What We Should Pay Attention to When Weighing Sensors for Electronic Scales

Everyone knows that the sensor is the most important part of the electronic scale. Its performance and working conditions determine the accuracy and stability of the electronic scale. Since the sensor is easily influenced by the external environment, when we actually select the sensor for the electronic scale, we must consider the use of the scale, the scale needs to support the number of points and other aspects to consider:

The choice of the number of sensors and range:

The selection of the number of sensors is based on the use of the electronic scale and the number of points the scale body needs to support (the number of support points should be determined based on the principle that the geometric center of gravity of the scale body is coincided with the actual center of gravity). 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 the sensor range can be determined based on the comprehensive evaluation of factors such as the maximum weighing value of the scale, the number of sensors selected, the weight of the scale body, the maximum partial load that may be generated, and the 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 weighed, there are loads such as the scale body weight, 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 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 - scale body weight

Wmax—the maximum value of the net weight of the object

N - The number of support points used by the scale

K-0 - insurance factor, generally between 1.2 and 1.3

K-1—impact coefficient

K-2—Center of Gravity Offset Factor

K-3—wind pressure coefficient

For example: a 30t electronic truck scale, the maximum weighing is 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, the impact coefficient K-1 = 1.18, Center-of-gravity displacement coefficient K-2—=1.03, 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 15t (generally the tonnage of the sensor is only 10T, 15T, 20t, 25t, 30t, 40t, 50t, etc., unless specifically ordered).

According to experience, the sensor should generally be operated within its 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 works within 20% to 30% of its range, so that the weighing reserve of the sensor is increased to ensure the safety and life of the sensor.

To consider the range of application of various types of sensors:

The accuracy level of the sensor includes the non-linear, creep, creep recovery, hysteresis, repeatability, and sensitivity of the sensor. When selecting sensors, do not simply pursue high-level sensors, and consider not only the accuracy requirements of electronic scales, but also the costs.

The choice of sensor grade must meet the following two conditions:

1. Meet the requirements of instrument input. Weighing display instrument displays the weighing result after the sensor's output signal 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 to say, 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 * Maximum Weighing of Scale

The number of scales * Number of sensors * Sensor range

For example: a weighing package weighing 25kg, the maximum number of divisions is 1000; the scale body uses three L-BE-25 sensor, measuring range is 25kg, the sensitivity is 2.0±0.008mV/V, the arch bridge pressure force 12V; scale using AD4325 meter. Q. Can the sensor be matched with the meter?

Solution: After consulting, the input sensitivity of AD4325 meter is 0.6μV/d, so according to the matching formula of sensor and meter, the actual input signal of the meter is: 2×12×25/1000×3×25=8μV/d>0.6. Μv/d, so the sensor used meets the instrument's input sensitivity requirements and can match the selected meter.

2. Satisfy 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.