Closed loop motor speed controlwith eddy current brake
Compact system-no mechanical hassles
Opto electronic speed sensor
Digital display of speed on the panel

Accurate speed control is a requirement in many industrial and process control systems. The main characteristics of such a system are its steady state error and disturbance rejection properties.
Speed control of a d.c. motor is also one of the basic systems covered in a first course on automatic control system. The present unit, built around a small permanent magnet d.c. motor, is designed to bring out the salient features of such a system. Facilities are available to directly measure the principal performance factors of the speed control system, viz., steady state error and load disturbance rejection, as a function of the forward path gain. In addition, the experimental work involves the determination of the motor transfer function and the characteristics of the tachogenerator.
An important feature of the unit is the built-in absolute speed measurement through optical pickup from a slotted disk followed by a frequency counter. The 4-digit speed display is therefore completely independent of the tachogenerator characteristics. The high accuracy of speed reading is due to a built-in crystal oscillator.
Another interesting design feature is the use of an ‘electronic tachogenerator’ – a frequency to voltage converter, for the generation of speed feedback signal. This highly linear, non-contact transducer is ideally suited for the small d.c. motor being used in the unit.
Variable loading of the motor is achieved by a built-in eddy current brake. This brake has superior characteristics compared to friction brake especially for a small motor. The motor unit, housed in a cabinet with transparent panels, provides a good view of the mechanical
In addition, a 31⁄2 digit DVM is available on the panel for the measurement of various d.c. signals.
A measuring CRO is the only accessory that will be required for conducting the experiments.


• Effect of loading on the speed of the motor in
the open loop
• Steady state error variation with forward gain

• System time constant variation with forward gain
• Effect of forward gain on disturbance rejection
• Determination of the motor transfer function and
tachometer characteristics

Features and Specifications
• Speed control of a 12V, 4W permanent magnet
d.c. motor
• Speed range: 0 to 3000 rpm (typical)
• Opto-interrupter based speed sensing

• 4-digit speed display in rpm
• Electronic tachogenerator for feedback
• Separate unit for motor in a see-through cabinet
• Smooth, non-contact eddy current brake for loading


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