Structure principle and maintenance of Sigma 1-13 centrifuge

Structure principle and maintenance of Sigma 1-13 centrifuge

Guo Jian, Feng Yanfeng, Gao Yanyan, Cheng Huan

(Laboratory Instrument Factory, Academy of Military Medical Sciences, Beijing 100850, China)

[Abstract] The circuit structure and control principle of sigma 1-13 centrifuge are introduced. Three troubleshooting examples are listed. The troubleshooting ideas are expounded. Suggestions on how to prevent faults are put forward.

Key words: centrifuge; structure; principle; fault; maintenance; prevention

Principle and Maintenance of Sigma 1-13 Centrifuge

GUO Jian, FENG Yan-feng, GAO Yan-yan, Cheng Huan

(Experimental Instrument Plant, Academy of Military Medical Sciences, Beijing 100850, China)

Abstract The circuit structure and control principle of the sigma 1-13 centrifuge are introduced. Three troubleshooting examples are listed. The troubleshooting methods are described and suggestions on the failure prevention are put forward.

Key Words centrifuge;structure;principle;failure;maintenance;prevention

In medical research, the centrifuge is a commonly used experimental equipment. The sigma1-13 centrifuge uses a brushless variable frequency motor, which has the advantages of low noise, fast lifting speed, compact structure and simple operation. It is the smallest one in the German sigma brand. The miniature centrifuge is popular among researchers. At present, the centrifuge has been discontinued, and the market substitute is sigma1-14. However, there are still a considerable number of centrifuges in our laboratory. In the practice of repairing this centrifuge, the author has accumulated a certain degree of its structural principle and troubleshooting, and shares it with his colleagues here.

1 Structural principle

As shown in Figure 1, the working principle of the centrifuge is as follows: After closing the door, the two micro-switches are closed, and the 220V AC voltage is rectified and filtered to form a 310V DC voltage U+. At the same time, the CPU control module is powered on, and the “Cover” indicator next to the “Open” button is illuminated. Press the “Start/Stop” button to start, the “Cover” indicator is off, and the “Run” indicator next to “Start/Stop” is flashing. The centrifuge motor starts to rotate under the control of the CPU module through the drive of the inverter module. At the same time, the speed sensor feedbacks the speed signal, and the CPU module outputs a suitable control signal by comparing the set speed and the measured speed to stabilize the motor speed at the set speed.

When the centrifugal time is up, or the "Start/Stop" button is pressed, the motor starts to decelerate. If the energy fed back by the motor during deceleration causes the DC voltage U+ to exceed a certain value, the comparator output of the brake circuit outputs a control signal to the FET. Turned on, the excessive DC voltage is released on the braking resistor, thus protecting the inverter circuit [1]. When the motor is completely stopped, the “Run” indicator is off and the “Cover” indicator is on. At this time, press the “Open” button to open the solenoid valve and open the door. At the same time, the two micro switches are turned on and the power of the whole machine is turned off. .

If the current is too large during motor operation, the voltage on the current sampling resistor will rise. After the voltage rises to a certain value, the overcurrent protection circuit works, and the signal is fed back to the CPU module. The CPU module stops outputting the control signal to the inverter circuit. Thereby effectively protecting the circuit.

2 failure example one

2.1 Failure phenomenon

After turning on the power, close the door, the “Cover” indicator lights up, press the “Open” button, the indicator light goes out and lights up again, and the open cover solenoid valve does not move. But the motor can start and stop normally.

Figure 1 Schematic diagram of the control principle of sigma1-13 centrifuge

2.2 Troubleshooting

Checking the circuit is to damage the FET IRF 830 that controls the solenoid valve. The cause is most likely caused by abnormal current surge. As shown in Figure 2, after replacing the new FET IRF830, the fault is solved.

Figure 2 Schematic diagram of the open cover solenoid valve control circuit

3 failure example two

3.1 Failure phenomenon

The opening function is normal. After pressing the “Start/Stop” button, the motor speed is very slow and cannot be normally operated according to the set speed.

turn.

3.2 Fault Finding

Such faults are mostly faults in the speed measuring circuit [2].

As shown in Fig. 3, the speed sensor UGN3177 is a latch type Hall integrated circuit. When the motor rotates, the "N" and "S" poles of the magnetic ring alternately approach the Hall sensor, and the "OUTPUT" terminal outputs a pulse signal with a frequency and The motor speed is proportional [3]. Since the sensor is located directly below the motor, it is easy to corrode the sensor and its leads when liquid leaks into the centrifuge. As a result, the CPU module cannot measure the motor speed and the motor cannot operate normally.

Replace the new UGN3177 and solve the problem.

3.3 Troubleshooting

After the centrifuge is used, remove the rotor and clean up the debris and liquid in the cavity. Otherwise, the debris will fall into the lower part of the motor and easily corrode the motor and the speed sensor [4]. When the author repairs, the speed sensor and the terminal are sealed with silica gel to prevent leakage corrosion.

Figure 3 Schematic sensor and its lead diagram

4 failure example three

4.1 Fault phenomenon

Turn on the phone, there is a sparking sound inside, and it smells burnt.

4.2 Fault Finding

When the chassis was opened, it was found that a screw with a fixed door lock fell between the FETs of the inverter circuit on the circuit board, causing two of the six FETs IRF830 to be damaged.

