The term “data acquisition” has different meanings for different people. Researchers use it to describe the process of gathering real-world data to validate models and simulations. Engineers working on a process control application might use the term to describe distributed sensor measurement as part of a large SCADA system. In its broadest sense, data acquisition is the process of gathering information in an automated fashion from analog and digital measurement sources and presenting that information in a meaningful way.
Since their introduction 20 years ago, PC-based data acquisition devices have found incredibly broad usage in areas as diverse as monitoring agricultural applications to testing the next-generation NASA space telescope. Their general-purpose and software-defined nature makes them a viable solution in virtually any application involving electrical signals 1MHz and less. While the fundamental architecture of integrated analog-to-digital converters (ADCs), a PC peripheral bus, and software has remained consistent over the years, the technologies employed for each component have evolved considerably. ADCs have followed the trend of other semiconductor technologies in providing significantly improved performance at declining costs. The cornucopia of vendor-specific computer buses in decades past has been consolidated into a handful of standard buses, including USB, Ethernet, PCI, and more recently, PCI Express. Also, application software such as the NI LabVIEW graphical programming environment has grown easier to use while providing even more advanced analysis and visualization capabilities.
1. Three Key Trends in Data Acquisition
In the last few years, three trends have emerged to significantly impact the evolution of PC-based data acquisition. The most visible trend has in no small part been driven by the transition from desktop PCs to laptops. Since 2005, laptop computers have outsold desktop PCs worldwide, and this transition continues to accelerate. USB 2.0 has become a standard bus for connecting peripheral devices – including data acquisition devices – to laptops. USB 2.0 provides added functionality for data acquisition compared to plug-in PCI bus devices. Benefits of USB, such as autodiscovery, setup, and the ability to locate the device up to 5 m from the PC with a standard USB cable, improve both ease of use and flexibility. The bus apportions up to 60 MB/s of bandwidth, and technologies such as NI signal streaming ensure that multiple data acquisition data streams can operate simultaneously. With new computing platforms such as tablet PCs and handheld devices adopting USB, the adoption and growth of USB 2.0 data acquisition devices continues.
Figure 1. Mobile computing has contributed to widespread adoption of USB data acquisition devices.
A second trend in the data acquisition market is related to the improved performance and declining prices of ADCs. Through the 1980s and 1990s, the ADC was clearly the most expensive component on a data acquisition device. Today’s modern ADCs have faster conversion speeds, higher resolutions, and an order of magnitude lower price point. Lower ADC prices have facilitated the integration of signal conditioning features on data acquisition devices to improve safety, accuracy, and ease of use. Many data acquisition devices now include digital isolators to protect the device, computer, and operator from potentially hazardous electrical signals while improving measurement accuracy by breaking ground loops and rejecting error-causing common-mode voltages. Other signal conditioning features such as amplifiers, filters, and sensor-specific circuitry on new devices such as NI C Series data acquisition (DAQ) devices further improve accuracy and simplify connectivity to common sensors.
A third data acquisition trend is the use of onboard field-programmable gate arrays (FPGAs) for inline signal processing and data reduction. NI R Series intelligent DAQ devices incorporate the latest Xilinx FPGAs, which you can program in LabVIEW to process acquired data on the device without having to transfer data over a bus to the PC processor. The flexibility of these devices makes them ideal for custom data acquisition requirements, embedded applications, and the development and testing of custom digital interfacing. As FPGAs continue to move along the price/performance evolution curve, and as programming them in LabVIEW becomes even easier, expect the integration of FPGAs on data acquisition devices to continue to expand.
Figure 2. FPGAs programmed with LabVIEW add onboard intelligence to NI R Series DAQ devices.
2. A Glimpse into the Future
Another corollary of falling ADC prices is that the economics allow for individual channels on a data acquisition device to have their own ADC, rather than using multiplexers to share a single ADC. This means data acquisition devices can get more granular in their channel count. You can already see this transition occurring in the latest NI C Series modules and platforms. Many of these modules are designed to work with a specific signal type (such as a thermocouple) and provide a dedicated ADC on each channel. This facilitates lower-channel-count modules and devices, which you can group together to develop a custom data acquisition system with the exact channel count and mix to fit a specific application need. Expect to see this transition from fixed I/O channel counts toward improved granularity and modularity to continue.
As mentioned previously, USB 2.0 is continuing to see expanding usage in portable measurement applications. However, other PC bus technologies will also see broad adoption in future data acquisition applications. One example is the next generation of USB, which has been announced by Intel and others, and whose specification is currently being finalized. USB 3.0 is targeted to reach bandwidths up to 10 times the current bandwidth of USB 2.0 by using two additional high-speed signal pairs. This "superspeed" mode is expected to provide roughly 4.8 Gbit/s of bandwidth, enabling very high speed I/O streaming. The first commercial silicon for USB 3.0 is expected in 2009 or 2010.
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Wireless is one of the most promising technologies for data acquisition. Wireless technologies have undergone a consolidation and standardization of technologies similar to what occurred for plug-in and cabled PC buses. For high-speed continuous transmission, IEEE 802.11 (Wi-Fi) has seen incredible adoption in mobile computing applications – recently making the jump from your laptop to your Apple iPhone. Maybe even more importantly for data acquisition applications, vendors have improved the industrial ruggedness of Wi-Fi products. Many vendors supply network components such as routers and access points that have industrial dust- and water-resistant ratings. Additionally, IT requirements have significantly enhanced the security and reliability of Wi-Fi networks with technologies such as WPA2 data encryption. Today, Wi-Fi access points can be connected to Ethernet-based data acquisition systems such as NI CompactRIO and NI Compact FieldPoint. However, the economies of scale, reliability, and ease of use of Wi-Fi make the technology ripe for integration into future data acquisition devices.
Future data acquisition devices will continue to leverage and benefit from technology advancements in the broader computing and consumer electronics industries. Expect to see continued growth and adoption of USB, more integration of signal conditioning, and added flexibility with onboard FPGAs – programmable with LabVIEW – on data acquisition devices. Looking forward, further granularity and modularity, next-generation bus technologies, and integrated wireless capabilities will help define the data acquisition landscape of the future.
– Brian Betts
Brian Betts is a data acquisition technical marketing group manager for National Instruments. He holds a bachelor’s degree in mechanical engineering from Texas A&M University.