Data Acquisition Processor Plays Role in Unique Infrastructure Monitoring System

Small, unpowered acoustic sensors are used in a SoundPrint system to detect potential failures in buildings, parking structures, bridges, pre-stressed concrete pipelines, arenas, and containment vessels.

Pure Technologies Ltd. has created a patented infrastructure monitoring system that uses acoustical techniques to detect potential failures in buildings, parking structures, bridges, pre-stressed concrete pipelines, arenas, and containment vessels. Called SoundPrint®, the system uses an array of sensors to measure the energy released when tensioned steel wires fail. When the system detects a potential wire break, the information is sent via the Internet to the company's headquarters where the signal is processed further. If it is determined to be an actual failure, the building owner is notified immediately. SoundPrint®'s hardware platform is a PC equipped with a data acquisition processor (DAP) board. The DAP board, which provides analog-to-digital (A/D) conversion and an onboard microprocessor, made the PC a viable platform for this application by handling the signal processing necessary to pick out events of interest. "After an event is recorded on the DAP, it is transferred to the PC where we deal with it further to determine if it really does indicate a problem," explains Monroe Thomas, Systems Manager at Pure Technologies. "This way, the only data that must be transferred across the PC bus is critical data, and this overcomes the limitations of the PC bus."

Pure Technologies Ltd. is based in Calgary, Alberta. The company introduced SoundPrint® in 1993 as an efficient and affordable method for detecting corrosion-related infrastructure problems that can affect the integrity of a building or other concrete structures containing tensioned steel wires. "Corrosion is the main reason why the wires under tension fail," explains Thomas. "Those that are exposed to the environment are obviously at risk as moisture can enter the system at any time before, during, or after construction. And there are other conditions such as hydrogen embrittlement where a wire might look normal but has no more ductility left. These and other corrosion-related problems can cause wires to break and when they do, the integrity of the structure can be at risk." Repairs have been carried out on a number of structures based on information generated by SoundPrint®. The system saved the owners of these properties millions of dollars by allowing them to precisely target the repairs and to prevent premature decommissioning.

Acoustic Analysis Monitors Infrastructure

“Microstar understands how people write software, and tailored their API so it really makes sense.”
Monroe Thomas, Vice President, Pure Technologies Ltd

Inside the technology

In most cases, the sensors used in a SoundPrint® system are small, unpowered acoustic sensors. The designers of the system chose these devices because they can detect small signals and do not need a power supply. The ability to detect small signals is necessary because when some wires break, only a small amount of energy is released. "Some wires we deal with are bonded, which means they are embedded in concrete or grout," Thomas explains. "These don't travel far when they break. Consequently, the amount of energy that is released is relatively small compared to unbonded wires such as those you would find on a suspension bridge. These travel a greater distance when they break and release quite a bit more energy." By not requiring their own power supply, these sensors help simplify the configuration of a SoundPrint system. "In large buildings, we typically place 20 to 30 sensors per floor so we're dealing with hundreds of sensors," says Thomas. "By combining these unpowered sensors with methods we have developed for transmitting small signals over long distances, we can minimize the amount of wiring required."

Unpowered sensors are used for all structures except pipelines. In pipelines, the SoundPrint® system picks up acoustic signals by means of a hydrophone array placed inside the pipe. When a wire in a concrete pipeline breaks, the signal is transmitted to the inside of the pipe where it is carried through the water to the hydrophone. Pure Technologies can insert a hydrophone array into a pipeline while it is active, eliminating the need to take it out of commission to install a SoundPrint® system.

Signals from the sensors travel to a custom amplifier/signal conditioner/multiplexer developed by Pure Technologies for this application. Then the signals must be converted from analog format to digital format and further processed to determine whether they have detected an actual wire break. Part of the processing, for example, involves filtering the signal to reject acoustic events caused by ambient activity such as traffic or construction. Data from events that pass the primary filtering process are then transmitted automatically to a data-processing center by means of the Internet. There, the information is run through more sophisticated proprietary algorithms to analyze the event further.

