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Fluxvalve Theory
10. The fluxvalve , consists of a sensitive pendulous element which is free to swing within limits (usually ± 25°) but fixed to the aircraft in azimuth. The element is suspended by a Hooke's Joint with the whole assembly being hermetically sealed in a case partially filled with oil to dampen oscillations. A deviation compensator is usually mounted on top of the unit.
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11. The pendulous detector element resembles a three spoke wheel with the spokes 120° apart and slotted through the rim. The rim forms a collector horn for each spoke. The horns and spokes are made up of a series of metal laminations having a high magnetic permeability. Each spoke has a vertical cross-section similar to that shown in Fig 12-2. The spoke consists of two superimposed legs which are separated by plastic material and opened out to enclose the central hub cone. This cone has an exciter coil wound round it on a vertical axis, and each spoke has a pick-off coil wound round both legs on a horizontal axis. The exciter coil is fed with 400 Hz single phase AC. The output of the secondary or pick-off coil is an 800 Hz single phase AC current, the amplitude and phase representing the relationship of magnetic North to the aircraft longitudinal axis (magnetic heading).
Fig 12-2: Vertical Cross-section of Spoke
12. In order to appreciate the operation of the fluxvalve it is necessary to consider an individual spoke. The function of a spoke will be developed in a series of diagrams (Figs 12-3 to 12-10).
13. If a single coil is placed in a magnetic field, the magnetic flux passing through the coil is maximum when the axis of the coil is in line with the direction of the field, zero when the coil lies at right angles to the field, and maximum but of opposite sense relative to the coil when turned 180° from its original position. For a coil placed at an angle θ to a field of strength H (Fig 12-3) the field can be resolved into two components, one along the coil equal to H cos θ and the other at right angles to the coil equal to H sin θ. The H cos θ component is parallel to the coil and is the effective flux producing element. Therefore, the total flux passing through the coil is proportional to the cosine of the angle between the direction of the coil axis and the direction of the field. The coil output curve is shown at Fig 12-4. If the coil is in the horizontal plane with its axis parallel with the aircraft longitudinal axis, its output is affected by the horizontal component of the Earth's magnetic field and the flux passing through the coil is proportional to the magnetic heading of the aircraft.
Fig 12-3: Magnetic Flux Components
Fig 12-4: Variation of Flux with Theta
14. Unfortunately, the simple concept just described cannot be used without modification as a heading reference system for two important reasons. Firstly, the voltage induced into a coil depends
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on the rate of change of flux. Therefore, once established on a heading, there would be no change of flux and, consequently, no induced voltage. Secondly, the output of the simple detection device would be subject to heading ambiguity, i.e. there are always two headings which cause the same induced output voltage. Therefore, the problem that must be solved is how to produce an output waveform which is proportional in some way (frequency, phase or amplitude) to the components of the Earth's field and linked with the coil. This is achieved in the fluxvalve by introducing an alternating magnetic field in addition to the static field caused by the horizontal component of the Earth's magnetic field.
15. Fig 12-5 shows the relationship between flux density (B) and magnetizing force (H) known as the hysteresis loop for the permalloy commonly used in the legs of the flux valve spokes. Permalloy has a very high magnetic permeability (μ = B/H) and a corresponding low hysteresis loss. In the following discussion the hysteresis loop is represented by a single line curve.
Fig 12-5: Hysteresis Curve for Permalloy
Fig 12-6: Simple Fluxvalve
Fig 12-7: The Effect of Excitation Current in the Top Leg Only
16. One spoke of the three-spoke fluxvalve is shown diagrammatically in Fig 12-6. It consists of a pair of soft iron (usually permalloy) cones each wound with a primary coil. The winding on one core is the reverse of that on the other. The AC supply is just sufficient, at peak power, to saturate magnetically each of the parallel soft iron cores. A secondary coil, wound round the two primaries, is linked with the circuit, and any change of flux through it induces a voltage and current flows.
17. Fig 12-7 shows the 400 Hz alternating flux induced in the top leg by the excitation current considering only the top leg of the spoke and the effect of the excitation.
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18. Now considering the bottom leg only; the flux induced in this leg by the excitation current will at any instant be in the opposite direction to that induced in the top leg, i.e. the flux in the bottom leg is 180° out of phase with the flux in the top leg as shown in Fig 12-8.
