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DEMODULATORS convert ac error signals to dc error signals. The dc signal is required to drive a
dc servo amplifier.
A SERVO AMPLIFIER used in an ac or dc servo system must have a flat gain, minimum phase
shift, low output impedance, and low noise level.
AC SERVO MOTORS are used in servo systems that move light loads. Large ac motors are too
inefficient for servo use when large loads are to be moved.
DC SERVO MOTORS can control heavy loads, and are widely used in servo systems. The speed
and direction of the dc servo motor can be varied easily by varying the armature current.
MAGNETIC AMPLIFIERS are used when power from a conventional servo amplifier is too small
to drive large servo motors (either ac or dc).
The MULTI-LOOP SERVO SYSTEM combines several closed and/or open servo loops together
to control a common load.
ANSWERS TO QUESTIONS Q1. THROUGH Q25.
A-1. A system in which the precise movement of a large load is controlled by a relatively weak control
signal.
A-2. Usually the operator senses the desired load movement and reduces the input to stop the motor.
A-3. Feedback.
A-4. Input signal and feedback.
A-5. To move the load and provide feedback data to the error detector.
A-6. Classifications in accordance with position, velocity, and acceleration functions.
A-7. Amount and direction of rotation.
A-8. Hunting.
A-9. Velocity loop senses velocity rather than position. When velocity loop is nulled, an error signal is
still present and the load continues to move.
A-10. Tachometer.
A-11. The closed-servo loop can regulate load speed under changing conditions.
A-12. Underdamped.
A-13. Overdamped.
A-14. To minimize overshoot and/or oscillations.
A-15. Anticipating.
A-16. It should oscillate.
