Structure of truck scale and ways to reduce tolerance

Now it is more and more common to use electronic truck scales. As for the repair and general maintenance of electronic truck scales/weighbridge, let's talk about the following informaton as a weighing bridge supplier:

The electronic truck scale is mainly composed of three parts: the loadcell, the structure and the circuit. The accuracy is from 1/1500 to 1/10000 or less. The use of double integral A/D conversion circuit can meet the accuracy requirements and has the advantages of strong anti-interference ability and low cost. In the implementation of national metrology regulations, the errors of the electronic truck scale itself and the additional errors in use are issues that manufacturers and users must pay attention to.

First, the method of reducing errors in the design and production of electronic weighbridge:

1. Guarantee of loadcell technical indicators

It is the key to ensure the quality of electronic truck scale to select loadcells with various technical indicators that meet the accuracy requirements. Linearity, creep, no-load temperature coefficient and sensitivity temperature coefficient are important indicators of the loadcells. For each batch of loadcells, sampling inspection and high and low temperature experiments must be carried out in accordance with the sampling rate required by the relevant national standards.

2. Temperature coefficient of electronic truck scale circuit

Theoretical analysis and experiments prove that the temperature coefficient of the input resistance of the input amplifier and the feedback resistance are important factors affecting the temperature coefficient of the electronic truck scale sensitivity, and a metal film resistor with a temperature coefficient of 5×10-6 must be selected. High temperature tests must be carried out for every electronic truck scale produced. For some products with a small amount of out-of-tolerance temperature coefficient, metal film resistors with a temperature coefficient of less than 25×10-6 can be used to compensate. At the same time as the high temperature test, the product was subjected to temperature aging to improve the stability of the product.

3. Non-linear compensation of electronic truck scale

Under ideal circumstances, the digital quantity of the electronic truck scale after analog-to-digital conversion and the weight imposed on the electronic truck scale should be linear. When performing accuracy calibration during the production process, use the internal computer program for single-point calibration. Calculate the slope between the number and the weight according to the ideal straight line and store it in the memory. This cannot overcome the non-linear error generated by the sensor and integrator. Using multi-point correction, using multiple straight lines to approximate a curve effectively reduces the non-linear error without increasing the hardware cost. For example, an electronic truck scale with 1/3000 accuracy adopts 3-point calibration, and an electronic truck scale with 1/5000 accuracy adopts 5-point calibration.