Calibration and Test Method for Weighing System of Batching Machine

1. Preparation before calibration

 Before calibration, the metrology technical agency should prepare enough M1 standard weights, and require the client to prepare a certain amount of test materials, handling equipment and auxiliary personnel.

2. Static calibration steps

 1) During the calibration process, a dedicated operator of the entrusting party should be accompanied by a dedicated operator, and carefully read the operating instructions. Before calibration, set the batching scale and auxiliary equipment in the manual position to ensure the safety of calibration.

2) Perform visual inspection. Check the legal measurement management signs, descriptive signs, verification marks and safety measures, power-on self-check procedures, use conditions and uses of the batching scale, and observe whether the scale body of the batching scale is in a stable state and whether there is any abnormal contact under the scale body. Whether the windproof equipment around the scale body is in contact with the charging hopper.

3) Accuracy calibration of zero setting and peeling device. The calibration of the zero point and the peeling device is critical to the calibration and adjustment of the batching scale. According to the different sensor types, it can be divided into two kinds of batching scales: analog signal and digital signal. Digital signal application is more common, but the analog signal batching scale still occupies in the project, these two types of batching scales are slightly different in the debugging process. Before calibration, the meter must be set to zero. The digital signal batching scale can directly use the zero setting or detare function, and then perform the zero setting and detare device accuracy test; the analog signal batching scale cannot display negative values or operate The table does not have the zero-setting function, you need to add a small weight to find the zero point, then adjust the resistance of the adjustable resistor, and set the zero point (if there is a zero-point tracking function, you can use a 10e weight to eliminate the effect of zero-point tracking, and then use Add a small weight to find the zero point).

4) Partial load test. The eccentric load test method is determined according to the number of load cells and the installation position. The batching scale used in the project generally has 1, 2, 4 or more sensors. The top view of the loading hopper is generally circular (water scale, Additives), square, rectangle. According to the actual situation (such as placement position), apply a standard weight approximately equal to 1/10 to 1/5 of the maximum weighing to each eccentric load position of the batching scale for testing. For batching scales with no more than 4 supporting points, Eccentric load test weights should be placed at the four corners of the loading hopper (evenly distributed) to perform 4 sets of eccentric load tests; for batching scales with more than 4 supporting points, place the weights above each supporting point (evenly distributed) to perform Corresponding multiple sets of eccentric load tests. The error of the eccentric load test should meet the relevant requirements of JJG 555-1996 "General Verification Regulations for Non-Automatic Weighing Instruments". Note that the eccentric load test is purposeful before the weighing test. In actual work, the author has found that some batching scales have eccentric load problems (such as the installation position is not level enough, and some sensors in multiple sensors are faulty), which leads A lot of work is increased; if the partial load test is performed first, the fault problem can be eliminated first, and then the follow-up test can be performed, which reduces the work load and improves work efficiency.

5) Weighing test. From the zero point, add weights to the maximum weight in the order from small to large, and unload the weights to the zero point in the same way. At least 5 different weighing points should be selected for weighing test, which should include minimum weighing, 50% maximum weighing, maximum weighing and other key weighing points (refer to JJG 555-1996 "General Verification of Non-Automatic Weighing Apparatus" The maximum allowable error change in the “Regulations” is the turning point weighing).

6) Discrimination test. During the weighing test, it is carried out at three weighing points: minimum weighing, 50% maximum weighing and maximum weighing.

7) Repeatability test. It can be carried out according to the method in the verification regulation of JJG 539-1997 "Digital Indicator Scale". Two sets of tests are carried out at 50% of the maximum weighing and close to the maximum weighing, and each group is repeated 3 times. The difference between the maximum value and the minimum value of the three measurements should not be greater than the absolute value of the maximum allowable error under the weighing (accuracy level is required by level).

 8) Calibration and parameter setting of batching scale

The result of static calibration is generally judged according to the requirements in JJG 555-1996 "General Verification Regulations for Non-Automatic Weighing Instruments". If the test finds that the batching scale cannot reach the corresponding accuracy (the general accuracy level of the batching scale is level), it needs to be calibrated. The calibration process of the batching scale should be carried out according to the manual, but there are a few things to note: if allowed, the previous parameter settings can be recorded before the calibration; if the calibration operation fails, read the details in the manual carefully, mainly related to the various parts of the batching scale. Whether the various parameter settings have been changed, or set these parameters to the factory state according to the manual, and then perform calibration. In addition, the display refresh cycle of the batching scale is also an important parameter. Its setting range is generally 0.2 seconds to 2 seconds. For commercial concrete batching scales, the setting value should not be too large. The recommended value is between 0.2 and 0.5. ; If the cycle is too long, the response of the sensor will slow down, thereby affecting the accuracy of weighing.

After the calibration, the weighing test and repeatability test should be performed again. If the test result meets the requirements of JJG 555-1996 "General Verification Regulations for Non-Automatic Weighing Instruments", the static calibration is completed.

3. Dynamic test method

 The dynamic test is to simulate the weighing load process in the actual use of the inspected batching scale, so it is usually tested with the expected weighing material of the batching scale, so it is also called the material test. The method is to put the materials weighed by the batching scale on a static weighing instrument with higher accuracy for weighing, and the indication value of the static weighing instrument is used as the agreed true value of the material. In this process, we use the premise that the weighed material is relatively stable in a short period of time, and use the weighed material as a medium for value transfer and a temporary standard to realize the value transfer. This static weighing instrument is called a control weighing instrument. For control weighing instruments, we have such requirements: if the control weighing instrument is calibrated or verified immediately before the material test, it should ensure that its error is not greater than the maximum allowable deviation of automatic weighing and the maximum allowable preset error (if applicable) 1/3 ; In other cases, ensure that the error is not greater than the maximum allowable deviation mpd of the automatic weighing and 1/5 of the maximum allowable preset error (if applicable). Only in this way can the principle requirements of value transfer be met. The dynamic test must be performed after the static calibration. The test method is as follows:

1) Test the relative error between the agreed value and the displayed value of each group of secondary materials;

2) The number of groups should be determined according to the capacity of the supporting host, the number of tests should not be less than 10, and the interval between each group should be greater than 15 minutes.

3) Matters needing attention

 According to the recommendations of JJG 564-2002 "Gravity Automatic Loading Weighing Apparatus" verification regulations, it is required that the carrier should be equipped with corresponding positions or facilities to facilitate the safe and reliable placement of the largest weight or mass. In the actual verification process, we found that the design of the water scale and additive scale in the commercial concrete batching scale are often designed as cylindrical loaders and cannot be built-in weights. Therefore, pay attention to cleaning up the residues before performing static calibration and calibration. clean. The calibration of the weight reduction instrument should also pay attention to the proper handling of residues.

The above is the author's discussion on the calibration method of the commercial concrete batching scale in combination with actual work, hoping to be helpful to the reader's work. If there is anything wrong, readers and colleagues are welcome to criticize and correct.