Principle Of Controller Operation - MAGUIRE MPA-6 Series Installation Operation & Maintenance

M P A  M A G U I R E P R O D U C T S , I N C .
S e r i e s

PRINCIPLE OF CONTROLLER OPERATION

The MAGUIRE Digital Controller provides the precise speed regulation and metering control
necessary to assure absolute accuracy over color usage. The Controller signal cord is plugged
into an outlet that is energized only when the process machine screw runs. During each screw
return cycle, the motor runs and color is metered into the throat of the process machine.
Since metering rate is directly related to motor output shaft rotation, accuracy is obtained by
controlling the exact degree of rotation of the drive motor. The unique Maguire Products Digital
Controller is designed to do this with precision. Our standard Model divides each full motor
rotation into 159 increments; each increment representing a small fraction of a gram of color being
carefully measured out.
The digital counter located on the face of the controller provides the means for predetermining the
exact degree of rotation and, therefore, the precise amount of color that will be added during each
cycle. When the pre-set count is reached, the motor will automatically shut off, ensuring that no
excess color is metered. To determine the proper setting for the counter, a simple formula is used
based on percent of color required and total shot weight in grams (or pounds per hour for
extrusion applications).
Motor speed is automatically controlled by the internal microprocessor to allow color metering to
occur uniformly over the entire screw return cycle. The operator need not concern himself with
motor speed adjustment. Changing cycle times or fluctuations in plant voltage are automatically
detected and compensated for and, therefore, will have no effect on metering accuracy.
The controller contains a 1/27 HP D.C. Permanent Magnet motor with variable speed control of
from approximately 50 to 3000 RPMs. In the standard configuration, the motor is close coupled to
a heavy-duty gearbox with a reduction ratio of 53:1. Final output speed of the motor is, therefore,
approximately 1 to 56 RPMs. As the motor turns, a "hall effect" pickup device on the motor sends
3 pulses per revolution to the microprocessor controlling it. The gearbox ratio of 53:1 means that
159 pulses (3x53) are received for every single revolution of the motor output shaft.
The purpose of the thumbwheel switch is to pre-set the exact number of pulses that the motor is
going to run before stopping. The microprocessor in the controller automatically multiplies the
counter setting by a factor of 10. A setting of 16 on the counter will allow the controller to receive
160 pulses or run approximately 1 revolution before stopping. Regardless of how fast or how slow
the motor runs, color metering will stop after 1 turn.
In addition to this precise control of color quantity being metered, the microprocessor also controls
motor speed using the same pulses for digital tachometer feedback. This ensures that motor
speed is precisely regulated regardless of changing torque requirements or variations in plant
voltage.
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