Definition
A large weighing balance is a precision mass metrology instrument used to measure larger mass objects. Its core function is to provide accurate and reliable quality data over a wide range of volumes. These instruments typically have high maximum weighing values to meet the needs of weighing heavy samples or large volumes of materials in a laboratory or industrial setting. It is designed and operated in accordance with a series of international and national standards to ensure the accuracy and comparability of measurement results.
Principle
Modern large weighing balances mainly work on the principle of electromagnetic force balance or strain gauge sensor. In an electromagnetic force balance balance, when the object is placed on the scale, the lever system is deflected, which is detected by the displacement sensor and converted into an electrical signal. After this signal is processed by the control system, the driving coil generates an electromagnetic force in the magnetic field of the permanent magnet that is balanced with gravity, and the mass of the measured object can be accurately calculated by measuring the amount of current required to maintain the balance. Its equilibrium relationship can be expressed as:F = BIL = mg, among themFis the electromagnetic force,Bis the magnetic induction strength,Ifor the current,Lis the length of the wire,mFor quality,gis gravitational acceleration.
The strain gauge balance uses a Wheatstone bridge composed of resistive strain gauges. When the scale pan is loaded, the elastomer deforms, causing the resistance value of the strain gauge attached to it to change, thus breaking the balance of the bridge, producing an electrical signal output proportional to the load, and displaying the mass value after amplification and analog-to-digital conversion.
Measurement method
When measuring with a large weighing balance, it is important to follow a standardized operating procedure to ensure data accuracy. First, the instrument should be placed horizontally on a stable, vibration-free table and preheated to achieve thermal equilibrium. Calibration is required before formal weighing, usually using standard weights that have been traced to the meter. When measuring, the DUT should be lightly placed in the center of the scale pan, and the displayed value should be stable before reading. For samples that are susceptible to environmental influences or generate static electricity, measures should be taken, such as the use of windscreens or ionizers. For situations where high-precision results are required, the method of averaging multiple measurements can be used.
Influencing factors
The measurement accuracy of large weighing balances is affected by a variety of environmental and operational factors. Environmental factors include air buoyancy, temperature fluctuations, airflow disturbances, ambient vibrations, and changes in relative humidity. Air buoyancy has different effects on objects of different densities, which can be corrected by formulas. Operating factors involve the calibration status of the balance, the placement of the sample, the choice of weighing vessel, and the skill of the operator. In addition, the long-term stability, linear error, and repeatability of the instrument are important performance indicators that affect the final measurement results. Understanding and controlling these factors is fundamental to reliable data.
Application
Large weighing balances play a key role in many fields. In scientific laboratories, it is used to formulate large quantities of chemical reagents, perform material density determinations, or prepare bulk samples. In industrial production, it is commonly used in raw material warehousing inspection, production process control and weight verification of finished product packaging. It can be used in agriculture for weighing analysis of seeds, fertilizers, or harvested crops. In the pharmaceutical industry, it is used for weighing large quantities of APIs. Its high range and sufficient resolution make it an important tool for bridging laboratory analysis with large-scale production.
Selection
Choosing the right large weighing balance requires a comprehensive consideration of technical parameters and actual needs. The core parameters include maximum weighing value and readability (index value) to ensure that the balance range covers the daily weighing range while the resolution meets the minimum net weight measurement requirements. The repeatability of the balance, bias load error and other performance indicators should be evaluated to meet the relevant standards. The environment in which it is used determines whether a windscreen or a protective design against vibration and static electricity is required. In terms of functionality, data interfaces, statistical functions, compliance software support, etc. can be considered. In addition, the size of the instrument and the size of the scale should match the placement space and sample container. It is recommended to refer to the requirements of the International Organization for Metrology (OIML) or national metrology technical specifications, and make a comprehensive judgment based on specific application scenarios.