The Main Error Sources and Solutions of Electronic Scale

Working principle of electronic scale: the electronic scale is to measure the value of gravity by using the deformation of elastic body under the action of gravity. The electronic scale is mainly composed of weighing platform, weighing sensor, junction box, shielded signal cable and weighing display instrument. The process is as follows: put the object to be weighed on the weighing table, the weighing table will be elastic deformed due to the action of gravity, and the elastic body of the deformed sensor will generate an excitation voltage, which is proportional to the weight of the object, and finally converted into a digital signal through the amplification circuit, and displayed by the display.

The error of electronic scale is the quantitative description of the accuracy of the result of symmetrical quantity. In the application of electronic scales, errors are often encountered. This not only affects the reliability of the electronic scale, but also damages the interests of the users of the electronic scale. It is an important problem to study the error source of electronic scale. It is helpful to improve the quality and efficiency of electronic scale verification by analyzing the weighing performance of electronic scale and mastering its error source.

The source of electronic scale error can be divided into measuring device, environment, method and personnel error, which can be divided into system, random and gross error. Some errors can be eliminated, and some errors cannot be eliminated.

The error of electronic scale also comes from these aspects, even if the operation is correct, it can not reach the completely correct value, and there are differences between the test results of electronic scale. Error sources: through the analysis of the principle of the electronic scale, it is found that different components will produce different errors. Here are four main error sources: 

(1) Weighing error: linear change of sensor weighing, zero drift and weighing table rubbing are the direct causes of weighing error. The sensor weighs the linear change. Due to the influence of temperature difference, impact force and floating dust, there is no linear relationship between the load of the sensor and its corresponding output voltage, which makes the weighing linearity of the electronic scale sensor change greatly. Sometimes, the error of some weighing points is large, so the relative error of weighing will be greatly reduced when the linear calibration of weighing is carried out, that is, the weighing of electronic scale is calibrated in sections. Zero drift. Electronic scales in the process of use by the size of different and repeated impact load, the force of the sensor is very complex, eventually leading to changes in the contact of the sensor, so that the original state of the timing has changed, resulting in zero drift, resulting in errors.! Wipe it. In this case, the output signal of the load cell is naturally small. In this case, the small weighing is basically normal. After increasing the load, the displayed value decreases significantly.

(2) Four angle eccentric load error: after the electronic scale is loaded, the change of the measured weight position on the scale platform should not cause the change of the weighing measurement results. Therefore, the bias error of the four corners comes from the sensitivity of the load cell. Due to the difference of key materials such as elastomer and resistance strain gauge of electronic scale load cell, as well as the imperfection of manufacturing process, the absolute sensitivity of each load cell is different, resulting in the same excitation voltage, and the signal output of each load cell is different, resulting in the four corner bias error. In order to reduce the four corner bias error, the electronic scale is connected with a potentiometer in each sensor branch. By adjusting the resistance value, the signal output of each branch can be balanced by using different partial voltage of different resistance.

(3) Repeatability error: under the same load and the same environmental conditions, the repeatability error is the difference between the output readings of load cells obtained from several successive process tests. It is caused by some relatively fixed factors. In addition to the repeatability error caused by the changes of environmental conditions such as temperature, humidity, wind force and gravity field, it mainly includes the repeatability error caused by the lateral force of the electronic scale sensor and the condition of the sensor is not satisfied. Due to the limitation of the field environment, the repetitive error caused by the lateral force of the electronic scale sensor is easy to cause the load receiver to move up and down, which makes the force of the weighing platform symmetrical load sensor not vertical. The lateral force on the sensor is caused by the design and manufacturing error of the force transmission mechanism of the scale body, which is embodied in the repeatability error of the horizontal degree of the upper and lower mounting base of each sensor, the overall stiffness of the scale body and the related local stiffness. When the electronic scale weighs, certain conditions must be met for the force transmission characteristics of the mechanical force transmission mechanism of the scale, the consistency of the sensor parameters, and the excitation voltage of the sensor. The force transmission mechanism of the scale should ensure that the load on the sensor is proportional to the measured weight, so as to ensure the accuracy of the weighing measurement results.

Repeatability error caused by angle difference when weighing the electronic scale, the signal of the sensor is transmitted to the weighing display instrument through the junction box. If some parameters of the sensor are inconsistent or the potentiometer in the junction box is not balanced, the angle difference of the electronic scale will be caused. At this time, the weight will produce repeatability error at different positions of the weighing table.

(4) Discriminating force error: discriminating force reflects the reaction ability of the electronic scale to small load changes. The purpose of discriminating force test is to test the connection and friction of the scale structure, so the friction and stress in mechanical connection are the main sources of discriminating force error. In addition, because the discrimination is aimed at small changes, the resolution of load cell and weighing instrument also has a great impact on the discrimination error. In addition, there is another error caused by the acceleration of gravity, which is not discussed in detail in this paper.

For the above mentioned factors that affect the measurement accuracy of the electronic scale, the solutions have been given in the process of its description. Here I want to propose another method to improve the performance of the electronic scale, that is, to use a better performance MCU to improve the performance of the electronic scale. For example, we can use a single-chip microcomputer with 8K byte flash ROM in it, which has low power consumption and low price. It can be widely used in control and measurement system. The measurement module includes sensor, signal acquisition and filtering circuit. The sensor adopts double hole parallel beam force sensor, whose characteristic is that no matter it is placed in any position, it will not affect the output value. The control signal is sent out by the single chip microcomputer, and the adverse influence of the control on the single chip microcomputer can be eliminated by the solid-state relay. It has the characteristics of fast reaction, no contact and long service life. The display and input devices can also be selected arbitrarily. In a word, the intelligent chip with better adaptability and control can improve the measurement accuracy of the electronic scale.

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