From USB to PXI, Systems Aid Data Capture
by Rick Nelson, Executive Editor
Modular data-acquisition (DAQ) hardware coupled with capable software can provide flexible acquisition and analysis capabilities across a wide variety of applications. However, the very flexibility that can enhance your application can make it difficult to select the right system. You’ll need to choose from among a range of hardware configurations and connectivity options. Further, you will need to decide what level of hardware and software integration you want to perform yourself.
CompactDAQ Platform with LabView Software
You do not want to purchase more than you need, but neither do you want to lock yourself into a system that can’t be expanded to serve any anticipated high channel-count needs. In addition to selecting sensors, signal-conditioning circuits, and DAQ mainframes, you will need to decide what to do with the data you capture.
Previous articles have looked at wireless DAQ systems,1 provided an overview of DAQ technologies,2 and focused in on a specific modular DAQ architecture introduced this year by VTI Instruments.3 This article offers a look at the trade-offs involved in implementing modular DAQ systems.
Looking to the Future
National Instruments (NI) is a long-time proponent of modular systems, and Jim Schwartz, product marketing engineer at NI, said he sees the company’s competitors moving toward modular solutions in the DAQ space. Schwartz succinctly spelled out what to keep in mind when choosing a DAQ system: “A lot of it has to do with the types of measurements you are making. You really need to be able to plan out what you are going to measure and what your needs are in terms of future expandability—whether you need to add modules or channels or new capabilities in software.”
Schwartz continued, “You must be able to envision your system early on and understand whether you are going to need different channel types. If you start with a portable USB system, you are going to run into limits with channel types and channel count. If you start with a more modular system like CompactDAQ or PXI, there are going to be many opportunities to add signal conditioning and more thermocouple, accelerometer, and strain-gage channels. It’s really about how far you need to look into the future with your system.”
NI divides its DAQ offerings into single device and system classifications, each of which, in turn, divides into subcategories. The single-device category includes portable DAQ and desktop DAQ products. The latter offers PCI or PCI Express (PCIe) connectivity and plugs into a standard PC; you can expand beyond a single device if your PC has more than one slot available. The portable DAQ product connects to a laptop or desktop PC by means of USB, Wi-Fi, or Ethernet. NI’s portable DAQ products have sample rates to 2 MS/s, and built-in signal conditioning is available. Desktop DAQ products support sample rates to 10 MS/s; built-in signal conditioning is not available.
34980A Switch/Measure Unit
NI’s system-level modular DAQ products divide into the CompactDAQ platform and the PXI platform. CompactDAQ offers USB, Wi-Fi, and Ethernet connectivity, supports sample rates to 1 MS/s, accommodates up to 250 I/O channels, and comes with built-in signal conditioning. NI PXI DAQ products—with PXI or PXI Express (PXIe) connectivity—offer sample rates to 10 MS/s and support 1,000 or more I/O channels; built-in signal conditioning is available. All NI’s DAQ products come with NI LabVIEW SignalExpress LE.
Elizabeth Smith, product marketing manager for DAQ at NI, noted that it is important to think beyond traditional DAQ when choosing a modular product. CompactDAQ is a platform for DAQ applications with analog and digital I/O, whereas, she said, “The PXI platform covers DAQ but also makes available a suite of high-end modules including digitizers, switches, and RF instruments.” She cited as an example an RF test system that would include a DAQ board to measure temperature or some basic analog inputs. “PXI can be a really good platform for those types of applications,” she said.
Agilent Technologies has several platforms to address DAQ applications. According to Sheri DeTomasi, product marketing manager for software and modular products, “In 2010, Agilent introduced a number of products for DAQ, including new DMMs, digitizers, switches, and sources. In the last year we have added the low-cost M9381A PXI DMM, the high-voltage M9216A DAQ, and the M9185A D/A Converter to that portfolio.”
Like NI, Agilent offers DAQ products that range from low-cost, low channel-count systems to complex solutions. Said DeTomasi, “We can leverage our technologies across multiple platforms, and engineers can choose the platform that best fits their application needs.” When engineers need low to medium channel-count solutions, she said, the 34972A/34980A platforms offer the lowest cost per channel in an easy-to-use platform. When engineers require more channels or capabilities not offered in the 34972A/34980A platform, Agilent also provides DAQ capabilities in the PXI platform.
DT9826-8 and DT9826-4 USB DAQ Modules
Agilent has an application note that can help you choose between platforms such as the 34980A and PXI.4 In general, the former is easy to use, comes with DAQ software, minimizes operating noise, and readily supports transducer-based measurements. It also is suitable for low channel-count (up to 50) production use. The PXI platform offers high speeds and signal bandwidths to 40 GHz and supports high channel counts (up to 5,000).
Buy or Build?
