In today's society, electronic balances are more and more widely used and popularized in the field of analytical chemistry because of their fast weighing speed, easy operation, high sensitivity and high precision, and the ability to directly connect to a computer or some instruments for data transmission. So how to use electronic balance for accurate weighing? The following is the analysis and insights made by Shanghai Bilang Instrument Co., Ltd. Everyone is welcome to correct, add and discuss!
1. Weighing principle of electronic balance:
The electronic balance is designed according to the principle of electromagnetic balance and is composed of a magnet, a coil connected to the weighing pan, a displacement sensor, a current control circuit and an amplifier. The coil is placed in the magnetic field formed by the magnetic steel, and the weight of the weighing pan and the weighed object acts on the coil. After energizing, after fully preheating the balance, the strength of the magnetic field remains unchanged, the length of the coil is fixed, and the magnitude of the electromagnetic force (F = ΦIL) generated by the coil placed in the magnetic field is proportional to the current strength. On the contrary and make it balanced with -mg = ΦIL, then the mass of the object is proportional to the current intensity. The displacement sensor is located at a predetermined center position. When placing or removing objects on the weighing pan, the displacement sensor changes the current of the coil through the controller according to the detected displacement signal until the coil returns to the center position. This current changes The quantity is displayed by magnifying and converting to the quality of the sample.
Second, to ensure the accuracy of weighing using electronic balance, should pay attention to the following:
1. Fully preheat the electronic balance. It can be seen from the working principle of the electronic balance that the magnitude of the electromagnetic force is proportional to the magnetic flux φ of the magnetic steel, the current I flowing through the coil, and the coil length L. For a balance, to ensure accurate weighing, it must be ensured that φ and L are a certain value, the coil length L will not change, but the magnetic flux φ changes with the temperature of the balance. Only after the balance has been fully warmed up (general information describes warming up for 30 minutes, it is recommended to press the power button to shut down but not unplug the power when not in use), in order to keep the internal temperature of the balance relatively stable. This is the first step to ensure accurate weighing results.
2. Calibrate the electronic balance. If any electronic balance is not calibrated, it is inaccurate to use it for weighing. We use the balance to weigh the quality of the sample, not the weight. According to the weighing principle of the electronic balance, it directly measures the weight of the object, that is, mg = ΦIL. In fact, the mass of the sample is based on m = ΦIL / g (only the quantity is considered here, and the direction is not considered), so, use electronic When the balance weighs the sample mass, it is not only related to the balance itself, but also to the acceleration of gravity where the balance is located. If C = ΦL / g, m = ΦIL / g can be transformed into m = CI. C is related to the acceleration of gravity at the position of the balance and the length of the coil and magnetic flux. C varies in different places and under different environmental conditions. Assuming that the balance is sufficiently warmed up somewhere, then C is a constant in a short period of time. Correcting it with a standard weight of known weight is equivalent to finding and storing the C value. The balance automatically weighs the sample. transfer. In order to eliminate the influence of environmental factors, even if the balance does not have a moving position, the balance should be calibrated frequently, and it is best to calibrate each time it is used. In general, calibration is the most important part to ensure accurate weighing.
3. Maintain the balance level, good weighing habits (handle gently, close the balance windshield at any time, keep the balance clean, etc.), appropriate environmental conditions (such as the balance should be placed to avoid electromagnetic interference, vibration, direct sunlight and air convection , Maintain a relatively stable temperature and appropriate humidity), the correct way of weighing (before the sample, fully understand the physical and chemical properties of the sample, select the appropriate method of weighing, such as using the method of weight loss to weigh easily hygroscopic samples, without the use of heat Weighing the container or directly weighing the supercooled and superheated samples) is the prerequisite for ensuring accurate weighing.
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