Maintenance principle and method of the hottest te

2022-08-17
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Introduction to maintenance principle and method of automatic temperature controller

I. working principle and control process

1. Circuit composition and component function of each part

the attached figure is the electrical principle diagram of ksw-3 automatic temperature controller. The triode BGL, coils L1, L2, L3 and capacitors C1, C2, C3, C5, C8 in the figure constitute a high-frequency inductive three-point oscillation circuit. The oscillation signal is detected and output by D1. BG2, R6 and R7, relay J and other components form a primary DC amplification circuit. AC contactor CJ can control the power supply of high-temperature electric furnace, and the conditions can meet the requirements. In addition to providing AC low voltage to the temperature conversion circuit and red and green indicator lights, power transformer B also outputs 12V DC voltage through D3 and D4 rectification as the power supply of oscillation circuit and amplification circuit. Ammeter A is connected in series to the power supply of the high-temperature furnace, and displays the high temperature together with the indicator lights XD1 and xd2. Set the power on and power off of the furnace without affecting the experimental results. The temperature conversion circuit is composed of thermocouples R, R9 ~ R13 and C9. D5 is connected at both ends of the thermocouple in parallel to prevent disconnection of the thermocouple. The instrument is damaged due to excessive current. In addition, the resonant circuit composed of oscillation coils L3 and C8 and the millivoltmeter constitute the indication control part

2. working principle and control process

turn on the power supply, the oscillator and amplifier begin to work, the oscillation signal is output by the BGL emitter, after D1 detection, BG2 is turned on, relay J is held, driving the AC contactor cjicf product also has easy forming and closing, and the high temperature furnace begins to heat up. The temperature in the furnace is converted into an electrical signal (electromotive force) by the thermocouple and transmitted to the moving coil millivoltmeter, which deflects the pointer with aluminum sheet to the right. When the pointer enters the gap of the oscillation coil L3 (at a predetermined temperature), the total inductance of L3 is greatly reduced due to the high-frequency eddy current effect on the aluminum sheet, resulting in an increase in the current impedance of the resonant circuit of L3 and C8 to the oscillation frequency. The oscillation amplitude decreases or even stops. At this time, the base signal transmitted to BG2 after D1 detection is greatly weakened, so that BG2 is cut off, the contact of relay J is released, and the AC contactor CJ is opened. The contact is released. Cut off the power supply of the high-temperature furnace, and the high-temperature furnace stops heating. When the furnace temperature gradually drops, the electromotive force of thermocouple r also weakens, making the millivoltmeter pointer deflect to the left. When the pointer exits the gap of oscillation coil L3, the circuit resumes oscillation. BG2 is turned on, j is held, CJ is powered on, the contact is closed, and the high-temperature furnace begins to heat up again. Such repeated actions will maintain the furnace temperature within the predetermined range and realize automatic temperature control

II. Troubleshooting

1. Visual inspection and judgment

(1) judgment: XDL (red) and xd2 (green) indicators on the control panel indicate the insulation and heating of the high-temperature furnace (i.e. power off and power on). Close K2 under normal conditions; The oscillation and amplification circuit starts to work, relay J is held, the green light is on, and then K1 is connected, CJ acts, and the contact is closed. If the green light is not on, the red light is on. And the ammeter has no indication and CJ has no action sound. It can be judged that the AC and DC circuits and temperature conversion circuits of the power supply are working normally, and the fault may occur in the circuits of oscillation, detection and amplification; If the high-temperature furnace can be heated after being powered on, but when the millivoltmeter pointer deflects to the predetermined temperature, the green light will not go out and the red light will not go on. If the high-temperature furnace continues to heat up, that is, the control fails, it can be judged that the AC and DC sub circuits of the power supply are normal. According to Zhou Binbin, the three sub circuits of current circuit, temperature conversion and detection are normal, while the two circuits of oscillation and amplification may fail

(2) inspection: remove the housing and carefully inspect whether the relay, AC contactor, transformer and other components have obvious scorch marks, and whether the wiring terminals, circuit connecting wires, components and so on are disconnected or desoldered. Then turn on the power. Test the above components in turn with an electric pen. Check whether there is electricity at the input and output ends of the connecting wire

2. voltage detection

if the fault of the instrument has not been found and eliminated after the above inspection, it is necessary to use the DC voltage block of the multimeter to measure the voltage value of each pole of the triode BGL and BG2 to the ground respectively. It should comply with the values listed in the attached table

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