Someone at school he studied physics?For some, it was interesting and understandable, while others pored over books, trying to memorize complex concepts.But each of us to remember that the world is based on physical knowledge.Today we talk about concepts like inductance current, the circuit inductance, and find out what are the capacitors and what the solenoid.
electrical circuit inductance
inductance serves to characterize the magnetic properties of the electrical circuit.It is defined as the coefficient of proportionality between the current and the electric current flow in a closed magnetic circuit.The flow created by this current through the surface of the circuit.Another definition states that the inductance of a circuit parameter determines the EMF of self-induction.The term is used to indicate the circuit element and has to effect the characteristic of self-induction, which was opened by Henry D. and M. Faraday independently.The inductance associated with the shape, size of the circuit and the value of the magnetic permeability of the environment.In SI units, this value is measured in Henry and designated as L.
self-inductance and the measurement of inductance inductance
is the quantity, which is the ratio of the magnetic flux passing through all the turns to the circuit current strength:
- L = N xF: I.
circuit inductance is dependent on the shape, size and contour of the magnetic properties of the medium in which it is located.If the closed-loop electric current flows, there is a changing magnetic field.This subsequently lead to the emergence of EMF.Birth induced current in the closed loop is called "self-inductance".By Lenz law does not change the magnitude of the current in the circuit.If the inductance is detected, it is possible to apply an electric circuit, wherein a resistor included in parallel and coil with an iron core.Consistently with them connected and electric lamps.In this case, the resistance of the resistor is equal to the dc resistance of the coil.The result is a bright burning light.The phenomenon of self-induction is one of the main places in electronics and electrical engineering.
How to find inductance
formula that is simple to find the value, the following:
- L = F: I,
where F - flux, I - current in the circuit.
through the inductor can be expressed by self-induction EMF:
- Ei = -L x dI: dt.
conclusion from the formula of the numerical equality of induction emf which arises in the circuit when changing the current one ammeter one second.
variable inductance makes it possible to find the energy of the magnetic field:
- W = L I2: 2.
"Spool of thread"
inductor is insulated copper wire wound on a solid foundation.With regard to insulation, the choice of material is wide - this nail and wire insulation, and fabric.The magnetic flux depends on the square cylinder.If the current increase in the coil, the magnetic field will become more and vice versa.
By applying an electric current to the coil, then it arises a voltage opposite to the voltage, but it suddenly disappears.This kind of stress is called self-induction electromotive force.At the moment when the voltage across the coil current changes its value from 0 to a certain number.The voltage at this point has a value change, according to Ohm's law:
- I = U: R,
which characterizes the strength of the current I, U - shows the voltage, R - resistance of the coil.
Another special feature of the coil is the following fact: if you open the circuit "coil - current source," the EMF will be added to the stress.The current is also beginning to grow, and then starts to decline.Hence the first law of commutation, which states that the current in the inductor does not change instantaneously.
coil can be divided into two types:
- With magnetic tip.In the role of the heart are the ferrite material and iron.The cores serve to increase the inductance.
- with nonmagnetic.They are used in cases where the inductance of not more than five MH.
devices differ in appearance and internal structure.Depending on such parameters is the inductance of the coil.The formula in each case different.For example, a single-layer coil inductance will be equal to:
- L = 10μ0ΠN2R2: 9R + 10l.
And now for multilayer another formula:
- L = μ0N2R2: 2Π (6R + 9l + 10w).
main conclusions related to the work of coils:
- on cylindrical ferrite biggest inductance occurs in the middle.
- For maximum inductance must be close to wind the coil windings.
- inductance of the smaller, the smaller the number of turns.
- The toroidal core distance between the turns of the coil does not matter.
- inductance value depends on the "turns of the square."
- If inductance connected in series, their total value is equal to the sum of the inductances.
- In parallel connection is necessary to ensure that the inductance were separated on the board.Otherwise, they will be wrong readings due to the mutual influence of magnetic fields.
solenoid
By this term is understood as a cylindrical coil of wire that can be wound in one or several layers.The length of the cylinder is significantly greater than the diameter.Due to such characteristics when an electrical current in the solenoid cavity born magnetic field.The rate of change of magnetic flux proportional to the current change.The inductance of the coil in this case is calculated as follows:
- df: dt = L dl: dt.
Yet this kind of coils called an electromechanical actuator with a drawn-core.In this case, the solenoid is provided with a ferromagnetic outer magnetic core - the yoke.
In our time, the device can combine the hydraulics and electronics.On this basis, established four models:
- first able to control the line pressure.
- second model differs from other forcibly guided locking clutch in the torque converter.
- third model in its composition contains pressure regulators, responsible for the work shift speeds.
- fourth controlled hydraulically or valves.
necessary formulas for calculations
To find the inductance of the coil, use the following formula:
- L = μ0n2V,
shows where μ0 vacuum permeability, n - is the number of windings, V - the volume of the solenoid.
also to calculate the inductance of the coil can be and with the help of another formula:
- L = μ0N2S: l,
where S - the cross-sectional area is, and l - length of the solenoid.
To find the inductance of the solenoid, the formula is applied, any that is suitable for solving a given problem.
work on AC and DC
magnetic field that is generated within the coil is directed along the axis, and is equal to:
- B = μ0nI,
where μ0 - is the magnetic permeability of the vacuum, n - is the number of turns, andI - current value.
When current flows through a solenoid, the coil stores energy, which is equal to the work required to establish the current.To calculate the inductance in this case, the following formula is used:
- E = LI2: 2,
where L indicates the inductance value, and E - store energy.
