The weighing sensor has the problem of temperature zero drift. The reason for this problem is that due to the asymmetry of the component parameters in the sensor bridge circuit, the temperature coefficients and linear expansion coefficients of the sensitive grid materials of the elastomer and the resistance strain gauge are different, and the length of the bridge lead wire is inconsistent. The overall temperature coefficients of adjacent bridge arms after the bridge is assembled are different. When the weighing sensor is not subjected to an external load, the ambient temperature changes, and the resistance changes of adjacent bridge arms are different, resulting in an unbalanced bridge output, that is, temperature zero drift. At present, there are two technologies to solve the problem of temperature zero drift of weighing sensors: analog compensation technology and digital compensation technology. Analog compensation technology is applicable to analog weighing sensors and digital weighing sensors. Analog compensation is to record the normal temperature zero value, low temperature zero value, and high temperature zero value of the weighing sensor, and then calculate the difference at different temperatures, and then calculate the length of the compensation line according to the temperature coefficient of the compensation material. Manually weld the compensation line to achieve temperature zero compensation. Digital compensation technology
is that the digital weighing sensor records the normal temperature zero point value and temperature value, low temperature zero point value and temperature value, high temperature zero point value and temperature value inside the digital weighing sensor, and then calculates the compensation parameters at different temperatures and stores them in the weighing sensor. The compensation parameters are used to correct the output data to overcome the influence of temperature changes on the data. Digital compensation technology requires that there is a temperature sensor inside the digital weighing sensor, which can collect the internal ambient temperature of the weighing sensor in real time.
1  Digital weighing sensor temperature zero point compensation system

In order to detect the temperature zero point drift of the digital weighing sensor, it is necessary to provide a temperature changing environment for the digital weighing sensor, maintain communication with the digital weighing sensor, send recorded data and compensation parameter calculation instructions at each temperature node, and the digital weighing sensor calculates the compensation parameters according to the recorded data and stores them. According to the national standard GB/T 7551-2008 "Weighing Sensor", the temperature zero point test of the weighing sensor should be performed according to the temperature cycle of normal temperature → low temperature → high temperature → normal temperature.

The temperature zero point automatic compensation host computer is divided into two modules: the temperature cycle control module of the zero point temperature tank and the temperature zero point compensation data acquisition and management module.
(1) Design of the temperature cycle control module of the zero point temperature tank
Communicate with the temperature controller of the zero point temperature tank through the RS232 serial port to complete the equipment initialization and startup control of the zero point temperature tank. Set the temperature cycle parameters of normal temperature → low temperature → high temperature → normal temperature according to the process requirements, including temperature value, execution time, temperature threshold and time advance, etc. The temperature cycle includes compensation cycle and verification cycle, which respectively provide a changing temperature environment for the temperature zero point compensation of the digital weighing sensor and the index test after compensation.
(2) Design of the temperature zero point compensation data acquisition and management module
After the digital weighing sensor is connected to the multi-channel compensation controller, the multi-channel compensation controller is started to establish network communication with the host computer.
① Scanning of digital weighing sensor
The multi-channel compensation controller scans the weighing sensors in the entire communication network, and the communication status is returned to the host computer according to a certain protocol. The host computer displays different states according to normal communication and abnormal communication.
② Basic parameter management of digital weighing sensor
Read and record parameters such as weighing sensor type, production number, strain gauge type, serial number, etc. Allow different types of sensors to be compensated and verified in the same batch, and uniformly assign channel numbers and record them.
③ Temperature zero point compensation and verification
During the temperature zero point compensation cycle, collect and save the data of each digital weighing sensor in real time. According to the process requirements, send the recording data and compensation parameter calculation instructions to the digital weighing sensor at the specified time point of the normal temperature → low temperature → high temperature → normal temperature cycle. After the compensation cycle ends, it automatically enters the verification cycle. During the temperature zero point verification cycle, collect and save the data of each digital weighing sensor in real time, collect and record the data at the specified time point of the normal temperature → low temperature → high temperature → normal temperature cycle according to the process requirements, and calculate the temperature zero point index at the end of the cycle. The upper computer intuitively displays the compensation and verification status of each digital weighing sensor.
④ Database design
The digital weighing sensor parameter library includes: weighing sensor type, production number, strain gauge type, temperature zero point compensation mark and index, etc.
The process database includes: the production number, serial number, AD value and temperature value of the weighing sensor during the temperature cycle, etc.

Operation status library: records the system operation status, providing a basis for troubleshooting and continued operation after fault recovery.

Setting parameter library: saves the setting status of this batch of tests, including temperature cycle time and temperature value, etc.

⑤Data management

Weighing sensor parameters, operation status parameters, and setting parameters can be queried and printed, and process data can be queried by category.

2  Conclusion

The accuracy level of the weighing sensor is divided into four levels: A, B, C, and D according to the national standard GB/T 7551-2008
"Weighing Sensor". The number of divisions of each level is different. For example, the range of the C-level division is 500-10000, and the C3 level means the number of divisions is 3000. The higher the accuracy level, the smaller the error of the weighing data. The indicators that affect the accuracy level of weighing sensors include nonlinearity, hysteresis, repeatability, creep, temperature sensitivity, temperature zero point, etc. In order to improve the weighing accuracy of weighing sensors, specific compensation measures need to be taken for different indicators during the production process to reduce weighing errors.