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Different principles, the type of laboratory heating plate is also different
Date of publication：2019-07-11

Laboratory electric heating plate is suitable for most of the vessel, glass, ceramic, metal, using a simple keyboard keys, the controller design, LCD screen display, safety lock, hour meter function, as well as the high temperature alarm prompt, convenient use, add module and control system design, intelligent process control system, separate section control, temperature up to + / - 1 ℃.

According to the different energy conversion modes, we can divide the laboratory heating plates into the following types, among which zui is common: resistance heating, induction heating, arc heating.

1. Resistance heating: resistance heating USES the joule effect of current to convert electrical energy into heat energy to heat an object. Usually divided into direct resistance heating and indirect resistance heating. The supply voltage of the former is applied directly to the heated object, and when there is a current flow, the heated object itself heats up. An object that can be heated directly by resistance must be a conductor with a high resistivity. Since the heat is generated from the heated object itself, it is internal heating, and the thermal efficiency is very high. Indirect resistance heating requires heating elements made of special alloy or non-metallic materials, which generate heat energy that is transmitted to the heated object by means of radiation, convection and conduction. As the heated object and heating element are divided into two parts, the type of heated object is generally unlimited and easy to operate.

2, arc heating: arc heating USES the high temperature produced by the arc to heat objects. Arc is the phenomenon of gas discharge between two electrodes. The arc's voltage is low but its current is high. Its strong current is maintained by a large number of ions vaporized on the electrode, so the arc is susceptible to the influence of the surrounding magnetic field. When an arc is formed between electrodes, the temperature of arc column can reach 3000 ~ 6000K, which is suitable for high temperature melting of metal. Arc heating has direct and indirect arc heating. The arc current from direct arc heating passes directly through the heated object, which must be an electrode or medium of the arc. The arc current of indirect arc heating does not pass through the heated object. The characteristics of arc heating are: high arc temperature, energy concentration, steel arc furnace melting pool surface power can reach 560 ~ 1200 kw/m2. However, the noise of arc is large, and its volt-ampere characteristic is negative resistance characteristic (descending characteristic). In order to maintain the stability of the arc when the arc is heated, the instantaneous value of the circuit voltage when the arc current instantaneous passes zero is greater than the value of the arc starting voltage, and in order to limit the short-circuit current, a certain number of resistors must be connected in series in the power circuit.

3, induction heating: induction heating USES the conductor in the alternating electromagnetic field to produce induced current (eddy current) caused by the thermal effect of the conductor itself heating. According to different heating process requirements, the ac power supply frequency used for induction heating includes power frequency (50 ~ 60 hz), intermediate frequency (60 ~ 10000 hz) and high frequency (higher than 10000 hz). Power frequency power supply is the ac power supply commonly used in industry, the power frequency of most countries in the world is 50 hz. The voltage applied to the induction unit by the power supply for induction heating must be adjustable. According to the power of the heating equipment and the capacity of the power supply network, high-voltage power supply (6 ~ 10 kv) can be used to supply power through the transformer. The heating equipment can also be directly connected to the 380-volt low-voltage power grid.

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