1、 Wrong choice

With the development of technology, there are more and more kinds of X-ray fluorescence analyzers, and the trade names are also confused. In addition, the user's limited understanding of relevant knowledge makes it more difficult for the user to choose the instrument reasonably.

Mistake 1: emphasize "fluorescence", many users mistakenly believe that only the tube excitation instrument using X-ray tube as the excitation source is the X-ray instrument, and emphasizes the so-called "fluorescence" blindly. In fact, as mentioned above, whether X-ray tube or radioisotope source is used as the excitation source, as long as the instrument excited by X-ray and the fluorescence X-ray from the measured sample to obtain its chemical composition and content is an X-ray analyzer.

Source excitation and tube excitation have their own advantages and disadvantages. The source excitation type instrument is simple and compact in structure, especially the X-ray emission from radioisotope source is a natural phenomenon, and its intensity is very stable. Although there is natural attenuation, this attenuation is in accordance with the descriptive physical law, that is, we can calculate it accurately, and the half-life of the isotope source selected as a commercial instrument is relatively long, which can hardly be reflected in a short period. The biggest weakness of the source is that it emits small X-ray intensity and the energy distribution is not adjustable. Therefore, the types of analyzable elements are limited, the geometric arrangement of optical path must be very compact, the analysis time is longer, and the spectral line processing and quantitative analysis calculation are difficult.

The source of excitation of tube excited instrument is X-ray tube. Compared with radioisotope source, the biggest advantage is its adjustability. By adjusting the flow and high pressure, the intensity and distribution of X-ray can be changed in a certain range, and the excitation efficiency of certain elements can be increased or reduced selectively, and the analytical ability can be improved. Moreover, the output intensity of X-ray tube is much higher than that of radioisotope source, and the geometric arrangement of optical path is limited. Collimator, filter, slit and so on can be used to further improve the performance. The biggest problem of X-ray tube is stability. The stability of high voltage power supply for X-ray tube must be less than three thousandths. The X-ray tube itself needs cooling. Besides, the factors such as ambient temperature and power grid fluctuation will affect the stability of X-ray output of X-ray tube, thus affecting the stability of the instrument. Therefore, generally speaking, the requirements of the tube excitation instrument for the environment and peripheral conditions are much higher than that of the source excitation instrument.

Mistake 2: emphasis on hardware and software and technology. The successful application of any kind of analytical instrument in a certain field is the result of the combination of hardware, software and analysis technology, which is indispensable. There is no doubt that hardware is the foundation, but hardware doesn't make any decision. From the application point of view, hardware can only play its role through software, and the analysis technology involves every link of instrument application. A good instrument must be based on the research of analytical technology. Otherwise, it will be difficult to meet the needs of many users. Such an instrument is equivalent to no soul. For the software inspection, we must not stay on the surface articles such as the beautiful picture or not, whether the pattern is complete or not. The key is whether the algorithm adopted is advanced and effective, and on the basis of what analysis technology, whether it is suitable for the characteristics of the main samples being analyzed, and whether it is suitable for the quality and ability of the operator.

Mistake 3: pay more attention to price than service. Price is certainly an important factor in the purchase of goods, but it should not be the decisive factor. The quality and price of each component of the analytical instrument are very different, and directly determine the price of the instrument. It is difficult to guarantee the quality simply in pursuit of low price. For devices like X-ray analyzer, service is often more important. The service mentioned here refers not only to installation and commissioning, spare parts supply, maintenance service, etc., but also to application technology service. For most users, it is not necessary to study and analyze technology and guide application. In this case, technical service is very important.

Error 4: listen to others, see less. Users often carry out some research and investigation when selecting equipment. On the one hand, they understand the basic situation of some instruments and manufacturers and make some comparisons with each other; On the other hand, they will go to some users who are similar to their own situation to investigate. That is, of course, necessary. But the most important thing is to choose according to their actual situation and specific needs. For example, the main purpose of the whole plant quality control is that there are many kinds of samples, which need to be fully analyzed, with high accuracy requirements and good application environment. X-fluorescence spectrometer can be considered; The main purpose of production process control is to consider the multi element analyzer, calcium iron instrument and other source excitation instruments in the case of poor application environment; Raw materials are not good, fluctuate greatly, and there is no pre homogenization measures or very crude. The analysis instruments should be configured higher. It is better to consider online analysis instruments. Online calcium iron instrument plus multi element analyzer or small multi-channel X-ray fluorescence spectrometer is a good combination. Of course, it can be used to activate the on-line analyzer with neutron activation if possible, and the raw material is stable and pre homogenized is very effective, The configuration of the analyzer can be lower, and the multi element analyzer and even the off-line calcium iron meter can solve the problem; The operators have high quality, and the instrument can choose small multi-channel X-ray fluorescence spectrometer with various functions and greater flexibility. Otherwise, the source excitation instruments with single function and simple operation should be considered.

2、 Technical index error

The technical indexes of evaluating the quality of an instrument are multiple and comprehensive. The user mainly cares about and values the range of analysis elements, that is, what we usually call the analyzable elements, the length of analysis time, and the accuracy. The importance of technical indicators ultimately depends on the purpose of application.