Modular platforms bring about the build vs. buy question: Should you integrate the system yourself or buy it fully configured from a vendor or integrator?
DeTomasi said Agilent’s customers have many options, noting, “Our internal teams can provide anything from applications services to totally integrated solutions.” Agilent, she said, also has a solution partner program specifically for modular products—21 partners can provide anything from integration services to software development.
Software certainly is part of the equation, and Agilent offers a variety of tools. For the 34972A and 34980A platforms, DeTomasi said, the company provides BenchLink Data Logger, BenchLink Data Logger Pro, a built-in web interface, and drivers for easy integration into the most common software development environments including Agilent’s VEE Pro and T&M Toolkit; NI’s LabVIEW, LabWindows CVI, Teststand, and Switch Executive; and Microsoft’s Visual Studio.NET, C/C++, and Visual Basic 6. The PXI platform, she said, includes soft front-panel and instrument drivers to work in the environment of choice, whether it’s Agilent VEE, NI LabVIEW, LabWindows CVI, Visual Studio, C, C++, C#, Visual Basic, or MATLAB.
Agilent also offers PXI DAQ products that can be combined with the company’s modular RF and microwave modules so customers can make low-frequency parametric measurements along with high-frequency measurements in one PXI or AXIe chassis. In addition, DeTomasi said, “By basing our instrument connectivity on PC standard interfaces, we can combine our high-performance benchtop instruments with our modular systems to create a hybrid solution to best fit the customer’s need.”
Multifunction USB DAQ
Data Translation has introduced a variety of DAQ products over the past few months, according to Kristin Sullivan, vice president of marketing and sales at the company. In June, the company announced the release of new low-cost, simultaneous, multifunction DAQ modules for USB. The DT9826-4 and DT9826-8 combine high performance, 24-bit analog measurement, digital I/O, counter/timers, and a tachometer channel within a single plug-and-play device. Both modules are offered as board-only versions for OEMs.
In May, the company introduced the DT9838 strain- and bridge-based acquisition module for USB. The DT9838 offers high-speed performance in a compact form factor for applications including strain, load, pressure, and other bridge-based measurements. The bus-powered module removes the need for an external power supply and provides 24-bit resolution; direct connectivity; 52 kS/s simultaneously sampled analog inputs; full-, half-, and quarter-bridge completion; up to 10-V internal excitation; transducer electronic data sheet (TEDS) smart-sensor compatibility; and channel expansion using an RJ45 synchronization connector to synchronize up to four DT9838 modules.
And in April, the company introduced the DT9862S high-speed simultaneous USB DAQ module offering a bandwidth of 300 MHz with crystal-controlled sampling for low-jitter, precise applications. In addition, an external clock input enables the user to lock the under-sampling to a multiple of the signal under test. Said Sullivan, “RF communications applications such as sonar and satellite surveillance are just a couple of areas where under-sampling is required for high-quality measurements.”
Data Translation offers an application note to help customers choose appropriate DAQ products.5 Said Sullivan, “Customers choose their best solution based on an assessment of their application requirements including bus platform, input/sensor types, input ranges, number of inputs, required resolution, whether simultaneous sampling is required, whether isolation is required due to noise/interference in sampling environment, and whether or not portability is required.” Data Translation, she said, offers USB and Ethernet (LXI) DAQ with direct-sensor connections to the most commonly used sensors including thermocouples, RTDs, strain gages, loads cells, and other bridge-based sensors.
Ethernet for Expandability
As for upgrading, Sullivan said, “Future expandability is inherent using Ethernet instruments because you can add more instruments to your network.” DT Ethernet modules, she said, offer acquisition synchronization using LXI triggering. To expand channel count using a USB module, she added, several DT modules provide an RJ45 (LVDS) synchronization connector that can be used to connect and synchronize multiple modules.
As for putting a complete modular DAQ solution together, Sullivan said, “Data Translation offers USB and Ethernet DAQ modules and instrumentation with supporting software—in many cases, this is the complete solution. DT also works with OEMs to provide customized solutions that can be embedded into applications. In addition, we work with a number of third-party integrators.”
As for software, Sullivan said, “All Data Translation devices have comprehensive driver and software support compatible with Windows XP/7/Vista. Customers may choose to use one of our development libraries (DT-Open Layers for .NET or Win32) or one of our ready-to-run applications. All Data Translation Ethernet devices include a comprehensive web application, SCPI support, and an IVI-COM driver that works in any development environment that supports COM programming.”
Sullivan cited Data Translation’s proprietary ISO-Channel technology as a unique feature of the company’s DAQ products. ISO-Channel eliminates ground-loop problems by using a differential, isolated, floating front end. “To measure floating signal sources,” she said, “ISO-Channel technology uses differential analog input signals, a 24-bit delta-sigma A/D converter for each channel, and channel-to-channel isolation.”
