Four-Quadrant Analysis of DC Motor Control Operation of a bidirectional DC motor drive is best analyzed by using a four quadrant rectangular coordinate graph. The horizontal axis is armature voltage (-V to +V relative to a common zero volts). The vertical axis is armature current (+I for clockwise motor rotation, and -I for counterclockwise rotation). Beginning in Quadrant 1, as the armature voltage is increased, the motor’s armature current increases, which increases the motor’s RPM and thus delivers more torque to the load. Transfer to Quadrant 4 operation usually occurs when the applied armature voltage is reduced in an effort to slow the motor’s speed. Load inertia causes the motor to rotate at a speed greater than the armature current caused by the applied voltage. Consequently, the motor begins to function as a generator, producing an armature current in the opposite direction. Armature current actually reverses, relative to the applied armature voltage. The more quickly quadrant transition is sensed and accounted for by the DC drive electronics, the more accurate and efficient the speed regulation. As the load reduces the motor’s inertia and slows the motor’s speed, motor torque returns to the same polarity as motor direction, and Quadrant 1 operation resumes. Quadrant 3/Quadrant 4 operation is the same, for counterclockwise rotation.