Replace the same type of FET, measure the board, and found no obvious damage to the components.

Turn the phone back on, close the door, the “Cover” indicator lights up, press the “Open” button, the indicator light goes out and lights up, but the open cover solenoid valve does not move. The motor cannot be started by pressing the "Start/Stop" button.

4.3 Failure Analysis

First, find out why the open-cover solenoid valve cannot operate. Refer to Figure 2 to measure two optocouplers SFH6106-3.

Both the FET and the IRF 830 are normal. Turn on the power, online measurement found that the test point voltage of the +15V power supply is 0. Looking at the board, the circuit that generates the +15V power supply is shown in Figure 4 and Figure 5. The resistance between +15V and signal ground was measured and found to be a short circuit.

This +15V power supply mainly supplies power to the comparator LM393 of the brake circuit and the drive part of the inverter circuit. It is highly probable that when the inverter circuit is damaged, it will cause a breakdown of the voltage regulator chip TL431C or LM393.

Figure 4 +15V power circuit schematic

Using the troubleshooting method one by one, the TL431C is soldered first, and the resistance between the +15V and the signal ground is still short-circuited. Then the LM393 is soldered, and the short-circuit state on the measuring board disappears. Measuring the resistance between pins 4 and 8 of LM393 is a short circuit, indicating that the chip has been broken down. Re-solder the TL431C, turn it on again, measure the +15V power output normally, press the "Open" button, the solenoid valve will act, the cover will open, and the "Cover" indicator will be off. This proves that the original TL431C is not damaged.

Replace the new LM393, close the door again, press the “Start/Stop” button, the “Cover” indicator will be off, the “Run” indicator will not light, the motor will not start, and after a few seconds, the “Cover” indicator will light. Analysis, the CPU module is likely to receive some kind of information, is in a protected state.

Looking at the circuit, the CPU module and the inverter circuit transmit signals through seven optocouplers SFH6345. Among them, six SFH6345 are used to drive the inverter circuit, and one is used to transmit the overvoltage and overcurrent protection signals.

Figure 5 Schematic diagram of overvoltage and overcurrent protection circuits

As shown in Figure 5, the working principle of the overvoltage protection circuit is: when the DC voltage U+ exceeds a certain value, the 7-pin of the comparator LM393 outputs a high level, and the FET IRF830 is turned on, and the excessive voltage is released through the braking resistor. . At this time, the output of pin 1 is still low, the photocoupler SFH6345 is turned on, and the CPU module does not need over-voltage protection. If the brake circuit fails, the voltage U+ rises again, causing the LM393's 1 pin output to be high, then the SFH6345 is turned off, the CPU module receives the signal, and interrupts the output of the signal to the inverter circuit, thereby protecting the inverter circuit.

The working principle of the overcurrent protection circuit is: when the current flowing through the motor exceeds a certain limit, the voltage across the current sampling resistor R68 rises, causing the transistor V23 to be turned on, thereby turning off the SFH6345, and the CPU module starts overcurrent protection.

4.4 Troubleshooting

In the standby state, the on-line measurement of the LM393 pin 1 voltage is 0, the optocoupler should be turned on, but the voltage of pins 5 and 6 of the SFH6345 is measured to be 5V, indicating that the optocoupler may be damaged. After replacing the new SFH6345, the test machine, the motor starts normally, and all functions are normal.

4.5 Troubleshooting

This failure caused only a series of component damage due to the drop of a small screw. Therefore, when designing products, instrument manufacturers should avoid designing frequently moving parts on the top of the board as much as possible. Otherwise, it is easy to cause the fasteners to loosen and fall on the circuit board. When space cannot be avoided, consider installing isolation measures such as baffles.

5 Summary experience

(1) At present, there is no circuit schematic in the user manual of the medical research experimental instrument, and even the structural principle block diagram is not available. Factory maintenance generally uses the method of directly replacing the circuit board, which is expensive. In particular, after some imported instruments are discontinued, the supply of repair parts is interrupted. After the failure, it can only be scrapped and wasted limited research funding. In the previous maintenance, the author pays attention to the continuous accumulation of circuit schematics and other data, gradually understands the circuit working principle of the instrument, and adopts the "component-level maintenance" method to let the experimental instruments "return to life", effectively ensuring the smooth progress of scientific research.

(2) When there are many devices on the instrument circuit board that are damaged, first understand the working principle and control flow of each function module of the circuit board, and use the principle of “easy first and then difficult” and “successful” to eliminate the fault step by step. Finally, the troubleshooting ideas of fault instance 3 are summarized as Figure 6 below for reference.

Figure 6 Fault diagnosis example 3

[references]

[1] Zhang Yanbin. Xiao Sunxue Frequency Conversion [M]. Beijing: China Electric Power Press, 2010: 105-119.

[2] Zhao Xiaoguang. Common troubleshooting and device replacement of eppendorf 5415C centrifuge [J]. Medical and health equipment, 1997, 6: 39-40.

[3] Tan Jiancheng. Motor Control ASIC [M]. Beijing: Mechanical Industry Press, 1997: 355-357.

[4] Chen Hongjun, Zhang Hua. Maintenance and maintenance of medical equipment [J]. Medical and health equipment, 2011, 32 (8): 96-98.

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