The Advantages and Disadvantages of Calibration Method of Electronic Belt Balance

1 Overview

Electronic belt scale as a dynamic continuous measuring instrument, the accuracy of its use in addition to product quality, installation position and installation quality, but also closely related to the periodic verification and test system.The system of reasonable verification and test method and short verification and test period is beneficial to improve the accuracy of the use of electronic belt scales.In the national metrological verification regulation JJG 195-2002, in addition to the material test, as a running inspection device can use weights, hanging code, standard electrical signals to simulate the effect of constant load per unit length, can use the simulated load device (cyclic chain code, chain code, trolley code) to simulate the effect of material through the belt scale.Standard electrical signals, such as hanging code, chain code simulation calibration device is commonly used foreign manufacturer, and the car yards simulation calibration device is domestic belt scale developed by the user in the 1980 s, but the application range is very narrow, now almost no application, and circular chain code in written to the national metrological verification procedures JJG 195-2002, the thermal power industry has a large number of applications.Material test facilities have also been part of the user's attention, with calibration hopper scale material calibration device and some simple calibration facilities in some production sites, improve the material test conditions.Due to the large number of domestic application of electronic belt scales, the requirements for their calibration technology are increasingly high, so in recent years, the calibration technology of domestic electronic belt scales has a great development, part of which belongs to innovative technology.

1.The code

Hanging code test is a method of hanging a certain weight on a certain part of the bearer for testing, these parts can be: test blade, test derrick, test rod mounting hole and so on.The code hanging test when the belt conveyor is in a static state is called static code hanging test, and the code hanging test when the belt conveyor is started is called dynamic code hanging test. The advantage of dynamic code hanging test is that the test results reflect part of the interference in the state of the belt conveyor.The hanging code test is simple and easy to implement, and easy to realize the remote control operation or automatic operation of weight loading and unloading.The results of the hanging code test are often different from the results of the material test, that is, the accuracy is slightly poor, especially for the single roller scale bar steelyard with poor collimation, inaccurate roller spacing and poor stability of the carrier.But by comparing with the material test, the correction coefficient is found out, and its repeatability is often better, so it can also get higher test accuracy.As an auxiliary test method, this method is widely used at present.

2.The preliminary conclusions of the experiment are as follows:

2.1 If the effective weighing section of the belt balance can be accurately measured

Length, then in most occasions array belt scale can be used to calibrate the belt scale by hanging code, without physical calibration comparison;

2.2 The systematic error between the hanging code and the real object is 0.2%-0.3%, and the value of the hanging code is less than the value of the real object.

In the past, the comparison test between the hanging code test and the material test of the idler type carrier has been carried out in China, which can often achieve better results. Therefore, the above test of Nanjing Sangai Industrial Holding Co., Ltd. has enhanced the confidence that the dynamic hanging code test can partially replace the material test.

3 Chain code

Roller chain is made up of many quality equal to the roller by chain plate spacing is close connected into a whole chain of test, the above laid roller chain belt, through a fixed rope on both ends fixed on the upright post, when the belt conveyor starting, roller in situ rotation on the belt, namely to simulate the material with the movement of the belt, equal to reduce labor intensity, improve the work efficiency of the calibrationSafe and reliable operation.

4 Cyclic chain code

Circulating chain code is composed of a number of standard mass block end to end of the closed chain, with the conveyor belt movement, the gravity of continuous, circular action on the belt scale.In May 2003 on the implementation of JJG 195-2002 belt scale is one of the content of the new national metrological verification procedures: "use test should be used in the actual use of material, difficult to use the material for use in the testing of belt scale, using the load test can be used in the simulation device instead of actual material used in the inspection".The condition is that the test result of the simulated load device must be "the test result modified by the material test according to the requirements of the simulated load test".And clearly stipulate: "Usually can be used cyclic chain code repeatability of 0.1% of the simulation load device for the 0.5 level belt scale, 1 level belt scale and 2 level belt scale in use test;In-service inspection of stage 1 and stage 2 belt scales using other simulated load devices ".The "maximum error" of belt scale material test device is less than cyclic chain code;The "maximum relative error" and "standard deviation of the actual use and discovery of the relative error" of the cyclic chain code are better than the material test equipment of belt scale.

5.Superposition method of standard material and normal conveying material

The method of superposition of standard material and normal conveying material is adopted to carry out on-line self-calibration of belt scale.The so-called "standard material" is actually transported material, but it is only part of the material taken out of the transported material. After weighing, it is informed of its weight value, and it is added to the normal conveying material in the self-calibration.

The specific calibration process is completed as follows:

(1) after the installation and alignment calibration of two belt scales, the main metering belt scales and auxiliary calibration belt scales are compared and calibrated in the process of conveying materials. Only the cumulative amount of materials displayed on the two scales is equal, and it is not required to be consistent with the actual conveying material amount;

(2) Under the condition of normal material conveying, start the material sampling device to collect part of the material and enter the weighing hopper through the material conveying device for weighing;

(3) start online self-calibration, the weighing hopper scale after the material falls into the material flow from between the two scales, until the weighing hopper is emptying, because the auxiliary calibration belt balance bears more material after the weighing hopper scale than the main measuring belt balance, so the two belt scales get two groups of weighing values;

(4) two groups according to difference of the value should reflect and after weighing hopper weighing material weight value of the related parts, if inconsistent, modified computer-aided calibration, the use of the material test correction mode the full value of coefficient of belt scale, because the two platform scale than prior calibration, so the main metering belt scale is revised according to the same full value coefficient.At this point, online self-calibration is completed, which solves the problem that belt scales are not easy to be calibrated online in real objects for many years.

6 Material test

Material test is still the most authoritative verification and test method, because the test process of material is important to consume a lot of manpower and material resources, so the belt scale precision requirements of the industry, such as power plants, some metallurgical and chemical plants using the material calibration device with check hopper scale.The material test device provided as a commodity is a high precision electronic hopper scale, which can be installed in the middle of the belt conveyor conveying material process to be used as a control weighing device for material weighing.In order to ensure the accuracy of the use of electronic hopper scale, with a set of M1 grade standard weight, standard weight loading and unloading are completed by the electric mechanism, through the transmission of the value, to ensure the detection accuracy of the system.

Conclusion: through the belt scale calibration method and belt scale weighing the pros and cons of analysis results and the real ratio on the results, further proof that the material test are not direct calibration belt scale, let users understand the belt scale must be normal measurement, through the actual material after test the other methods only after obtaining correction coefficient of the accuracy of the daily maintenance of belt scale test method.

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