Some Problems About Belt Weigher

1、 Modular belt scale module type

Belt scale is actually a single roller belt weighing device. Because of the application of single-point sensor, it can be used to improve the accuracy of weighing display, so that the roller can be directly loaded on the weighing sensor. Now the precision of the fine display can reach 0.1 μ V/d, 0.4 in general μ The v/d display has become a very common technical index. In this way, the former single roller belt weighing device can be avoided to balance the balance mechanism of the weighing bracket. Because the current modular belt weigher obviously reduces the weight of the carrier, effectively improves the range of the sensor, and uses the single point sensor, improves the anti bias load capacity. Multiple modules are used in series, which can greatly improve the accuracy

2、 A new method of online range calibration of belt scale

Inspired by the measurement method of "multi-point signal average", a method of online range calibration of belt scale is proposed. Whether the belt scale can work normally is a practical problem that every user is very concerned about. In order to judge whether the belt scale works normally, it is recommended that users measure and record the zero point of the belt scale before using the belt scale every time or every day according to the requirements of the verification regulations. Judge the belt tension, roller and support operation of the belt scale according to the change of zero point, and confirm whether the belt weighing device and belt conveyor are working normally. For the change of belt scale range, it is checked by hanging code, chain code and physical verification. As we all know, physical verification is the only method to evaluate the accuracy of belt scale, but it takes time and effort, especially for belt scale with large range. However, the verification of hanging code and chain code is convenient, but there are some problems. For example, there are no materials on the belt scale during chain code verification. Although the hanging code can be checked when there is material running, the accuracy of range verification will be significantly affected due to the influence of material heterogeneity. In the condition of material operation, the method of using hanging code can reduce the influence of material heterogeneity to the minimum, so as to improve the accuracy of online calibration range. The method of online verification proposed by the author is very simple. When the belt scale carries the material for weighing, in order to check the range and wait for a period, add a hanging code to the belt scale carrier. After repeated measurement, add the signal with hanging code and no hanging code, and subtract the two signals on average, then the net weight result with hanging code can be obtained.

The verification principle is as follows: m is the mass of the material of belt scale, M is the quality of hanging code, and the total time of verification is NT. That is, in each cycle, the measurement with hanging code and the measurement without hanging code account for half of the cycle T / 2. N samples were taken in t / 2 cycle. During this period, the cumulative signals of both states are:

e1=n Σ i=1M+m)( T2n ·i) e2=n Σ j=1m( T2n ·j)

The total calibration time is nt, which means that N cycles of signals are accumulated. That is e1=n Σ e1=N Σ n Σ i=1(M+mi)( T2n ·i)E2=n Σ e2=N Σ n Σ j=1mj( T2n ·j)

The two signals are subtracted, because the material on the belt scale is basically constant during calibration. Therefore: n Σ n Σ i=1mi( T2n ·i)=N Σ n Σ j=1mj( T2n ·j)

So the result after subtraction, the average value is the quality value of the hang code.

1n · n (E1-E2) =m this method can not only check the range of belt scale online. Because it is sampling and verification in a long period of time, it can be independent of belt effect. The mutual correlation function between the two signals can also be calculated according to the measured values of the two signals to check the confidence of the verification.

3、 Physical verification device of 0.2 belt scale

As we all know, physical verification is the only method of verifying belt scale internationally. Therefore, when considering the accuracy of 0.2 into the new belt scale standard, there should be a basic concept of quantity for the accuracy of the physical verification device of the 0.2 belt scale. For the belt scale of grade 0.2, the accuracy of the first calibration is 0.1%, that is, one thousandth. According to the principle of error distribution, the accuracy of the material used to verify the belt scale should be three times higher, that is, ten thousand (0.03%). By analogy, the accuracy of the physical verification device should be one in ten thousand (0.01%). Taking the physical verification with 30t as the maximum range as an example, the accuracy of the material used for verification should be controlled within 9kg. According to the measurement requirements of OIML R76 non automatic weighing instrument. The scale or other calibration scale has a graduation number of n = 6000 or more. This has more strict requirements for the display and sensor used in the scale. In the actual operation of verification, the leakage of materials should also be strictly controlled, especially for the verification of a large number of belt scales. The truck scale or track scale is used as the "standard weighing instrument" of physical weighing. The control of material accuracy directly affects the result of verification. On the other hand, it is very time-consuming and expensive to carry out an experimental verification of a large number of belt scales. It is generally several years before a physical verification is considered abroad. In daily life, the belt scale is checked by zero point and hanging code to judge whether the belt scale works normally. By the way, it is not worth recommending to test the chain code for a large scale.

