At high currents, the ferromagnetic cores may get enough hot that they may fracture and permanently change the nominal inductance of the inductor. Solenoid vs inductors Solenoids are often confused with the inductors. The solenoids are coils of wires that are intended to be used as electromagnets.
Many inductors are also coils of wires but they are intended to offer inductance in a circuit. The inductors using cylindrical coils are also called solenoidal coils only because of their solenoid like construction. Though, they are not intended to be used as an electromagnet in a circuit. The solenoids are specifically used as electromagnets and usually have a moveable or static core.
Commonly, solenoids are used as electromagnets in electric bells, DC motors, and relays. Solenoidal coils as inductors The simplest and most common inductors are solenoidal coils. These inductors are cylindrical coils wound around air-core or ferromagnetic core.
These inductors are easiest to construct. A solenoidal or cylindrical coil can be easily designed to vary inductance by incorporating a mechanism to slide in and out ferromagnetic core of the coil.
By moving the core in and out of the coil, the effective permeability of the coil can be varied and so, the inductance of the coil. This is called permeability tuning. This is used to adjust frequencies in radio circuits.
The core can be made movable by attaching it to a screw shaft and fixing a nut at the other end of the coil. When the screw shaft is rotated clockwise, the core moves inside the coil increasing the effective permeability and so the inductance. When the screw shaft is rotated anti-clockwise, the core moves out, decreasing the effective permeability and so the inductance.
Toroids as inductors Toroid is another most common form of inductors these days. Toroids have a donut-shaped ferromagnetic core on which the coil is wound.
The toroids need fewer turns and are physically smaller for the same inductance and current-carrying capacity compared to solenoidal coils. Another major advantage with toroids is that the flux is contained within the core which avoids any unwanted mutual inductance. High-current toroidal conductors.
Image: Signal Transformer, a Bel Group. However, it is difficult to wind the coil in a toroid. It is even much difficult to permeability tune a toroid. Designing variable inductors on toroid involves complex and cumbersome construction. The circuits where mutual inductance is wanted, the different coils need to be wound on the same core in case toroid is used as an inductor.
Pot cores as inductors In typical inductors — solenoidal coils and toroids — the coil is wound around the ferromagnetic core. The pot core is another type of inductor in which the coil winding resides inside the ferromagnetic core. In pot core, the ferromagnetic core is in the form of two halves. The coil is wound and wrapped by one of the halves.
The two halves have holes between them, from which the coil wire is taken out. The entire assembly is held together by a bolt and nut. The pot cores like toroids offer large inductance and current-carrying capacity in small size with less number of turns. The flux, like in toroids, remains contained within the assembly.
So, there is no unwanted mutual inductance with pot cores. Again, like in toroids, it is difficult to vary inductance in pot cores. It is only possible to vary inductance in pot cores by varying the number of turns and that by using taps at different points of the coil.
Transmission line as inductor Inductors are mainly useful in AC circuits. For DC, inductors almost behave like a conducting wire offering some negligible resistance and nothing else. In AC, inductors find their actual applications. The audio frequency circuits generally use toroids, pot cores or audio transformers as inductors. The audio circuits typically use inductors of value ranging from few Milli-Henrys to 1 Henry. The inductors along with capacitors have been used in audio circuits for tuning.
Nowadays, active ICs have almost replaced inductors and capacitors in audio circuits and applications. As the frequency increases, inductors with lower permeability cores are used. At the lower end of radio frequencies, the same inductors that are used in audio applications are used.
At radio frequencies up to few MHz, toroids are quite common. For radio frequencies from 30 to MHz, air-core coils are preferred. For radio frequencies greater than MHz, transmission line inductors are useful. The transmission lines of short length quarter wavelength or less of the signal wavelength can be used as inductor for tuning high-frequency radio signals.
The transmission line used as the inductor is generally coaxial cable. Inductor in DC circuit Practically, inductors are not useful in DC circuits as they will show no inductance for constant currents. However, assuming an inductor connected in a DC circuit can be useful in understanding its working principle and its behavior to pulsating DC voltages. Suppose a pure inductor is connected to a voltage source via a switch. When the switch is closed, the voltage is applied across the inductor causing a rapid change in current through it.
As the applied voltage increases from zero to a peak value in a short time , the inductor opposes the flow of changing current through it by inducing a voltage opposite in polarity to the applied voltage.
The induced voltage during energizing of the inductor is called back EMF and is given by the following equation —. L is the inductance offered by the inductor. A sudden change in current through the inductor gives infinite voltage, which is not feasible. So, current through the inductor cannot change abruptly. The current faces the effect of inductance for every small change in magnitude and slowly rises to its peak constant value.
So, initially, the inductor acts as open circuit when the switch is closed. The back EMF remains across the inductor until the current is changing through it. The induced back EMF always remains equal and opposite of the rising applied voltage. As the voltage and current from the source approach a constant value, the back EMF drops to zero and the inductor acts as a short circuit like a connecting wire.
While energizing, the power stored by the inductor is given by the following equation —. V is the peak voltage across inductor. I is the peak current through inductor. I is the maximum current through it. Not all the inductors are solenoids. A solenoid is a coil with a ferrous core that moves. An inductor is a wire coil with a fixed core, which may or may not be present.
The core of a solenoid will move when electricity flows through it. A magnetic field is created when the current runs through an inductor. Car Door Locks is one of its applications. Choke is the name of the application. It is made up of long, thin wire wound into a long coil shape.
0コメント