Sigma centrifuge operation method, common faults and solutions

The Sigma ultracentrifuge was manufactured by Sigma. It was first used as a laboratory centrifuge after it was introduced in the Chinese market in the 1980s. Because of its good centrifugal performance, it also uses a microcomputer chip for central control and automation. It has a high degree of certain self-diagnosis function and is widely used in the gradient centrifugation process in the biopharmaceutical industry. Ultracentrifuges are mostly products of the 1990s. They have a long service life and the equipment failure rate is increasing year by year. In particular, the speed control system is more complicated, and there are more fault points. More than 80% of centrifuge failures occur in the speed control system.
The speed control system of the ultracentrifuge consists of a speed detection circuit, an overspeed protection circuit, a speed control circuit and a motor drive circuit. The system converts the speed signal obtained by the speed detection circuit into a relatively standard square wave signal through an amplification and modification circuit. The speed signal enters the speed control circuit, and according to the acceleration/deceleration control signal given by the main control board of the microcomputer, the acceleration, deceleration and holding speed are controlled, and the speed control signal is sent to the motor drive circuit, and the drive is controlled by the motor drive circuit to achieve the drive The speed of the motor is controlled to control the speed of the centrifugal rotor, and the speed of the centrifugal rotor is then passed through a speed detecting circuit to form a feedback signal to the speed control system.

Precautions:
1. The body should always be in a horizontal position, the voltage of the external power supply system should be matched, and a good grounding wire is required.
2. Before starting the machine, check whether the rotor is installed securely, and whether there is any foreign matter falling into the machine cavity.
3. The sample should be pre-equilibrated. When using a centrifuge tube, the centrifuge tube and the sample should be balanced at the same time.
4. When the volatile or corrosive liquid is centrifuged, use a centrifuge tube with a cover to ensure that the liquid does not leak, so as not to corrode the machine cavity or cause an accident.
5. Wipe the frozen centrifuge chamber with light action to avoid damage to the temperature sensor inside the chamber.
6. Record the usage status after each operation, and regularly check the performance of the machine.
7. If abnormal phenomena are found during the centrifugation process, the power should be turned off immediately and reported to the relevant technical personnel for inspection.

Method of operation
1. When using a centrifuge, the centrifuge tube and its contents must be precisely balanced on the balance beforehand. The difference in weight should not exceed the range specified in each centrifuge instruction. Each centrifuge has its own rotor. To allow the difference, the singular tube must not be loaded in the rotor. When the rotor is only partially loaded, the tubes must be placed symmetrically in the rotor so that the load is evenly distributed around the rotor.
2. If you are going to centrifuge at a temperature below room temperature. The rotor should be placed in the refrigerator or pre-cooled in the rotor room of the centrifuge before use.
3. During the centrifugation process, it is not allowed to leave at random. The instrument on the centrifuge should be observed at any time for normal operation. If there is abnormal sound, it should be stopped immediately for inspection and timely troubleshooting.
4. When each rotor has its allowable speed and the cumulative limit of use, the manual should be consulted when using the rotor, and it should not be used too fast. Each turn must have a use file to record the accumulated use time. If it exceeds the use limit of the turn, it must be used at the reduced speed.
5. When loading the solution, it should be carried out according to the specific operation instructions of various centrifuges. According to the nature and volume of the liquid to be centrifuged, select the appropriate centrifuge tube. Some centrifuge tubes have no cover, and the liquid should not be packed too much to prevent centrifugation. Pulling out, causing the rotor to be unbalanced, rusted or corroded, and the centrifuge tube of the preparative ultracentrifuge often requires that the liquid must be filled to avoid deformation of the upper portion of the plastic centrifuge tube during centrifugation. After each use, the rotor must be carefully inspected, cleaned and dried in time. The rotor is the key component of the centrifuge that must be protected. When moving, be careful not to collide and avoid causing scars. Apply a layer of glazing protection. Never use a centrifuge tube that is significantly deformed, damaged or aged.

