An electric oven is an instrument that measures the moisture content of a substance in a laboratory. It uses a resistance wire to heat the air, and the tube automatically controls the temperature to remove the moisture of the material. The electric oven has the characteristics of simple operation, sensitive action, accurate temperature control, safety and reliability, and high work efficiency. Therefore, it is widely used in industries such as industry, agricultural technology, scientific research and medical treatment. According to the power and temperature control range, it is divided into high and low temperature. The working temperature is above 50 °C, which is called high temperature oven, which is called oven. The working temperature is below 50 °C, which is called low temperature oven, also known as incubator. Due to different industrial uses, its volume is divided into large, medium, 4, and three. The following is an example of the Y801A electric oven. The working principle and common fault analysis and troubleshooting methods are briefly described.
Y801A type electric oven is an automatic constant temperature oven designed according to the switching characteristics of the tube and the electromagnetic induction principle of the relay. Its electrical schematic is shown in Figure 1. In the figure, the electron tube G and the DC electromagnetic relay J, the electric contact type mercury thermometer KK, and the capacitor C, the resistor R, R and other components constitute an electronic relay automatic control circuit; the operating voltage of each pole of the electron tube is respectively determined by the power transformer B Level supply; one end of the resistance wire R is connected to the mains phase line, the other end is connected to a static contact of the relay; the red and green signal lights HZD and LZD respectively indicate the heat preservation and heating; the motor D drives the fan to accelerate the air circulation in the oven Convection makes the temperature inside the box rise more evenly; the KK set at the power supply line is a mechanical temperature safety controller installed to prevent damage to the instrument when the temperature is too high.
It is known from the working principle of the oven that the temperature in the oven is generated by the work of the resistance wire R. In order to keep the oven constant, it is necessary to require the temperature to rise to the set value, and the resistance wire stops working; when the temperature drops slightly, the resistance wire can continue to work. In other words, the constant temperature of the oven within the set range is maintained by the automatic switching on and off of the input power source. The power supply is turned on and off by the contact and release of the relay contacts. The action of the relay is in turn controlled by the tube gate. Therefore, the normal operation of the tube directly affects the pull-in and release of the relay contacts. If the temperature in the oven rises to the set value, the power supply cannot be disconnected and heating continues, indicating that the relay contacts are not released.
Remedy: 1 Check if the tension spring of the relay is off; whether the contact is “burned out†and stick together; whether the mercury column in the electric contact thermometer is interrupted; whether the wire connected to the thermometer on the top of the oven is disconnected or the terminal is in contact bad. 2 Check the resistance R with a multimeter. R Is the internal open circuit or solder joint desoldering; measure whether the 7-pin (gate) of the tube has a voltage of about 20 V; check whether the 7-pin of the tube holder is in good contact. If the fault has not been eliminated after the above inspection and repair, the power switch can be turned on and off repeatedly by hand. When the switch is closed, the relay contact can be flexibly released. If it cannot be released flexibly, the reverse tension spring may be heated for a long time. Loss of elasticity, causing the movable contact to not return flexibly after the relay coil is de-energized. In this case, you can turn off the power, remove the spring, and cut it off for a while; if not, you can replace it with a new spring that is elastic and large.
3. The temperature rise in the oven has not reached the set value, and the power is turned off.
Third , other failure analysis and elimination
1. The relay contacts do not pull properly and emit continuous “嗒嗒嗒†noise. Most of this phenomenon occurs when capacitor C fails (leakage or breakdown). The reason is: after the capacitor fails, it loses the filtering effect on the screen current of the tube. The current through the relay coil is no longer a smooth pulsating DC current, but a positive and negative pulse current. That is, when the secondary output of the transformer is positive for half a cycle, the relay coil is energized to make the movable contact pull in; when the secondary output of the transformer is negative for half a cycle, the relay coil is de-energized, the armature is demagnetized, and the movable contact returns under the action of the spring. .
2. The oven heats up normally and the fan does not turn.
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