Preparation and steps for calibration of weighing instruments

1. Basic work before calibration

When you consider starting to calibrate a weighing instrument with calibration weights, it is important to clarify some things and plan ahead.

< a> Firstly, determine the technical aspects of the weighing instrument (such as maximum weight and d value) and plan B in case of unsuccessful calibration< a> Generally speaking, the entire measurement range needs to be calibrated, and the calibration is carried out at the location where the instrument is used. In this case, please confirm if you have enough weight to smoothly carry out the calibration process< a> In addition, the weighing instrument needs to be kept running for approximately 30 minutes before starting calibration. In addition, the temperature must be stable to match the temperature at the calibration site< a> It is very important to keep the weighing instrument in a horizontal position, especially when it comes to portable precision weighing instruments. Suggest conducting some pre tests by placing calibration weights near the highest range of the instrument. This is necessary to ensure the smooth operation of the instrument< a> If the weighing instrument malfunctions during the calibration process, a "discovery time" adjustment should be created before calibration, and a "departure time" adjustment should be created after calibration is completed< a>

2. Eccentricity test

In some cases, the weighing instrument is not always perfectly positioned in the middle of the carrier. Meanwhile, when the load is not placed in the appropriate center of the receiver, the measurement value of the weighing instrument may be slightly different. That's why eccentricity testing is necessary to understand the degree of influence of the load area< a> During the eccentricity test, place the reference load on a specific area of the receiver to determine the results. Afterwards, according to the calibration procedure, place the load at four different positions on the load receiver< a> Note that during the eccentricity test, the test load should be one-third of the maximum load of the weighing instrument. In addition, it is recommended to use a test load for testing, as this can easily determine the center of gravity of the load in a specific area< a>

3. Repeatability testing

Due to the prevalence of repeatability issues in most instruments, weighing instruments also face the same problem. It indicates that a specific load is measured multiple times and the results are always different. That's why repeatability testing is necessary before calibration< a> Testing is conducted by replacing the same load multiple times at the same location on the receiver. This is done to avoid any bias errors. In addition, the testing was conducted under constant and similar settings as well as similar processing< a> The load is located near the highest load of the instrument. Usually, this test is conducted within a load. However, it can execute simultaneously under different load values. During the testing process, the machine is at zero value and then loaded onto the receiver. At this point, after the carrier has stabilized, record the indication. Now, remove the load again and if necessary, zero the instrument. Repeat the process to identify repeatability issues< a>

4. Weighing Test

The weighing test aims to determine whether the weighing machine provides accurate calibration through many steps, including reducing and increasing weight< a> Normally, testing starts from zeroing the instrument and no load is applied to the instrument. Ensure to load at the first test point and record the indication after stabilization. Repeat the process by increasing the load on the rising test points. After recording the maximum load, start reducing the load by decreasing the test points< a> There are no hard rules to calibrate the increase and decrease of load. People can choose any one of them for weighing testing. Usually, 5 to 10 different loads or test points are used. Remember to keep the highest load near the highest range of the instrument< a>

5. Other tests

There are other tests according to the standard. However, many of them are not performed during normal calibration, but they can be used for initial validation. These tests include:

● Minimum weight test

● Discrimination test

● Tare weight test● Magnetic interaction test

● Changes in indication test