Common malfunctions

1, Sigma centrifuge TACH alarm failure
Fault phenomenon
The centrifuge stops running, and the TACH flashes on the fault display. The TACH alarm is caused by the failure of the speed detection circuit of the centrifuge.
Fault circuit analysis
The main function of the speed detecting circuit is to detect the speed of the centrifugal rotor and the centrifugal shaft. Since the centrifugal rotor speed of the ultracentrifuge is high, in order to ensure the reliability of the speed detection, two pairs of photoelectric pair tubes DL, T1 and D2, T2 are respectively used. A speed loop mounted on the centrifugal shaft and the centrifugal rotor is detected to obtain respective actual speed signals of the centrifugal shaft and the centrifugal rotor. In order to determine whether the speed detection is in a normal state, a photocell detection circuit is added to the circuit, which is mainly used for monitoring the state of the photoelectric pair tube, and supplies 12V working voltage to the phototube through the resistor R1. When the state of the phototube is in a normal state, the resistor R1 The voltage drop on the voltage is low. Once the voltage drop across the photodiode open resistor R1 becomes high, the system has a TACH alarm.
Troubleshooting and processing methods
When troubleshooting the TACH alarm, first measure the voltage across the resistor R1. If the voltage across the resistor R1 is high, first check whether the connector of the photo-electric tube is reliably connected. The two sides of the connector can be cleaned with an electronic cleaner. After repeated insertion and removal, if the fault phenomenon is not eliminated after the reliable connection, the fluorescent tubes D1 and D2 in the tube of the centrifuge photoelectric device are damaged. Since the replacement lamps D1 and D2 are connected in series, any one of the luminous tubes Damage will cause TACH alarm failure, and should be checked one by one.

2, Sigma centrifuge SPEED alarm failure
Fault phenomenon
The centrifuge stops running, the SPEED flashes on the fault display, and the SPEED alarm is caused by the abnormal output of the speed matching circuit of the centrifuge.
Fault circuit analysis
In the normal detection state, the signals obtained by the photosensitive tubes T1 and T2 are square wave signals with a voltage amplitude of about ±1V, and the frequency is about 10 times of the speed of the rotating shaft and the rotor, and the respective signals are amplified by the analog signal amplifiers A1 and A2, respectively. Times, obtain a square wave signal with a voltage amplitude of about ±6V, and modify the signal by a Schmitt trigger composed of an OR circuit to obtain a standard square wave signal, wherein the speed signal obtained by the centrifugal shaft (S/ O TACH) is sent to the speed control and overspeed protection circuit as a speed actual signal (TACH), and is sent to the microcomputer main control board for speed display and speed control. The speed signal obtained by the centrifugal rotor (DISK TACH2) is sent as a speed matching comparison signal to Speed ​​matching circuit. The speed matching between the centrifugal shaft and the rotor is completed by the frequency comparator U2. The frequency of the speed signal of the rotating shaft should always be lower than the frequency of the rotor matching comparison signal. Once the speed of the rotating shaft is higher than the speed matching of the rotor Signal, the system has a SPEED alarm.
Troubleshooting and processing methods
In the case that the speed detection circuit is confirmed to be in good condition, the SPEED alarm fault can generally be determined as a speed matching fault, and the output voltage of the frequency comparator U2 can be detected to confirm, usually due to the signal frequency received by the receiving tubes T1 and T2 of the photoelectric pair tube. Caused by chaos, usually first check whether the speed ring on the centrifugal shaft is smudged. If the speed loop on the centrifugal shaft is dirty, use a cotton ball with 95% alcohol for cleaning and wiping; secondly, check the speed photoelectric pair on the centrifugal shaft. Whether the receiving tube is damaged or not, the performance of the measuring tube of the measuring speed photoelectric tube is lowered, which will cause the output of the clutter signal, causing the output of the speed matching detecting circuit to be abnormal, and generally need to replace the photoelectric pair tube.

