Inside view : Induction Heater

Induction cooking heats a cooking vessel by magnetic induction, instead of by thermal conduction from a flame, or an electrical heating element. Because inductive heating directly heats the vessel, very rapid increases in temperature can be achieved.

An induction cooker transfers electrical energy by induction from a coil of wire into a metal vessel that must be ferromagnetic. The coil is mounted under the cooking surface, and a high frequency (e.g. 24 kHz) alternating current is passed through it. The current in the coil creates a dynamic magnetic field. When an electrically conductive pot is brought close to the cooking surface, and the pan is thicker than the skin depth, the magnetic field induces large eddy currents in the pot. The eddy currents flow through the electrical resistance of the pot to produce heat; the pot then in turn heats its contents by heat conduction.

The cooking vessel typically needs to be made of a suitable stainless steel or iron. The increased magnetic permeability of the material decreases the skin depth, concentrating the current near the surface of the metal, and so the electrical resistance will be further increased. Some energy will be dissipated wastefully by the current flowing through the resistance of the coil. To reduce the skin effect and consequent heat generation in the coil, it is made from litz wire, which is a bundle of many smaller insulated wires in parallel. The coil has many turns, while the bottom of the pot effectively forms a single shorted turn. This forms a transformer that steps down the voltage and steps up the current. The resistance of the pot, as viewed from the primary coil, appears larger. In turn, most of the energy becomes heat in the high-resistance steel, while the driving coil stays cool.

Often a thermostat is present to measure the temperature of the pan. This helps prevent the pan from severely overheating if accidentally heated empty or boiled dry, but also can allow the induction cooker to maintain a target temperature.



Ku Band LNB Disassembled

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A low-noise block downconverter (or LNB) is the receiving device of a parabolic satellite dish antenna of the type commonly used for satellite TV reception. The device is sometimes wrongly called an LNA (Low-noise amplifier), LNC (for low-noise converter) or even LND (for low-noise downconverter) but as block-downconversion is the principal function of the device, LNB is the preferred term, although this acronym is often incorrectly expanded to the incomplete descriptions, low-noise block or low-noise block converter.[1][2] [3] [4]

The LNB is a combination of Low-noise amplifer, block downconverter and IF amplifier. It takes the received microwave transmission, amplifies it, downconverts the block of frequencies down to a lower block of intermediate frequencies where the signal can be fed to the indoor satellite TV receiver using relatively cheap cable.

The signal from the dish is picked up by a feedhorn and is fed to a section of waveguide. In this waveguide a metal pin, or probe, protrudes into the waveguide at right angles to the axis and this acts as an aerial, and feeds the signal to a printed circuit board in the LNB.

The LNB is usually fixed on the satellite dish framework, at the focus of the reflector, and it derives its power from the connected receiver. This phantom power is sent “up” the same cable that carries the received signals “down” to the receiver. The corresponding component in the transmit link uplink to a satellite is called a Block upconverter (BUC).