The electronic balance is a commonly used weighing instrument in the laboratory. It is widely used in production, scientific research, universities, trade, etc. The electronic balance is a commonly used measuring instrument. After a long period of use, its accuracy measurement performance and just The factory indicators will deviate from each other. Therefore, after the electronic balance is used for a long time, the electronic balance needs to be periodically calibrated and calibrated. Usually, the metrological verification is carried out once a year. The user can send the electronic balance to the metrological test and verification institution for verification. Now, the verification procedure of the electronic balance is based on the JJG98-90 non-automatic electronic balance test verification procedure. Although the conditions of the same procedure are different, the verification results of different verification personnel will also have certain differences. Which factors will cause the difference in the verification results of the electronic balance?

        There are mainly the following aspects:

        1. Electronic balance storage time:

        The storage time of the electronic balance in the verification room will also have a corresponding impact on the verification results. Therefore, when sending the electronic balance, it is recommended to open the box for more than 24 hours in the verification room, so that the temperature and storage environment of the electronic balance and the weighing chamber are basically Consistently, while the internal mechanical mechanism of the electronic balance reaches a corresponding balance, this factor is often overlooked, especially when the electronic balance is expedited.

        2. Warm-up time of the electronic balance

        Whether the warm-up time of the electronic balance is sufficient is the key factor to ensure the stability of the electronic balance. The length of the preheating time is related to the verification scale value of the electronic balance and the number of verification scales, and is also related to the performance of the electronic balance produced by each manufacturer. Article 18 of the verification procedure stipulates that the electronic balance is usually preheated for more than 30 minutes before the verification. The specific preheating time shall be based on the requirements specified in the instruction manual of each electronic balance. The length of the electronic balance's warm-up time and the accuracy of the electronic balance also have a certain relationship. Generally, the higher the accuracy of the electronic balance, the longer the warm-up time. Therefore, before the user can verify each electronic balance, it is best to read the instruction manual and preheat according to the time specified in the manual to check the electronic balance.

        3, preload

        Preloading is rarely understood by anyone. The so-called preload is that after the electronic balance stops working, it may go to sleep after a period of time. In order to let the electronic balance enter the working state quickly, load it with the weight multiple times before the balance is checked. In this case, the difference between the indication value of the electronic balance process and the return value can be reduced. The weighing result and the zero return condition at the time of loading can be basically avoided.

        4, electronic balance reading time

        Whether the value of the electronic balance is stable or not is usually indicated by a prescribed symbol on the display. When the indication is stable, the steady indicator (or symbol) lights up, or the unstable lamp (or symbol) disappears. The stability range is generally adjustable, and the setting of the stability range is inversely proportional to the stable indication time that appears on the display. The electronic balance from loading to reading stability is actually a process of oscillation balance.

        5, the test of discriminating power

        In JJG-98-90 non-automatic electronic balance verification procedure 6.3.2.2, the electronic balance discrimination test "on the balance of the electronic balance at no load or loading, the equivalent of the digital scale graduation value of 1.4d An applied load is gently placed on or removed from the electronic balance. At this point, the original indication must be changed." The provisions here are not clear enough. Imagine that the discriminative force test is performed at a certain weighing point. When the indication error of the weighing point is different, the load of 1.4d is also changed. Will the effect be the same? It can be explained by the following example:

        The calibration scale value e of an electronic balance is 0.1g, the actual division value d is 0.1g (ie e=d=0.1g), the indication value of the electronic balance at the 200 weighing point is 200.0g, and the identification of the 200g weighing point is determined. force.

        When the resolution in the electronic balance is sufficiently high, the load on the electronic balance pan is 200 g, with an indication of 200.0 g. This 200.0g is actually the result of digitizing the analog balance of the electronic balance. At this time, the actual analog value may be any value from 199.96g to 200.04g. It is assumed that the electronic balance indication error is -0.4d. If the 1.4d weight is added, it is only equivalent to 1.0d, of which 0.4d is used to offset the error of -0.4d. When the indication error of the electronic balance is +0.4d, it is actually equal to 1.8d. Obviously the effect is different. That is to say, the indication error of the electronic balance at this time affects the test result of the discrimination force. According to the spirit of the R76 international recommendation, in the discriminating force test, it is determined whether the load on the weighing pan changes after 1.4d, and the indication value is changed. First, the indication value of the weighing point should be corrected by increasing or decreasing several small weights of 0.1d. For the error, the indication error was uniformly corrected at -0.5d, and then the load was changed by 1.4d for observation. The operation method is as follows: (taking the above electronic balance as an example)

        First put 10 small weights equivalent to 0.1g on the weighing pan, press the tare key to make the electronic balance display 0.0g. Put 200g standard weight, when the electronic balance shows 200.0g stably, remove several 0.1g small weights one by one on the weighing pan, change the electronic balance value to 199.9g, then add a small 0.1g Weight, then add the 1.4g weight to the weighing pan at a time, then the value of the electronic balance should be changed to 200.1g.

        6. At present, there are many types of electronic balances in the market. When the electronic balance is verified, it should be determined according to the electronic balance. Only the correct operation can correctly evaluate the measurement performance of the electronic balance.