This chapter includes the study of different types of DC motors, speed measurement of DC motor, model of separately excited DC motor, several types of DC motor speed controller. It also discusses briefly about microcontroller, RS232 serial port, MPLAB IDE and Visual Basic 6.0.
DC Motor :
There are several types of DC motors that are available. Their advantages, disadvantages, and other basic information are listed below in the table.
Speed Measurement of DC Motor:
To start with this project, we need a device that will measure the speed of the motor shaft. There are several methods which can use to measure the speed of motor. Here, we shall discuss about speed measurement of dc motor.
Speed Measurement by Using Tachometer:
Tachometer is an instrument that measure the speed of the motor based on the concept of back EMF induced in motor while it is running. The EMF is voltage, appeared on the commutator segments, caused by the rotation in the magnetic field by some external force.
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The magnitude of the EMF is given by ,
E φ N ……………….
Where K E = a constant based on motor construction φ = magnetic flux N = speed of motor (in rpm) The actual relationship between motor speed and EMF follows and is derived from equation N= (EMF)/ K E φ …………………… Thus, the motor speed is directly proportional to the EMF voltage and inversely proportional to the field flux. For permanent magnet DC motor, when the EMF measured is increases, the speed of the motor is also increases with the gain. So, the speed of motor can be measured by measuring the back EMF using tachometer.
Speed Measurement by Using Optical Encoder
The best way to measure speed is to fit an optical encoder. This shines a beam of light from a transmitter across a small space and detects it with a receiver on the other end. If a disc is placed in the space, which has slots cut into it, then the signal will only be picked up when a slot is between the transmitter and receiver.