19. Since the top and bottom legs are identical, the amplitudes of the flux of the two legs are equal but 180° out of phase with each other relative to the pick-off coil, which is wound round both legs. Therefore, the resultant flux cutting the pick-off coil, which is the algebraic sum of the flux in the top and bottom legs is zero as shown in Fig 12-9.
Fig 12-9: The Effect of the Excitation Current in Both Legs
Fig 12-8: The Effect of the Excitation Current in the Bottom Leg Only
20. If the horizontal component of the Earth's magnetic field (H) is now added in line with the spoke, it will induce a steady flux in both legs of the spoke which will be added to the flux due to the excitation current. The effect, as shown in Fig 12-10, will be to bias the datum for the magnetizing force, due to the excitation current, on the B-H curve by an amount equal to H. The strength of the excitation current is so arranged that the effect of the introduction of the Earth's magnetic field component is to bring the flux density curves in Fig 12-10 onto the saturation part of the hysteresis curve. The resultant flux cutting the pick-off coil, which is the algebraic sum of the fluxes in the top and bottom legs, will no longer be
Fig 12-10: The Combine Effects of the Excitation Current and the Component of the Earth's Field
zero but will have a resultant proportional in amplitude to heading. The emf induced in the pick-off coil
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is proportional to the rate of change of flux cutting the coil and therefore will have a waveform approximating to a sine wave at 800 Hz, i.e. twice the frequency of the excitation current as shown in Fig 12-10. It has been found by experiment that the amplitude of the emf is proportional to H. Therefore, the emf in the pick-off coil is a measure of H, i.e. the horizontal component of the Earth's magnetic field in line with the spoke. This should be apparent from Fig 12-10 in that, if a greater H is detected, the excitation current is biased further from the mid-point of the hysteresis curve, and the imbalance between the upper and lower leg fluxes will increase. Therefore, a greater resultant flux exists which will induce an emf of greater amplitude in the pick-off coil. A plot of the amplitude of the pick-off coil output voltage would show that it varies as the cosine of the magnetic heading.
21. Limitations of the Simple
Single Spoke Detector. It should be apparent that there are two magnetic headings corresponding to zero flux (90° and 270°) and two headings corresponding to a maximum flux. The two maximum values give the same reading on an AC voltmeter since the instrument cannot take into account the direction of the voltage. For any other value of flux (other than zero), there will be four headings corresponding to a single voltmeter reading. This ambiguity is overcome by using a fluxvalve having three spokes (each spoke similar to the single spoked device previously discussed) with 120° separation as shown in Fig 12-11. Regardless of the heading, at least two of the spokes will have a voltage induced and their vector sum points to magnetic North (Fig 12-12). The simple one-spoke detector suffers from another limitation in that the value of H changes with magnetic latitude. This produces a change in the static flux linking the spoke, even though the heading may remain unchanged. This limitation is
Fig 12-11: Detector Unit and Transmission System -
schematic
Fig 12-12: Operation of the Three-spoke Fluxvalve
Fig 12-13: Eliminating Latitude Ambiguity
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overcome in the three-spoke fluxvalve because the flux associated with each spoke will change in proportion to the change in H. The resultant field across the receiver stator is still aligned with H (Fig 12-13).
22. In the three-spoke fluxvalve a single primary coil excites all six cores. If a single arm of the fluxvalve is considered, it will be apparent that the top and the bottom of the exciter coil have opposite polarity. The flux induced in the upper core of the spoke is equal and opposite to that induced in the lower core and this is exactly the effect produced by the primary windings in the simple fluxvalve. The three arms of the fluxvalve are wound with secondary or pick-off coils which are star connected. The exciter coil is fed with 400 Hz single-phase current so that each of the three pick-off coils has an emf at 800 Hz induced in it whose amplitude is proportional to the magnetic heading of the aircraft. Each core of the fluxvalve is fitted with a flux collector horn to concentrate the Earth's lines of force through the core. This increases the static flux and therefore the induced voltage.
What else can I help you with?
Difference between leakage flux and mutual flux?
when a current flow through the coil then flux produced around the coil . if the flux linked same produced coil only then the flux is said to be leakage flux. flux produced by one coil ,but linked with another coil then the flu is said to be mutual flux.
