DC MOTORS Flashcards
(13 cards)
In fact, in many cases, a D.C. machine can be used ……………………….
In fact, in many cases, a D.C. machine can be used either as a motor or a generator.
FLEMINGS LEFT HAND RULE
The direction of rotation of a motor can be determined by Fleming’s Left Hand Rule. To do this, align the first finger with the field from the North Pole to the South Pole.Point the second finger in the direction of the current flowing into or out of the armature and the thumb will indicate the direction of motion.
Explain Back EMF
–The movement of the conductor in the magnetic field induces in it an electromotive force (EMF)
which we know from Lenz’ law will oppose the rate of change of magnetic flux producing it. So
an EMF is induced into the rotating part of the motor which tends to oppose the rotation of the
motor. That is to say, the induced voltage will oppose the supply voltage. It is therefore called
the back EMF.
–The back EMF is proportional to motor speed and can never be as great as the supply input
voltage. The difference between the applied EMF and the back EMF is always such that current
can flow in the conductor and produce motion.
Rotary actuators are used for:
a. undercarriage retraction.
b. centre of gravity assessment.
c. operation of fuel cocks.
d. movement of control surfaces.
C
Actuator normal travel is controlled by:
a. a clutch.
b. limit micro switches.
c. mechanical indicators.
d. mechanical stops.
B
AC current from an engine driven generator is converted to DC current by:
a. a commutator
b. a convertor.
c. an alternator.
d. a rotary actuator.
A
On a twin engined DC aircraft having two DC generators load sharing is achieved by:
a. equalising engine RPM’s
b. an equalising circuit to sense the difference and equalise the voltages of the two generators
c. synchronising relays and voltage coil tuners
d. an equalising circuit to sense the difference and equalise the field currents of the two
generators
B
Pilots are informed of rotary actuator positions by:
a. non return valves.
b. lights or dolls eye indicators.
c. travel indicators.
d. veger counters.
B
To supply direct current from a generator giving alternating current it is normal to fit:
a. a commutator
b. a rotary inverter.
c. an alternator.
d. a static inverter.
A
Press to test lights are used:
a. to indicate to the pilot that the circuit has power and is complete.
b. to control the movement of a rotary actuator.
c. to indicate to the pilot that the circuit has operated.
d. only to indicate to the pilot that the equipment has malfunctioned.
A
A device for changing AC to DC is:
a. an inverter.
b. a rotary transformer.
c. a rectifier.
d. an alternator.
C
An inching control is used in conjunction with:
a. a linear actuator.
b. a rotary actuator.
c. a combination of linear and rotary actuator.
d. a rectifier.
A
Friction clutches are fitted to actuators for:
a. protection against mechanical overload.
b. protection against brake on loads.
c. protection against non return valve failure.
d. protection against supply failures.
A
