AMMY-1000B Scanning Electron Microscope Vacuum System Analysis and Maintenance Kong Mingguang (Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031) This article systematically analyzes the principle of AMRAY-1000B scanning electron microscope vacuum system, and gives maintenance examples.
The products of the 1980s are stable and reliable. In 1985, our company purchased the AM-RAY-1000B scanning electron microscope imported from the scientific instrument factory of the Chinese Academy of Sciences. The equipment plays an important role in our research work. However, due to the extended service of the instrument, the vacuum system is prone to various degrees of failure. This article analyzes the instrument's vacuum system and gives maintenance examples.
1 Vacuum system The vacuum system that makes up the AMRAY-1000B Scanning Electron Microscopy includes suction equipment, vacuum measurement devices, and various valves and valve control systems.
Gas extraction equipment generally includes mechanical pumps, diffusion pumps, and ion pumps.
2 The working principle of the vacuum system (see).
AMRAY-1000B vacuum system diagram The working process of the vacuum system: Open the cooling water, when the air compressor reaches 4 bar, turn on the vacuum power (VAC.POWER) to open the mechanical pump, press the ready state (STAND.BY) at this time the mechanical pump A section of the pipeline from the head of V2 and V3 to the outlet of the mechanical pump is evacuated. When pumping to a certain extent, TC1 provides a signal to the control system to enable V2 to open, and the mechanical pump evacuates the preceding stage, when pumped to meet the conditions of the diffusion pump opening. At that time, the TC2 signal to the control system, the diffusion pump electric furnace heating, then maintain 20 ~ 30min, so that the diffusion pump fully heated to enter the working state.
After the diffusion pump enters the working state, the prepared state (STAND.BY) V2 is turned off, and V3 is turned on. The mechanical pump evacuates the sample chamber. When the pumping reaches the requirement, TC4 provides a control signal. At this time, V3 and V4 are turned off for several seconds. After that, V4, V5, V2 are turned on at the same time, and the diffusion pump draws high vacuum across the entire system.
3 vacuum control AMRAY-1000B scanning electron microscope vacuum control manual and automatic two ways.
(1) Manual control The manual control is to use a manual switch to control the pull-in of the relay, and the action of the relay contact controls the AC voltage sent to the solenoid valve. (2) Automatic control When an automatic program is used to replace all the manual switches, the vacuum control is changed from manual to automatic. It is mainly composed of thermocouple amplifier circuit, 3s delay line and valve control circuit.
4 vacuum system maintenance vacuum system failure is generally two kinds: First, the system leaks, and second, control failure.
(1) Vacuum leak detection When the lens barrel low vacuum does not meet the requirements, there are generally two cases, one is that the vacuum system does not maintain a vacuum state for a long time or the room humidity is too high, this situation can increase the vacuum time Another solution is that there is a leak in the vacuum system, which requires careful inspection to find out the cause of the leak and resolve it.
The basic method of low vacuum leak detection is to use a combination of flexible observation and progressive leak detection. For the general air leakage, first check the moved or disassembled parts. The part that often moves should also attract attention. For example, the various handles of the sample table, the manual isolation valve V1 is often in an active state, and it is easy to leak. When all are ineffective, the vacuum system can be checked step by step using manual operations. It is also possible to use the structure and working principle of the vacuum system to determine the part of the leak. For example, when the vacuum indicates normal when the filament is changed, when the mechanical pump re-pumps the sample chamber, the vacuum gauge pipe indication rises very slowly, and it takes about 1Cmn or more for the V4 to open. When the V4 is turned on, the vacuum The pipe indicator on the watch rises quickly. Then it can be judged that the V1 is not closed tightly. After removing the VU and washing it with a new seal, it returns to normal.
When there is a leak in the vacuum system, it will affect the normal operation of the automatic control, so the first inspection to determine whether the vacuum leak or automatic program failure.
(2) Control part inspection When the system does not leak, and the automatic program can not be normal operation, first turn into manual control, check the valve with manual switch action, if the valve is not open automatically, and can be opened manually, indicating the control The execution part is normal and the fault is in the automatic control part. If the valve cannot be opened manually, you should first check whether the relay is operating, whether AC 110V is sent to the valve coil, whether the valve coil is burned, and so on.
5 Vacuum System Maintenance Example 5.1 Phenomenon In the preparation state, the front stage and the pipeline vacuum indication are normal, and the ready state is turned off. When the mechanical pumping sample chamber is in operation, the pipeline vacuum indication is lowered to a very low value, and the gauge is not moved for a long time.
Analysis and processing According to the phenomenon can be judged V5, V3 and the former normal, one by one to turn the handle of the sample stage, observe the vacuum table pipe to indicate whether the reaction, so you can check the handle for air leakage, such as the needle does not respond, indicating the handle does not leak. When the large rubber band of the sample stage and the sealing surface of the sample chamber were inspected, it was found that there were fiber hairs on the rubber band, and after cleaning, the trouble was eliminated.
5.2 Phenomenon When the sample chamber venting switch is pressed, V4, V5 are off, V2 is on but V6 is not on and cannot be vented.
Analysis and treatment First of all, change to manual deflation, first open the V2 valve, and then open the V6 valve, the result is normal, indicating that the automatic control part is faulty. After power off, check the transistor Q12 on the PC board and find that it is damaged. After the replacement, troubleshoot. Example 3 Phenomenon: Start the mechanical pump, turn on the vacuum power supply, pump for a long time, the pipeline vacuum has no indication, and the sound of the mechanical pump is normal.
Analysis and Processing First, open the V2 valve manually to see if the fore-stage vacuum indication is normal. As a result, the fore-stage vacuum indication is also not normal. Since the possibility of simultaneous damage of TC1 and TC2 is very small, it can be considered that the thermo-regulator TC1 has no problem. At this time, it is necessary to check if the solenoid valve on the mechanical pump is turned on. As a result, it was found that the rectifier diode at the end of the valve was burned out and replaced with a new one, and the fault was eliminated.
5.3 Phenomenon Open the mechanical pump and vacuum power supply. The vacuum indication of the pipeline is normal. Press the ready status. V2 light is on, but there is no indication in the fore vacuum and the light of the diffusion pump electric furnace is off.
Analysis and processing The vacuum indication of the pipe is normal and the V2 lamp is on, indicating that the vacuum automatic program is working properly. To use the manual opening V2, you can hear the open sound of the valve, indicating that the thermocouple TC2 or its amplifier may be damaged. Replace thermocouple TC2 troubleshooting.
6 Maintenance of vacuum system (1) When the electron microscope is not working, it is necessary to insist that the inside of the lens barrel is always kept under vacuum. During the operation of the instrument, sufficient attention is paid to the working conditions of the vacuum system. (2) The mechanical pump is preferably cleaned annually and the pump oil replaced once to remove impurities and moisture. (3) Pay attention to the temperature of the cooling water when working with the diffusion pump. When the water temperature is too high, it will affect the pumping speed of the diffusion pump. After a sudden stop of the water, the protection relay on the diffusion pump will jump off. When the electric furnace is cut off, the relay cannot be automatically reset after the relay is opened. When the cooling water is normal and then switched on, use the hand. Press the button in the middle of the relay to reset it.
(Continued from page 62.) Many of the world's top manufacturers of analytical instruments and laboratory equipment are now looking forward to gaining a long recovery by adding product market share or relying on acquisitions after two years of adjustment and reorganization. In late 2003 and early 2004, companies have announced to the outside world the company's specific operating strategy or have been implemented. These moves by companies will inevitably have a direct impact on the 2004 rankings.
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