On the prototype SoundPrint® system, the designers tried to use an ordinary PC and data acquisition board to perform A/D conversion and signal processing functions. The PCs at that time operated at clock speeds of 200 MHz or less, however, and had trouble handling the volume of incoming data. "The busses were slow and the PCs weren't able to continuously stream that much information from the data acquisition boards," says Thomas. "We needed to perform fairly intensive signal processing analysis that requires lot of CPU time. It couldn't be done because the computer was busy transferring data over the bus."

Although they could have configured the system with a dedicated data acquisition system to handle the A/D conversion and a separate PC to perform the signal processing, the designers of the SoundPrint® system rejected that option. "The problem with a dedicated instrument is that it's not flexible," says Thomas. "We would have to build a separate system configuration for each of the different structures we monitor. What we wanted was a system built around a general-purpose Windows NT PC that we could customize for each different monitoring situation simply by making changes to software."

A single-board solution

The solution was to configure a PC with a data acquisition processor (DAP) board from Microstar Laboratories, Bellevue, Washington. The unique capability offered by DAPs is an onboard microprocessor that runs a multitasking, real-time operating system optimized for high-performance real-time data acquisition and control applications. The DAP board executes all processor-intensive routines in real time and performs any necessary data reduction so that the software on the PC can handle demanding applications such as acoustic signal processing. There's never any danger of having gaps in the data regardless of how many computer cycles are dedicated to the foreground application.

Pure Technologies chose DAP boards from Microstar after looking at conventional A/D boards. In addition to the main advantage of having an onboard microprocessor, the Microstar products use Windows NT drivers that are "superior to many of the drivers for other boards because they are simple to install and they consume few system resources," according to Thomas. Another advantage is the ability to do data streaming entirely independently of the host PC. "A/D boards require data to be transferred across the PC bus, which is what we were trying to avoid," Thomas says. He acknowledges that with recent innovations such as PCI bus mastering, competing products are beginning to be able to transfer 32 or 64 channels across a bus without CPU intervention. "But Microstar is still ahead of the competition," Thomas says. "Its DAP 4400 Series has up to four simultaneous A/D converters, each capable of handling 16 channels at very high speeds. We still prefer Microstar's products because we can use one of their boards instead of four of the competition's."

Another reason why the designers of the SoundPrint® system preferred Microstar DAP boards is that they appreciated the logical API structure. "Microstar understands how people write software and tailored their API so it really makes sense," Thomas adds. Pure Technologies programmed the DAP to perform several preliminary signal processing steps. In one, the board looks for a logical "1" sent from a dedicated first-stage trigger box. A 1 indicates that an event of interest may have occurred. When the DAP receives a 1, it passes the signal to the host PC, which writes it into its memory and also transmits it to the data-control center. The DAP also provides a timed triggering mechanism that pulls in a signal once a minute. This provides information about the background acoustic environment and lets the operators know that the system is working. As Thomas explains, "Sometimes wires don't break for months. The way we determine whether the system is working is by having background acoustic checks."

In future versions of the SoundPrint® system, Pure Technologies is hoping to eliminate the dedicated hardware that provides trigger impulses to the DAP and perform the equivalent functions -- fast Fourier transformations (FFTs) and frequency domain analysis -- on the DAP itself. Until recently, DAPs were not able to perform FFTs fast enough to handle in real time the large amount of signal data that the SoundPrint® systems collects. However, Microstar recently announced a new DAP that contains a 400 MHz Pentium-compatible chip. "We are seriously looking at that board as a way of implementing more sophisticated triggering functions within the PC," Thomas says.

The SoundPrint® system offers owners a reliable and affordable method of infrastructure monitoring, helping ensure safety and protect their investment. Pure Technologies was able to design an efficient, self-contained system by building it on top of the Windows NT-PC platform. A DAP board helped make this possible by eliminating the need for huge volumes of data to be transferred across the PC bus.