Why do you have variation in leakage reactance of induction motor?
leakage reactance in induction motor depends on the reluctance of the path in which the leakage flux is establishing. with the increase in stator current the leakage flux also increases but it cannot maintain linear relationship because of saturation of the leakage flux path, even though current is increasing the flux will not increase and it'll be constant after saturation. this leakage flux links with the stator winding and induces emf which will be opposite to the supply voltage causes drop in applied voltage , the drop in the applied voltage is represented with the leakage reactance. as flux is responsible for the induction of emf , the increase in current does not increase flux after saturation and therefore emf also doesnot increase so the leakage reactance is not constant throughout the machine operation...
What are the differences between the natures of dc flux and ac flux?
dc flux is caused by dc current (flux and current are proportional), it is a constant value. Put an inductor (or transformer winding) across a battery and you will get dc flux. ac flux is caused by ac current (flux and current are proportional), it is a moving value, the flux moves with the current, typically cyclical but the waveform is arbitrary as long as we're moving.
How does flux increase?
Flux incresed with the increase of scalar quantity
Why transformer is called constant flux machine?
when a load is connected to a transformer current(say I2) flows through secondary coil thus an M.M.F (N2I2) is produced ,this produces the secondary flux. This flux reduces the the main flux induced in the primary & also reduces E.M.F E1 in the primary As a result more current is drawn from the supply. This additional current drawn is due to the load component(say I2' ) This I2' is anti-phase with I2.This I2' sets a flux which opposes the secondary flux & helps the main flux. The load component flux neutralises the secondary flux produced by I2 .The M.M.F N1I2' balances N2I2.Thus the net flux is always at constant level. As practically flux is constant,the core loss is constant for all loads. Hence a transformer is always called a Constant Flux Machine.
What is flux and in which operation is it used?
Flux is used to prevent oxidation while soldering wires and components in electronics.
Where is a flux valve installed?
ln a extreme aircraft wing
How do you change a mixing valve in a faucet?
mixing valve in a faucet: ok I will assume you are refering to a shower valve, that is the only faucet w/a mixing valve: shut off the hot and cold water. cut out valve or unsweat it. clean and flux new valve, pipe and fittings(if used) sweat in new valve
Which way should you turn the water valve on the washer to ensure proper operation?
To ensure proper operation of the washer, turn the water valve clockwise to open it and counterclockwise to close it.
What is the condition from improper operation of a heart valve called?
alvirita
Why is your PCV valve vibrating when the engine is running?
That is normal operation.
How do you set the timing on a 1991 xr200r?
Turn the rear gear valve to the 'on' position, then adjust the flux capacitor regulation system freely.
How does a throttle valve snap valve work?
A snap throttle valve on a vehicle works by using dual internal valves that give a full on or off operation.
What does the Orbit sprinkler valve diagram illustrate?
The Orbit sprinkler valve diagram illustrates how water flows through the valve to control the operation of the sprinkler system.
In transformer core flux depends on voltage whereas leakage flux depends on current?
In a Transformer, Core flux is the difference of primary flux and Secondary flux which are opposite to each other in direction. There difference is equal to the no load flux at all loads. So, some of primary flux passes through the core and remaining becomes leakage flux (Because Secondary flux forces it to get out of the core). Same is the case with Secondary flux. Now, flux is directly proportional to Voltage and Current. When Current increases due to increased load (and voltage remains same): Then both primary and secondary flux increase. Because both of them increase, so there difference remains same. And all remaining flux is forced out. Hence leakage flux increases with current, but Core flux remains constant. When Primary Voltage is increased: Then only primary flux increases. So difference of this new increased primary flux and previous same secondary flux increases. Hence Core flux increases with voltage, But leakage flux does not. That's how In transformer core flux depends on voltage whereas leakage flux depends on current.
Can you do Welding Operation without flux?
Yes .... but most welds will not be as good as those using flux. SMAW with bare electrodes produces poor results. GTAW and GMAW are done without flux when an inert gas is used to protect the puddle. Some Oxy-fuel welding can be done with out it. In most applications flux is used not only to protect the molten puddle but also add ingredients to the weld.
The purpose of a bypass valve in larger-size gate valves is to?
In an application of pressure reduction, the warm up valve (bypass valve) is used to warm the steam line, within recommended time frames, before the control valve is placed into operation. A steam control valve should not be used for warm up of a steam distribution line.
