Electrical Engineering

If you don't it could fry your equipment. A capacitor can hold a charge for anextremely long time even years depending on the physical size and capacitance. It can hold a strong enough charge to kill.

Voltage can never be induced in a straight open wire because flux through a wire is zero but a coil made up of a wire can have induced voltage.

Methods

Move a magnet to and fro through the coil, the magnitude can be changed by altering the relative velocities between them

Move the coil relative to he still magnet

Place the coil in a time varying magnetic field such that the flux linked through the coil changes with respect to time

Place the coil tn an uniform magnetic field and alter its area with respect to time

It is because there is a light bulb and things like that......

It depends on the context. In a.c. circuits, 'reverse polarity' describes a situation in which a device, such as a socket outlet, is wrongly wired -with the line and neutral conductors interchanged.

Coast is a term used in the electrical for motors. When a motor in denergized and the rotor continues to spin it is said to be coasting, until it comes to a hault.

High voltage power lines are targeted at the cause of many bad things, but the truth is (in most cases) they have a negligible impact on the bad things they are accused of causing.

Emotional problems is a case in point. The weather has more of an effect.

Splicing is the joining of cable , rope , wire , or any other type of strand-like material.

A: this chip is defined as a timer but it can be used for other reasons and applications.

The power dissipated across a resistor, or any device for that matter, is watts, or voltage times current. If you don't know one of voltage or current, you can calculate it from Ohm's law: voltage equals resistance times current.

So; if you know voltage and current, power is voltage times current; if you know voltage and resistance, watts is voltage squared divided by resistance; and if you know current and resistance, watts is current squared times resistance.

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.

73 Radio Magnetic Compass

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

FIS Book 4: Instruments 74

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.

75 Radio Magnetic Compass

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

FIS Book 4: Instruments 76

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

77 Radio Magnetic Compass

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.

A: To begin with the leads polarity of the meter must be ascertain. Assuming the red is positive voltage then that lead will have a positive potential to check a diode connect the red lead to the anode and the black to the cathode and it should read some Resistance

Motor size depends upon number of factore.

1- flow of pupm

2- required head

3- efficiency of pupm used

4- efficiency of electric motor used

The formula is

H.P required= Q.H\ 3960. Pump efficiency. Motor efficiency

where Q= GPM

H= Ft

Efficiency= In fraction( 70 % = 0.7)

Engr. Usman Khalid

+923336901945

usman.engr87@gmail.com

series

I'm not sure where you are getting your information. Capacitors come in a large range - nano farad to several farad. The higher the farads, the bigger (in general) the capacitor will be. For example, amazon has a 1 F, 20 volt cap for ~76.00. I would consider this to be "generally available in the market". If you want a 1 farad cap for 120 volts, it's going to be substantially bigger than this one (20 volt is ~5 lbs.).

Measures current, both AC or DC, usually in Amps.

The High voltage transformer allows the microwave to run using the magnetron. With ony 120v to the magnetron, the cooking will be like with a 50-100W microwave. The high current is to manage current to the MOT with out oveheating while delivering current to the other parts of the microwave

<<>>

A CT. and PT. are required for any service enterance distributions over 200 amps. The CT's maximum amperage output is 5 amps and the PT's output is usually 120 volt in North American installations. These two values are inputted into a Watt hour meter. The total on the meter is then calculated by the utility company's rate and a bill for use is sent to the customer.

K refers to kilo, which is 1,000. So 4,500 ohms could be written as 4.5k ohms and pronounced 4.5 kilo ohms.

what level of maintenacne is found at the forward support company

A: nothing should happen since a 1N4001 is capable to sustain 100v in the reverse direction. 52v is within the 100v reverse breakdown voltage.

The direction of a singular phase induction ac motor can be reversed by switching the capacitor in relation with the motor windings. When started in the reverse direction, the motor will maintain the same torque level that it had in the forward direction.

We can perform stability test on restricted earth fault by following these steps :-

1 - choose one phase of primary windings like phase R and make short circuit connection between phase R before CT ,and N after CT .

2 - Prepare primary injection current equipment and connect it's first cable on phase R after CT , and its second cable at any earthed conductor near Neutral .

3 - start injection current up to 100 AMP , if the relay isn't trip , this mean the system is stable ,Also if the relay operate which mean there is a fault in connections which must be modified .

with best wishes ... Eng Ahmed Abdel men3m .