Figure 1. NI CompactDAQ provides USB or Ethernet data acquisition, signal conditioning, and sensor connectivity for up to 256 measurement channels.
1. Flexibility with Measurement Modules
Because many data acquisition systems have fixed functionality, they can connect only to specific sensor types. Other systems are modular but capable of measuring only low-speed and static signals such as DC voltage and temperature. NI CompactDAQ can measure dynamic signals such as sound, vibration, pressure, and electrical transients at up to 1 MS/s per channel in addition to static signals such as DC voltage and temperature. Other modules provide single-point and waveform output capability at rates up to 100 kS/s per channel or digital I/O at rates up to 10 MHz. Because NI CompactDAQ is a modular system, you can add more measurement types and channels to the system by simply plugging in additional modules. All modules are automatically synchronized, and a single NI CompactDAQ system can simultaneously stream high-speed analog input, analog output, digital input, and digital output over a USB or Ethernet connection.
Table 1 lists modules that are common in structural health monitoring (SHM) applications. For a complete list of C Series modules, refer to the C Series Compatibility Chart.
|Analog Input||NI 9205||32||±10 V||16-bit||Analog inputs||250 kS/s|
|NI 9211||4||±80 mV||24-bit||Thermocouple||14 S/s|
|NI 9215||4||±10 V||16-bit||Simultaneous analog inputs||100 kS/s/ch|
|NI 9219||4||Various||24-bit||Universal AI||100 S/s/ch|
|NI 9234||4||±5 V||24-bit||Accelerometer (IEPE excitation)||10 kS/s/ch|
|NI 9235/6||8||±30 mV/V||24-bit||Strain/bridge||10 kS/s/ch|
|NI 9237||4||±25 mV/V||24-bit||Strain/bridge||50 kS/s/ch|
|Analog Output||NI 9263||4||±10 V||16-bit||Voltage AO||100 kS/s/ch|
|NI 9265||4||0 to 20 mA||16-bit||Current AO||100 kS/s/ch|
|Digital||NI 9401||8||5 V TTL||─||DIO||10 MHz|
|Relay||NI 9481||4||250 VAC||─||Solid-state relay||50 Hz|
Table 1. NI C Series Modules Common in SHM Applications
2. NI CompactDAQ Advantages
NI CompactDAQ is much more flexible than traditional instruments at adapting to changes in test requirements. Traditional instruments pack processors, memory, software, and displays into a fixed-functionality box that can quickly become obsolete. Instead, NI CompactDAQ uses the speed, power, and data storage capability of your PC. If you need more data storage or faster data processing, you can upgrade your PC memory instead of buying a new higher-end instrument. And adding a new type of measurement or expanding channel count is as easy as plugging an additional module into the NI CompactDAQ chassis.
Unlike other data acquisition systems, NI CompactDAQ does not use electromechanical relays to switch analog input signals. Relays wear out over time, potentially causing system and test failure. Relays are also limited to switch rates of about 1000 S/s. Instead, NI CompactDAQ uses solid-state multiplexers that do not wear out over time and can switch input channels at rates up to 250,000 times per second for accurate and reliable high-speed measurements.
Connectors, Signal Conditioning, and Data Acquisition in a Single Package
Assembling a data acquisition system often involves cabling signal conditioning and connector blocks to a separate device to digitize input signals. These cables and connector blocks add cost and can contribute to noise and error in the system. NI CompactDAQ combines signal connectors, signal conditioning, and analog-to-digital converters in a single package. This feature eliminates the time and guesswork associated with cabling together multiple components and reduces the number of components that can contribute to noise or failure.
NI CompactDAQ modules include connectors matched to the measurement capability of the module. For example, general-purpose voltage input modules have removable screw terminals, while modules for dynamic and transient signals have BNC connectors. By matching the connectors with the measurement capability of the modules, NI CompactDAQ simplifies sensor and signal installation and further reduces the potential for error by eliminating wire cutting, stripping, and crimping.
Figure 2. C Series modules for NI CompactDAQ include sensor-specific connectors with built-in signal conditioning and A/D converters.
Foolproof Sensor Measurements
NI CompactDAQ can measure the most common sensor types such as thermocouples, strain gages, and accelerometers in addition to voltage and current. The NI-DAQmx software included with NI CompactDAQ offers the DAQ Assistant, a guided wizard utility that automatically scales measured signals into engineering units such as degrees Celsius for thermocouple measurements. This feature eliminates manual scaling with complex formulas and lookup tables.
Easy PC Connectivity
USB has greatly simplified PC-based test and measurement. Because USB is a plug-and-play bus, the NI CompactDAQ USB chassis and all I/O modules are automatically detected and configured when connected to a USB port. Unlike legacy GPIB and serial devices that require an interface board, NI CompactDAQ connects directly to the USB port through a standard USB cable. This cabling feature eliminates another hidden cost associated with traditional instruments. With simple USB cabling, you can easily move an NI CompactDAQ system from one PC to another.
To make networking technology more accessible to the non-IT professional, NI CompactDAQ Ethernet chassis use the Zero Configuration Networking (Zeroconf) collection of standards. With Zeroconf technology, you can plug an NI CompactDAQ system directly into your computer or local subnet, and it appears automatically in the NI Measurement & Automation Explorer (MAX) configuration utility without any network setup or configuration. In addition, a new Web configuration interface built into the firmware of the Ethernet helps you manage your system through a Web browser without installing any software on your host machine.
3. Instant Measurements with NI CompactDAQ
Flexible Software – Turnkey Data Logging, LabVIEW, Visual Studio .NET, and ANSI C/C++
Every NI CompactDAQ chassis is shipped with the free NI LabVIEW SignalExpress LE data-logging software package. With this ready-to-run software, you can acquire data from multiple devices that run NI-DAQmx and log the data to file or export the data to a spreadsheet.
For greater flexibility, NI CompactDAQ also includes NI-DAQmx driver and measurement services software for NI LabVIEW, NI LabWindows™/CVI, ANSI C/C++, and Visual Studio .NET. In addition to basic driver functionality, NI-DAQmx features a configuration management and testing utility, the DAQ Assistant wizard utility, and high-performance features such as multithreading and data compaction. LabVIEW is an industry-leading graphical development environment for designing test, measurement, and control systems. It combines the flexibility of a programming language with built-in tools designed specifically for test, measurement, and control to create applications ranging from simple temperature monitoring to sophisticated control systems.
To learn more about data-logging software from National Instruments, view the Three Levels of Data-Logging Software from National Instruments tutorial.
Figure 3. LabVIEW SignalExpress UI (example)
4. Additional Resources
For more structural health monitoring resources, visit the Structural Health and Seismic Monitoring home page.
The mark LabWindows is used under a license from Microsoft Corporation. Windows is a registered trademark of Microsoft Corporation in the United States and other countries.