As an important component of weighing modules, electronic weighing instruments play a crucial role in indication and regulation during the weighing process. The data displayed by electronic weighing instruments serves as the basic basis for trade settlements, ensuring fair and just transactions in the market. To implement the State Administration for Market Regulation’s 'Special Rectification of Electronic Scales,' and to jointly combat behaviors such as underweighting on electronic scales and cheating with truck scales, protect consumers' legitimate rights and interests, maintain market order, and optimize the business environment, manufacturers should also address these issues through technological upgrades and product improvements.
The main method of cheating is to alter the weight display data by receiving instructions through illegally installed wireless receiving devices on various modules of the electronic truck scale.
Diagram of a new anti-cheating sensor
With the widespread use of electronic truck scales, manufacturers of their weight indicators (electronic weighing instruments) are using dynamic encryption algorithms in the transmission of electrical signals from weighing sensors. This makes it increasingly difficult to tamper with data on the transmission bus. At present, most cheating occurs by illegally installing wireless receiving devices on the analog signal part (usually mV signals) at the front end of the weight sensor's data processing and conversion device (A/D), as shown in Figure 2.
Add detection elements inside the weight sensor, such as photoresistors or signals from switches like opening the weight sensor cover. Such signals are considered online monitoring and require the instrument to be powered on. When the instrument is powered off, it cannot detect these signals.
The weighing digital module AD typically operates at a low-frequency mode with a sampling rate of 10~20Hz. When weight is applied to the weighing platform, the force on each weighing sensor varies depending on the position of the loaded weight. Once the loaded weight stabilizes, the force on each individual weighing sensor remains constant, and the sensor outputs a stable and unchanging DC signal. After the DC signal is converted by the AD, it becomes a digital signal, which is then transmitted dynamically to the weighing display for calculation.
Once the load weight stabilizes, the AD sampling rate of the digital weighing module is increased to above 2048Hz. The acquired AD signals, after Fourier transformation, can detect periodic waveforms in the weight signal, which can be used to determine if there is a remote control signal present. The remote control signal is generated via PWM, and the superimposed remote control signal is periodic. By increasing the sampling frequency, the waveform can be fully recorded, and Fourier transform technology can be used to determine whether a remote control signal exists. Without a remote control signal, the waveform contains almost only a DC component, whereas a waveform with a remote control signal contains certain frequency components.
The system conducts anti-tampering tests on individual weight sensors. The weight remotely altered has a significant impact on the overall force on a single weight sensor, making it easier to set alarm thresholds and reduce false alarms. When the instrument detects a remote control signal, it can accurately indicate which weight sensor at a specific address has the remote installed, and also provide the reference weight from the remote. The instrument can alert the user through flashing status indicator lights, a buzzer, screen lock, external speaker, and other methods. In addition, through the IoT weight display, messages can be pushed to a mobile phone or sent as SMS alerts in various ways.
