Electronic Balances have become the mainstream tools for laboratory and industrial measurement due to their advantages of easy operation and efficient weighing. However, in practice, the accuracy of weighing results is often disturbed by multiple factors, among which the difference in gravitational acceleration and temperature change are the two decisive factors, and their mechanism and countermeasures need to be analyzed in depth from the level of technical principles.
Gravitational acceleration
The essence of weighing an electronic balance is to convert the mass of an object into an electrical signal through an electromagnetic force balance sensor – when the object is placed on a weighing plate, the electromagnetic force needs to precisely counteract the object's gravity, and the magnitude of gravity is directly related to the acceleration of local gravity. However, the acceleration due to gravity is not constant.
Influence mechanism
The higher the latitude and the lower the altitude of the Earth, the greater the gravitational acceleration (e.g., about 9.78 m/s² at the equator and 9.83 m/s² at the poles), and the density of the earth's crust and the distribution of groundwater will also cause local subtle fluctuations. If the balance is not calibrated for the place of use, the same object can be weighed in different regions and can cause significant errors.
Compensation Scheme
Limitations of built-in weight calibration
Traditional electronic balances often have built-in calibration weights, and the local gravitational acceleration is calculated by weighing the built-in weights, but this method requires additional mechanical structure, and the weights are susceptible to contamination and difficult verification after long-term use, which may introduce "time drift error".
Advantages of standard weights included
The use of independent standard weights (such as F1 weights) to load the weighing pan directly, and the automatic calibration of gravitational acceleration through the electronic system, has become the mainstream solution for high-precision balances due to the traceability of weight accuracy and higher compensation accuracy.
Temperature fluctuations
The influence of temperature changes on electronic balances runs through the whole process of "warm-up-weigh-environment", and its core is to destroy the stability of the electromagnetic force balance.
Principle of thermal effect
Heat generation of transformers, rectifiers and other components inside the balance, or sudden changes in ambient temperature, will cause the magnetic flux density of the magnet to decrease. For example, during the warm-up phase, for every 1°C increase in coil temperature, the magnetic flux can decrease by 0.02%, which in turn reduces the electromagnetic force and drifts towards a "positive deviation".
The sensitivity temperature coefficient should not be overlooked – in the case of the METTLER TOLEDO AL series, for example, the sensitivity drifts by 0.00025% for every 1°C change in temperature, and a 5°C fluctuation in ambient temperature can result in a 1.25mg error for weighing a 100g object.
Precise control measures
Standardization of preheating time - balances with different precision need to be preheated strictly - 0.01mg index balances need to be preheated for at least 5 hours, and 0.001mg ultra-micro balances need to be preheated for more than 24 hours until the indicated values are stable and there is no one-way drift before being set to zero.
Structurally optimized design – the new generation of balances moves heating elements (e.g. transformers) to the outside or separates the weighing chamber from the electronic module to reduce heat conduction interference; Constant temperature laboratory environment control needs to control temperature fluctuations within ±0.5°C.
Other factors
Environmental control - keep away from the air flow and vibration sources of doors and windows, and be equipped with a voltage regulator to cope with voltage fluctuations (recommended voltage stability ≤±1%).
Dynamic calibration habits - when the temperature changes by more than 2°C, or when the balance is moved, it needs to be calibrated with the attached standard weights immediately; Calibrate at least once every 4 hours in daily use.
Maintenance points - regularly clean the weighing pan and draft shield with absolute ethanol to avoid dust adsorption affecting the balance; It is recommended that high-precision balances be fully verified by a metrology institute every year.
All in all, the weighing accuracy of an electronic balance is the result of the combined effect of "principle design-environmental control-operation specification". Only by deeply understanding the influence mechanism of gravitational acceleration and temperature changes, combined with standardized calibration procedures and environmental management, can the measurement error be controlled within the micron-level accuracy range, providing reliable data support for scientific research and industrial production.
