About 0.2 level belt scale

About 0.2 level belt scale

[Abstract] The author believes that the international OIML canceled the original belt scale with the highest level of 0.2 and changed it to the highest level of 0.5. The main reason is that

In the inspection of the belt scale, the uncertainty of the material weighing cannot meet the requirements. For the 0.2-level belt scale, the error between the certification and the first verification is 0.1%, which means that the verification error of its materials should be at least 0.03%. At present, the accuracy (ie repeatability) of foreign belt scales has reached 0.1%

Not a few, and the length stability is very good, but it is still set at 0.5 level.

[Keywords] 0.1-level belt scale; control weighing instrument; material verification

In recent years, some domestic belt scale manufacturers have produced better quality belt scales, so it is considered whether the level of the belt scale can be changed back to the earlier OIML R50 regulations, that is, the highest level of the belt scale is 0.2, instead of the current regulations The 0.5 level.

Here I would like to talk about my views on this issue, but I am not going to analyze the error of the belt scale itself. I only offer some views on the verification of the belt scale.

According to the provisions of the maximum allowable error of belt scales, for the 0.2-level belt scale, the maximum allowable error value of the first verification and subsequent verification is required to be 0.1%. The internationally recognized method of belt scale verification/calibration is physical verification. Other verification methods, such as chain codes, cannot be completely reliable because they cannot faithfully reflect the influence of belt tension. It should be particularly pointed out here that the current domestic cyclic code method cannot accurately determine the quality of the unit length ring code and there is no national statutory verification procedure and standard. From the legal point of view, this verification is not strict. For physical verification, in accordance with Article 8.1.6 of the National Metrological Verification Regulations of JJG195-2002 "Continuous Accumulative Automatic Weighing Apparatus (Belt Scale)", "The control method for determining the quality of the test material in the material test (the agreed true value) should be able to meet The measurement error shall not exceed 1/3” of the maximum allowable error corresponding to the first verification of automatic weighing. The maximum allowable error of 5.2.1 mentioned here, for the 0.2-level belt scale, means that the maximum allowable error of the first verification and subsequent verification mentioned above is 0.1%. This requires that the maximum allowable error of the weighing instrument used to weigh the materials used in the belt scale verification shall not exceed 0.03%. Belt scales are weighing instruments used to weigh bulk materials. The belt scales usually used in ports, mines, power plants, and factories have ranges from tons per hour to 1,000 tons per hour, or even 10,000 tons per hour. Verification/calibration of belt scales is often a very time-consuming and laborious project. I have verified a large-range belt scale at Qinhuangdao No. 7 Wharf. The reputation range of the belt scale is 6500t/h, and the range for physical calibration is about 4400t/h. This is a very large project. Because it was to certify its products, seven measurements were taken. Such a large amount of material experiment, even if it is a verification in use, which is only performed once, the workload is considerable. It is necessary to prepare more than ten coal carts and carry out accurate measurement.

Usually three kinds of weighing devices are used to weigh the materials of the belt scale. Track scales, truck scales and check-out special bucket scales. According to the R50 International Recommendation and the JJG195-2002 National Metrological Verification Regulation, the error requirement for the selection of the so-called "control weighing instrument" is that it is recommended to use a non-automatic scale for weighing. According to the actual situation in my country, most of the rail scales that can be used in the field material test are dynamic rail scales, with an accuracy of up to 0.1% (first inspection accuracy); outdoor truck scales have an accuracy level of n=3000 divisions. For scales, although some manufacturers now give higher levels of divisions to truck scales, many foreign counterparts do not accept this precision. Most of the special bucket scales for calibration are built indoors, with the best environmental conditions, and can be used immediately after calibration. The disadvantage of bucket scales is that they are only suitable for small-scale belt scales. The accuracy level of belt scales is expressed in percent error, while non-automatic weighing instruments used as control weighing instruments are expressed in piecewise constant value errors.

This brings problems to the error calculation of the measurement results. For example, the accuracy of the first inspection at n=3000 and n=2500 are both 1.5e, but there is a slight difference when converted to a percentage error. The latter is greater than one thousandth.

In the final field material experiment, the loss of materials and the climate and other factors must also be given great attention in order to obtain reliable results.