4、 "Durability" of conveyor belt scale

"Durability" and "reliability" should belong to the same concept, that is, to give a period of time for the equipment used to guarantee the specified technical indexes and requirements under normal use conditions. For non automatic weighing devices. OIML R76 international proposal is determined by continuous loading experiments on the weighing apparatus. However, such regulations will cause great difficulties for large scale, large scale, automatic weighing instrument and dynamic weighing instrument in practice, so that it is impossible to estimate the "durability" of the device by such intuitive experimental method. For example, dynamic track scale and dynamic vehicle scale, because their measurement results are directly related to the dynamic track scale or dynamic vehicle scale lead rail or approach road, the change of weighing instrument itself or the change of approach rail and road surface after long-term use may cause inaccurate measurement. This shows that the "durability" or "reliability" of such a type of weighing apparatus is not only related to the factors of the weighing apparatus itself, but also to its measuring conditions. For this purpose, it is stipulated that the results of the verification of the track scale (including zero point and range adjustment) shall not exceed the error in the use of the track scale within three months or half a year after the initial verification. As far as the belt scale is concerned, the belt conveyor has more significant influence on the measurement results of the belt scale than the track scale. Some manufacturers of belt weighers not only have specific requirements for the adjustment of belt conveyor, but also require that at least two idler at both ends of belt weighing device be changed into the idler made by the manufacturer. In addition, many foreign leather scale manufacturers will guarantee to the users that the belt scale provided by it is in /5700 Ω＝ 0.5088% is close to 0.5714% of the original value, which has a greater impact on sensor output.

5、 The relationship between adjustment quantity and influence quantity

The adjustment of any angle potentiometer in parallel junction box will affect the change of output impedance of other angle sensors in the same direction, that is, the interaction between sensors will cause the change of indication value. The difference displayed on the scale display = adjustment amount + total influence amount = [1 + K (n-1) / n] · adjustment amount, in which the total influence amount = [k (n-1) / n] · adjustment amount, average influence amount = [k/ (n-1)) × Adjustment amount (where n is the number of sensors, K is the quality factor K ≤ 1 of the output circuit). In the process of off load debugging of actual weighing group, the influence amount is not distributed on average, mainly because the force component of the scale table has a great influence in the near place and little in the distance. The center of gravity of the weight is different, and the actual force value of the four sensors at the end is quite different from that of the central sensor. The accuracy of digital angular error correction is not ideal when the sensor is under uneven force. The above suggestions for the improvement of parallel junction box are only small improvements based on the original circuit, only the innovation on the circuit can solve the problem fundamentally. It is feasible to replace the digital junction box and digital instrument, but it has the disadvantages of high cost and too delicate, which is not convenient to popularize.

6、 New product introduction

The most prominent feature of the patent product of "multi-purpose analog junction box" verified by a large number of practice is that adjusting any angle does not affect other corners, basically, the error of unbalanced load of the balancer can be adjusted quickly after the debugging and rechecking; The detection element is not only used for the leveling of sensors, but also for the convenience of detecting the output values of each sensor. With specific values, it can guide the installation and maintenance; The traditional analog scale signal is not discernible and the sensors interact with each other, which makes it difficult to debug and trouble check, and makes the analog scale technology mature. The maintenance version can adapt to sensor sensitivity over tolerance ± The angle difference of 20% is adjusted, and the influence of any angle on other angles is very small. The new junction box has the characteristics of quick debugging, guiding installation, convenient maintenance and stable weighing accuracy, and its cost is only increased by several decades. The analog scale with patent new junction box can be compared with the digital automobile scale, and it is also the end of monopoly market share for some manufacturers by changing sensor sensitivity. Patent simple junction box is designed and manufactured with some patented technology. The main feature is to solve the influence of the adjustment loop on the output zero point. The adjustment is linear and even, and its value can be measured directly, and the adjustment amount is 6%. Compared with the traditional parallel junction box, the stability of the junction box is increased by 2-3 times; The sensitivity to temperature and humidity is one order of magnitude; The total amount of adjusting any angle affecting other angles is reduced by about 1.8 times; The manufacturing cost is equal, which is a kind of transition product with complementary patent new junction box. It is believed that in a short time, the patent (simple) new junction box will replace the existing parallel (serial) junction box with excellent quality and high cost performance, which has a very good application prospect. The error of re verification shall not exceed the specified error in the use of belt scale under the condition that zero point and range are no longer adjusted in half a year or one year after the initial inspection. I think this is also a specific and operational requirement for "durability" or "reliability" of belt scale.

7、 Adjustment and deflection of belt scale

When the belt scale is installed, the adjustment of belt conveyor is a necessary work for the manufacturer of belt scale. As everyone knows, the excessive run out and deflection of belt will have a significant impact on the measurement results. However, according to the author's observation, many belt scale manufacturers seldom pay attention to the belt scale load-bearing device, whether there is excessive deviation error after installation, and the attention to the lateral limit of the belt scale is not enough. In fact, both of these will have a great impact on the measurement accuracy of belt scale.

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