3, Sigma centrifuge OVERSPEED alarm failure
Fault phenomenon
The centrifuge stops running, the OVERSPEED flashes on the fault display, and the overspeed alarm fault is caused by the abnormal output of the overspeed detection circuit.
Fault circuit analysis
The overspeed alarm circuit generates a standard signal with a frequency of 15.5 kHz from the UI, and compares it with the speed signal of the centrifugal rotor through the frequency comparator U3. If the speed signal of the centrifugal rotor is equal to or higher than the frequency of the overspeed comparison signal, the frequency comparator The low potential signal will be output and the system will overspeed alarm.
Troubleshooting and processing methods
First check whether the speed ring on the centrifugal rotor is worn. If it is found that there are many scratches on the surface of the speed ring, it needs to be replaced. Secondly, it is necessary to judge the frequency of the speed signal (DISK TACH2) to check whether the receiving tube T2 of the photoelectric pair tube is normal. It can be judged by replacing the new centrifugal rotor photoelectric tube.

Precautions for speed control system troubleshooting
(1) Whether it is SPEED alarm fault or TACH alarm fault, it is often caused by the damage of the speed measuring photoelectric tube. After each replacement of the photoelectric pair tube, although the fault phenomenon disappears, but the fault handling is still not completed, it should be replaced. The photoelectric photoelectrically adjusts the tube, and gently rotates the centrifugal shaft for one week. By adjusting the adjustable resistance CR1 in the speed detecting circuit, the value of each pulse voltage generated by the photoelectric pair tube in one rotation of the rotating shaft is adjusted to 0.9V or more.
(2) In the fault handling of the L-8M ultracentrifuge speed control system, if the speed control board is replaced or the components on the speed control board are replaced, the entire speed detection circuit should be applied after the startup check failure phenomenon is eliminated. For simple calibration, the standard square wave signal of 7.75 kHz is cut by the manual button to the output of the speed detection circuit. At this time, the speed display should display 7750 rpm, otherwise the speed detection and display circuit needs further inspection.

Sigma Centrifuge Fault Analysis and Troubleshooting <br> According to the maintenance manual. The "E29" code is interpreted as the Motor doesn't turn the motor not working), and the "E40" code explains the Acceleration of the unit is too slow. This machine has been in use for more than 3 years and has not been internally dusted. First of all, the cause of the failure may be that there is too much dust on the motherboard. Causes the machine to overheat protection. Unpack the machine casing, start the test after dust removal, and work normally. In order to confirm whether the fault is actually discharged, carry out continuous test. The same failure occurred after 20 minutes. Because the two codes accompanying the fault phenomenon are related to the rotation of the motor, the motor's rotary drive part is analyzed according to the circuit diagram (see Figure 1): the drive signal is controlled by the optocoupler to drive the switch. Invert the +325 V DC to AC to drive the motor to rotate. After careful measurement, it was found that the voltage drop on the left side of R51 was 12V in the event of a fault, while the right side was still 20V.
After analysis, the fault may be caused by the breakdown of the optocoupler or the drive tube, which causes the voltage to drop because the component is broken through the short circuit and causes the temperature t to rise. Test the temperature of the optocoupler and drive tube by hand. 1 optocoupler temperature is normal. The temperature of the switch tube is relatively high. Suspected that it was broken down. Replace 6 drive tubes! The fault still exists, indicating that the drive tube itself is not! problem. Rs is a chip resistor. The circuit diagram shows that the resistance is 4.7 ohms but the actual measurement is 40.3 Q. In Rs, a 5.1 n resistor is connected in parallel, and the test machine works again normally, and the fault is completely eliminated.

4, Sigma centrifuge fault repair summary <br> The cause of the voltage drop is mostly due to the breakdown of components, the voltage drop caused by the resistance value change is relatively rare. In the future maintenance work. Must consider many factors and comprehensive analysis. This will quickly troubleshoot.
The working principle of the eppendorf centrifuge. After closing the door, the two micro switches are closed, and the 220 V AC voltage is rectified and filtered to form a 310 V 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 feedback speed signal. 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 centrifugation time is up, or the “Stat/Stop” button is pressed, the motor starts to decelerate. If the energy fed back by the motor during deceleration causes U+ to exceed a certain value, the comparator output control signal of the brake circuit turns the FET on. The excessive DC voltage is released on the braking resistor to protect the inverter circuit. 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.