Electronic weighing instruments, as an important component of the weighing instrument 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. In order 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, safeguarding consumers' legitimate rights and interests, maintaining 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 (usually in mV form) generated by the weighing sensor is transmitted through the data processing conversion device and calculation (usually an analog-to-digital "A/D" chip and processor "MCU"), and displayed by the indication device as the weighing result. It prevents cheating of the weighing sensor appearance.
2. Brief Description of Cheating Methods
With the widespread use of electronic truck scales, the manufacturers of their weighing indicator (electronic weighing instrument) adopt dynamic encryption algorithms in the transmission of the electrical signal from the weighing sensor. The difficulty of tampering with data on the data transmission bus is increasing. Currently, most of the cases involve illegally installing wireless receiving devices at the front end of the analog signal (usually in mV form) of the data processing conversion device "A/D" of the weighing sensor, as shown in Figure 2.
The main cheating method is to receive instructions through illegally installed wireless receiving devices in each module of the electronic truck scale to tamper with the weighing display number. According to.
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3.1
Conventional anti-cheating measures and flaws
Wireless shielding device
The wireless frequency spectrum is wide, and it is difficult for the wireless shielding device to detect and block communication at every frequency. Moreover, there are numerous wireless frequencies used in public places, which can easily lead to false alarms. Radio broadcast frequency bands:
535.5kHz - 1606.5kHz;
Domestic beauty and hair care, health care, marriage service and other commercial advertisement broadcasts:
3.2
Test current scheme
a. Module test current, output internal code changes
1.77MHz - 1.78MHz, 
24.85MHz - 24.94MHz, 
26.96MHz - 27.24MHz;
Total communication frequency band:
164.6KHz - 285kHz,
5.09MHz - 5.5M, 
7.1MHz - 7.3MHz, 
14.0MHz - 14.35MHz, 
18.068MHz - 18.168MHz, 
21.0MHz - 21.45MHz, 
24.89MHz - 24.99MHz, 
29.1MHz - 29.3MHz, 
50.2MHz - 50.4MHz, 
145MHz - 146MHz, 
430MHz - 440MHz; 
Voice communication frequency band: 30kHz - 470GHz.
WLAN/WF/BLE: 2.4GHz - 2.4835GHz, 5.725MHz - 5.825MHz
The digital sensor's digital module adds current test 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 does not change. From the actual test results, when the wireless device is increased or decreased, the internal code of the weighing sensor changes very little and can be ignored. The internal code detection cannot be determined.
b. Instrument test current The weighing display can save the current of the current in the current normal working mode as a reference, and then give a deviation range 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 is set (too large makes it impossible to detect the wireless device, and too small causes measurement errors in the system itself), and low-power wireless devices on the market can operate normally within the set fluctuation range of the instrument. In addition, the current deviation is affected by the junction box, the insulation of the weighing sensor bus, and other factors, which can easily lead to false alarms. If the wireless device uses external power supply and does not use the weighing instrument power supply, the instrument detection current will fail. The electrical connection of the weighing display is shown in Figure 4.
3.3
Add protective cover
Adding 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/open lid detection
Adding detection points inside the weighing sensor, such as photoresistors, and 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.
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Anti-cheating prevention and control principle
This scheme conducts anti-cheating processing from the perspective of signal principle. It is not physically protected, is not related to the wireless frequency, does not check the current, and does not test the internal code. The remote control can completely solve the problem by using an external battery. Use
New solution specifically addresses the simulation part of the installation of the remote control to the weighing sensor. Other parts such as the bus and junction box adopt 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 usually operates in a low-frequency mode of 10 to 20 Hz. When the weight is loaded onto the weighing platform, the force on each weighing sensor varies due to different loading positions, and after the loading weight stabilizes, the force on a single weighing sensor remains unchanged. 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 above 2048Hz. After the AD signal is collected, it undergoes Fourier transformation, and periodic waveforms can be detected in the weight signal, allowing 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, whether there is a remote control signal can be determined. The waveform without a remote control signal contains only DC components, while the waveform with a remote control signal contains certain frequency components.
The system conducts anti-cheating tests on individual weighing sensors. The remote control change in weight has a large proportion of the overall force on the individual weighing sensor, making it convenient to set an alarm threshold, with lower false alarms. 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 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, etc.
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5.1
Application Examples
Special junction box (4/10 wires) + 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 4/10 wires) and anti-cheating weighing display need to be replaced to complete the anti-cheating transformation. 5.2 Special digital sensor + special weighing instrument, product composition (as shown in Figure 6). The complete digital anti-cheating solution is composed of specialized anti-cheating digital sensors and anti-cheating weighing displays, suitable for new scale installation use.