At present, the common maintenance problems of electronic scale sensors in China are based on the principle of mostly using resistance strain type weighing sensors, and their applications are becoming more and more common. Electronic scales have the advantages of fast weighing, intuitive display, and less prone to wear and tear, and have gradually replaced mechanical scales. The electronic scale mainly consists of a load-bearing transmission system, weighing sensors, and display instruments.
The working principle of commonly used resistance strain type weighing sensors is that the elastic body undergoes elastic deformation under the action of external forces, causing the resistance strain gauge attached to its surface to also deform. After the deformation of the resistance strain gauge, its resistance value changes. As the strain gauge is connected to a balance bridge, the change in resistance value of the strain gauge will cause the bridge to be unbalanced, and the signal will be output from the surface, completing the process of converting external forces into signals.
The electronic scale exhibits the following phenomena, which should be suspected to be a malfunction of the weighing sensor:
(1) The electronic scale does not display zero and the display screen keeps flashing.
(2) After the electronic scale displays zero, add and place weights without displaying the weighing number.
(3) The electronic scale is not accurate in weighing, and the displayed weighing numbers do not match the number of weights added.
(4) The repeatability of electronic scales is poor. Adding the same weight sometimes results in accurate and sometimes inaccurate weighing.
(5) When the electronic scale is unloaded or loaded, the displayed numbers are unstable, drifting or jumping.
These phenomena may all be caused by a malfunction of the weighing sensor. If it can be accurately determined that the fault is in the sensor, it can greatly improve work efficiency and accelerate the speed of electronic scale repair. Separate the sensors that need to be judged from the system and measure the input impedance and output impedance separately. The normal input impedance value is 380 Ω, and the normal output impedance value is 350 Ω. If the measured data is not within this range, the sensor has been damaged. If there is an open circuit in the input impedance and output impedance, the sensor signal cable can be checked for any disconnection. When the signal cable is intact, it indicates that the sensor strain gauge has been burned, usually due to large current entering the sensor. When the measurement of input impedance and output impedance resistance is unstable, it may be due to the insulation layer of the signal line breaking, decreased insulation performance, or the sensor being damp, resulting in poor insulation between the bridge circuit and the elastomer. The zero output signal value of the sensor is generally between -3mv and 2mv. If it far exceeds the standard range, it may be due to overload during sensor use, causing plastic deformation of the elastic body, making the sensor unusable. If there is no zero point signal or the zero point output signal is very small, it may be due to the strain gauge inside the weighing sensor falling off the elastic body or having a support to support the weighing body.