Expertise & Technical documentation

Error Verification of Static Track Scale

According to the use status, the track scale can be divided into static track scale and dynamic track scale. Static track scale refers to the track scale in which the vehicle is still weighing on the track scale table. Its measurement method is vehicle measurement. Compared with the dynamic track scale, the static track scale has higher weighing accuracy. With the development of computer technology and sensor technology, static track scale has developed from pure mechanical track scale to static electronic track scale, and is widely used in material transportation of metallurgical, coal, electric power, petroleum, chemical and other enterprises in China. Static electronic track scale is developed after the 1990s, which is specially used to measure the weight of railway vehicles and their loads. Compared with the traditional mechanical scale, it has the advantages of simple structure, easy operation, fast measurement speed, high precision, intuitive display, convenient microcomputer management of data and so on. The adjustment of bias load error of electronic track scale is the main content of track verification project. The adjustment of bias load error determines whether the weighing instrument is qualified or not. At the same time, it is also related to the correctness of value transmission and the accuracy of daily measurement. Therefore, the adjustment of bias load error must be carried out simultaneously with the verification.
Composition of static electronic track scale
The static electronic track scale is mainly composed of mechanical part, electrical part and computer software part. The mechanical part mainly includes weighing table and sensor. Each static electronic track scale has 8 sensors, generally using column or bridge sensors. The electrical part includes junction box, weighing instrument, etc. The static electronic track scale has many components and complex structure.
1、 Inspection before verification
In order to ensure the smooth verification of the track scale, the parts directly affected by the deviation of the track scale must be checked before verification. Firstly, power on and preheat the weighing instrument of the track scale, and pay attention to observe whether the self inspection and automatic zero clearing of the instrument are normal. Then check the countertop of the rail scale to see whether the rail and guard plate have top, clamp and grinding. Finally, check the foundation pit to see whether the foundation and fasteners of each support point are loose, whether the adjustment of the limit device is appropriate, and whether the force of each sensor is uniform. For the first inspection of the track scale, it shall also check whether the parameters set by the weighing instrument meet the requirements, and confirm whether all the fine adjustments of the junction box are aligned. If there is no problem with the above inspection, the eccentric load verification can be carried out. For the first inspection of the track scale, the scale car can be used for calibration, and then verified.
2、 Eccentric load verification
Eccentric load refers to the indication value of the same load at different positions. According to the requirements of eccentric load items in the national metrological verification regulation of the people's Republic of China: jjg781 - 2002 digital indicating track scale: "verify the beginning and support points of the carrier, the middle and end of two adjacent pairs of support points". Generally, 8 30t or 40t pressure sensors are used for static electronic track scales, which are distributed under the carrier according to 4 pairs of support points. Therefore, there are seven "eccentric load verification points", as shown in Figure 1. According to the requirements of the regulation, the verification application uses the weight trolley in the t6f weight verification vehicle, applies a 24t load, goes back and forth according to the "eccentric load verification point", and records the indicated values of each point. If the error is not exceeded, the verification continues; In case of out of tolerance, this data can be used as the basis for adjusting eccentric load. Generally, the D value of electronic track scale is set at about 20kg. There are two methods to verify the bias load error: one is to determine the error indication by adding or reducing the weight to find the flicker point; Second, modify the division value of the weighing instrument so that D ≤ 0.2e is directly displayed. The maximum allowable error of the rail scale is ± 1.0e. Here, the calibration division value shall be equal to the use division value, i.e. e = D. All points exceeding the tolerance must be corrected.
3、 Adjustment of eccentric load error
The adjustment of partial load error is a repeated and meticulous work, which can not be anxious for success. The correction error must be carried out on the premise that variables occur at each eccentric load verification point. If a variable occurs, it must be handled. If it is not handled, the commissioning and verification of unbalanced load will not continue. In order to leave enough room for the adjustment of the junction box and avoid fine adjustment to the detection limit, if the error value is E > ± 2.0e, the height of the sensor shall be adjusted. The error value E < ± 2.0e can be adjusted through the junction box. When adjusting the eccentric load on the junction box, the number of the corresponding sensor shall be found. During adjustment, pay attention to the balance of each pair of sensors. The error is very small in the middle of two adjacent pairs of support points. If the middle of two adjacent pairs of support points exceeds the tolerance, the fine adjustment of the relevant four sensors shall be adjusted. Note that the adjustment direction must be consistent, and the adjustment amount of each should be 1 / 4 of the error amount of this point.
The author summarizes many years of adjustment experience and believes that the instrument flicker point is not the best point for adjustment. The flicker point is actually a critical point, which is unstable. The best point should be 0.5E after the flicker point. This point is the best and most stable, and it is also the real starting point of E value. For the sake of adjustment accuracy, it is better to use a digital multimeter to monitor during adjustment, pay attention to observe the change of an e value, and calculate the amount that should be adjusted to eliminate the error at this point. In this way, it is easy to find the best point of adjustment. If there is no multimeter, it is also possible to observe the flicker of the weighing instrument while adjusting, but it is difficult to master the balance and deepening adjustment 0.5E of the two sensors.

The junction box of large scale weighing instrument has two types: voltage control type and current control type. With the error of the same polarity, their adjustment direction is just the opposite. Therefore, we should carefully grasp it and avoid the bigger the error. The change law of fine adjustment of junction box is: adjust clockwise, and the resistance increases; Adjust counterclockwise to reduce the resistance. To eliminate a positive error, the current control type junction box shall be adjusted clockwise. The voltage controlled fine-tuning should be adjusted counterclockwise. Use a multimeter to monitor, mainly to monitor the change of fine adjustment. The adjustment method adopted by the author is to modify the D value of the weighing instrument to 5kg, so that the error value display is more intuitive and the trouble of adding and subtracting weights to find flicker points is avoided. Then use the weight car to start from the end and adjust the point to which it is pressed. Identify the number of the adjusted sensor and master the balance parameters. The adjustment and fine adjustment shall be carried out slowly. Pay attention to the change of weighing instrument and multimeter to minimize the error. It is not required to be absolutely right. After all inspection points have been adjusted, use the weight truck to go back and forth to see if the indication of each point has changed or exceeded the error. After confirmation, the D value that can be recovered for daily use shall be submitted to the verification personnel for re verification. Generally, after the eccentric load is adjusted, the discrimination test and repeatability test can pass smoothly. In the process of verification, if wind, rain, snow or other conditions that may affect the verification work, the verification shall be suspended.

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