Load CellThe selection of sensors should be based on the application situation, including the number of sensor support points, range, accuracy level, and environmental adaptability.
Selection of weighing sensor range.
Based on experience, sensors should generally be operated within 30% to 70% of their range. However, for some weighing instruments that have significant impact during use, such as dynamic track scales, dynamic car scales, steel scales, etc., when selecting weighing sensors, it is generally necessary to expand their range to ensure that the sensor operates within 20% to 40% of its range, thereby increasing the weighing reserve of the sensor, To ensure the safety and lifespan of the sensor and avoid overloading.
General rules for selection of weighing sensors
The general rules for selecting weighing sensors in electronic scales require a comprehensive evaluation of the type of weighing sensor to be used. Below are several aspects to consider when selecting the structure, range, and accuracy level of the weighing sensor.
1、 Selection of structure and form
The selection of a weighing sensor with a certain structural form mainly depends on the structure of the weighing instrument and the environmental conditions under which it is used. If you want to make a low profile weighing instrument, you should generally choose cantilever beam and wheel amplitude sensors. If there is no strict requirement for the height of the appearance, column sensors can be used. In addition, if the environment in which the weighing instrument is used is very humid and there is a lot of dust, it should be selected with a better sealing form; If there is an explosion hazard in the environment, intrinsic safety sensors should be selected; If in an elevated weighing system, safety and overload protection should be considered; If used in high-temperature environments, a weighing sensor with a water-cooled jacket should be selected; If used in high cold areas, sensors with heating devices should be considered.
In the selection of form, one factor to consider is the convenience of maintenance and the required cost, that is, whether the maintenance components can be obtained smoothly and quickly once the weighing system malfunctions. If it cannot be achieved, it indicates that the form selection is not appropriate enough.
2、 Selection of measuring range
The closer the weighing value of the weighing system is to the rated capacity of the sensor, the higher its weighing accuracy. However, in practical use, due to the presence of self weight, tare weight, vibration, impact, and eccentric load of the scale body, there are significant differences in the principle of selecting sensor limits for different weighing systems.
As a general rule, there can be: * Single sensor static weighing system: fixed load (weighing platform, container, etc.)+variable load (load to be weighed)≤ The rated load of the selected sensor X 70% * Multi sensor static weighing system: fixed load (weighing platform, container, etc.)+variable load (load to be weighed)≤ Select a sensor with a rated load X and a number of sensors X of 70%, where the 70% coefficient is added considering factors such as vibration, impact, and bias load. It should be noted that first of all, the rated capacity of the sensor should be selected to meet the values in the manufacturer's standard product series as much as possible. Otherwise, using non-standard products will not only be expensive, but also difficult to replace after damage. Secondly, in the same weighing system, it is not allowed to use sensors with different rated capacities, otherwise the system will not function properly. Furthermore, the so-called variable load (load to be weighed) refers to the actual load applied to the sensor. If there is a mechanism (such as a lever system) that multiplies and attenuates the force value during the transmission process from the weighing platform to the sensor, its impact should be considered.
3、 Selection of accuracy
The accuracy level of the weighing sensor should be selected to meet the accuracy level requirements of the weighing system, as long as it can meet this requirement. If a 2500 degree sensor can meet the requirements, do not choose a 3000 degree sensor.
If several sensors of the same form and rated capacity are used in parallel in a weighing system, the comprehensive error isΔ, There are:&Delta=& Delta/ N1/2 (2&flash; 12) where:Δ: The comprehensive error of a single sensor;
n: Number of sensors. In addition, electronic weighing systems generally consist of three major components: weighing sensors, weighing displays, and mechanical structural components. When the tolerance of the system is 1, the comprehensive error (Δ) of the weighing sensor, which is one of the main components of the non automatic weighing system, can generally only reach a proportional component of 0.7. Based on this and equation (2-12), it is not difficult to make a choice about the required sensor accuracy.
4、 How to achieve certain special requirements
In some weighing systems, there may be special requirements, such as in track scales where the elastic deformation of the weighing sensor is expected to be smaller, which can reduce the sinking of the weighing platform during weighing and reduce the impact and vibration of the truck when entering and exiting the weighing platform. In addition, when constructing a dynamic weighing system, it is inevitable to consider whether the natural frequency of the weighing sensor used can meet the requirements of dynamic measurement. These parameters are not listed in the general product introduction.
