The purpose of the system is to continuously monitor static and dynamic measurements from distributed sensors inside the Arena di Verona. The system is composed of ten data acquisition units with small hardware for minimal visual impact in the Roman amphitheater. A monitoring PC was placed at the ticket office entrance. We use NI hardware and software, and Structural-X software, which we developed using LabVIEW, to monitor the structural health of the building by acquiring data from the following sensors:

• Uniaxial accelerometers that analyze the vibration characteristics of the structure
• Potentiometer-type displacement sensors that check the status of cracks and fissures
• Environmental sensors that check temperature and humidity at certain points of the structure

System Hardware Components

The system consists of the following components:

• One NI 9792 programmable WSN gateway that operates as the collection and management point for all acquisition units
• Six NI WSN-3202 wireless sensor network (WSN) modules that collect slow-changing data such as temperature, humidity, and displacement, and communicate wirelessly with the master box 
• Three NI 9144 EtherCAT RIO chassis with C Series modules that collect dynamic data from accelerometers and other static variables, and communicate with the master box using a deterministic Ethernet connection 
• A PC that monitors data acquisition using the Structural-X supervisory software application built in LabVIEW that is accessible through an Internet connection from remote workstations

Hardware

The six NI WSN-3202 wireless measurement nodes acquire measurements from displacement (potentiometers), temperature, and humidity sensors. Four modules acquire data from four other potentiometers. The nodes transmit acquired sensor data over an IEEE 802.15.4 wireless network.

The dynamic measurement stations are composed of an NI 9144 EtherCAT chassis with NI 9215 and NI 9234 modules. The measurements made by each box varies—the first box measures four accelerometers; the second box measures four accelerometers, two potentiometers, one temperature sensor, and one humidity sensor; and the third box measures eight accelerometers, two potentiometers, one temperature sensor, and one humidity sensor. We decided to use EtherCAT hardware based on the need for perfect synchronization between the distributed accelerometers.

Inside each box are other devices such as a 24 V DC power supply, electrical safeguards, an uninterruptible power supply (UPS), and measurement conditioning for potentiometric sensors. The master box houses the NI 9792 that is used as the master data acquisition controller. The NI 9792 is a programmable WSN gateway that manages the NI WSN nodes on the wireless IEEE 802.15.4 network and the network of NI 9144 EtherCAT chassis, and features centralized data collection and management functions. The master box is also home to a 24 V DC power supply, electrical safeguards, a UPS, and an Ethernet hub. The supervisory PC is a Panel PC placed at the ticket box office for data display, storage, and box configuration.

Software

We programmed the NI hardware using LabVIEW and the necessary libraries. The NI 9792 WSN gateway was programmed using the LabVIEW Real-Time Module and the NI 9144 EtherCAT chassis was programmed using the LabVIEW FPGA Module, and EtherCAT management tools.

The developed software, Structural-X, is based on two software applications: the first one (EMBEDDED) runs on the real-time master and the second one (CLIENT) runs on the supervisory panel PC. Structural-X EMBEDDED collects data from all the devices of the system and publishes data on the network. Structural-X CLIENT verifies conversion parameters of the sensors; configures acquisition and storage parameters; and compensates for offset measurements. The software helps the user check the system’s status and the graphs of acquired measurements in the time and frequency domains. All data is stored locally with data storage frequency set during configuration and is accessible through an Internet connection from remote workstations.

By combining the WSN nodes with the NI CompactRIO EtherCAT system we designed a structural health monitoring (SHM) system that can acquire, process, and share both static and synchronized dynamic data, and also minimizes installation footprint with its distributed architecture.