Preparation and steps involved in calibration of weighing instruments

　　1. Basic work before calibration

When you consider using calibration weights to start calibrating weighing instruments, it is important to understand some things and plan ahead.

Firstly, determine the technical aspects of the weighing instrument (such as maximum weight and d value) and plan B in case of unsuccessful calibration.

Generally speaking, the entire measurement range needs to be calibrated, and calibration is carried out at the location where the instrument is used. In this case, please confirm if you have sufficient weight to smoothly carry out the calibration process.

In addition, before starting calibration, the weighing instrument needs to be kept running for approximately 30 minutes. In addition, the temperature must be stable to match the temperature at the calibration location.

It is very important to keep the weighing instrument in a horizontal position, especially when it comes to portable precision weighing instruments. It is recommended to perform some pre testing by placing the calibration weight near the highest range of the instrument. This is necessary to ensure the smooth operation of the instrument.

If the weighing instrument malfunctions during the calibration process, a "upon discovery" adjustment should be created before calibration and a "upon departure" adjustment should be created after calibration is completed.

　　2. Eccentricity test

In some cases, weighing instruments are 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 values of the weighing instrument may vary slightly. That's why eccentric testing is necessary to understand the degree of influence in the load area.

During the eccentricity testing process, the reference load is placed in a specific area on the receiver to find the results. Afterwards, according to the calibration procedure, place the load in four different positions on the load receiver.

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.

　　3. Repeatability testing

Due to the widespread issue of repeatability in most instruments, weighing instruments also face the same problem. It indicates that a specific load has been measured multiple times and the results are always different. This is why repeatability testing is necessary before calibration.

Perform the test by replacing the same load multiple times at the same position of the receiver. This is done to avoid any bias errors. In addition, testing is conducted in constant and similar settings and similar processing.

The load is located near the highest load of the instrument. Usually, this test is conducted within one load. However, it can be executed simultaneously under different load values. During the testing process, the machine is at zero and then loaded on the receiver. At this point, after the carrier stabilizes, record the indication. Now, remove the load again and if necessary, zero the instrument. Repeat the process to identify repeatability issues.

　　4. Weighing test

The weighing test aims to determine whether the weighing machine provides accurate calibration through many steps, including reducing and increasing weight.

Normally, testing starts with zero adjustment of the instrument and no load is applied to the instrument. Ensure loading at the first test point and record the instructions after stabilization. Repeat the process by increasing the load at the rising test point. After recording the maximum load, start reducing the load by reducing the test points.

There are no hard and fast rules to calibrate increased and decreased loads. People can choose any one of them for weighing tests. Typically, 5 to 10 different loads or test points are used. Remember to keep the highest load near the highest range of the instrument.

　　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 verification. These tests include:

● Minimum weight test

● Discrimination test

● Tare weight test

● Magnetic interaction test

● Changes in indication tests