3350904-Microprocessor and Controller Applications Date: - / - / - Experiment No-02
3350904-Microprocessor and Controller Applications Date: - / - / - Experiment No-02
3350904-Microprocessor and Controller Applications Date: - / - / - Experiment No-02
Date: - ____/____/___________
EXPERIMENT No-02
Theory:
Schematic Diagram:
Switch S1 open and switch S2 closed –Closed loop control system without inner velocity
feedback loop
Switch S1 and switch S2 both closed - Closed loop control system with inner velocity
feedback loop
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3350904-Microprocessor and Controller Applications
Closed loop speed control is achieved when switch S1 is closed. A voltage proportional to
negative of output speed. Vf is obtained through tachogenerator. This is subtracted from the input
Vi using operational amplifier as a summer. The error is amplified by servo amplifier whose output
is used to drive the motor.
The servo amplifier is required to give the necessary output power that is both voltage and
current to drive the motor. Viscous load is obtained from the generation of eddy currents through
placement of magnet arrangement which gives a load torque approximately proportional to the
speed of disc. This system is of first order and is stable with the output always lagging behind the
command input.
Circuit Diagram:
There may be various circuits for speed control of DC motor using tachogenerator. One
circuit is shown in figure-2. In this circuit speed is sensed by tachogenerator.
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3350904-Microprocessor and Controller Applications
Power Circuit
The synchronous ramp generator produces ramp voltage. The circuit comprises of
operational amplifier. A comparator is charged and discharged with reference the voltage applied
to the inverting and non-inverting input is applied the full wave rectified pulses.
This is a sort of voltage comparator. One input is the reference signal while the other input
is feedback signal proportional to the speed of motor. The output is a positive signal proportional
to the error.
Phase comparator
The phase comparators receives one signal from ramp generator and other from error
detector. The phase comparator produces output which is used to fire SCR through transistor and
pulse transformer.
Power Circuit
It is full wave rectifier. D1 and D2 are two diodes. The motor armature is in series with
SCR and the whole is connected across positive and negative terminals of the rectifier. The field
winding of the motor is also connected across this DC. The motor armature gets supply when SCR
is triggered.
The motor runs with set speed. If the motor speed reduces due to some reason, the output
form the comparator changes to level up. This decreases the firing angle and speed rises vice versa.
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Sign of Faulty