Structural Health Monitoring

Campbell Scientific data acquisition systems' versatile capabilities make them ideal for structural and seismic monitoring. Our dataloggers have been used in applications ranging from simple beam fatigue analysis, to structural mechanics research, to continuous monitoring of large, complex structures.

Highway overpasses, roads, buildings, retaining walls, bridges, and amusement park rides are the types of structures for which our systems provide remote, unattended, and portable monitoring. Our data acquisition systems make reliable structural measurements, even in harsh environments.

Structural Monitoring System Benefits

1. Processing for rainflow and level crossing algorithms can accommodate a large number of cycles.
2. On-board, programmable, excitation is provided for ratiometric bridge measurements.
3. Systems provide triggered output with pretrigger data capture capability.
4. Most sensors and communications options can be used, allowing systems to be customized to meet exact needs.
5. Systems operate reliably in harsh environments.
6. Scan rates range from a few hours to 100,000 times per second.
7. Systems can report conditions by calling out to pagers, radios, or phones.
8. Systems support long-term, unattended data storage and transfer.
9. Pick-and-click software facilitates programming.

Dataloggers used in Structural Monitoring and Control

The versatility of our datalogger systems allows them to be customized for each application. We offer a range of dataloggers from the most basic system with just a few channels, to expandable datalogger systems that measure hundreds of channels. Scan rates can be programmed from a few hours to 100,000 times per second, depending on the datalogger model. Measurement types, recording intervals, and processing algorithms are also programmable. Dataloggers not only provide advanced measurement capabilities, but can also control external devices.

On-board processing instruction sets contain programmed algorithms that process measurements and output results in the desired units of measure. For example, data can be displayed as rainflow or level crossing histograms. These rainflow and level crossing algorithms allow processing for extended periods of time, not just a limited number of cycles. The instruction sets also allow for triggered output with pretrigger data capture capability. Triggers can be based on sensor output, time, and/or user control. For example, if an overpass is being monitored, data collection can be triggered by a sensor detecting the approach of a car, an earthquake, pre-programmed times, or by pushing a button.

The control functions of our dataloggers combined with their programmability allow them to sound alarms, actuate electrical devices, or shut down equipment based on time or measured conditions. Systems can also call out to phones, pagers, radios, and other devices to report site conditions. Voice-synthesized modems are available, so the system can actually call and tell you what is happening.

Sensors used in Structural Monitoring

Because our dataloggers are compatible with nearly every commercially available sensor, you can use the sensors that best meet your application. Typical sensors used for structural and seismic monitoring by our systems include:

1. Carlson strain meters
2. vibrating wire strain gauges
3. foil strain gauges (set up in quarter, half, or full bridge strain configurations)
4. inclinometers
5. crack and joint sensors
6. tilt sensors
7. piezoresistive accelerometers
8. piezoelectric accelerometers
9. capacitive accelerometers
10. borehole accelerometers
11. servo force balance accelerometers

Because our dataloggers have many channel types and programmable inputs, all these sensor types can be measured by one datalogger. Channel types include analog (single-ended and differential), pulse counters, switched excitation, continuous analog output, digital I/O, and anti-aliasing filter. Using switched or continuous excitation channels, our dataloggers provide excitation for ratiometric bridge measurements.

Our configurable datalogger models, the CR9000X and CR9000XC, allow you to customize a system with the channel types that best fit your application. The number and type of channels on most of our dataloggers are expandable using multiplexers and other measurement peripherals. Our dataloggers have input resolutions to 0.33 microvolts, allowing strain measurements with a resolution of a single micro-strain.

Communications

The availability of multiple communications options for retrieving, storing, and displaying data also allows systems to be customized to meet exact needs. On-site communication options include direct connection to a PC or laptop, PC cards, storage modules, and datalogger keyboard/display. Telecommunication options include short-haul, telephone (including voice-synthesized and cellular), radio frequency, multidrop, and satellite.

