Practical weighing sensor detection device for cement enterprises

The load cell is a sensing element that converts the gravitational load from a mechanical quantity into an electric quantity. Therefore, it is the basic link of the electronic scale measurement system. Directly determine and affect the measurement accuracy and stability of the work. For manufacturers of electronic scales, it is often necessary to check and verify the linearity, repeatability, and (1 to 3 months) power-on test of the selected load cell, so as to observe and evaluate its stability and reliability. For manufacturers of electronic scales, due to the harsh working environment of load cells, damage and replacement are more frequent. In order to find faults and choose a new load cell, its performance must also be tested. However, this detection is generally inconvenient to send to the load cell manufacturer. Therefore, it is necessary to provide suitable simple and practical detection devices.

1 The structure of the weighing sensor calibration device

In the early 1970s, the author designed a kilogram-level load cell detection and calibration device. After years of use, it is proved that it can fully meet the general requirements. Its structure is shown in Figure 1.

The calibration device consists of a hanging rack, a bench rack, a weight holder and a standard weight. The hanging frame structure is generally made of stainless steel plate with a thickness of about 2.5mm. However, depending on the size of the measured load, the thickness of the plate can be adjusted accordingly, and ordinary steel plate materials can also be used, but it is good to carry out anti-rust treatment, in order to ensure the rigidity and reduce the weight of the hanging code, several small holes can be punched in the hanging rack . The contact surface between the indenter of the hanging frame and the indenter of the load cell must be made into a spherical surface to automatically adjust the center and make a point contact with the indenter of the sensor. The contact point between the hanging rack and the weight support hook must be made into a blade-shaped or arc-shaped surface to ensure that the line of force passes through the center line vertically and is not affected by frictional resistance. It would be better if the weight of the hanging rack and the weight holder can be rounded up to an integer, because then the amount of influence of the self-weight of the calibration device is quantitative. The structure of the bench frame should pay attention to the stability, and the upper panel of the load cell must be flat and the thickness should not be less than 15mm to ensure that the bearing surface has sufficient rigidity. The weight support hook is generally made of a hook with a support plate, but the corresponding structure design can also be made according to the way the weight is hung. The weights used generally use standard weights to ensure measurement accuracy.

2 Steps of calibration verification method
    1) Place the bench frame on a stable and inelastic foundation. The plane on which the bench frame is placed on the load cell should be basically level.
    2) Fix the load cell on the bench frame with the backing plate.
    3) Put on the hanger, and make the indenter of the hanger press positively on the indenter of the sensor.
    4) Hang the weight holder on the hanging rack.
    5) Connect the bridge power supply of the load cell, and connect the output to a high-precision millivoltmeter (the accuracy should be higher than 70% of the sensor's nominal accuracy) (the current output value can also be measured if necessary).
    6) According to the measuring range of the sensor and the number of points to be measured, load (weight) and unload step by step on the weight support hook, and record the output data of the sensor. In this way, performance indicators such as zero point output, linearity accuracy, repeatability accuracy and hysteresis of the sensor can be detected, and it is natural to determine whether the sensor is normal and good or bad.
    For pull (force) type load cell detection, the hanging rack is not required. Hang the sensor directly on the hook on the back of the load-bearing surface of the bench frame, and hook it with the weight support hook below. The remaining steps are the same as the pressure (force) sensor measurement method described above.

The detection device has the following characteristics:
     1) The device is simple, occupies a small space, and can be made by yourself.
     2) Since the standard weight is used as the load, the direct load measurement method is adopted, and the center is automatically adjusted. Therefore, the measurement accuracy is good.
     3) Either single-point measurement or multi-point measurement; it can detect loading data and unloading data, and long-term load simulation test can be performed. Complete functions, flexible operation, simple and convenient.

 4) The device ^ is suitable for the detection and calibration of small-range load cells, especially for sensors with a measurement upper limit of 200 kg.