Mistake 1: one-sided pursuit of high indicators. For industrial analysis, the type of sample analyzed is determined, even single, and the requirements for the results are also determined. The pursuit of indicators far above these requirements is actually a waste of resources. For example, most cement plants only do calcium and iron control, and calcium, iron, silicon and aluminum are required for rate control. In the whole analysis, Na, Mg, s, K and other elements are required. A few thousand yuan calcium iron meter can meet the control requirements. If we pursue the ability to measure silicon and aluminum, it needs a multi-element analyzer of about 100000 yuan, The multi-element analyzer can meet the requirements of rate control four main element analysis. If we must put forward the requirements of higher precision and speed, we need a small multi-channel X-ray spectrometer with about million yuan. Because of the certainty of the sample being analyzed, empirical coefficient method is the most effective method. If we must pursue the method without standard sample, it will not achieve the effect of empirical coefficient method. The elements tested are determined and the quantity is limited. The fixed path can solve the problem. In pursuit of variable path, it not only costs more money, but also sacrifices stability and analysis time; For the instrument of quantifiable dispersion, the ADC channel number is not more and better.

Mistake 2: one sided pursuit of accuracy: when it comes to instrument performance, it is often natural to take the accuracy of the results as the first judgment standard, and in daily application, a lot of energy will be used to judge the "accuracy" of the instrument. The most common is to "correct the results" with chemical analysis. Accuracy is important, but as an industrial analysis, precision must not be ignored. First, the precision problem should be paid attention to. That is, the results of multiple measurements of the same sample should be consistent with each other. The difference between each measurement result and the mean value should be small enough. As for the difference between the measured value and the true value, it is often a systematic deviation and can be corrected mathematically.

Mistake 3: we don't pay attention to stability and reproducibility. The so-called stability refers to the standard deviation of the same sample measured continuously for many times (usually 21 times), while the reproducibility is the consistency between the results measured again after a long interval of the same sample. These two indexes are the key indexes of industrial analysis instruments. The results of industrial analysis are mainly used for the control and parameter adjustment of production process. The relative changes of the analysis results directly relate to process control and adjustment. The accurate measurement of relative change is based on stability and repeatability.

Error 4: the shorter the analysis time is, the better. X-ray measurement is a statistical measurement of random events, which is determined by statistical rules. The absolute quantity of count depends on the measurement time and directly determines the measurement error. Long enough measurement time is the precondition of measurement accuracy. In order to ensure the measurement accuracy, enough measurement time must be available.

3、 Analyze the technical mistakes

Analysis technology is the guarantee of obtaining the correct results. The analysis technology runs through the whole process of instrument application. The choice of analytical method must meet the needs of instrument application.

Mistake 1: preparation of standard sample is too troublesome, it is better to use the method of non standard sample. In fact, X-ray fluorescence analysis is a comparative analysis, especially empirical coefficient method. The correspondence between the measured X-ray intensity and the concentration of corresponding elements is completely based on the standard sample. Enough standard samples must be prepared. The quality of the standard sample determines the reliability of the analysis results directly. The basic parameter method and other non-standard sample analysis methods are generally used for the preliminary analysis of completely unknown samples. So-called nonstandard samples only need no series of standard samples.

Myth 2: standard samples can be purchased by others. Since the raw material and proportion of each user are different, the more similar the standard sample is to the unknown sample, the better the determination result is for the X-fluorescence analysis. Therefore, in order to obtain good analysis results, each user should prepare the standard sample by himself. Several problems should be paid attention to in the configuration of standard sample:

(1) It must be mainly prepared with raw materials for production, and a small amount of chemical reagents can be used for some components;

(2) The number of standard samples shall be greater than the number of elements to be analyzed (at least two more);

(3) The content range of the elements measured in the standard sample should cover the concentration range of the corresponding elements in the unknown sample completely;

(4) There should be no correlation between the concentrations of each element in the standard sample.

Error 3: evaluation of working curve. Generally, the quantitative evaluation standard of working curve is mainly related coefficient and standard deviation. Mathematically, the closer the correlation coefficient is to 1, the smaller the standard deviation is, the better. But it is necessary to check whether it is in accordance with the physical significance and whether the slope size is appropriate.

Error 4: the more the factors affecting the elements in matrix correction are set, the better. If the influence factors are selected without considering the physical meaning, the correctness and reliability of unknown sample analysis cannot be guaranteed. The setting of influencing factors should follow the principle of adjacent elements, main elements, elements with large concentration range and heavy elements. On this basis, the design should be conducted according to experience.

Some suggestions

（1） The selection of instruments must adapt to the actual situation of the enterprise, and select the instruments according to the expected main use and the raw materials, processes and personnel quality of the enterprise;

（2） The best instrument also depends on human use, and the important role of analytical technology in the application of the instrument should be paid full attention;

（3） On line analysis: in recent years, the success of neutron activation online analysis has made online analysis a highlight of cement industry analysis. Its outstanding feature is the realization of feedforward control and organic combination with production process. As a simple and practical domestic online analysis system, the combination of on-line calcium iron analyzer and multi element analyzer or small multi-channel X-ray fluorescence spectrometer is also a good choice. Online analysis has been paid attention by the technical personnel in the cement industry, and will occupy a more important position in the process control of cement production.

(from the network, invasion and deletion)