The electric drying oven is an instrument for measuring 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 drying box 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 drying box, which is called drying box; the working temperature is below 50 °C, called low temperature oven, also known as incubator. The common fault analysis and troubleshooting methods are as follows: Turn on the power: 1 observe the signal light, if the red light does not light, and after half a minute, the relay does not work, the tube filament is not lit, you should first consider that the AC circuit may not be connected, you can use the electric pen to enter the city from the power The line begins to check the fuse RD. , safety controller KK, power switch K and other wiring points and transformer primary power. If it is normal, the transformer may be damaged and can be further checked and replaced with a multimeter. 2 The red light is on and the tube filament is not bright. This is obviously the damage of the tube or the failure of the socket. Care should be taken to check whether the sockets 4 and 5 are in good contact and the connection is broken. Remove the tube and measure the 4 and 5 feet with the ohmmeter of the multimeter. If it is blown, replace the tube of the same type. 3 tube light is bright, but the relay does not work, it may be: a. The secondary winding of the transformer 250V is disconnected or the internal coil is blown; b. The relay coil is burned out or disconnected; c. The tubes 1, 6, 2, 9, 3, 8 have poor contact, or the internal screen, cathode or second grid (2, 9 feet) of the tube is open. When searching for faults, the power can be turned on, and the secondary output voltage of the transformer is measured in turn by a multimeter. The voltage of each leg of the electron tube should meet the reference data listed in Table 1. If the measured data differs greatly from the reference value, the performance of the tube should be considered to be deteriorated, and the same type of tube should be replaced. 2. After the temperature in the drying cabinet rises to the set temperature, the power supply cannot be automatically cut off and the heating is continued. According to the working principle of the drying box, the temperature in the drying box is generated by the work of the electric resistance wire R. In order to make the drying box constant temperature, 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 drying 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 dry box 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 connecting the thermometer on the top of the drying box is disconnected, and whether the terminal is broken Poor contact. 2 Check the resistance R with a multimeter. Whether R is internal open or solder joint desoldering; measure whether the 7-pin (gate) of the tube has a voltage of about 20V; 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 drying oven has not reached the set value, and the power supply is disconnected. When the drying box is in normal operation, the resistance wire R in the box is controlled by the electronic relay. However, when a component of the circuit fails (such as the open circuit of the resistor R), the input power supply is out of control, causing the temperature to rise continuously, causing a larger fault. To this end, a set of "temperature safety controller" KK is connected in series in the power supply line. When the circuit is out of control and the temperature exceeds the limit, the KK contact is automatically separated, and the power of the drying box is cut off, thus ensuring the safety of the instrument. . If the temperature rise in the dry box does not reach the set value, the power supply will be disconnected. The reason may be that the temperature adjustment bolt position on the temperature safety controller moves, so that the glass rod moves into the copper tube prematurely, and the controller The two energized contacts are separated. Solution: First set the electric contact thermometer KK at 150 c (=, then energize the drying box, and when the temperature inside the box rises to 150 c (=, adjust the adjustment bolt of KK to separate the two energized contacts. In addition, the fuse RD is blown during the heating process, which also causes the above failure, which cannot be ignored. 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 drying oven warms up normally and the fan does not turn. The drying oven is warming up normally, indicating that the input mains is normal. If the fan does not turn, you should find the components and parts related to the motor. First check whether the fuse of the fuse RD is blown, whether the connecting wire is open; Capacitor C: Whether the terminals of the motor are loose or desoldered, then remove the lead of one end of the capacitor from the terminal of the motor, and check whether there is leakage or a multimeter with a multimeter or breakdown. If the fault is still not eliminated after the above check, the motor may be faulty, and the motor may be removed for inspection, repair or replacement.
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1. Can't warm up.
It can be seen from the electrical schematic diagram that the parts and components that affect the normal heating of the drying box mainly include: AC circuit, transformer, relay and electronic tube. If any of these parts and components fail, the AC circuit of the electric drying box will be disconnected, so that it cannot be properly heated. The troubleshooting method is as follows.
When the secondary output of the transformer is exchanged for the second positive half cycle, the relay coil is energized and the moving contact is attracted. The change in the secondary voltage of the transformer so as to cause the relay contacts to continuously pull in and release, causing a continuous "beep" sound. In the inspection, you should first check whether the capacitor connection is open or desoldered, and then replace it with a capacitor of the same capacity. In addition, if a newly purchased dry box or a newly replaced relay has a similar failure, the spring tension on the relay may be too tight, and the adjustment bolt may be appropriately loosened.