Basic principle of weighing sensors

1、 Principle of resistance strain type weighing sensor

1. The resistance strain type weighing sensor is based on the principle that an elastic body (elastic element, sensitive beam) undergoes elastic deformation under external force, causing the resistance strain gauge (conversion element) attached to its surface to also deform. After the deformation of the resistance strain gauge, its resistance value will change (increase or decrease), and then the corresponding measurement circuit will convert this resistance change into an electrical signal (voltage or current), Thus completing the process of converting external forces into electrical signals. From this, it can be seen that resistance strain gauges, elastomers, and detection circuits are essential components in the resistance strain type weighing sensor. Elastomer is a structural component with a special shape. It has two functions: firstly, it bears the external force exerted by the weighing sensor, generates a reaction force against the external force, and achieves relative static equilibrium; Secondly, it needs to generate a high-quality strain field (region), so that the resistance strain gauge pasted in this region can ideally complete the transformation task of strain and electrical signals.

Taking the elastic body of the sensor series weighing sensor of Guangzhou Zhongxin Automation Technology Co., Ltd. as an example, let's introduce the stress distribution.

2. A rectangular cantilever beam with blind holes

The bottom center of the blind hole is subjected to pure shear stress, but tensile and compressive stresses will occur in the upper and lower parts. The main stress direction is tension and compression. If the strain gauge is attached here, the upper half of the strain gauge will be stretched and the resistance value will increase, while the lower half of the strain gauge will be compressed and the resistance value will decrease. The strain expression for the center point at the bottom of the blind hole is listed below, without further derivation.

3. Detection circuit

The function of the detection circuit is to convert the resistance change of the resistance strain gauge into a voltage output. Because the Wheatstone bridge has many advantages, such as being able to suppress the influence of temperature changes, suppressing lateral force interference, and conveniently solving the compensation problem of weighing sensors, the Wheatstone bridge has been widely used in weighing sensors.

Because the sensitivity of the full bridge equal arm bridge is the highest, and the parameters of each arm are consistent, the influence of various interferences is easily offset, so the weighing sensors all use the full bridge equal arm bridge.

2、 How to choose a weighing sensor

1. The weighing sensor is referred to as the heart of electronic scales, and its performance largely determines the accuracy and stability of electronic scales. When designing electronic scales, it is often necessary to encounter the problem of selecting sensors.

A weighing sensor is actually a device that converts a quality signal into a measurable electrical signal output. When using a sensor, the first thing to consider is the actual working environment in which the sensor is located. This is crucial for the correct selection of sensors, as it relates to whether the sensor can work properly, its safety and service life, and even the reliability and safety of the entire weighing instrument.

The selection of sensor range can be determined based on a comprehensive evaluation of factors such as the maximum weighing value of the scale, the number of sensors selected, the self weight of the scale body, the possible maximum bias load, and dynamic load. Generally speaking, the closer the range of a sensor is to the load assigned to each sensor, the higher the accuracy of its weighing. However, in practical use, due to the load added to the sensor, in addition to the weighed object, there are also loads such as the weight of the scale body, tare weight, eccentric load, and vibration impact. Therefore, when selecting the sensor range, many factors should be considered to ensure the safety and lifespan of the sensor.

Based on experience, sensors should generally be operated within 30% to 70% of their range. However, for some scales that have significant impact during use, such as dynamic track scales, dynamic car scales, steel scales, etc., when selecting sensors, the range should generally be expanded to ensure that the sensor works within 20% to 30% of its range, and the weighing reserve of the sensor should be increased to ensure the safety and lifespan of the sensor. The selection of sensor type mainly depends on the type of weighing and installation space, ensuring proper installation and safe and reliable weighing; On the other hand, consider the manufacturer's suggestions. Manufacturers generally specify the applicable range of sensors based on their stress conditions, performance indicators, installation forms, structural types, and elastic material characteristics. For example, aluminum cantilever beam sensors are suitable for pricing scales, platform scales, and desk scales; The steel cantilever beam sensor is suitable for hopper scales, electronic belt scales, sorting scales, etc; Steel bridge type sensors are suitable for track scales, truck scales, overhead crane scales, etc; Column type sensors are suitable for truck scales, dynamic track scales, large tonnage hopper scales, etc.

So, the sensors used meet the requirements of instrument input sensitivity and can match the selected instrument. Meet the accuracy requirements of the entire electronic scale. An electronic scale is mainly composed of three parts: the scale body, sensors, and instruments. When selecting the accuracy of sensors, the accuracy of sensors should be slightly higher than the theoretical calculation value, because theory is often limited by objective conditions, such as poor strength of the scale body, poor performance of instruments, and harsh working environment of the scale, which directly affect the accuracy requirements of the scale. Therefore, it is necessary to improve the requirements from various aspects, We also need to consider economic benefits to ensure that we achieve our goals.

The Sensor Business Unit of Guangzhou Zhongxin Automation Technology Co., Ltd. has established long-term and close communication and cooperation relationships with many top sensor brands around the world, becoming an important partner for many world-class weighing sensor brands to enter the Chinese market and explore the Chinese market. It is the most authoritative first level agent sales channel for selling world-class sensors in China, We specialize in providing automation equipment, instruments, and spare parts for well-known industrial brands in Europe, America, Japan, South Korea, and China. Through our professional services and honest management, we have established a good reputation and reputation in the domestic sensor industry, helping customers quickly achieve their demand goals in their work. Guangzhou Zhongxin Technology Sensor Business Unit provides customers with the most cost-effective products, ensuring fast delivery time and 100% original import, Provide high-quality products and services with dedication, provide accurate selection for customers, and guide installation and debugging. Strive to build the first brand of sensor sales in China and become the most excellent and leading professional distributor of imported industrial spare parts in China; Provide high-quality products and services with dedication, provide accurate selection for customers, and guide installation and debugging. The company is mainly divided into Sensor Business Unit, Industrial Automation Control System Engineering Project Business Unit, and Automation Control Equipment Product Business Unit.

The products distributed by the agent are widely used in industries such as petrochemical, steel, metallurgy, transportation construction, cement, mining, equipment manufacturing, weighing equipment manufacturing, environmental protection, pharmaceuticals, food production, papermaking, textiles, animal husbandry, electricity, energy, aerospace, etc.

3、 Classification of weighing sensors

1. Divided by force mode:

a. Pressure type

b. Pull type

c. Tension compression type

d. Beam type

2. By elastomer material:

a. Stainless steel: mainly used in corrosive environments such as food, chemical, and pharmaceutical industries;

b. Alloy steel: in corrosive environments;

c. Aluminum alloy: generally used in markets with small range and low price.

3. Classified by output data category:

a. Analog sensor: Output is an analog signal, such as voltage, current, etc;

b. Digital sensor: Directly output the desired digital signal, such as kilograms, tons, etc.

4. By applicable temperature

a. Normal temperature: used in regular places without special requirements for temperature;

b. High temperature: used in environments with high temperatures (usually above 100 ℃) such as metallurgy and nuclear power;

c. Low temperature: Used in places with temperatures below -30 ℃, such as freezing tests

5. By precision

6. According to the appearance structure

a. Columnar type

b. S-type

c. Spoke type

d. Beam type

e. Single point equation

4、 Basic applications of weighing sensors

Weighing sensors are mainly used in various electronic scales, industrial control fields, online control, safety overload alarms, material testing machines, and other fields. Such as electronic truck scales, electronic platform scales, electronic forklifts, dynamic axle load scales, electronic hook scales, electronic pricing scales, electronic steel scales, electronic track scales, hopper scales, ingredient scales, canned scales, etc.