Electronic weighing instruments, as an important component of the weighing system module,
play a significant role in indicating and regulating during the weighing process. The data indicated by the electronic weighing instrument serves as the basic basis for trade settlement, ensuring fair and impartial transactions in the market. To implement the "Special Rectification Campaign for Electronic Weighing Instruments" issued by the National Market Supervision Administration and jointly combat behaviors such as "short weight" in electronic weighing instruments and cheating through truck scales, protecting consumers' legitimate rights and interests, ensuring market order, and optimizing the business environment, manufacturers should also solve these problems through product technology upgrades.
1. Weighing Principle
Place the item to be weighed on the carrier, and the electrical signal generated by the weighing sensor (usually a mV signal) is transmitted through the data processing conversion device and calculation (usually an analog-to-digital "A/D" chip and processor "MCU"), and is displayed by the indication device as the weighing result. It prevents cheating by preventing the transmission of the weighing sensor's appearance.
2. Brief Description of Cheating Methods
Figure 1: Schematic Diagram of New Anti-Cheating Sensor
With the widespread use of electronic truck scales, the manufacturers of weighing indicator (electronic weighing instrument) for the scale sensors adopt dynamic encryption algorithms in the signal transmission. It becomes increasingly difficult to tamper with the data on the data transmission bus. Currently, most of the methods involve illegally adding wireless receiving devices to the analog signal (usually a mV signal) at the front end of the data processing conversion device of the weighing sensor, as shown in Figure 2. The main cheating method is to receive instructions through the illegally installed wireless receiving devices in each module of the electronic truck scale to tamper with the weighing display data.
3.1. Conventional Anti-Cheating Measures and Defects
The wireless frequency spectrum range is wide, and it is difficult for wireless shielding devices to detect and block communication at every frequency. Moreover, there are many wireless frequencies in public areas, which easily leads to false alarms. The digital sensor has an additional current testing function, as shown in Figure 3. The signal line of the wireless device is connected to the analog part of the weighing sensor, and the power is taken from the digital bus end. The entire wireless receiving device consumes current without passing through the digital module, and adding or reducing the test current of the wireless device module has no change. From the actual test results, the change in the internal code when increasing or reducing the wireless device is very small and can be ignored. The weighing display can save the current of the current working mode as a reference and give a range of deviations to determine whether there is an external device connected. For example, a single weighing sensor consumes 20mA of current, and 10 sensors consume a total of 200mA of current. To ensure the normal and stable operation of the system, a current fluctuation range of 5mA deviation (setting too large makes it impossible to detect the wireless device, and setting too small causes measurement errors in the system itself) is set. Low-power wireless devices on the market can operate normally within the set fluctuation range of the instrument. In addition, the detection current of the instrument is affected by factors such as the junction box and the insulation of the weighing sensor bus, which easily leads to false alarms. If the wireless device uses external power supply, the instrument's detection current will fail. The electrical connection of the weighing display is shown in Figure 4.
3.3.
Add a protective cover
Add a metal protective cover outside the weighing sensor to protect the weighing sensor. Firstly, it increases the cost of the weighing sensor, and secondly, the shielding device is easily damaged by cutting machines and other mechanical equipment. 3.4.
Photoelectric/Opening Detection
Increase detection in the weighing sensor, such as photoresistors, and the signals of switches such as the opening of the weighing sensor, similar signals belong to online monitoring and require the instrument to be in a normal power-on state. When the instrument is in a power-off state, it is impossible to detect.
4. Anti-Cheating Prevention Principle
This scheme conducts anti-cheating processing from the perspective of signal principles. It is not Physically protecting, independent of wireless frequencies, without checking current, without testing checksums. The problem can be completely solved by using an external battery for the remote control. Use
A new solution specifically addresses the simulation part of installing the remote control to the weighing sensor. Other parts such as the bus and junction box use dynamic 256-bit dynamic digital encryption transmission, along with frame data validation. Additionally, the internal motherboard and display board of the instrument cannot be changed to alter the display. The AD sampling frequency of the weighing digital module typically operates in a low-frequency mode of 10-20 Hz. When weight is loaded onto the weighing platform, the force exerted by each weighing sensor varies due to different loading positions. Once the loading weight stabilizes, the force on a single weighing sensor remains unchanged, and the output of the weighing sensor is a stable and constant DC signal. This DC signal is converted by AD and encrypted for dynamic transmission to the weighing display for conversion. 
When the loading weight stabilizes, the AD sampling speed of the digital weighing module increases to over 2048Hz. After the AD signal is collected, it undergoes Fourier transformation, allowing the detection of periodic waveforms in the weight signal, enabling the determination of the loaded remote control signal. The remote control signal is generated through PWM, and the superimposed remote control signal is a periodic signal. By increasing the sampling frequency, the waveform can be completely recorded. Through Fourier transformation technology, it is possible to determine the presence of a remote control signal. Waves without a remote control signal contain only DC components, while waves with a remote control signal contain certain frequency components.
The system conducts anti-cheating tests on individual weighing sensors. The remote control change in weight significantly affects the overall force distribution on a single weighing sensor, making it convenient to set an alarm threshold. False alarms are lower. When the instrument detects the remote control signal, it can accurately indicate that the remote control is installed at the corresponding weighing sensor address, and provide a remote control reference weight. The instrument can alert the user through status indicator lights flashing, buzzers, lock screens, external speakers, etc. Additionally, through the IoT weighing display, messages can be pushed to mobile phones or sent as short message alerts in various alert methods. 
Note: Fast Fourier Transform is an efficient algorithm that utilizes the mathematical characteristics of DFT and the divide-and-conquer strategy to decompose large DFT problems into multiple small DFT problems, and through a clever merging strategy, obtain the final result. The purpose of Fast Fourier Transform is to convert a discrete signal defined in the time domain (or spatial domain) into the frequency domain for analysis or processing. Frequency domain analysis can reveal the spectral components of the signal, which is very important in signal processing, image processing, audio analysis, and other fields.
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5.1
Application Examples
Special junction box (4-wire/10-wire) + Special weighing instrument, product composition, as shown in Figure 5.
If the customer uses analog weighing sensors on-site, the original analog weighing sensors can be retained for continued use (if the on-site sensors are digital and need to be replaced as a whole), only the anti-cheating special junction box (supporting 4-wire/10-wire) and anti-cheating weighing display need to be replaced to complete the anti-cheating transformation.