Correct Use and Maintenance of Electronic Balance

　　1. Electronic balance and its classification 　　

　　The balance that uses electromagnetic force to balance the weight of the object being weighed is called an electronic balance. Its characteristics are accurate and reliable weighing, fast and clear display, automatic detection system, simple automatic calibration device, overload protection and other devices.

　　According to the accuracy of electronic balance, it can be divided into the following categories: 　　

　　1. Ultra-micro electronic balance The maximum weighing capacity of an ultra-micro balance is 2 to 5 g, and its scale division value is less than 10-6 of the (maximum) weighing capacity. For example, Mettler's UMT2 electronic balance belongs to the ultra-micro electronic balance. 　　

　　2. Microbalance The weighing capacity of microbalance is generally between 3 and 50g, and its graduation value is less than 10-5 of the (maximum) weighing capacity, such as Mettler's AT21 electronic balance and Sartoruis' S4 electronic balance. 　　

　　3. Semi-micro balance The weighing capacity of a semi-micro balance is generally between 20 and 100g, and its graduation value is less than 10-5 of the (maximum) weighing capacity. Electronic balances such as Mettler's AE50 and Sartoruis' M25D belong to this category. 　　

　　4. Constant-weight electronic balance: The maximum weighing capacity of this type of balance is generally between 100 and 200 g, and its graduation value is less than 10-5 of the (maximum) weighing capacity. For example, Mettler's AE200 electronic balance and Sartoruis' A120S and A200S electronic balances are all constant-weight electronic balances. 　　

　　5. Analytical balance is actually an electronic analytical balance, which is a general term for constant balance, semi-micro balance, micro balance and ultra-micro balance. 　　

　　6. Precision electronic balance This type of electronic balance is a general term for electronic balances with accuracy level II.

　　2. Precautions 　　 for purchase and use

　　(1) How to choose an electronic balance When choosing an electronic balance, you should consider whether the absolute accuracy (division value e) of the electronic balance meets the precision requirements of weighing. For example, if you choose a balance with a precision of 0.1mg or 0.01mg, you should not simply ask for a balance with a precision of 1/10,000 or 1/100,000, because some foreign manufacturers use relative accuracy to measure balances, otherwise the purchased balance will not meet the needs of the user. For example, in actual work, we encounter such a situation: a Mettler electronic balance with an actual scale division value d of 1mg, a calibration scale division value e of 10mg, and a maximum weighing value of 200g is used to weigh an object of 7mg. This cannot produce an accurate result: the "JJG98-90 Trial Verification Regulations for Non-Automatic Balances" stipulates that the maximum allowable error is of the same order of magnitude as the calibration scale division value "e". The maximum allowable error of this balance is 1e, and it is obviously not possible to weigh an object of 7mg; it is not the best choice to weigh an object of 15mg with this type of balance, because the relative error of the test result will be very large, and a higher level balance should be selected. Some manufacturers have specified the minimum weighing value when leaving the factory. Therefore, we must consider the accuracy level when purchasing and using electronic balances.

　　(2) Requirements for weighing range When selecting an electronic balance, in addition to considering its accuracy, you should also consider whether the maximum weighing capacity meets the requirements of the measuring range. Usually, the maximum load plus a small insurance factor is sufficient, that is, the commonly used load can be relaxed a little, not the larger the better. 　　

　　About the calibration of electronic balance (be sure to read the instructions carefully before use) During the verification (test), we found that the error was large when the balance was tested for the first time. The reason is that a considerable number of instruments have not been calibrated for a long time interval, and it is believed that the balance can be weighed directly when it displays zero. (It should be pointed out that the display of zero point when the electronic balance is turned on does not mean that the accuracy of the data weighed by the balance meets the test standard, but only that the zero-position stability of the balance is qualified. Because the compliance of other technical indicators must be considered comprehensively to measure whether a balance is qualified or not). Due to long storage time, position movement, environmental changes or to obtain accurate measurements, the balance should generally be calibrated before use. The calibration method is divided into internal calibration and external calibration. The German-made Schattlis, Swiss-made Mettler, and Shanghai-made "JA" series electronic balances are all equipped with calibration devices. If you do not read the instructions carefully before use, it is easy to ignore the "calibration" operation, resulting in a large weighing error. The following takes the JA1203 electronic balance of Shanghai Balance Instrument Factory as an example to explain how to perform external calibration on the balance. Method: Press the CAL key lightly. When the display shows CAL-, release the key and the display will show CAL-100, where "100" is a flashing code, indicating that the calibration weight needs a 100g standard weight. At this time, put the prepared "100g" calibration weight on the weighing pan, and the display will show "---" waiting state. After a long time, the display will show 100.000g. Take the calibration weight and the display should show 0.000g. If it is not zero, reset it and repeat the above calibration operation. (Note: In order to obtain accurate calibration results, it is best to repeat the above calibration) Some people think that the heavier the object weighed within the range of the electronic balance, the greater the damage to the balance. This understanding is not entirely correct. Generally, the maximum safe load of a scale is the maximum static load it can withstand without causing permanent changes in its measurement performance. Since the electronic balance uses the principle of automatic electromagnetic force compensation circuit, when the scale pan is loaded (be careful not to exceed the weighing range), the electromagnetic force will push the scale pan back to the original equilibrium position, so that the electromagnetic force is balanced with the gravity of the object being weighed. As long as the weighing size is within the allowable range, the impact on the balance is very small, and the accuracy of the electronic balance will not be affected by long-term weighing.

　　1. Place the balance on a stable workbench to avoid vibration, airflow and sunlight. 　　

　　2. Adjust the bubble of the level to the middle position before use. 　　

　　3. The electronic balance should be preheated according to the instructions. 　　

　　4. When weighing volatile and corrosive items, they should be placed in a sealed container to avoid corrosion and damage to the electronic balance. 　　

　　5. Regularly calibrate the electronic balance by yourself or have it calibrated externally to ensure it is in the best condition. 　　

　　6. If the electronic balance fails, it should be repaired in time and should not be operated while it is faulty. 　　

　　7. Do not overload the balance to avoid damage to it. 　　

　　8. If the electronic balance is not to be used for a long time, it should be temporarily stored.