4.3 Servomechanics (2)

Question 1

which direction do the magnetic field electrical field currents flow in the receiver when the transmitter and receiver are equally connected?

Answer 1

Opposite direction but of the same magnitude

Question 2

in aligned synchros, what current can be regarded as negligible?

Answer 2

the magnetising current

Question 3

when is torque moment present?

Answer 3

when magnetising fields are present, which allows current to flow
when a differential angle between transmitter rotor and receiver rotor

Question 4

at what angle is the torque moment at its greatest?

Answer 4

90 degrees

Question 5

at what angle is the torque moment at its least?

Answer 5

0/180

Question 6

what must the design of a synchro take into consideration?

Answer 6

the effect of bearing friction and brush friction to keep it at a minimum

Question 7

what must be low enough to allow low levels of current to flow?

Answer 7

resistance levels

Question 8

what is the task of a differential transmitter?

Answer 8

to add or subtract angles

Question 9

a differential transmitter is constructed with coils wired in a star shape on the rotor with a circular cross section. why is it constructed in this way?

Answer 9

so it doesn’t influence the magnetic field of the stator

Question 10

in differential transmitters, if both shafts are rotated in the same direction, what is the action?

Answer 10

subtraction

Question 11

in differential transmitters, if both shafts are rotated in the opposite direction, what is the action?

Answer 11

addition

Question 12

in differential transmitters, the coupling and the translations are chose in such a way for what reason?

Answer 12

so that the maximum voltages between two stator terminals are of the same magnitude as the maximum voltages between two rotor terminals.

Question 13

what is the role of a control synchro chain?

Answer 13

deliver voltage which depends on the differential angle between the transmitter rotor and receiver rotor

Question 14

how is sufficient voltage produced from a small angle between the stator field and rotor coil axis?

Answer 14

because of its construction due to many windings
magnitude proportional to number of windings

Question 15

why does a CT have a circular cross section?

Answer 15

to ensure magnetic field of the stator is not influenced

Question 16

how many degrees are the coils in a resolvers stator and rotor displaced?

Answer 16

90 degrees

Question 17

what can resolvers only exsist as?

Answer 17

control transmitters and receivers

Question 18

why are servo systems used instead of torque synchro chain?

Answer 18

when larger rotational moments are required

Question 19

in servo systems, what are CT and CX roles?

Answer 19

to deliver a voltage based on a measure of differential angle between CT and CX and passed to an amplifier to drive the servo motor

Question 20

in servo systems, how is the motor made to rotate?

Answer 20

the phase of the excitation voltage will make the motor rotate left or right depending which phase it is till the point CT no longer generates a voltage

Question 21

in servo systems, at small angles, what does the motor have?

Answer 21

the full power of the amplifier to allow for accurate start up when on load
(has hunting issue)

Question 22

in servo systems, how is hunting prevented?

Answer 22

damping by means of reverse coupling

Question 23

in rate generators, what should it provide?

Answer 23

a voltage which has a frequency that is equal to the excitation voltage

Question 24

in rate generators, what is amplitude proportional to?

Answer 24

the rotational speed

Question 25

in rate generators, what does the direction of rotation affect?

Answer 25

phase

in phase or out of phase

Question 26

in rate generators, what is the construction?

Answer 26

2 coils displaced 90 degrees by each other with a squirrel cage rotor

Question 27

in servo motors, what motors are used and why? (3)

Answer 27

two phase asynchronous motors

robust,
simply constructed
no parts subject to wear apart from bearings

Question 28

in servo motors, what is needed from a motor in this system? why?

Answer 28

It to activate maximum moment at start up

Because it works against high mechanical loads
Has weak rotation moment-rotation speed behaviour

Question 29

in servo motors, how is maximum moment at start up achieved?

Answer 29

By increasing rotor resistance

Question 30

what is the efficiency of a servomotor? and what is the reason for this?

Answer 30

10-20%

due to high rotor resistance required for maximum moment at startup

Question 31

how are synchro signals transformed into resolver signals?

Answer 31

scott connected transformers

Question 32

in scott connected transformers, what should the voltages be?

Answer 32

voltages should be the same

maximum voltage between synchro terminals should be of the same magnitude as the maximum voltage between the resolver terminals

Question 33

in scott connected transformers, where must tapping occur?

Answer 33

in the centre of the coil so the coupling factor K = 0.5

Question 34

what can be done to synchros?

Answer 34

set in any position
as they have circular cross section and no external markings

Question 35

what is a transformer?

Answer 35

helps with the conversion of electrical power

Question 36

in transformers, what is their construction?

Answer 36

two electrical coils of wire, (primary and secondary)
wrapped around a soft iron core

Question 37

in transformers, how are the primary and secondary windings connected?

Answer 37

magnetically linked through the common core to allow electrical power to be transfered