Centrifuge Failure Analysis and Maintenance
Centrifuge Failure Symptom Once the centrifuge power switch is turned on, the machine does not start up and all displays on the display panel are off, but the internal 12V, 5V DC power supply voltage is normal.
Failure analysis After the centrifuge power is turned on, the initialization process is first performed to detect the core circuit. If there is a problem in the initialization process, the shutdown process enters an infinite loop. According to the failure phenomenon, it can be preliminarily judged that the machine does not perform the initialization process, resulting in no initialization. The main reasons for the process are:
(1) The microprocessor upd7810 on the control board is not reset;
(2) There is no clock signal;
(3) ROM program damage;
(4) Maintenance and repair of microprocessor upd7810 In the inspection process, the principle of easy-to-failure should be adopted. First, check the reset condition of the microprocessor. With a low-level signal sent to the 28-pin reset end of the microprocessor upd7810, the machine is turned on, enters normal operation, and the display panel is working properly. This indicates that the fault occurred in the reset circuit. After the machine has been working for a period of time, the performance of the components has changed, resulting in a reset pulse that does not meet the requirement (a normal reset pulse is about ten ns). After the capacitor C3 in the reset circuit is readjusted, the machine is operating normally. If the Z11 and TL7705 manifolds are damaged, they can be directly replaced by an integral circuit r=RC>12ns in the case that they cannot be purchased.
Centrifugal machine fault phenomenon two after starting, when the rotor speed increases when the speed reaches 830r/min or so, the rotor warning light flashes, the rotor stops increasing speed, enters the free decay state.
Fault analysis The main cause of this type of fault is the rotor speed detection circuit. For example, RPG (rotor pulse generator) sensors are bad; transistor aging, deterioration of characteristics, decrease of current amplification factor, or change of resistance value are the causes of such failures.
Maintenance method checks RPGA point pulse signal about 3Vp-p, and the pulse width changes with increasing speed, which shows that the RPG sensor works normally, the transistor Q4 collector, Z32 input terminals are 2.8Vp-p pulse signal, Z32's The output is a +5V DC level (normally a 5Vp-p pulse signal). Since the threshold voltage of Z32 is about 3V, the input 2.8Vp-p pulse cannot turn on the inverter. At this time, the detection state of the micro-processing is incorrect, and the rotor warning light is blinking. Check Q4 collector current is lower than normal, in the case of Q4 aging is not serious, the output voltage of Q4 can be raised to high, that is, reduce the collector resistance R31, increase the collector current, so that Q4 achieve Saturation is on, the collector output is about 5Vp-p pulse signal machine resumes normal work.
The phenomenon of failure of the centrifuge three After the vacuum system is turned on, it takes about 5 to 6 hours to reach a high vacuum, and it takes only about 1 hour to reach high vacuum.
Failure analysis leads to the main causes of such failures: (1) abnormal vacuum pump operation; (2) poor vacuum system seal; (3) bad vacuum pump heater.
After the inspection and repair method was inspected, the vacuum pump was working properly, and after the vacuum system had no problem of poor sealing, the vacuum pump heater was found to be bad after further inspection, resulting in high vacuum pumping failure. Because there are no spare parts, so use the same size of the outer diameter of the electric furnace plate, calculated by 220V800W electric furnace wire 2/3 length of about 40Q, replace the original 110V300W heater wire, cut the size of the two muffles and the size of the mound The sheet is placed on the chassis between the oven and the heater to make insulation, and the installation is very effective. It has been used on several centrifuges and all work well.
Centrifuge fault phenomenon at room temperature around l6 °C, boot temperature shows a 10 °C, can set the temperature normally, but the instrument does not work.
Failure analysis causes temperature detection to be caused by the following reasons: (1) bad thermal sensor; (2) failure to detect temperature circuit.
The inspection method checks that the thermal sensor is normal, the output of the op amp upc451 is 0V, and the output of the VR7 op amp (Figure 4) remains unchanged. Therefore, it is determined that the operational amplifier is bad. Due to the fact that the same type of four-op amp upc451 is not available in the market, the LM324 with the same component foot arrangement is directly replaced. The measured temperature is slightly deviated from the actual temperature after the substitute. This is due to the incomplete performance of the two integrated circuits. Uniformly caused. It requires temperature calibration
After measuring the temperature calibration After finishing the instrument, in order to calibrate the measured temperature, the temperature measurement circuit must be adjusted.
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