• 2-phase A.C. Servomotor
• Servo Potentiometer for position sensing
• Transient response capture/display
• In-built rms voltmeter on panel

Introduction  

2-phase ac servomotors have been traditionally used for position/speed control applications especially in light weight, precision instrumentation area in airborne systems. These motors, though more expensive than industry standard split-phase induction motors and ac driven stepper motors, have a much better torque-speed characteristics. (Additional information may be found in our experiment entitled ‘Study of AC Servomotor, Model:ACS-01).

The present unit is designed around a 12 V ac servomotor and exposes the basic characteristics and dynamics of a position control system. A block diagram of the system is shown in Fig. 1. It may be observed that the error detector consists of two servo potentiometers rather than a synchro pair. This is done primarily to limit the cost of the unit to make it affordable to the target market-educational institutions in the country. This variation does not in any way compromise the performance of the unit or the knowledge gained by the students.

Besides introducing the basic features like balanced modulation of the error signal, phase reversal around the set point and phase difference between the reference and control phases of the motor, the experiment involves study of the step response of the closed loop system. Being a mechanical system the response is too slow for a comfortable viewing on a CRO, except on an expensive storage oscilloscope. A microprocessor based waveform capture/ display card in the unit stores the step response in real time and displays the same once steady state is reached.

Experiments  

• Error detector characteristics, phase reversal
• Amplifier gain measurement
• Phase difference between control and reference windings
• Step response study

Features and Specifications

• 2-phase a.c. servomotor - 12V/ 50Hz per phase
• Small generator for loading
• 4-digit speed display
• 3-digit time constant display
• 3½ digit r.m.s. voltmeter
• 3½ digit d.c. panel meter
• Voltage regulated internal supplies
• Detailed literature with sample results

Schematic Diagram