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3.0
OPERATION
3.1
Theory of Operation
The WFD-3 is PWM motor speed controller. The control uses an embedded micro-controller to
provide line synchronization, phased back EMF sampling and direction control logic with anti-plug
motor reversing. The phased EMF sample provides precise back EMF sample for improve motor
speed regulation. The Anti-plug feature prevents reversing the drive before the motor armature
has stopped. This prevents excessive motor current and brush arcing in the motor.
The Micro-Controller synchronizes all input commands to the incoming line frequency and assures
proper phase angle firing of the power PWM devices. The Analog speed signal is coupled to a
Voltage-to-Frequency convert and is electrically isolated from the off-line control. The remote
direction control inputs are optically coupled to the controller. An isolated 12-vdc-power supply is
provided for all remote input control functions. The user can use this supply to operate remote
input relays or switches for direction control. The supply has a solid-state circuit breaker, which
protects the 12-volt I/O control from external shorts. The circuit breaker will reset when the 115-
vac power is cycled off.
Optional optical tach input is provided which can be used with a 5 or 12 VDC 60-line encoder. The
encoder input is also provided as an output on the remote I/O connector. This output is an isolated
24-vdc pulse representing the encoder input. When an encoder is installed on the motor shaft, the
WFD-3 can be set for encoder feedback by installing a jumper on JP3. When the jumper is
installed, the controller uses the tachometer to regulate motor speed. When the jumper is removed,
the controller will use the motor back EMF for speed regulation.
3.2
Control Calibration
The WFD-3 controller is factory calibrated to produce 2300 rpm with an input of 10 volts. This is
performed using a 100 line Tach and a permanent magnet 1/8 motor. No adjustment is required
to operate different drive motors. However, there may be a need to check or recalibrate the WFD-
3 for use with a different motor or motor speed range. To calibrate the WFD-3 perform the following
steps:
Warning - The WFD-3 is a direct off-line controller. Do not use grounded instruments during
calibration. 115 VAC is exposed on the PC Board. Only qualified personal should perform test
or calibrations on the control.
Remove the cover from the WFD-3 controller. Connect a calibrated digital voltmeter to the
1)
speed reference signal on JP1-3 (-) and JP1-4 (+).
If encoder is installed on the drive motor connect a frequency counter to the encoder output
2)
JP1-7(+) and JP1-2(-). A 60-line tachometer will produce a direct readout of motor RPM.
If a tach is not installed, use a hand tach to measure actual motor RPM.
Connect the WFD-3 to a suitable 115vac source. Make sure that the motor is free to rotate
3)
then power up the WFD-3 control.
10
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