One, the scales are warming up
The preheating time of the balance is crucial for ensuring the stability of its readings. The duration of the preheating time is related to the balance's verification division value and the number of divisions. Article 18 of the procedures stipulates that the balance should be preheated for more than 0.5 hours before verification, but what is an appropriate length of preheating time beyond 0.5 hours? This depends on the requirements specified in each balance's user manual, and there is a close relationship between the preheating of the balance and its accuracy.
The temperature variation of the electromagnetic force balanced sensor primarily originates from environmental temperature changes and the heating of the overcurrent components. The fundamental working principle of an electronic balance is based on equilibrium; once it is unbalanced, the electromagnetic force is utilized to restore the balance of the scale. This electromagnetic force is proportional to the current passing through the coil, which is directly related to the object's mass, and is also proportional to the magnetic flux B of the magnet steel, the current I passing through the coil, and the length L of the coil.
When the balance is in the preheating stage, as the internal temperature rises, magnetic flux B gradually decreases, and I also diminishes, which leads to a reduction in F, causing the balance to lose equilibrium and the reading to exhibit a positive, one-directional drift. Electronic balances must be fully preheated before measurement. Only after adequate preheating, allowing the magnet to reach thermal equilibrium, does this change process end and the balance achieve balance. Then, using the tare/zero function, the display is set to zero, at which point the balance is truly ready for use.
Two: Balanced Pre-Pressure
The balance may enter sleep mode after a period of inactivity. To expedite its return to working condition, load the balance with weights multiple times before calibration. Otherwise, the difference between the process reading and the return reading will significantly increase. During loading, it is not necessary to be concerned with the weighing results or the zeroing process.
The Impact of Gravity Acceleration
Electronic balances primarily use electromagnetic force balance sensors to convert the measured mass into gravitational force and then into an electrical signal. The measurement results are closely related to the acceleration due to gravity. The magnitude of the acceleration due to gravity is influenced by various factors such as the latitude of the location, altitude, crustal density, and groundwater changes, varying with the location. Therefore, electronic balances must implement compensation for the acceleration due to gravity based on the specific location of use.
The internal calibration weight compensation method and its shortcomings. Current electronic balances commonly employ the internal calibration weight compensation method, which involves setting a calibration weight within the electronic balance and determining the local g-value through its measurement. This method requires the addition of mechanical loading mechanisms and self-calibrating weights to the electronic analytical balance, thereby increasing the product cost and process complexity. Moreover, after long-term use, the internal weights are difficult to undergo calibration checks and surface cleaning, which can easily lead to time-drift errors in the electronic analytical balance.
Attached Calibration Weights Compensation Method. By replacing the calibration weights with general standard weights, which serve as an accessory for the electronic analytical balance, they can be directly loaded onto the weighing pan for measurement. This allows for automatic calibration of gravitational acceleration, achieving automatic compensation for the impact of gravitational acceleration on the balance's weighing. Due to the guaranteed accuracy of the attached calibration weights, the compensation precision for gravitational acceleration is high and has been widely applied.
Impact of Environmental Temperature Fluctuations
Furthermore, temperature variations can lead to sensitivity drift in electronic balances, thereby causing measurement deviations. The temperature coefficient of sensitivity, Tc = 2?×10^-6/°C, indicates that for every degree Celsius change, sensitivity varies by 0.00025%. If a 100g object is weighed, a significant error of up to can occur when the environment changes by 5°C. Therefore, when there is a significant change in ambient temperature, electronic balances should be calibrated to ensure the accuracy of weighing results.
The balance is crucial for the transmission of quality value, and the calibration of an electronic balance is a prerequisite for its metrological performance. Moreover, calibration of the electronic balance provides an important safeguard for precise quality control. To achieve a higher grade for the electronic balance, it is necessary to refer to the national metrological verification regulations and conduct inspections based on the comprehensive performance characteristics of the electronic balance.
