There are many high-temperature areas on the earth, the most obvious of which is the desert area. With the development of science and technology, people's activities have also entered the desert. Then any items used in the desert must be able to withstand high temperatures, even low temperatures. The temperature contrast between day and night in the desert is very large.

When many users use high-temperature aging laboratories, they usually encounter some problems: for example, after the temperature in the box rises to the set temperature, the temperature continues to rise. What is the main reason for this?

From the working principle of the high-temperature aging laboratory, it can be seen that the temperature in the box is generated by the work done by the resistance wire R. To keep the high-temperature aging room constant temperature, it is necessary to require that the resistance wire stops working after the temperature rises to the set value; when the temperature drops slightly, the resistance wire can continue to work.

The constant temperature of the high-temperature aging laboratory within the set range is maintained by the automatic connection and disconnection of the input power supply. The on and off of the power supply is completed by the contact of the relay. The action of the relay is controlled by the gate of the electron tube. Therefore, whether the electron tube works normally or not directly affects the contact of the relay. If the power supply cannot be disconnected and continues to heat when the temperature in the high-temperature aging chamber rises to the set value, it means that the relay contacts are not released.

How to eliminate these problems?

① Use a multimeter to check the resistor R. Is R internally open or the solder joint is desoldered; measure whether there is a voltage of about 20V at the 7th foot (gate) of the electron tube; check whether the 7th foot of the tube socket is in good contact. If the fault is still not eliminated after the above inspection and repair, you can repeatedly open and close the power switch of the high-temperature aging chamber by hand to observe whether the relay contacts can be flexibly released when the switch is turned off. If not, it may be that the back-pull spring is heated for a long time and loosens and loses its elasticity, causing the moving contact to be unable to return flexibly after the relay coil is powered off. In this case, you can turn off the power supply of the high-temperature aging chamber, remove the spring, and cut off a section to try; if it doesn't work, you can replace it with a new spring with high elasticity to solve this problem.

② Check whether the tension spring of the relay falls off; whether the contacts are "burned" and stuck together; whether the mercury column line in the electric contact thermometer is interrupted; whether the wire connecting the thermometer on the top of the high-temperature aging chamber is disconnected, and whether the terminal is in poor contact