Maintenance principle and method of temperature automatic controller

First, the working principle and control process

1. The circuit components and component functions of each part are shown in the schematic diagram of the electrical principle of the KSW-3 temperature automatic controller. The triode BG1, the coils L1, L2, L3 and the capacitors C1, C2, C3, C5, C8 and the like in the figure constitute a high-frequency inductance three-point oscillating circuit. The oscillating signal is output via D1 detection. BG2, R6 and R7, relay J and other components constitute a primary DC amplifying circuit. The AC contactor CJ completes the power control of the high temperature furnace. The power transformer B provides AC low voltage to the temperature conversion circuit and the red and green indicator lights, and also outputs 12V DC voltage through D3 and D4 as the power supply for the oscillation circuit and the amplification circuit. The ammeter A is connected in series with the power supply of the high temperature furnace, and together with the indicator lights XD1 and XD2, the power supply and the power failure of the high temperature furnace are displayed. The temperature conversion circuit is composed of thermocouples R and R9 to R13, C9. D5 is connected to both ends of the thermocouple to prevent the thermocouple from being disconnected. Damage to the meter due to excessive current. Further, a resonance circuit composed of the oscillation coils L3 and C8 and a millivoltmeter constitute an indication control portion.
2. The working principle and control process are connected to the power supply, the oscillator and the amplifier start to work, the oscillation signal is output by the BGl emitter, and after the D1 detection, the BG2 is turned on, the relay J is held, and the AC contactor CJ is sucked, and the high temperature furnace starts to increase. temperature. The temperature inside the furnace is converted into an electric signal (electromotive force) by a thermocouple to the moving coil type millivoltmeter, and the pointer with the aluminum sheet is deflected to the right. When the pointer enters the gap of the oscillation coil L3 (predetermined temperature). Due to the high frequency eddy current effect on the aluminum sheet, the total inductance of L3 is greatly reduced, resulting in an increase in the current impedance of the resonant circuit of L3 and C8 with respect to the oscillation frequency. The amplitude of the oscillation is reduced, and even the vibration is stopped. At this time, the base signal transmitted to BG2 after D1 detection is greatly weakened, so that BG2 is cut off and the contact of relay J is released. The AC contactor CJ opens with it. Contact release. Turn off the high-temperature furnace power supply, and stop the heating in the high-temperature furnace. When the furnace temperature gradually decreases, the electromotive force of the thermocouple R also decreases, causing the millivoltmeter pointer to deflect to the left. When the pointer exits the gap of the oscillating coil L3, the circuit resumes oscillation. BG2 is turned on, J is held, the power of CJ is turned on, the contacts are sucked, and the high temperature furnace starts to warm up again. By repeating this operation, the furnace temperature is maintained within a predetermined range, and automatic temperature control is realized.
Second, troubleshooting

1. Visual inspection and judgment (1) Judgment: The XDl (red) and XD2 (green) indicators on the control panel indicate the insulation and heating of the high temperature furnace (ie, power off and power on). Under normal circumstances, K2 is closed; the oscillation and amplification circuit starts to work, the relay J is held, the green light is turned on, and then the K1 is turned on, the CJ action, the contact is closed, and if the green light is not lit, the red light is on. And the ammeter has no indication, when the CJ has no action sound. It can be judged that the AC and DC circuits and the temperature conversion circuit of the power supply part are working normally, and the fault may occur in the oscillation, detection, and amplification part of the circuit; if the power is turned on, the high temperature furnace can be heated, but when the millivoltmeter pointer is deflected to a predetermined temperature, The green light does not go out, the red light does not shine. The high temperature furnace continues to warm up, that is, the control failure, it can be judged that the power supply part of the AC, DC circuit, temperature conversion, detection three parts of the circuit is normal, and the oscillation and amplification of these two parts of the circuit may malfunction.
(2) Inspection: Remove the casing and carefully check whether the relay, AC contactor and transformer components have obvious burnt marks, and whether the terminals, circuit connecting wires, components, etc. are disconnected or desoldered. Then turn on the power. Use the electric pen to test the above components in turn. Connect the input and output terminals of the wires to have power.
2. If the fault is still not detected and eliminated after the above-mentioned inspection of the voltage detection instrument, it is necessary to measure the voltage value of each pole of the triode BG1 and BG2 by using the DC voltage of the multimeter. The values ​​listed in the attached table should be met.