Meeting Customer Needs
DAQ vendor innovations are spurred on by customer needs. As reported in the June issue, Anirudh Narayanan, lead applications engineer at VTI Instruments, said the goal in the design of the SentinelEX family was to provide a platform that would not box customers into separate, unique hardware and software platforms for each application space in which they work, whether requiring modal, static/structural, acoustic, thermal/environmental, or distributed/rugged measurements.3
Dewetron was similarly driven by customer requirements when it introduced its DEWE2 Series in 2011. Grant M. Smith, president, described DEWE2 as embodying a new architecture for the company, with the DEWE2 combining signal-conditioning and A/D cards into single modules. That move, he said, increased accuracy by up to 400%. In addition, he said, the system offers enhanced modularity, noting, “These modules can be plugged in by the customer at any time, completely changing the configuration of the system in moments.”
The modularity meets a different customer requirement as well, Grant said. “Our customers have been clamoring for faster delivery for some time now. This new architecture finally makes it possible for us to achieve that.”
Dewetron’s most recent product is the DEWE-3050 Benchtop DAQ System, which accepts up to 96 channels of differential signal conditioners or up to 32 isolated high-bandwidth plug-in signal conditioners. The front panel contains a 17-inch high-resolution touch-screen display—a ruggedized “tablet” that can be removed from the unit and placed feet away from the mainframe.
Grant described the DEWE-3050 as a traditional DEWE system that can accommodate cards with any sample rate—up to 25 MS/s per channel. He added, “The DEWE2, being new, is limited to cards with sample rates of 200 kS/s per channel maximum. So for customers who want the most channels in a single chassis with the highest possible sample rate, classic DEWE platforms like the DEWE-3050 still are the way to go.”
Driving DAQ Evolution
Agilent, Data Translation, Dewetron, NI, and VTI Instruments will continue to evolve their DAQ products as will other companies mentioned in EE’s May report on the topic.2 Microstar Laboratories, for example, in April announced an enhancement of its xDAP family of DAQ-processor systems with the release of its Rotating Machinery Analysis module, which includes software tools to facilitate mixed-time measurements and rotation measurements of machinery. Calculations are performed in real time so data arrives fully processed from the xDAP system and ready to log, display, or use immediately in a host system.
In addition, United Electronic Industries (UEI) announced in May that its UEILogger Series now offers increased logging speeds (up to 15 times faster), data storage, and functionality. The new logger supports sample rates as high as 500 kS/s for 16-bit samples and 250 kS/s for 18- to 24-bit A/D samples.
UEILogger is based on UEI’s PowerDNA Ethernet DAQ cubes, for which each cube consists of a core module (with a processor and a network interface) and three or six open I/O slots. Users select the deployment option and I/O boards that meet their system requirements. A six-slot Cube provides up to 150 analog inputs, 192 analog outputs, 288 digital I/O lines, 48 counter or quadrature channels, 72 ARINC-429 channels, and 24 serial or CAN-bus ports.
And finally, Measurement Computing announced the release of the multifunction PCIe-DAS1602/16 DAQ Board for the PCI Express/PCIe bus in June. The 16-bit PCIe-DAS1602/16 offers 16 analog inputs, a 100-kS/s sample rate, 32 digital I/O channels, two analog outputs, and three counter inputs. The PCIe-DAS1602/16 also is connector- and software-compatible with the MCC PCIM-DAS1602/16 for existing customers who need to migrate to PCIe. The PCIe-DAS1602/16 has a variety of software options. Support includes out-of-the-box TracerDAQ along with drivers for Visual Studio and Visual Studio.NET, DASYLab, and NI LabVIEW.
You can expect firms to continue building innovative DAQ products. You’ll have a variety of modules from which to choose, and you can select modules and build a system yourself or have a vendor or integrator do that for you. As for your decision in that regard, Schwartz at NI said, “It really depends on how comfortable you are with software.” If you have 16 thermocouples, he said, you can easily find a 16-channel module that can handle the job. The difficult part is deciding how to handle the data you collect.
1. Nelson, R., “Wi-Fi Extends the Reach of Data Acquisition,” EE-Evaluation Engineering, February 2012, p. 12.
2. Nelson, R., “DAQ Technologies Support Broad Measurement Range,” EE-Evaluation Engineering, May 2012, p. 20.
3. Nelson, R., “Open Architecture Boosts Dynamic Signal Analysis,” EE-Evaluation Engineering, June 2012, p. 20.
4. Comparing the Agilent 34980A and PXI for Switch Measurement Applications, Agilent Technologies, Application Note, 2012.
5. Choosing Data Acquisition Boards and Software, Data Translation, Application Note, 2011.
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