Several factors in the selection of load cell

Load cell is an indispensable part of many weighing systems, which is a conversion device that converts gravity into electrical signals. Its accuracy has a great impact on the whole weighing system. If there is a problem with the weighing sensor, it will affect the normal weighing of the whole weighing system. Especially with the emergence of microprocessors and the continuous improvement of industrial automation technology, load cells have become indispensable equipment in process control.

It is understood that at present, the weighing sensors are mainly used in various electronic scales, industrial control fields, online control, overload alarm installation, material testing machines and other fields, such as electronic truck scales, electronic platform scales, electronic forklifts, dynamic axle load scales, electronic hanging scales, electronic pricing scales, electronic track scales, steel hopper scales, batching scales, filling ranges, etc.

The selection of sensor type mainly depends on the weighing type and installation space to ensure proper installation and safe and reliable weighing; On the other hand, the manufacturer's suggestions should be considered. The manufacturer will generally specify the scope of application of the sensor according to the characteristics of the sensor such as stress, performance index, installation form, structural type, elastomer material, etc. For example, the aluminum cantilever sensor is applicable to the pricing scale, platform scale, and case scale; Steel cantilever beam sensor is applicable to hopper scale, electronic belt scale, sorting scale, etc; The steel bridge sensor is applicable to the track scale, truck scale, overhead crane scale, etc; The column sensor is applicable to truck scale, dynamic rail scale, large tonnage hopper scale, etc. The actual working environment of the sensor shall be considered when selecting the load cell, because it is related to the normal operation, safety and service life of the sensor. Under the corresponding environmental factors, we must choose the corresponding load cell to meet the specific weighing requirements.

The selection elements of the weighing sensor mainly include four aspects, namely, the sensitivity of the sensor, the accuracy of the sensor, the stability of the sensor, and the number and range of the sensor.

1: Sensitivity

The higher the sensitivity, the better. Only when the sensitivity is high, can we obtain more accurate data when measuring the weight of objects. However, the higher the sensitivity is, the greater the influence of the outside on the weight sensor will be, and the external noise will interfere with the judgment of the sensor. Therefore, there are certain requirements for the anti noise performance of the sensor to minimize the impact of noise on the sensor.

2: Precision

The weighing sensor requires very high accuracy, which is a very important link in the weighing system. The higher the accuracy of the weighing sensor, the higher its price. However, as long as the accuracy requirements meet the instrument output requirements of the weighing system slightly higher, do not choose too high to avoid unnecessary costs.

3: Stability

Stability means that the sensor can continue to work normally after being used for a long time. The sensor with high stability has a longer service life. The factors affecting the stability of the sensor include not only the quality of the load cell, but also the working environment of the load cell. A good load cell environment has little impact on it.

Therefore, when selecting and purchasing a load cell, pay attention to its applicable environment. Select a load cell according to the specific environment. Selecting the correct load cell can reduce the impact of the environment on the load cell, and is conducive to extending the service life of the load cell. For example, in the flammable and explosive environment, it is necessary to select the load cell with explosion-proof function.

4: Number and range of sensors

According to experience, the sensor should generally work within 30%~70% of its range. However, for some weighing instruments that have large impact in the use process, such as dynamic track scale, dynamic truck scale, steel scale, etc., when selecting the sensor, the range should be generally expanded to make the sensor work within 20%~30% of its range, so as to increase the weighing reserve of the sensor, so as to ensure the safety and life of the sensor. Thirdly, the applicable range of various types of sensors should be considered.

The number and range of sensors for different purposes are different. The specific number and range shall be selected according to the weight and type of the object actually measured. Generally, the weight of the actual weighing object should be less than 70%, and the loss of the symmetrical weight sensor will be smaller, which is conducive to extending its service life.

Secondly, the number and range of sensors shall be selected. The number of sensors is selected according to the purpose of the electronic scale and the number of points that the scale body needs to support (the number of support points shall be determined according to the principle of making the geometric center of gravity of the scale body coincide with the actual center of gravity). Generally speaking, several sensors are selected for several supporting points of the scale body, but for some special scales such as electronic hook scales, only one sensor can be used. For some electromechanical scales, the number of sensors selected should be determined according to the actual situation.

The selection of sensor range can be determined according to the comprehensive evaluation of the maximum weighing value of the scale, the number of selected sensors, the weight of the scale body, the maximum possible bias load and dynamic load. Generally speaking, the closer the measuring range of the sensor is to the load distributed to each sensor, the higher the weighing accuracy. However, in actual use, since the load imposed on the sensor is not only the object to be weighed, but also the dead weight, tare weight, eccentric load, vibration impact and other loads of the scale body, many factors should be considered when selecting the sensor range to ensure the safety and life of the sensor. The calculation formula of sensor range is determined through a large number of experiments after fully considering all factors affecting the scale body.