It mainly consists of a shell, an electric heating element, a timer, a thermostat and a power regulator. Whether it is simple, one hundred or two hundred yuan, or fully automatic, one or two thousand yuan, the principle and composition are similar, the key is the different materials and control methods of its parts.
Electric ovens can be divided into mechanical control and electronic automatic control. The mechanical electric oven is simple in structure and cheap, but the time and temperature control are not accurate enough. Mechanically controlled timers are driven by motors or clockwork. After the set time, the timer will time and stop heating after the set time. Manually toggling the power adjustment switch is actually to choose whether to use the heater, turn off the heater or heat at the same time. The thermostat is a bimetallic temperature sensor, which adjusts the temperature through the thermal deformation of the metal sheet, as shown in the following figure.
When the temperature in the furnace exceeds the set temperature, the metal sheet is deformed, the two metal contacts ⑧ and ⑤ are separated, the current is interrupted, the heater is powered off, and heating is stopped.
Electric oven, its computer board wiring is more complicated, as shown above, which is the wiring diagram of a brand electric oven. In fact, the principle is the same as the one above, except that its timer and thermostat are replaced by chips. There are five chips in the above circuit. IC 1 is a digital pulse counting memory chip, which is the heart of the whole circuit. IC2 is a comparison amplifier and IC5 is a Schmitt trigger, which is used for current amplification and shaping. Ic3 and IC4 are used as music prompt lines. The circuit is complicated and the screen of the mobile phone is too small. In order to explain its principle, we extract the main circuit, remove the music circuit and simplify it into the following control chart to introduce its working principle:
The working voltage of-12 volts is obtained from 220V mains through voltage transformation and full-wave rectification. When K4 and K6 are turned on, the IC 1 internal pulse counting circuit starts counting, pin 28 outputs high potential, V2 is turned on, relay KA 1 is turned on, and the power regulating switch K 1 is selected, and the electric heating tube starts heating. When the furnace temperature reaches the set temperature, the resistance of thermistor R25 decreases, and the potential of pin 3 of IC2 decreases. When it is less than the standard potential of pin 2, pin 6 outputs a low level to pin 2 of IC5, pin 3 of IC5 outputs a high level, transistor V3 is turned off, relay KA 1 is turned off, and the heating pipe stops heating. When the furnace temperature is lower than the set value, the resistance of thermistor R25 increases, and the potential of pin 3 of IC2 increases. When it is higher than the standard potential of pin 2, pin 6 outputs high level to pin 2 of IC5, and pin 3 of IC5 outputs low level. Transistor V3 turns on the relay and the heater starts working again. When the pulse counter in IC 1 counts to the set time, its pin 1 outputs a low level, so that V2 is turned off, the relay is turned off, and the electric oven stops working. Look at several setting switches in the figure: K4 is connected to the 3 1 pin of the digital IC 1 chip, and can be used together with K8 and K9 to set the working time, K8 modulation minute and K9 modulation hour of the electric oven. K5 is connected with 32 pins, and the shutdown time can be scheduled; K6 is connected with 38 pins, and the start-up time is scheduled; K7 is connected to the 25 pins of the chip, so that it can be turned off immediately.
Generally, electric ovens use two far-infrared heating tubes and a quartz tube as a group, one for the top and one for the bottom. There are also high-end ultraviolet tubes and halogen tubes. When choosing an electric oven, choose a clean electric heating tube for easy cleaning. Also: First, choose a large-capacity electric oven, preferably more than 40 liters, with more inner layers, which can bake more food. Second, unlike microwave ovens, electric ovens are best controlled by electricity, because mechanical thermostats are not effective, which makes food uncooked and cooked unevenly. Third, try to buy high-grade ones, not simple ones, especially the upper and lower electric heating pipes must be controlled separately. Simple as buying a microwave oven or a microwave oven with barbecue.