Analysis: technical characteristics and applications of several common weighbridge load cells - Database & Sql Blog Articles

Load cells are essential components in modern weighing and sensing technologies. They serve as the core of weighbridges, enabling precise measurement of weight and force across various industries. This article explores the technical characteristics and applications of different types of load cells, including strain gauge, electromagnetic, photoelectric, capacitive, hydraulic, vibratory, magnetic pole deformation, gyroscope, and fiber Bragg grating (FBG) load cells.

Understanding these sensors is crucial for professionals working in automation, industrial control, and measurement systems. Each type of load cell has its own unique working principle, advantages, and limitations, making them suitable for specific applications. This article provides a detailed analysis of each category to help readers choose the most appropriate sensor for their needs.

I. Overview of Load Cells

The development of modern information technology relies heavily on three key areas: information acquisition, transmission, and processing. Sensors play a vital role in the first stage—information acquisition—as they act as the "sensory organs" of the system. In an automatic detection system, without sensors, it would be impossible to monitor and control parameters during production processes, making automation unachievable.

Load cells, also known as weighbridges, are at the heart of many weighing systems. With advancements in technology, especially with the rise of microprocessors, load cells have become indispensable in industrial process control. Today, they are used in almost every industry, from manufacturing to logistics, due to their accuracy, reliability, and versatility.

II. Strain Gauge Load Cell

A strain gauge load cell uses a metal conductor as a conversion element. The principle behind it is the strain effect, where the resistance of a metal wire changes when deformed (stretched or compressed). This change in resistance is measured using a Wheatstone bridge circuit, which converts the mechanical deformation into an electrical signal.

Strain gauge load cells are widely used due to their high accuracy, wide measuring range, and good frequency response. They can operate under harsh conditions and are easy to miniaturize. However, they may suffer from issues like hysteresis, creep, and nonlinearity, but these can be mitigated through proper design and calibration.

III. Electromagnetic Force Balance Sensor

Electromagnetic force balance sensors work based on the principle of Ampère's force. When a current-carrying wire is placed in a magnetic field, it experiences an upward electromagnetic force that balances the downward gravitational force of the object being weighed. This allows for highly accurate measurements, often up to 1/60,000 precision.

These sensors are commonly used in electronic analytical balances and require high manufacturing standards. Only a few manufacturers worldwide have mastered this advanced technology, making them suitable for high-end markets such as laboratory equipment and precision measurement devices.

IV. Capacitive Load Cell

Capacitive load cells convert mechanical quantities like displacement or pressure into changes in capacitance. They consist of two parallel electrodes, and any change in distance, area, or dielectric material between them affects the capacitance value.

Capacitive sensors are known for their high sensitivity, low power consumption, and strong overload capability. However, they may suffer from nonlinear output and parasitic capacitance, which can affect accuracy. They are often used in environments where high temperature and vibration are present, such as in steel mills.

V. Photoelectric Load Cell

Photoelectric load cells use optical gratings or coded discs to measure angular displacement. When a weight is applied, the movement of the grating or code wheel generates light signals that are converted into electrical signals for measurement.

These sensors are stable and resistant to interference, making them suitable for harsh industrial environments. However, their speed is limited, which makes them less ideal for high-speed weighing applications. Due to the maturity of other technologies, photoelectric load cells are now more of a transitional product in the market.

VI. Hydraulic Load Cell

Hydraulic load cells operate by detecting changes in hydraulic oil pressure caused by the weight of an object. The pressure increase is proportional to the weight, allowing for measurement of large masses. While they have a simple structure and large measuring range, their accuracy is generally lower than other types, typically below 1/1000.

They are commonly used in applications where high accuracy is not required, such as in loader scales and safety overload protection systems.

VII. Magnetic Pole Deformation Load Cell

Magnetic pole deformation load cells rely on changes in magnetic permeability caused by mechanical deformation. When an object is placed on the sensor, the stress induced in the ferromagnetic material alters the induced voltage in a secondary coil, which is then used to determine the mass of the object.

These sensors are not as accurate as others, with typical precision around 1/100. They are primarily used for large-tonnage weighing and are rarely found in practical applications today.

VIII. Vibrating Load Cell

Vibrating load cells measure the natural frequency of an elastic element, which is proportional to the square root of the applied force. By detecting changes in frequency, the weight of the object can be determined.

Vibrating wire and tuning fork sensors are common types. They offer high accuracy and are suitable for a wide range of weights, though their complex structures make them expensive and difficult to manufacture.

IX. Gyroscopic Load Cell

Gyroscopic load cells use the precession of a spinning rotor to detect external forces. The relationship between the precession angular velocity and the applied force allows for accurate measurement of mass and force.

These sensors have fast response times, no hysteresis, and excellent temperature stability. They are used in high-precision applications, such as aerospace and scientific research, where accuracy and reliability are critical.

X. Fiber Bragg Grating (FBG) Load Cell

Fiber Bragg Grating load cells are a type of optical fiber sensor that measures physical quantities like strain and temperature by detecting changes in the Bragg wavelength. These sensors are immune to electromagnetic interference, chemically stable, and suitable for harsh environments.

They offer advantages such as small size, high transmission capacity, and multi-point distributed measurement capabilities. Although still in the research and experimental phase, FBG load cells are gaining traction in fields like structural health monitoring and railway testing.

This article was written by Shanghai Xinying Weighing Apparatus Co., Ltd., a leading manufacturer of weighing and measurement solutions. For more information, please contact us:

Head Office: No. 5108 Nanfeng Highway, Fengxian District, Shanghai

Production Base: No. 788 Yanxiu Road, Qingpu District, Shanghai

Jiangsu Production Base: No. 88 Chuangye Road, Industrial Zone, Lishui County, Huai'an City

Phone: (021) 60548466

Fax: (021) 33616158

Sales Hotline: 13818755070

Service Hotline: 400 000 4208

Email: info@xinyingweighing.com

Website: www.xinyingweighing.com