A load cell is a sensing element that converts a gravity load from a mechanical quantity into a power quantity. Therefore, it is the basic link of the electronic scale measurement system. Directly determine and influence measurement accuracy and stability of 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 the stability and reliability of the work. For the use of electronic scales, due to the harsh working environment of the load cell, damage and replacement are more frequent. In order to find faults and to select new load cells, their performance needs to be tested. This type of inspection is generally inconvenient to be sent to a load cell manufacturer. Therefore, it is necessary to provide a suitable simple and practical detection device.

1 load cell calibration device structure
In the early 1970s, the author designed a kilogram-level load cell detection and calibration device. After years of use, it can fully meet the general requirements. Its structure is shown in Figure 1.
The calibration device consists of a hanging frame, a bench frame, a weight hook and a standard weight. The frame structure is generally made of stainless steel plate with a thickness of about 2.5 mm. However, depending on the size of the measured load, the plate thickness can be adjusted accordingly, and ordinary steel plate materials can also be used, but it is best to carry out anti-rust treatment. To ensure the rigidity and reduce the weight of the hanging code, a small hole can be made on the hanging frame. . The contact surface of the hanging frame indenter and the load cell indenter shall be made into a spherical surface to automatically align and be in point contact with the sensor head. The contact between the hanging frame and the weight hook shall be made into a knife edge or a circular arc surface to ensure that the force action line passes vertically through the center line and is not affected by the frictional resistance. It is better to make the weight of the hanging frame and the weight of the weighting hook into an integer, because 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. The upper panel of the load cell should be flat and the thickness should be no less than 15mm to ensure sufficient rigidity of the bearing surface. The weight hook is generally made of a hook with a pallet, but the corresponding structural design can also be made according to the method of hanging the weight. The weights used generally use standard weights to ensure measurement accuracy.

2 Calibration method steps
1) Place the bench frame on a stable and inelastic base. The plane on which the load cell is placed on the bench frame should be substantially horizontal.
2) Fix the load cell on the bench frame with the pad.
3) Put on the hanging frame and press the pressure head of the hanging frame to the pressure head of the sensor.
4) Hang the weight hook on the hanging frame.
5) Turn on the bridge power supply of the load cell, and the output is connected with a high-precision millivoltmeter (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 range of the sensor and the number of points to be measured, load (weight) and unload the load on the weight hook, and record the sensor output data. Therefore, the sensor's zero output, linear accuracy, repeatability accuracy and hysteresis can be detected, and the sensor can be judged whether the sensor is normal or not.
For the pull (force) type load cell detection, no hanging frame is required. Hang the sensor directly on the hook on the back of the carrying surface of the bench frame, and attach it to the weight hook below. The remaining steps are the same as those described above for the pressure (force) sensor.

The detection device has the following characteristics:
1) The device is simple, takes up a small space, and can be made by itself.
2) Due to the standard weight as the load, the direct loading measurement method is adopted, and the self-aligning function is adopted. Therefore, the measurement accuracy is good.
3) It can be used for single point measurement or multi-point measurement; it can detect load data, also can detect unload data, and can carry out load simulation test for a long time. Full-featured, flexible, simple and convenient.
4) The device is most suitable for small-scale load cell detection calibration, especially for sensors with an upper limit of 200kg.