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The microbalance should be fully preheated according to the instructions before weighing. The basic working principle of a microbalance is balance. Once it is out of balance, the balance is pulled back to equilibrium by electromagnetic force. When the balance is in the warm-up phase, as the internal temperature rises, B will gradually decrease, and I will also decrease, which will cause F to become smaller, the balance will lose balance, and the indication will show a positive one-way drift. Only after sufficient preheating, the magnetic steel reaches thermal equilibrium, and the process ends, and the balance reaches equilibrium. Then use the zero return / peeling function to make the display return to zero, then the balance is in the real usable state.
In addition, microbalances usually do not have a power switch similar to household appliances. As long as the balance is energized, there is no display on the display and the balance is already warmed up. The "ON/OFF" button on the balance is just a switch display. Therefore, the balance that is often weighed does not have to be unplugged, especially for high-precision balances. When conditions permit, long-term continuous power can keep the balance in a warm-up state. When the temperature of the sample and the container is not the same as the temperature of the weighing chamber, there is a temperature difference that causes the airflow in different directions along the outside of the weighing container, which creates an upward or downward force. This dynamic air buoyancy produces incorrect weighing results.
The amount of temperature symmetry of the hand also has an effect, and this artificial factor should be minimized. In order to reduce the effects of sample hygroscopicity and volatility, the weighing time should be minimized for such samples or in a closed container.
2. Calibration of the microbalance (be sure to read the instructions carefully before use)
In the verification (test), we found that the first measurement test of the balance has a large error. The reason is that a considerable part of the instrument has not been calibrated in a long time interval, and it is considered that the balance can be directly weighed by displaying the zero position. . (It should be pointed out that the micro balance starts to display zero point. It cannot be said that the accuracy of the balance weighing data meets the test standard, and only the balance zero stability is qualified. Because it is necessary to consider the other technology when measuring whether a balance is qualified or not. Compliance of indicators). Due to long storage times, positional movements, environmental changes or for accurate measurements, the balance should generally be calibrated prior to use. The calibration method is divided into internal calibration and external calibration. Germany's Saudi Lisi, Swiss-made METTLER, Shanghai-made "JA" and other series of micro-days have 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.
Some people think that the heavier the object weighed in the range of the microbalance, the greater the damage to the balance. This understanding is not entirely correct. The maximum safe load of a general weighing instrument is the maximum static load that it can withstand without causing a permanent change in its metering performance. Since the microbalance adopts the principle of automatic compensation circuit of electromagnetic force, when the weighing pan is loaded (be careful not to exceed the weighing range), the electromagnetic force will push the weighing pan back to the original equilibrium position, so that the electromagnetic force and the gravity of the object are called Balance, as long as the weighing size within the allowable range has little effect on the balance, it will not affect the accuracy of the microbalance due to long-term weighing.
3, the specific operation method of the balance <br> Trace, semi-micro and analytical balance are high-precision measuring instruments, mastering the correct operation method will help to quickly obtain reliable weighing results. The following are the basic methods and precautions for balance operation:
First check if the bubble is in the center of the level and adjust the leveling screw if necessary until the balance is level. Then calibrate the balance. The balance needs to be calibrated before the balance is first operated, or when the balance is replaced, the balance is leveled, and significant temperature, humidity or pressure changes occur around it.
In the third step, check whether the windshield is closed. If it is closed, it can be turned on: continuously energize the balance and turn it on, and the temperature balance can be formed inside the balance; use the peeling door to close the balance. The balance will therefore be in standby mode and the internal electronics will still be energized, thus omitting the warm-up process.
Fourth, the weighing container should be as small as possible, and avoid using plastic weighing containers. When the air humidity is 30-40% lower, do not use the glass mouth to avoid static electricity. The sample in the weighing container and its interior should be kept consistent with the ambient temperature, as temperature differences can cause airflow and cause changes in the wet film on the weighing container and sample surface. At the same time, the weighing container cannot be placed directly into the balance weighing chamber by hand, otherwise the temperature and humidity of the weighing chamber and the weighing container will be changed. There will also be a reaction to the symmetry process.
Fifth, the weighing sample should be placed in the center of the weighing pan to prevent four corner errors. For micro and semi-microbalances, the weighing pan needs to be briefly loaded (initial weighing) after a weighing pause of more than 30 minutes. The weighing sample can be removed from the weighing pan after the weighing process is completely completed, so as to avoid the change of the weighing chamber temperature and the air humidity caused by the weighing sample.
Sixth, before the start of weighing, it should be checked whether the display is in the zero state. If necessary, it is necessary to perform peeling to return to zero to prevent zero error. Then adjust the automatic stabilization detector until it is satisfied. If the stability detector's mark is dark (= weighing result display), the weighing value is read immediately.
Seventh, the weighing chamber and the weighing pan should be kept clean, and only the clean weighing container can be used for weighing.
4. Maintenance of microbalances <br> Periodically wipe the dust on the balance cover, the lower part of the weighing pan, the weighing pan and the bracket with a soft brush or a damp soft cloth dampened with soft soap.
The weighing pan and stand can be cleaned with tap water. It is important to note that all parts must be completely dry before they can be installed back to the balance.
Do not allow liquid to splash inside the balance or on the connection to the equipment behind the balance or on the transformer. If liquid is splashed on the balance, the balance must be disconnected immediately and reported.
If the balance is not used for a long time, unplug the power supply and thoroughly clean it, and store it in a place where there is no strong vibration, no vibration, no large temperature change, no direct sunlight, no moisture, it is best to put it in the original packaging. Stored in the box.
The problem of placing a desiccant in the weighing chamber is to add a desiccant to protect the weight. If a desiccant is placed in the microbalance weighing chamber, the water absorption and the water release of the desiccant form a gas flow in different directions, which causes a change in the buoyancy of the air, resulting in unstable weighing. Therefore, the desiccant in the weighing chamber should be removed to maintain a stable weighing environment.
Preheat calibration, operation method and maintenance of microbalance
1, preheating of the balance of the microbalance