Real-time monitoring and diagnosis of the operational status of engineering structures, timely detection of structural damage, assessment of their safety performance, prediction of performance degradation trends and service life, and proposing improvement measures are of paramount importance for enhancing the efficiency of engineering structures and safeguarding people's lives and property. This has become an increasingly urgent technical requirement for engineering structures [2]. Structural Health Monitoring (SHM) systems can collect various data reflecting the operational status of structures, use structural health diagnosis methods to real-time determine the location and extent of structural damage, assess their safety performance, predict performance degradation trends, and provide early warnings for dangerous situations. They are an effective means to ensure the safety of major engineering structures throughout their entire lifecycle, from construction and operation to demolition.

SHM systems can perform real-time online monitoring of engineering structures, primarily comprising a sensor subsystem, a data acquisition subsystem, a data analysis subsystem (damage identification, safety assessment, and early warning), a data transmission subsystem, and a database management subsystem [3]. Among these, the data acquisition subsystem collects relevant data from the sensor subsystem that reflects the current health status of the structure. The effective acquisition of data by this subsystem is a prerequisite for the data analysis subsystem to perform analytical operations such as damage identification, safety assessment, and early warning, and it determines the monitoring performance of the entire SHM system. Therefore, the data acquisition subsystem is the cornerstone of the SHM system.

Major engineering structures are characterized by their large volume, extensive span, and complex structures. Therefore, data acquisition systems for SHM projects targeting such structures have the following characteristics:

(1) Capable of acquiring data from a large number of diverse sensors.

SHM projects for major engineering structures often require the acquisition of large-scale, multi-type sensor signal data. For instance, the monitoring sensors for the Canton Tower include 16 types of sensors such as wind pressure, wind speed, tilt angle, GPS displacement, acceleration, corrosion sensors, and fiber Bragg grating strain and temperature sensors, totaling 807 sensors [4]. The monitoring project for Hong Kong's Tsing Ma Bridge used 6 types of sensors, totaling 543 [5]. Therefore, data acquisition equipment should, as much as possible, meet the requirements for large-scale sensor signal acquisition, and simultaneously, the acquisition of various types of sensor signals should be handled by a unified data acquisition device.

Sensors used in SHM systems can be categorized into three types: (1) General-purpose electrical sensors, which can measure physical quantities such as tension/compression, pressure, acceleration, strain, temperature, displacement, and tilt angle. Their main output signal types can be divided into voltage, current (4-20mA), and digital signals. (2) Optical sensors, with fiber Bragg gratings being a typical example, primarily measure strain and temperature. (3) Non-general-purpose sensors, which measure special signals such as electromagnetic cable force sensors and GPS displacement sensors, with output signals being digital (TTL or TCP/IP).

Electrical sensors can measure various types of physical quantities that reflect structural change information and hold a dominant position in the field of SHM. Among them, resistance strain gauges, accelerometers, and displacement sensors are three widely used types of electrical sensors.

Strain is a direct manifestation of structural deformation. SHM systems typically need to monitor structural strain, such as the structural monitoring system for complex hoisting equipment studied by He Peng [6], and the deep-sea pressure resistance monitoring project conducted by Yang Huawei [7]. Strain is generally measured by attaching resistance strain gauges, which measure strain based on the Wheatstone bridge principle and output bridge circuit signals.

Acceleration is an important indicator of structural vibration. Accelerometers are widely used in the field of SHM. For example, Feng Shuo proposed an optimized sensor placement method for structural monitoring using accelerometers [8], and Han Xuliang studied the structural response of high-rise buildings during typhoon passages [9]. Commonly used accelerometers are generally piezoelectric and output IEPE sensor signals.

Displacement is also an important indicator of structural movement. Displacement sensors are frequently used in SHM projects, such as the high-precision multi-target dynamic displacement monitoring method proposed by Zhou Zhou et al. using displacement sensors [10], and the spatial truss early warning system established by Wang Kaiyuan [11]. Displacement sensors typically output voltage signals. Additionally, pressure sensors and temperature sensors are also frequently used in SHM processes, and these sensors typically output current signals.

