CONTROL EXAM Flashcards
(28 cards)
Explain the operation of a Rotary Transformer
The synchro can be considered as a rotary transformer in which the magnetic coupling between primary and secondary coils varies proportionally to the angle between them.
Consider a 1:1 transformer whose primary can rotate 360° with respect to the secondary (Fig 1.1). The flux in the primary Φp varies proportionally to the input voltage and hence oscillates sinusoidally at 400hz. This alternating flux ‘links’ with the conductor which is the winding on the secondary, inducing an EMF due to Faraday’s Law.
Induced voltage in secondary winding of rotary transformer FORMULA
Vsec = Vpri.Cos OI
Draw a synchro device and explain it’s operation and composition
DRAW IT
Draw and explain a simple synchro TX/RX circuit in terms of induced magnetic flux and currents
DRAW IT
Explain the composition of a torque synchro chain
DRAW IT
An A/C voltage is applied to the rotor winding of the transmitter, causing a current to flow. The magnetic field generated by the current in the transmitter rotor will induce a voltage in each of the stator windings by transformer action causing currents to flow. These currents flowing in the three windings S1, S2, and S3 will generate three magnetic fields. These magnetic fields will combine together to produce one resultant field, which acts in the opposite direction to the original magnetic field of the transmitter rotor. This is correct according to Lenz’s Law which states that the resultant magnetic field must always oppose the inducing magnetic field of the rotor.
What happens in Torque Synchro chain when the RX is misalined by 30 degrees with the TX
dunno
What is the approximate accuracy of a synchro reciever indicator
10 degrees
2 uses of torque synchro devices in Naval Weapons Systems
- Radar System aerial rotation
2.Turret position indicator - 4.5” Gunnery System
2 advantages of Torque Synchro chain
- Smooth follow through 360 degrees - output always aligns with input - no 180 degree misalignment.
- Transmitter and reciever identical in construction - interchangeable
3 disadvantages of Torque Synchro chain
- Stuck Position Error - if reciever rotor sticks, it acts as a transmitter and introduces errors further down chain - thus not normally chained
- Effect of Increased Load - as driven load increases, so does the torque reaction between rotor and stator fluxes. As Flux produced is proportional to stator line currents, flux increases and causes higher heat loss
- Accuracy - Manufactured error not better than 1 degree due to reciever rotor inertia. Accuracy can be improved with gearing, but this also increases load.
Effect of CROSSING stator leads
Rotation INCORRECT, possible 120 degree offset
Effect of STEPPING stator leads
Reciever 120 or 240 degrees out of alignment, rotation CORRECT
Effect of CROSSING ROTOR leads
Reciever flux 180 degrees out of alignment, causing misalignment of 60, 120 or 180 with INCORRECT rotation
Effect of BREAKING STATOR lead
At Datum (0) or 180 no flux generated at reciever - no control of reciever
Thus device can only line up at 90 or 270
Explain composition of simple control chain (CX/CT)
The basic control synchro chain consists of a control transmitter (CX) and a control transformer (CT). Datum position of CT rotor is at 90 degrees to datum position of CX rotor. (to have ZERO EMF when CX at 0)
Synchro chain with crossed S1 and S2 leads
Reciever flux displaced by 120 degrees and rotates OPPPOSITELY to input.
How is the control chain used to drive a heavy load?
Windings not designed to deliver mechanical torque, but supply ERROR voltage to amplifying equipment to drive servo motor.Power to drive load is CONTROLLED NOT SUPPLIED by synchro chain, thus no load limit.
What is the error measuring device in a simple synchro chain
The CT (control transformer, right hand side)
What is the function of the Servo Amplifier
Phase discrimination (drives servo motor at a speed dependent on the size of the error signal) Direction of drive depends on phase ot error signal compared to reference signal.
What is placed in the chain to enable corrections/deflections to be input
dunno
Draw a CX-CDX-CT system
draw it
What is the equation for the CX-CDX-CT
CT=CX-CDX
Explain the term SECTOR VALUE and why/how we use it
The amount the load turns for one complete revolution of the synchro rotor, when the load is controlled only by that synchro element.
ALL ELEMENTS OF SYNCHRO CHAIN MUST BE OF SAME SECTOR VALUE.
SECTOR VALUE = 360/n
n= gearbox ratio (1:n)
TYPICAL RN GEAR RATIO IS 36:1, SECTOR VALUE OF 10 degrees.
What is the normal change over point in a Coarse/Fine chain?
Typical changeover angles are coarse to fine = 30 minutes, fine to coarse = 1° 30 minutes.
