The building materials quality automatic monitoring system is a system that can collect and process mechanical performance indicators using a specified universal testing machine. Its main component is the online testing module, with a focus on the data acquisition submodule and the intelligent detection submodule. The data acquisition submodule includes signal amplification and processing, while the intelligent detection submodule is responsible for detecting the acquired mechanical parameters. Automatic Monitoring System Overall Scheme 1. Determination of the Overall System Scheme Based on the performance and design requirements of the automatic monitoring system, the system scheme needs to be determined from the following aspects: ● Automatic acquisition of force and deformation test data; ● Automatic analysis and processing of the acquired data to derive the mechanical performance indicators required by the user; ● Determination of the data loading rate and solutions for key technologies during the test; ● Automatic saving of test data for user retrieval; ● High system cost-effectiveness, user-friendly interface, and convenient operation. To obtain reasonable results from the designed system and complete the automatic monitoring function, it is necessary to rely on each component of the system, namely the material testing machine, sensors, signal amplification and conditioning, data acquisition system, and data display section. Figure 1. System Principle Block Diagram 2. System Principle Block Diagram The system designed according to the above ideas can be illustrated by the block diagram shown in Figure 1. As can be seen from the above schematic diagram, the small signal output by the pressure sensor connected in series on the testing machine is sent to the signal amplification and conditioning module through a shielded cable to complete signal amplification, filtering, and polarity conversion. The amplified analog signal is converted into a digital quantity by the digitization module, transmitted to the microcontroller, and then processed by calculation and zero-point compensation before being displayed on the LCD module and simultaneously sent to the host computer via a serial interface. The keyboard provides a means of human-computer interaction, but it will not be analyzed in this design. The data storage module has a power-off protection function, mainly to save the current order number and ensure that the collected data and other information are not lost due to power failure. The system performance should be stable, reliable, accurate, easy to use, and have high fault tolerance, while ensuring a certain degree of scalability. 3 System Design Focus ● Online Testing Module The online testing module is the key to the entire material testing machine monitoring system, mainly including an image processing submodule, a data acquisition submodule, and an intelligent detection submodule. ● Data Transmission and Communication The focus of the communication program design is mainly to ensure the reliability of communication. Due to the long communication lines, they inevitably become sources of various spike interferences. Furthermore, the common ground line affects MCU, A/D, and other units, causing ground potential fluctuations, resulting in data jitter and even large errors. Therefore, opto-isolation of the communication interface circuit is essential. The selection of the communication interface chip is also crucial. The communication interface program of the host computer can be implemented using serial communication controls, etc.; computer serial ports 1 and 2 are connected to the two data acquisition subsystems (lower-level machines) respectively, using a cyclic scanning method to communicate with the lower-level machines within a time limit. Design of the Online Test Module 1 Image Processing Submodule The image processing module is mainly responsible for the drawing, display, and saving of test curves. The system has the following requirements for curve display. Figure 2 High Linearity Bridge Amplifier ① Intuitive Curve Display. Based on the maximum load of the testing machine, the maximum displacement of the cylinder piston, the expected tensile strength of the sample, the maximum deformation, etc., the maximum scale of the horizontal and vertical axes is basically manually input. The curve must be drawn proportionally based on this scale. ② The size of the curve display should be appropriate. The display size is too large, which may overemphasize the curve data and increase the burden on subsequent system processing due to the large curve image; the display size is too small, which affects the intuitive expression of the test loading process. ③ The horizontal and vertical axes need to change according to the user's requirements and cannot be fixed. This module can be designed using the Picture Box control in Visual Basic. 2 Data Acquisition Submodule The automatic data acquisition module includes two parts: signal transmission circuit and signal acquisition and processing. The core of the signal processing part is a microcontroller, which is fully menu-driven and automatically generates the number of sample groups, the number of samples, and the commission number according to the selected material type. After each group is tested, it is automatically sent to the host computer and stored in the internal circular data storage unit for future reference. Figure 3 Yield point detection program diagram ● Signal Transmission Circuit The core of the signal transmission circuit is a bridge amplifier with high precision, high stability, and high linearity. Since the sensor must work continuously and stably for a long time, the selection of the sensor must ensure high precision and stability. Therefore, a piezoresistive pressure sensor is selected. The sensitivity of the sensor can be corrected by adjusting the amplifier gain, so that it has good interchangeability when outputting at high level. To achieve good linearity and sensitivity, a high-linearity bridge amplifier as shown in Figure 2 can be used. ● Signal Acquisition and Processing The key to signal acquisition is the A/D conversion. The core of the A/D conversion module is the dual-slope A/D conversion circuit ICL7135. The ICL7135 is a commonly used 4.5-bit dual-slope monolithic integrated ADC chip with a resolution equivalent to 14 bits of binary data; it has high conversion accuracy, with a conversion error of ±1 LSB; it can perform A/D conversion on bipolar input analog voltages under a unipolar reference voltage; the analog input voltage range is 0～1.999V. The chip uses automatic zeroing technology to ensure long-term stability of the zero point at room temperature; the analog input can be a differential signal with extremely high input impedance. 3 Intelligent Detection Submodule Taking steel, a common building material, as an example, steel used as a building material typically needs to possess high strength, sufficient deformation capacity, and good processing performance. Therefore, as long as the maximum load, i.e., peak force, can be automatically detected, the yield point strength can be obtained. The flowchart of the detection procedure is shown in Figure 3. Design of the Data Transmission Communication Module Based on the system topology requirements, RS-232 serial communication or fieldbus methods such as RS-485 can be used. Considering the actual communication environment and distance, RS-232 is more suitable. Furthermore, this system is used in conjunction with a materials testing machine, and there is a certain distance between the system and the host computer; therefore, serial communication is adopted. The RS-232 interface includes receive signal lines RXD and TXD, and a series of control signal lines. In these control signal lines, when the RS-232 signal undergoes logic conversion: logic "0" corresponds to +5V to +15V, and logic "1" corresponds to -5V to -15V relative to ground.