Therefore, when understanding these technical parameters, the manufacturer should be consulted to avoid errors.
Range selection of weighing sensors
According to the recommendation of using 60% -70% of the rated range, assume that there are 4 sensors in a silo, and the total weight of the silo's self weight plus full material weight is 50T.
Then it can be calculated that the range of a single sensor is 50T÷ 60%÷ 4 pieces=20.83T. and 50T÷ 70%÷ 4 pieces=17.8T, which means the sensor is in the range of 17.8 to 20.83T.
After determining this range, select the sensor that best meets this range in the sensor specifications.
Accuracy selection of weighing sensors
The selection of the level of the symmetrical weight sensor must consider the following conditions:
The accuracy level of weighing sensors is divided into four levels: A, B, C, and D. Different levels have different error ranges. Class A sensors have the highest requirements. The number after the level represents the calibration graduation value, and the larger the number, the better the quality of the sensor. For example, C2 represents level C, with 2000 calibration graduation values; C5 represents Class C, with 5000 calibration graduation values. Obviously, C5 is higher than C2.
A. To meet the input requirements of the instrument, the output signal of the weighing sensor must be greater than or equal to the input sensitivity value required by the instrument.
B. To meet the accuracy requirements of the entire electronic scale.
An electronic scale mainly consists of three parts: the scale body, sensors, and instruments. When selecting the accuracy of sensors, the accuracy of the sensors should be slightly higher than the theoretical calculation value, as theory is often limited by objective conditions.
If the strength of the scale body is slightly poor, the performance of the instrument is not very good, and the working environment of the scale is relatively harsh, all factors directly affect the accuracy requirements of the scale. Therefore, it is necessary to improve the requirements from all aspects, while also considering economic benefits to ensure that the purpose is achieved. When selecting sensor accuracy, the accuracy of the sensor should be slightly higher than the theoretical calculation value.
Selection of sensor environmental adaptability
Sensors used in weighing systems generally need to work in various complex environments for a long time, enduring tests such as temperature, humidity, dust, corrosion, etc. Therefore, it is necessary to make a reasonable choice of sensor sealing type in advance. The following points should be considered:
1. Pay attention to the operating temperature range:
For sensors working in high-temperature environments, high-temperature resistant sensors are often used; In addition, harsh situations require the addition of insulation, water cooling, or air cooling devices.
2. Choose the appropriate sealing form:
Dust and humidity have a significant impact on the sensor. Sensors should be selected with appropriate sealing forms, and attention should be paid to avoiding the impact of dust, humidity, and heat on the sensor during installation.
3. Choose the appropriate material:
In highly corrosive environments such as acid and alkali, stainless steel materials with good corrosion resistance and good airtightness should be selected for sensors. At present, the sensor materials are sorted in order of priority as stainless steel alloy steel aluminum alloy. Choose according to the customer's usage environment.
4. Choose explosion-proof type:
Sensors operating in flammable and explosive environments have higher requirements for explosion-proof performance, so it is necessary to choose explosion-proof sensors and pay attention to the waterproof, moisture-proof, and explosion-proof properties of cable leads.
5. Shielding
The impact of electromagnetic fields on the output of disordered signals from sensors. Generally, sensors have this function and provide shielded wires. If the impact is too large, you can choose to use aluminum boxes to completely seal and multi-layer shielding wires, as well as shielding wires with thicker shielding layers that are not easily broken down.
6. The impact of outdoor dust and humidity on short circuits of sensors. Choose a moisture-proof sensor.
Selection of sensor sensitivity
Usually, within the linear range of the sensor, the higher the sensitivity, the better. Because only when the sensitivity is high, the output signal value corresponding to the measured value is relatively large, which is beneficial for signal processing. But when the sensitivity is too high, the overload capacity of the sensor is low, which affects its service life. External noise unrelated to the measurement can also be amplified by the amplification system, affecting measurement accuracy. Therefore, it is required to choose the appropriate sensitivity based on one's own requirements. Usually 2mV/V or 3mV/V.
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