## 2 Methods  
*INTERUNIS-IT\({}_{\circ}\) Limited Liability Company has developed SHM-systems for various structures and plants on the basis of A-Line AE system. SHM-system hardware is implemented as a distributed system for data collection and processing with digital data transfer. All components of SHM-system are built from the unified measuring devices and have a common control core. The proposed concept of SHM-system design implies the unification of different components into a single system:  
* Monitoring by multiple NDT methods.
* Monitoring of the structure's stress-strain state.
* Tracking of the working parameters of the industrial process [9]  
SHM-system is a system designed to assess the diagnostics of hazardous matters in real time without stopping, dismantling and shut down. SHM-system provides information about the status of the monitoring facility in the required quantity and quality for testing. The structure of SHM-system includes the following functional elements: equipment for primary data collection, multifunctional data acquisition and transmission modules, concentrators, galvanic isolation switching cabinet and central computer station (Figure 1).  
The equipment for primary data collection may include one or several types of acoustic emission sensors, strain gauges, corrosion rate meters; pH meters, vibration sensors, displacement meters and inclinometers, crack opening sensors; level gauges, thermocouples, pressure sensors, gas analyzers, video recorders and weather station. The specific composition varies depending on the structure and the goal of the monitoring.  
Multifunctional data acquisition and transmission module is the main element of this architecture and is a separate device in an explosion-proof enclosure with installed cable entries. Each module contains several measuring units that collect data from external sensors of various types, and, if necessary, supply power to them. In particular, analogue filtering, digitization and digital filtering of signals, as well as calculation of AE parameters (such as arrival time, amplitude, duration, etc.) and the registration of waveforms are performed in a measuring unit intended for operation with an AE sensor. The total number of sensors connected to the module can be up to 6. In addition, module includes a digital processing unit, communication unit and power unit. Multifunctional data acquisition and transmission modules are connected in series with each other by a cable that provides power and relay the data through the cascaded line. The modules are placed, as a rule, near the sensors, which together with digital data transmission, achieve high interference immunity.  
The concentrator is a separate device in an explosion-proof enclosure that receives information from several (up to 4) cascaded lines of modules and sends it further via the Ethernet interface.  
The switching cabinet of the galvanic isolation carries out a galvanic isolation between the primary supply voltage of 220 V/50 Hz and the secondary direct current (DC) voltage of 48 V, as well as the galvanic isolation between the measuring units.  
The central computer station, which is designed for receiving, transmitting, storing and analyzing data and for measuring channels control. The central computer station includes computing devices for data processing and storing, as well as a display and input devices, or a device for communicating with a remote-control terminal.  
The SHM-system can also include an automated workstation--a remote terminal used for remote access to a central computer station, monitoring data processing and performing backups of information.  
Figure 1: Example of structural health monitoring (SHM)-system structural scheme.