Torque-speed characteristics
Determination of motor parameters – inertia and friction
Digital display of time constant
Transfer function evaluation

A d.c. motor is commonly used as an actuator in many industrial control applications because of its features – large torque and ease of speed variation. The dynamic characteristics of such a system therefore depends on the motor parameters viz., moment of inertia, coefficient of friction, time constant and also the resistance and inductance of the control winding. It is therefore important to experimentally determine the mechanical and electrical parameters of the d.c. motor and also to evaluate its transfer function.
The present unit is designed to study a small permanent magnet d.c. motor. A still smaller generator directly coupled to the motor is used for the dual purposes of speed signal pick up and providing electrical loading. The shaft speed in rpm is displayed automatically on a 4-digit panel meter.
When the motor is suddenly switched ON a novel circuit computes and displays the time constant in milliseconds on a 3-digit panel meter. This avoids the need for an expensive storage CRO. The motor unit is housed in a cabinet with transparent panels, providing a good view of the mechanical system.


Torque-speed characteristics
Inertia and friction parameters
Back e.m.f. constant
Time constant
Transfer function

Features and Specifications
Study of a 12V, 8W d.c. motor
Small generator (2W) for speed pick up and loading
4-digit speed display
3-digit time constant display
31⁄2 digit voltmeter and current meter for d.c. measurement
IC regulated power supply
Supporting literature with experiment details


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