In summary, the sensor subsystem of SHM projects primarily outputs bridge circuit signals, IEPE sensor signals, voltage, and current signals. To facilitate comprehensive analysis of the structural operational status based on different physical quantities and to ensure the collaborative operation of various types of sensors, the data acquisition subsystem should be equipped with a unified data acquisition device to complete the acquisition of these four types of sensor signals.

(2) All sensor data should be acquired synchronously.

The prerequisite for the data analysis subsystem of an SHM project to perform damage identification and safety assessment is that the data acquisition subsystem can acquire parameter signals reflecting structural characteristics, such as strain, acceleration, and displacement. These sensor data, representing different temporal and spatial domains, are carriers of information about the structural operational status [12]. In SHM projects, a comprehensive analysis of these sensor data is often required to obtain the overall operational status of the structure. This comprehensive analysis should be based on the same moment or the same time period, which necessitates that all sensor data be acquired at the same instant, or even synchronously under the drive of the same sampling clock, to ensure the scientific validity and accuracy of the comprehensive analysis.

The data acquisition system should support synchronous acquisition of the same type of sensor signals. When performing SHM for an engineering project, it is often necessary to monitor changes in the same physical quantity at multiple locations, such as strain magnitude. By deploying the same type of sensor at each location, the sensor data from each location can only reflect the overall structural change at the current moment if acquired synchronously. Therefore, for every sensor of the same type, the data acquisition system should perform synchronous acquisition.

The data acquisition system should support synchronous acquisition of different types of sensor signals. When performing SHM for complex engineering projects, it is often necessary to monitor various types of sensor signal information, such as for transmission tower structures or sports venues. Multiple types of sensors can characterize structural changes from various angles, such as resistance strain gauges, accelerometers, and displacement sensors. Data from each type of sensor can only accurately reflect the current state of change in a complex structure during comprehensive analysis if acquired synchronously. Therefore, for different types of sensor signals, typically bridge circuit, IEPE sensor, voltage, and current signals, the data acquisition system should acquire them synchronously.

Furthermore, the data acquisition system should support synchronous acquisition of all sensor signals among distributed data acquisition devices. Currently, the volume and span of major engineering structures under construction and in service in China are continuously increasing. Over 50% of the world's top 10 cross-sea bridges, suspension bridges, and long-span cable-stayed bridges are in China, such as the Hangzhou Bay Bridge with a total length of 36 kilometers and the Shanghai Donghai Bridge with a total length of 32.50 kilometers. When performing SHM for long-span bridges, electrical sensor signals do not support long-distance data transmission. Therefore, data acquisition devices need to be deployed in a distributed manner to collect sensor data within each segment. Only by synchronously acquiring all sensor data across a long distance can a comprehensive analysis of the entire structure's operational status over a specific period be performed. Therefore, for widely distributed sensor systems, multiple distributed data acquisition devices need to work collaboratively to synchronously acquire all sensor data.

(3) Possesses powerful real-time data processing and analysis capabilities.

Certain requirements of SHM systems, such as real-time temperature compensation for sensors, cable force and structural frequency response based on accelerometers, real-time signal filtering, and real-time alarm functions, all necessitate that the hardware system can perform real-time data computation and analysis. With the continuous development and innovation in electronics technology, various instruments and equipment have acquired increasingly powerful processing capabilities. Data acquisition devices, while undertaking large-scale synchronous data acquisition, can also perform real-time analysis of the collected data, ultimately enabling independent monitoring functions for the equipment.

(4) Good long-term stability, strong durability, and high signal measurement accuracy.

Major engineering projects are characterized by complex structural forms, intricate service environments, and long service lives, such as bridges, tunnels, dams, and offshore oil platforms. SHM systems often need to operate for extended periods in harsh environments with large temperature differences, high humidity, severe corrosion, and numerous interference sources. Therefore, not only are durable, stable, and high-precision sensors required, but higher demands are also placed on