Now I analyze the verification data of belt scales in Qinhuangdao, and talk about my views on "0.2-level belt scales".

This belt scale is a vibrating wire belt scale from INFLO, and does not use strain gauge sensors as inspiration components. We tested two belt scales numbered BF4 and BF3, and the data is as follows:

BF4: Zero point (three turns) 323 seconds

0.093t -0.083t -0.027t -0.016t

Before adjustment, the indication value of the track scale (t) The indication value of the belt scale (t) Relative error (%)

                 4417.28 4489.1 1.626

                4254.92 4318.3 1.490

                4185.33 4245.0 1.426

After adjustment 4348.16 4352.2 0.0929

              4310.16 4307.3 -0.0664

       4316.336 4322.7 0.147

BF3: 4484.30t 4483.4t -0.020%

It was a winter night during the test, and the temperature was below zero. The belt scale numbered BF4 was installed not long ago, while the belt scale numbered BF3 was adjusted and used in July and August in the summer of the same year. During our test, it is not allowed to adjust the No. BF3 belt scale. We will directly test without measuring the zero point, in order to observe the influence of temperature. The "control weighing instrument" that measures the actual weight of the material is a British-made rail scale that has been verified by the rail scale measuring station not long ago, and is decoupled to dynamically weigh a single carriage. Such excellent test conditions are rare in China. of.

It can be seen from the above verification data that the repeatability (relative error) and long-term stability of the belt scale are 0.1%, which is credible. It needs to be emphasized again here, according to OIML R50 and JJG195-2002, the requirements for the measurement error of the material test control weighing instrument:

●If the control weighing instrument is calibrated immediately before the material test, its error should not be more than 1/3 of the corresponding maximum allowable error of the belt scale.

●In other cases, the error should not be greater than 1/5 of the corresponding maximum allowable error of the belt scale.

Even if the conditions of a control scale that is rare for weighing test materials like ours in Qinhuangdao, it cannot meet the requirements of OIML R50 and JJG195-2002 on the error of control scales. Strictly speaking, the dynamic rail scale, truck scale and static rail scale are used as control weighing instruments, and the error is not up to the requirement of the weighing accuracy of the test material when the belt scale of class 0.2 is first checked. Even if the indoor special calibration bucket scale can meet the test requirements, it needs to be carefully evaluated before it can be approved.

I discovered this problem before I retired, and felt that it would be difficult to achieve the actual calibration of the 0.2-level belt scale. If the tolerance of the first inspection is changed from 0.5 times the use error to 0.7 times, it is barely possible to operate.

In short, I think it is not necessary and possible to really make a 0.2-level belt scale that can pass the OIML R50 international recommendation. As far as I communicate with foreign colleagues and users, they are more concerned about the long-term stability and reliability of belt scales. Moreover, the long-term stability of foreign belt scales is 0.1%, and the uncertainty is maintained at 0.5% for a long time to be recognized by users. In 1998, I asked the port's weighing instrument management personnel at the port of Amsterdam. It is said that the belt scales they are currently using are generally inspected only once in five years or even ten years. Moreover, the buyer and seller who use the belt scale feel it necessary to ask the measurement department to verify it. In addition to the level 0.2 belt scale, it is extremely difficult to meet the requirements of its material calibration device. Manufacturers who are interested in manufacturing level 0.2 belt scales should also pay attention to that all the measurement and technical requirements for the belt scale simulation test are 1.5 times higher than those of the 0.5 level belt scale. . Finally, the performance of the belt scale equipped with the belt conveyor plays an extremely important role in the final verification, use accuracy and long-term stability of the belt scale. Therefore, it has been said that it is better to use a belt conveyor capable of weighing rather than a weighing machine for conveying materials. I think that the current domestic belt scale manufacturers should focus on how to improve the long-term stability and reliability of the belt scale, rather than one-sided pursuit of accuracy. In fact, only high stability and high reliability can have reliable accuracy. Strictly speaking, without stability and reliability, there is no precision at all. To be honest, who wants to use a measuring device that has one number today and another result tomorrow.

Finally, to submit the proposal to modify the accuracy level of belt scales to OIML for discussion and hope to be passed, not only detailed test results and documents must be provided. It should also be pointed out that whether a new proposal has been approved by everyone is not only a technical issue, but also a matter of the interests of product competition.