feature
that attempts to reduce power consumption. The system monitors that this power factor is held
within certain parameters. If it falls outside those parameters (the system is using more current
than expected), the system will flag an ERROR 29.
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