Frequently asked technical questions about coal petrographic testing instrument microscopy

Frequently asked technical questions about coal petrographic testing instrument microscopy

1. Are Zeiss microscopes really better than Leica microscopes?

The quality of the two is the same, but Zeiss does a good job in publicity, and users have wrong impressions caused by preconceptions. In fact, Leica and Zeiss are both 170-year-old German companies, and both are internationally renowned for their optical microscopes. One is in East Germany (Zeiss) and the other is in West Germany (Leica). The two companies compete on a global scale, so their product sequences all correspond. The correspondence table is as follows:

Correspondence table between West German LEICA and East German ZEISS product series

Note: When evaluating, you must look at the corresponding models to be comparable. For example, you cannot compare Zeiss' low-end LAB model with Leica's mid-to-high-end DM2700P. The two are not of the same grade and are not comparable. The price difference is much different, and the LAB cannot be compared with the DM2700P in terms of functions. Of course, the Zeiss LAB is also much cheaper than the Leica DM2700P.

Similar products include Japanese and domestic microscopes. The overall comparison is as follows:

Comparison of various microscopes that can be used for coal petrographic testing instrument at home and abroad

Conclusion: Currently, the most suitable model for automatic petrographic detection is the Leica DM2700P. The image is clear, the return position is precise, and it can be equipped with a high-precision focus control system.

From the perspective of practical use of coal rock analysis and coke detection:

•Manual coal petrographic detection only requires a clear image of the microscope. Excessive requirements are of no practical significance. From this point of view, even if it is equipped with a domestic microscope, it will not affect observation and detection.

•For automatic detection, on the premise of ensuring a certain degree of clarity, what is more critical is the accuracy of the focus return of the focusing mechanism. Otherwise, the huge result deviation caused by virtual focus misdetection will make the equipment unusable.

•Occasions where continuous operation occurs for a long time, such as: monitoring of incoming raw coal for enterprise production. The microscope lens is required to withstand the high temperature of the halogen lamp and have a long service life.

Therefore, among various microscopes used for coal petrographic detection, especially those used in factory environments where speed is required, the Leica DM2700P is the best choice for two reasons:

1.1 Focus slipping problem:

DM2700P has precise gear return, which is especially suitable for automatic quick return focusing. However, the focusing axis of Zeiss A1.POL is slipping and cannot automatically return accurately. Therefore, Zeiss automatic coal and rock all use digital zoom to approximate accurately. Digital zoom only changes the clarity of the picture through computer algorithms. It is actually detected under defocus conditions, and the resulting reflectivity value will be reduced. Very inaccurate.

1.2 Problems with long-term high temperature life of the lens:

Factories generally conduct continuous inspections for a long time. Due to material problems, the front lens of Zeiss light boxes cannot withstand the heat of the halogen lamp and will crack. As a result, the entire light path is no longer a true parallel light path, and stray light increases significantly.

Of course, to be fair, Zeiss microscopes also have some advantages. For example, the numerical aperture of the 50x oil immersion objective can be 1.0. The field of view of the eyepiece is slightly larger, and the number of holes in the objective lens transfer disk is larger. However, these are basically useless in actual observation of coal, rock and coke, and have no substantial significance. It does not mean that detection cannot be achieved if these parameters are not met. . Moreover, some parameters are counterproductive when they are too large, violating national standards.

2. Is the numerical aperture 1.0 of a 50x oil immersion objective lens better than 0.85?

What effect does numerical aperture have on observation?

2.1 Advantages: As NA increases, resolution will increase.

For example: 50x oil immersion objective:

Zeiss NA1.0, equivalent to a resolution of approximately 0.3μm;

Leica NA0.85, equivalent to a resolution of approximately 0.35μm;

Conclusion: The resolution has been improved by 0.05 microns. In actual observation, it is not necessary to see such a small size. Generally, the smallest coal char component identification size is also above 1 micron. Therefore, it has no substantial significance to the observation and has no impact on the results.

In addition, including the national standard setting unit: Xi'an Coal Research Institute uses an NA0.85 old Leitz microscope. If the NA must be required to be 1.0, can the national standard unit not be able to measure coal char petrography?

2.2 Disadvantages: Problems caused by increasing the numerical aperture.

•Will increase stray light;

•It will reduce the depth of focus, affect the accurate focus, and cause misdetection in automatic detection.

3. Is the number of field of view of the eyepiece required to be 23?

What effect does the number of fields of view have on observation?

Definition: Field number refers to the value expressed in mm of the field aperture diameter of the eyepiece.

Advantages: As the number of fields of view increases, the observable range will become slightly larger.

For example: 10x eyepiece:

Zeiss 10X/23; diameter 23mm

Leica 10X/22, diameter 22mm, equivalent to a slightly smaller field of view 1mm;

4. Does the number of holes of the objective lens converter have to be 6?

In the microscopic observation and inspection of coal and coke, only two lenses are actually enough: one is a 50x oil immersion objective lens; the other is a 20x dry objective lens. Therefore, the extra 4 holes with 6 holes are free and must be blocked to prevent dust from entering and affecting the observation.

The emphasis on this parameter has no real meaning! The Leica DM2700P microscope is equipped with 5 objective lens mounting holes. It is enough to use 2 and spare 3. Even if the number of objective lenses is increased to more than 5 in the future, they can be replaced and used without any impact.

5. Does the number of function turntable holes have to be 6?

In all microscopic observations of coal and coke, only two are actually used: one is a brightfield observation module; one is a polarizing module; therefore, the remaining four are idle, and there is no real meaning in emphasizing this parameter! Although there are only 4 Leica microscopes, 2 used and 2 spares are enough.