EMF self-induction occurs when the current in the solenoid.
In the case of AC operation appears an alternating magnetic field.Direction of the force of gravity may vary, and may remain unchanged.The first case occurs when using the solenoid as the solenoid.And second, when the armature is made of magnetic material.The solenoid has AC impedance, which is included in the winding resistance and its inductance.
The most common use of the solenoids of the first type (DC) - is the role of the progressive force of the drive.Strength depends on the structure of the core and the housing.Examples of use are the work of scissors when cutting checks in the cash register, the valves in the engine and hydraulic system, lock tabs.Solenoids of the second type are used as inductors for induction heating in a crucible furnace.
oscillating circuit
simplest resonant circuit is a series resonant circuit consisting of inductors and included a condenser, through which an alternating current.To determine the inductance of the coil, use the following formula:
- XL = W x L,
XL shows where the reactance of the coil, and W - angular frequency.
If a reactance of the capacitor, the formula would look like this:
Xc = 1: W x C.
important characteristics of the oscillation circuit is the resonant frequency, characteristic impedance and Q of the circuit.The first describes the frequency where the loop resistance is active.The second shows how the reactance at the resonant frequency between such values as the capacitance and inductance of the oscillating circuit.The third characteristic determines the amplitude and width of the amplitude-frequency characteristics (AFC) resonance, and shows the size of stored energy in the circuit compared to the energy loss in one oscillation period.The technique of frequency properties are measured using a chain response.In this case, the circuit is considered as a four-pole.When the image charts the value chain transfer coefficient voltage (K).This value indicates the ratio of the output voltage to the input.For circuits that do not include energy sources and different reinforcement elements, the coefficient is not greater than one.It tends to zero as at frequencies different from the resonant circuit resistance is high.If the minimum resistance value, the coefficient is close to unity.
In a parallel resonant circuit includes two reactive elements with different force reactivity.The use of this circuit means knowing that a parallel circuit elements necessary to add only their conductivity, but not resistance.At the resonant frequency of the overall conductivity of the circuit is equal to zero, indicating that the infinitely large AC resistance.For the circuit, which includes parallel capacitance (C), resistance (R) and inductance, the formula that unites them and the quality factor (Q), the following:
- Q = R√C: L.
When the parallel circuit of theone oscillation period takes twice the energy exchange between the capacitor and the coil.In this case, a loop current, which is much greater than the current in an external circuit.
Jobs
capacitor device is a two-pole low conductivity and a variable or constant capacitance value.When the capacitor is not charged, its resistance is close to zero, otherwise it is equal to infinity.If the current source is disconnected from the element, it becomes that source until his discharge.Using a capacitor is in electronics as filters that remove noise.The device in the power supply to power circuits are used to recharge the system at high loads.This is based on the ability of the element to pass a variable component, but the current unstable.The higher the frequency component, the less the resistance of the capacitor.As a result, through the condenser jammed all interference which go over a DC voltage.
resistance element depends on the capacity.For this reason it is wise to put capacitors with different capacity to capture all sorts of noise.Due to the ability of the device to pass a constant current only during the charge it is used as an element of timing generators or as a pulse shaping unit.
capacitors are of many types.Mainly used classification type insulator, since this parameter determines the stability of capacitance, insulation resistance and so on.Systematics of this magnitude following:
- Capacitors with gaseous dielectric.
- vacuum.
- Liquid dielectric.
- With a solid inorganic dielectric.
- With solid organic dielectric.
- Solid.
- Electrolytic.
There is a classification by purpose capacitors (general or special), the nature of protection from external factors (protected and unprotected, isolated and non-isolated, sealed and sealed) by the technique of installation (for attachments, printing, surface, with the conclusions of the screw,snap-pin).Also, the device can be distinguished by the ability to change capacity:
- Constant capacitors, that is, the capacity of which is always constant.
- Trimmer.They have the capacity does not change with the equipment, but it can be adjusted once or periodically.
- variables.This capacitors, which permit during operation of the apparatus change its capacitance.
inductors and capacitors
conductive parts of the device are capable of creating his own inductance.These are the structural parts, such as clutches, connecting bus, Current taps, conclusions and fuses.You can create additional inductance capacitor by attaching tires.Operation mode of electric circuit depends on the inductance, capacitance and resistance.The formula for calculating the inductance that occurs when approaching the resonant frequency, the following:
- Ce = C: (1 - 4Π2f2LC),
Ce which determines the effective capacitance of the capacitor, C shows the actual capacity, f - is frequency, L - inductance.
inductance value should always be taken into account when working with power capacitors.For pulse capacitors is the most important value of self-inductance.Their discharge accounts for induction loop and has two kinds - aperiodic and oscillatory.
inductance in the capacitor depends on the wiring of the elements in it.For example, when connected in parallel sections and tires, this value is the sum of the inductances of the package and the main bus terminals.To find this kind of inductance, the following formula:
- Lk = Lp + Lm + Lb,
Lk shows where the inductance device, Lp -Package, Lm - the main bus and Lb - lead inductance.
If the parallel connection of bus current varies along its length, then the equivalent inductance is defined as follows:
- Lk = Lc: n + μ0 l x d: (3b) + Lb,
where l - length of the tire, b- the width and d - the distance between the rails.
To reduce the inductance of the device, you must live parts of the capacitor arranged to mutually compensate the magnetic field.In other words, the current-carrying part of the same movement of the current need to remove from each other as far as possible, and with the opposite direction to pull together.When combining the current leads with decreasing thickness of the dielectric can be reduced inductance section.This can be achieved by further dividing one section with a large volume into several finer capacity.
