Definition
A semi-microelectronic balance is a high-precision mass measurement instrument that typically weighs between a few grams and tens of grams, while readability (or index value) typically reaches the 0.01 mg (0.00001 g) level. Suitable for sample weighing that requires higher than conventional analytical accuracy but does not reach trace levels. Its design takes into account high sensitivity and relatively loose environmental stability requirements, and is the core equipment of routine precision weighing in many laboratories.
Principle
Modern semi-trace electronic balances generally adopt the principle of electromagnetic force compensation. Its core component is an electromagnetic force system composed of permanent magnets and coils. When the sample is placed on the weighing tray, gravity causes the lever mechanism connecting the weighing pan to be displaced. This displacement is detected by the position sensor and converted into an electrical signal, and the control system immediately increases the current flowing through the coil, resulting in an electromagnetic recovery force equal to the gravity of the sample and in the opposite direction, returning the lever to the equilibrium position. According to the principle of electromagnetism, this compensation current is directly proportional to the mass of the sample. Finally, the instrument accurately calculates and displays the mass value of the sample by measuring and processing this current value.
Measurement method
To ensure accurate and reliable measurement results, a series of standard methods must be followed in operation. The first is preheating, which needs to be stabilized for enough time to achieve thermal equilibrium after the balance is energized. The second is calibration, which must be calibrated regularly with a standard weight that is traceable and meets the balance accuracy level. In actual weighing, common methods include direct weighing, subtraction, and incremental methods. For samples that are susceptible to environmental influences or are electrostatic, a closed weighing container is used. Make sure the balance is stable before each reading, and take care to center the sample on the scale. All operations should be gentle and avoid impact.
Influencing factors
The measurement accuracy of semi-trace electronic balances is affected by a variety of environmental and operational factors. Ambient airflow is a common source of interference, and even weak airflow can cause readings to drift, so it must be used in a wind-free and stable environment and is often equipped with a windscreen. Ambient temperature fluctuations can cause thermal expansion and contraction of mechanical components and drift of electronic component parameters, so it is recommended to work in a laboratory with stable temperatures. Vibrations, including ground vibrations and acoustic vibrations, can directly interfere with the force balancing system, so a solid anti-vibration table is required. In addition, the physical state of the sample, such as temperature, electrostatic, hygroscopicity, or magnetism, can introduce errors. Operator skill, such as how to open and close the windscreen and place the sample, is also crucial.
Applications:
With its high precision and good practicality, semi-micro electronic balances are widely used in R&D and quality control processes in many industries. In chemistry and materials science, it is used for the precise formulation of standard solutions, catalyst weighing, and nanomaterial sampling. In the food industry, it is used to detect moisture content, fat content, and proportion control of food additives. Environmental monitoring for accurate weighing of particulate matter collected on filter membranes. In the electronics industry, it is used to weigh key materials such as solder paste and conductive silver paste. The teaching of chemistry and physics experiments in higher education and scientific research institutions also generally relies on such balances for quantitative analysis training.
Selection considerations
Selecting the right semi-micro electronic balance requires a comprehensive evaluation of multiple technical parameters and actual needs. The primary parameters are maximum weighing values and readability, ensuring that the quality range of everyday samples is covered with margins while meeting the requirements for measurement uncertainty. This is followed by repeatability and linear error, which directly reflect the short-term stability of the balance and its accuracy over the full scale. The balance stabilization time is related to work efficiency, and a shorter settling time helps increase throughput. The size of the instrument and the design of the windscreen should be adapted to the experimental operating space and sample container. In addition, it is necessary to check whether the data interface meets the requirements of laboratory information management system integration and whether it has metrology certification that complies with relevant international standards (such as OIML R76 and ASTM E319). Finally, tolerance to the operating environment, ease of calibration, and long-term maintenance costs are also important decision-making factors.