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MECH 371 LAB #3 COMPLETE STUD GUIDE CONCORDIA UNIVERSITY
- Institution
- Concordia University ( )
MECH 371 LAB #3 COMPLETE STUD GUIDE CONCORDIA UNIVERSITY
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MECH 371 LAB #3 COMPLETE STUD GUIDE CONCORDIAUNIVERSITY
Objective
The objective of this lab is to study the time response of a first-order DC motor system
by observing its response, using a function generator and an oscilloscope, and comparing this
experimental response with a computer simulation response.
Introduction
This lab deals with a system called DC motor system. The figure below displays a
schematic circuit of a DC motor.
Figure 1. Schematic Circuit of an Armature-Controlled DC Motor
In the circuit, I is the field current and it is kept constant. R is the resistance and L is the
f
inductance of the armature winding, whereas V is the voltage applied to the armature.
a
According to Faraday's law of induction, the voltage V is induced in the armature, since the
b
conductors in the rotating armature cut across a magnetic field. The voltage V is called “back-
b
EMF”, because its polarity opposes the motion due to the applied control voltage. Furthermore,
V is proportional to the angular velocity ω of the motor shaft because of the equation V = K ω ,
b b b
where K is the back-EMF constant. The motor and its mechanical load are composed of a
b
, combined inertia J in parallel with a viscous damping B. The torque T developed by the motor,
m
which is also the load torque T , is proportional to the armature current I by the equation T =
L a m
K I , where K is the torque constant. Finally, the equation for the armature circuit is L(dI / dt) +
T a T a
RI + V = V , which
a b a
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