The history of weighing instrument development
The load cell refers to the use of the performance characteristics of the sensor to accurately measure the object. In our lives, from small daily necessities to weighing large cargoes such as ports to measure force, load cells have been widely used in various electronic weighing instruments.
“Balance” means “measure”. It is an instrument that uses Hooke’s law or the principle of lever balance of force to measure the mass of an object. It is the most commonly used and most numerous measuring device in various sectors of the national economy. Weighing instruments can be divided into three categories: mechanical scales, electronic scales, and electromechanical combined scales according to structural principles.
Data show that as early as the 16th century BC (Shang Dynasty, Western Zhou Dynasty), our country had a simple weighing instrument for weighing the quality of materials. Written record. Today, in our country, it is still the most popular weighing instrument among the people. In developed countries, the wooden steelyard is a historical relic that is hard to find.
Mechanical weighing instruments began in my country at the end of the 19th century (the end of the Qing Dynasty). At that time, the scales, scales and various mechanical truck scales and railroad scales commonly used in commercial and industrial and mining enterprises belong to this category. So far, my country’s mechanical weighing instrument manufacturing industry has a production history of more than one hundred years, and has a considerable technical level and production scale. At present, most of the commercial scales and industrial ground scales in use in our country are still mechanical scales.
In the 1960s, research succeeded in a mechanical and electrical combination of automatic scale-grating scale, which consists of three parts: lever system, grating device and electronic circuit. The lever system produces displacement under the action of the load, and the grating device converts this displacement into a digital signal and sends it to the electronic circuit. Finally, a digital tube is used to visually display the weight.
The contribution of load cells to the development of weighing instruments
Later, there was the load cell mentioned above. From a principle point of view, the load cell is a kind of load cell. Because it can only measure the force perpendicular to the horizontal plane pointing to the center of the earth, it is generally used in weighing instruments, while other load cells can measure force in any direction, so the application range is wider.
In addition, the two are different in many aspects such as measurement unit, accuracy grade, measurement range, loading direction, working temperature, natural frequency and so on. For example, the expected load of the load cell is always along the direction of the center of the earth (ie, the direction of gravity), while the force sensor can obtain loads occurring in all directions, regardless of the direction of the earth’s gravity and the installation method. For another example, the design and installation of the loading device should ensure that the load force is applied to the load cell to coincide with the force axis, so as to minimize the influence of the inclined load and the eccentric load.
According to the conversion method, load cells can be divided into 8 types: photoelectric, hydraulic, electromagnetic, capacitive, magnetic pole change, vibration, gyro, and resistance strain. Currently, the most widely used is the resistance strain.
The principle of the resistance strain type load cell is that the elastic body (elastic element, sensitive beam) is elastically deformed under the action of external force, so that the resistance strain gauge (conversion element) pasted on its surface also deforms; after the resistance strain gauge is deformed , Its resistance will change (increase or decrease). Then through the corresponding measurement circuit, this resistance change is converted into an electrical signal (voltage or current) and output, thus completing the process of converting the external force into an electrical signal.
It can be seen that resistance strain gauges, elastomers and detection circuits are indispensable parts of resistance strain load cells. Among them, the resistance strain gauge is to mechanically arrange a resistance stove on a substrate made of organic material, and the elastic body is a special-shaped structural part. It bears the external force of the load cell, and produces a reaction force to achieve a relative static balance; at the same time, a high-quality strain field (zone) is generated, so that the resistance strain gage pasted in this zone can ideally complete the strain electrical signal Conversion task. The function of the detection circuit is to convert the resistance change of the resistance strain gauge into a voltage output.
Application range and purpose of load cell
Weighing sensors are mainly used to measure weight, and are used in various electronic weighing instruments, industrial control fields, online control, installation overload alarms, material testing machines and other fields. The application equipment includes electronic truck scales, electronic platform scales, electronic forklifts, and dynamic axles. Weighing scales, electronic hook scales, electronic pricing scales, electronic steel scales, electronic rail scales, hopper scales, batching scales, filling scales, etc. Load cells generally cannot be found directly because they are usually hidden in the equipment and belong to accessories.
A load detection branch road is built at the entrance of the expressway. When the truck passes the dynamic weighing bridge, the load cell and the electronic scale will check and judge by themselves, and at the same time give signals to control the traffic lights. With the development of sensors and other electronic devices, they will become more and more intelligent. Unmanned control can prevent overweight vehicles from passing, and vehicles can be charged by weight.