How to choose the number and mileage of load cells

How to choose the number and mileage of load cells

The selection of the number of weighing sensors is based on the use of the electronic weighing instrument and the number of points the scale body needs to support (the number of supporting points should be determined according to the principle that the geometric center of gravity of the scale body and the actual center of gravity coincide). In general, the scale body has several support points to select several sensors, but for some special scale bodies such as electronic crane scales can only use a sensor, some mechanical and electrical combination scales should be based on the actual situation to determine the choice of sensors Number.

The selection of load cell range can be determined based on the comprehensive evaluation of the scale's weighing value, the number of selected sensors, the weight of the scale body, possible partial load and dynamic load. In general, the closer the sensor's range is to the load assigned to each sensor, the higher the accuracy of its weighing. However, in actual use, due to the load imposed on the sensor, in addition to the object being called, there are loads such as the weight of the scale body, tare weight, eccentric load, and vibration impact. Therefore, when selecting the sensor range, many factors must be considered to ensure The safety and life of the sensor.

The calculation formula of the weighing sensor range is determined after a large number of experiments after fully considering the factors that affect the scale body.

The formula is as follows:

C=K-0K-1K-2K-3( Wmax+W ) /N

C—the rated range of a single sensor ; W —the weight of the scale ; Wmax —the value of the net weight of the object being called ; N —the number of support points used by the scale ; K-0 —the coefficient of insurance, generally ranging from 1.2 to 1.3 Human ; K-1 - impact coefficient ; K-2 - center -of- gravity displacement coefficient of the scale ; K-3 - wind pressure coefficient.

For example: a 30t electronic truck scale weighing 30t , the scale body weight is 1.9t , using four sensors, according to the actual situation at that time, select the insurance coefficient K-0 = 1.25 , impact coefficient K-1 = 1.18 , center of gravity The offset coefficient K-2 = =1.03 , the wind pressure coefficient K-3=1.02 , try to determine the tonnage of the sensor.

Solution: According to the calculation formula of the sensor range:

C=K-0K-1K-2K-3( Wmax+W ) /N

Know that:

C=1.25× 1.18 × 1.03 × 1.02 × ( 30+1.9 ) /4

=12.36t

Therefore, an optional sensor with a range of 15 tons (generally 10T , 15T , 20t , 25t , 30t , 40t , 50t, etc., unless specifically ordered).

According to experience, the sensors should generally be operated within the range of 30% to 70% , but for some weighing instruments that have a large impact during use, such as dynamic track scales, dynamic truck scales, steel scales, etc., when selecting sensors, Generally, it is necessary to expand its range so that the sensor operates within 20% to 30% of its range, so that the weighing storage capacity of the sensor is increased to ensure the safety and life of the sensor.

Again, know the scope of application of different types of load cells.

The choice of sensor type mainly depends on the type of weighing and installation space, to ensure proper installation, weighing safe and reliable ; on the other hand, to consider the manufacturer's recommendations. Manufacturers generally specify the applicable range of the sensor according to the force conditions of the sensor, performance index, installation form, structure type, elastomer material, etc. For example, aluminum cantilever sensors are suitable for use in pricing scales, platform scales, case scales, etc .; Cantilever beam sensors are suitable for hopper scales, electronic belt scales, sorting scales, etc .; steel bridge sensors are suitable for track scales, truck scales, crane scales, etc .; column sensors are suitable for truck scales, dynamic track scales, large-tonnage hopper scales Wait.

Finally, we must know the selection method of the weighing sensor.

The accuracy level of the load cell includes the non-linear, creep, creep recovery, hysteresis, repeatability, and sensitivity of the sensor. When selecting a sensor, do not simply pursue a high-grade sensor, and consider not only meeting the accuracy requirements of the electronic scale, but also its cost.

The selection of the load cell grade must meet the following two conditions:

1. Meet the instrument input requirements. Weighing display instrument is to display the weighing result after the output signal of the sensor is amplified, A/D converted and other processing. Therefore, the output signal of the sensor must be greater than or equal to the size of the input signal required by the instrument. That is, the output sensitivity of the sensor is based on the matching formula of the sensor and the instrument. The calculation result must be greater than or equal to the required input sensitivity of the instrument.

Matching formulas for sensors and meters:

Sensor output sensitivity * Excitation supply voltage * Weighing of scales

The number of scales * Number of sensors * Sensor range

For example: a weighing package weighing 25kg , the number of division is 1000 ; the scale body uses 3 L- BE - 25 sensors, measuring range is 25kg , the sensitivity is 2.0 ± 0.008mV/V , the arch bridge voltage is 12V ; AD4325 scales with the instrument. Q. Can the sensor be matched with the meter?

Solution: After reading , the input sensitivity of the AD4325 meter is 0.6 μV/d , so the actual input signal of the meter can be obtained based on the matching formula of the sensor and the meter:

2 × 12 × 25/1000 × 3 × 25 = 8 μ V/d> 0.6 μ v/d

Therefore, the sensors used meet the input sensitivity requirements of the instrument and can match the selected instrument.

2. Meet the requirements of the accuracy of the entire electronic scale. An electronic scale is mainly composed of a scale body, a sensor, and an instrument. When the accuracy of the sensor is selected, the accuracy of the sensor should be slightly higher than the theoretical calculation value because the theory is often limited by objective conditions, such as a scale. The strength of the body is poor, the performance of the instrument is not very good, and the working environment of the scale is relatively harsh and other factors have a direct impact on the accuracy of the scale. Therefore, it is necessary to improve the requirements in all aspects, and consider the economic benefits to ensure that the purpose is achieved.

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