Precor AMT12 base, Service Manual

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DC Lift System
– Position Monitoring (If Equipped )
The unit also requires an absolute measurement of lift position. This is achieved through the use
of a potentiometer. The potentiometer is turned by being geared to the motor, which changes the
wiper resistance.
With +3.3V DC applied across the potentiometer, the center wiper connection will be a variable
voltage (between 0 and +3.3V DC), dependent on the position of the lift. This variable voltage is
applied to the input of an 8-bit A/D converter, which converts the analog voltage into an 8-bit binary
numeric representation that the processor can understand.
As the voltage returned by the potentiometer changes between 0 and 3.3V DC, the corresponding
A/D values change between 0 and 255. In this way, the processor can keep track of where in the
lift range the lift is truly positioned.
It is important to note that since the potentiometer is mechanically connected to the gearing of the
motor, it would be highly unlikely (if not, impossible) for a lift motor to go out of calibration without
having some damage that needs to be repaired. See the section on troubleshooting the lift system
if this occurs.