Electronic scale sensor problems and maintenance

At present, the maintenance of common problems of electronic scale sensors in China is based on the principle of resistance strain type load cells, which are increasingly common. Electronic scales have the advantages of rapid weighing, intuitive display, and low wear, and have gradually replaced mechanical scales. Electronic scales mainly consist of load-bearing transmission systems, load cells and display instruments. The working principle of the commonly used resistance strain type load cell is that the elastic body generates elastic deformation under the action of external force, so that the resistance strain gauge stuck on its surface also deforms along with it. After the resistance strain gauge is deformed, its resistance value changes. Since the strain gauges are connected in a balanced bridge type, a change in the resistance value of the strain gauges causes the bridge to become unbalanced and signals are output from the surface, thus completing the process of transforming the external force into a signal.

The following phenomena occur in the electronic scale. It is doubtful that the load cell is faulty:

(1) The electronic scale does not show zero and the display keeps blinking.

(2) After the electronic scale displays zero, weights are added and weights are not displayed.

(3) The weighing of electronic scales is inaccurate. The displayed weighing figures are inconsistent with the number of adding and releasing weights.

(4) The repeatability of electronic scales is not good, plus the same weight, sometimes weighing accuracy, and sometimes weighing is not accurate.

(5) When the electronic weigher is unloaded or loaded, the displayed figures are unstable, drifting or jumping.

All these phenomena can be the failure of the load cell. If you can accurately determine that the fault is in the sensor, this will greatly increase work efficiency and speed up the repair of electronic scales. The sensor that needs to be judged is removed from the system and the input impedance and output impedance are measured. The normal value of the input impedance is 380Ω, and the normal value of the output impedance is 350Ω. If the measurement data is not within this range, the sensor is damaged. If the input impedance and output impedance are disconnected, check whether the sensor signal cable is disconnected. When the signal cable is intact, the sensor strain gauge is burned, usually because of the large current entering the sensor. When the measured input impedance and output impedance are not stable, the insulating layer of the signal line may be broken, the insulation performance may be degraded, or the sensor may get wet, so that the bridge is not insulated from the elastic body. The zero output signal value of the sensor is generally between (-3mv and 2mv). If it is far beyond the scope of this standard, it may be due to the plastic deformation of the elastomer caused by the overload of the sensor, making the sensor unusable. If there is no zero signal or zero output signal is very small, it may be that the strain gauges in the load cell have been detached from the elastic body or there is support to support the scale body.

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