Software

Our Windows-based software simplifies datalogger programming, data retrieval, and report generation. The datalogger program can be modified at any time to accommodate different sensor configurations or new data processing requirements.

Example Application: Monitoring an Overpass

Campbell Scientific's monitoring systems are used for a variety of structural and seismic applications. Monitoring possibilities on an overpass include:

Data Acquisition (DAQ) Systems for Structural Monitoring and Control

The versatility of our modular DAQ systems allows them to be customized for each application.

Modular Design

The modular architecture of our GRANITE™ system allows each measurement module to independently connect to a PC or DAQ. As an independent module, the real-time measurements can be displayed directly on the PC. One or more measurement modules can be connected to the GRANITE DAQ to create the perfect networked configuration for each application. When connected, they form a time-synchronized, distributed DAQ system.

Distributed Networks and Synchronization

Multiple GRANITE measurement modules can be distributed throughout the structure. Each module is connected to a central GRANITE DAQ. This networking capability decreases the quantity and lengths of the sensor cables between the sensors and the GRANITE DAQ. Fewer sensor cables reduces cost, improves system simplification, and lessens the risk of signal corruption from noise.

Synchronization is key to the success of a distributed network. There are three significant levels to the GRANITE DAQ synchronization:

1. The GRANITE DAQ has a built-in GPS and precision master clock.
   1. The pulse-per-second signal from the GPS is accurate to 1 µs. If enabled, the GRANITE DAQ will phase lock its operating clock to within 200 ns of the GPS clock. So, multiple independent DAQ systems spread over potentially vast geo-spatial regions can be synchronized with a maximum timing error between DAQ systems of 1.2 µs.
   2. Independent of the GPS, a temperature-compensated, high-precision, on-board, real-time clock will keep its own time with an accuracy of ±3 min/year.
2. Within a single DAQ system, comprised of a GRANITE DAQ and GRANITE measurement modules, the measurements are all synchronized to the master clock of the GRANITE DAQ (sourced by either the GPS or precision on-board clock) via the CAN Peripheral Interface (CPI) or Ethernet Peripheral Interface (EPI) measurement buses.
1. CPI synchronization between measurement modules in the same DAQ is ±5 µs. The overall physical range of the bus varies up to 2,000 ft depending on the data rate.
2. EPI synchronization between measurement modules in the same DAQ is ±50 ns. The physical range of the bus is 300 ft per network connection. Daisy-chained connections can span thousands of feet.
3. For extremely time-based-sensitive applications, the GRANITE SPECTRUM measurement modules are used with EPI synchronization. Within each module, the analog electrical signal delay is calibrated and compensated to reduce the timing delay mismatch to ±10 ns channel-to-channel.

Sensors Used in Structural Monitoring

Because Campbell Scientific data loggers and GRANITE DAQs are compatible with nearly every commercially available sensor, you can use the sensor that best meets your application. Typical sensors used for structural and seismic monitoring by our systems include:

1. Carlson strain meters
2. Vibrating wire strain gages
3. Foil strain gages (set up in quarter-, half-, or full-bridge strain configurations)
4. Inclinometers
5. Crack and joint sensors
6. Tilt sensors
7. Piezoresistive accelerometers
8. Piezoelectric accelerometers
9. Capacitive accelerometers
10. Borehole accelerometers
11. Servo force balance accelerometers

Data Retrieval

Communication interfaces for retrieving, storing, and displaying data include direct connection to a PC or laptop, microSD cards, Ethernet, and several options for wireless communication (including built-in Wi-Fi).

Software

Our PC-based software options support connecting the GRANITE measurement modules directly to a PC or scheduling remote, automated data collection from the GRANITE DAQ. Real-time monitoring and control simplify the entire data acquisition process, while robust error-checking ensures data integrity. We can even help you post your data to the Internet.

Example Application: Monitoring an Overpass

Campbell Scientific’s GRANITE monitoring systems are used for a variety of structural and seismic applications. Monitoring possibilities on an overpass could include: