In the field of load cells, there are significant differences between the old and new national standards in terms of main technical indicators, basic concepts, and evaluation methods. These differences are mainly reflected in the types of load cells, such as S-type, cantilever type, spoke type, plate ring type, diaphragm type, bridge type, and cylindrical type.
As a core passive component in electronic technology, load cells, along with resistors and inductors, form the foundation of electronic circuits. Among them, capacitive sensors are particularly adept at converting changes in the measured quantity into changes in capacitance; essentially, they are capacitors with variable parameters.
The basic principle of a load cell is that an elastic body (including an elastic element and a sensing beam) undergoes elastic deformation under external force, which in turn causes the resistance strain gauge (as a conversion element) in close contact with it to deform accordingly. This deformation causes a change in the resistance of the strain gauge (increase or decrease). Subsequently, through a precise measuring circuit, this change in resistance is converted into an electrical signal, achieving an effective conversion from external force to electrical signal. In this process, the resistance strain gauge, the elastic body, and the detection circuit together constitute the core of a resistance strain gauge load cell, and none of them can be omitted.
Analysis of the characteristics of weighing sensors:
Advantages: The load cell is not sensitive to changes in the loading point, has good resistance to off-center loads, excellent linearity, is easy and convenient to install, has high stability after fixing, and has relatively low manufacturing cost.
Disadvantages: Its center of gravity is relatively high, and its overload capacity is relatively limited. In particular, it is challenging to achieve a high level of accuracy for large-capacity weighing sensors.
Performance characteristics of the load cell:
With continuous social progress and the sustained strengthening of national power, new materials are emerging in an endless stream, and the performance of existing materials has been further improved, with their application scope constantly expanding. Therefore, more stringent requirements have been placed on the testing of materials.
Currently, the most common weighing sensors on the market are mainly divided into two major series and four types:
Hydraulic series: including manual hydraulic load cells and electro-hydraulic servo hydraulic load cells.
The Electronic Universal Series covers both conventional and high-performance electronic weighing sensors.
Performance characteristics analysis:
Manual hydraulic load cells: This type of sensor relies primarily on a simple high-pressure oil source as its power source and is controlled by a manually adjusted valve. The loading process requires manual operation and is an open-loop control system. Limited by the oil flow rate and the main unit structure, the piston stroke of the cylinder in a manual hydraulic load cell is typically short, resulting in a relatively low testing speed. Due to price considerations, pressure sensors are usually used for force measurement (pressure sensors may be used for large tonnage applications), thus limiting accuracy and range. Generally, the accuracy is Class 1 or 2, and the range is typically 4% F (MISSING). Furthermore, due to the influence of cylinder friction, its tonnage is difficult to achieve very small capacities; the smallest in China is generally 5T. However, due to its low price and large tonnage capabilities, it is still widely used in finished product inspection and single material index testing.
Electro-hydraulic servo load cells: These sensors use a precision high-pressure oil source as their power source and are controlled automatically in a closed loop via a servo valve or proportional valve. They offer high control performance and can achieve various control modes, including load, strain, and displacement. Similar to manual hydraulic load cells, their testing speed is limited by the oil flow rate. However, due to the closed-loop automatic control, system stiffness becomes crucial for the normal operation of the entire system. To minimize the impact of the fluid on the overall stiffness of the machine, the stroke of electro-hydraulic servo testing machines is typically small. Furthermore, due to the influence of overall machine stiffness, electro-hydraulic servo testing machines generally have a large tonnage, typically exceeding one ton.
In summary, load cells, as a crucial component of electronic technology, exhibit significant differences between the old and new national standards, particularly in terms of type and technical specifications. These sensors effectively convert external force into electrical signals through elastic deformation and resistance changes in strain gauges. While offering advantages such as easy installation and high stability, they also face challenges like a high center of gravity and limited overload capacity. With advancements in materials science, the performance of load cells has been continuously improved, leading to their widespread application across various fields. From hydraulic to universal electronic series, different types of load cells offer unique characteristics, meeting the needs of diverse scenarios. Despite limitations in certain aspects, load cells continue to play an irreplaceable role in electronic technology due to their advantages and wide range of applications. In the future, with further technological development, the performance and application scope of load cells will continue to expand, bringing greater convenience to our lives and work.
