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


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 torquespeed 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.
Error detector characteristics, phase
Amplifier gain measurement

Phase difference between control and
reference windings
Step response study

Features and Specifications
2-phase servomotor – 12 volt/phase,
50Hz, 10 watt
Power amplifier for driving
Servo potentiometer type error detector
In-built 10.00 volt (rms) panel meter

Step response capture/display card
Detailed literature with typical results
Complete unit except a measuring CRO
220 volts, 50 Hz mains operation


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