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DAQ boards offer faster throughput, easier programming

Posted: 11 Oct 2007     Print Version  Bookmark and Share

Keywords:DAQ boards  PCI  USB  MATLAB  LabView 

As test and measurement and control applications become more stringent, makers of DAQ boards are responding with boards that offer faster throughput, higher levels of integration and flexibility, and easier programming.

A snapshot of some of the latest DAQ boards shows that almost all incorporate some form of simultaneous sampling to improve data throughput. This is achieved using either a simultaneous sample-and-hold (SSH) architecture derived from the multiplexed architectures commonly used by mid-to-high channel-count DAQ devices, or multiple DACs.

"More high-speed DAQ boards are employing simultaneous sampling architectures," said Jim Stevens, VP of engineering for Measurement Computing. "This reduces the channel-to-channel latency inherent with multiplexed designs, enabling true spectral analysis in dynamic applications."

According to Measurement Computing's Web site, DAQ boards typically offer measurements up to 64 channels with 16bit resolution, at data throughput rates of up to 20MSps. Typically, the boards include discrete digital bidirectional I/O lines, counter/timers and DACs to output analogue signals for control applications.

Measurement Computing's latest offerings include the USB-1608HS and USB-1608HS-2A0. These modules provide true simultaneous data capture of up to eight channels of 16bit single-ended or differential analog input at 250kHZ per channel. Both include 16bit digital I/0, and the USB-1608HS-2A0 has two additional channels of 16bit analogue output with a range of -10 to 10V.

Data sampling rates are increasing as board makers employ faster signal converters and other high-speed design techniques. "Several years ago, the fastest sampling rate was 200KSps, for audio," said Kaustubh Wagle, product marketing manager of high-speed digitisers for National Instruments. "Technology now allows a sampling rate of up to 500KSps."

NI's USB-6229 offers up to 32 analog inputs and a 250KSps single-channel sampling rate.

Boards with USB
More DAQ boards are incorporating USB. Besides Measurement Computing, NI announced the USB-6221 and USB-6229 DAQ boards. Both provide up to 32 analog inputs and a 250KSps single-channel sampling rate.

Although PCI and, to a lesser extent, PXI serve as the common interface bus in many of the latest boards, there's also a trend toward the USB. "USB has turned out to be a popular bus for DAQ because of portable applications," said Wagle.

Compared with PCI, USB boards experience higher latency issues because of the USB's operating system-based access and serial nature, which slow data transfer.

NI has attempted to overcome those obstacles in its USB DAQ boards with signal streaming technology, which makes it possible to acquire and generate multiple analog and digital I/O signals simultaneously.

The signal streaming technology combines hardware and software design elements to enable sustained high-speed and bidirectional streams over USB, by relying on message-based rather than register-based configuration. This technology enables configuration to take place on the device to minimise USB transfers. More synchronous analogue and digital data can be streamed for data-intensive applications than is possible using USB DAQ devices alone.

NI's USB boards have four 16bit, 833KSps analogue output channels, 48 digital I/0 channels with up to 32 clocked at 1MHz and two 32bit counter/timers.

The PXI bus also continues to make inroads. "PXI is enabling lots of new applications," NI's Wagle said. "It leverages the PCIe bus, a complete, open test and measurement platform based on industrial standards."

Adlink's DAQ-2016 has a maximum transfer rate of 800KSps per channel.

Intuitive cards
Adlink Technology Inc. has unveiled a high-sampling, multifunction DAQ card in both PCI and PXI form factors. The DAQ-2016 and PXI-2016 offer a maximum transfer rate of 800KSps per channel—making them suitable for large-scale data collection and industrial automation, according to Adlink.

The four-channel DAQ-2016 and PXI-2016 offer 16bit resolution and various analogue and digital trigger sources and modes for multichannel simultaneous sampling efficiency. Both can synchronise multiple external devices using a system synchronisation interface or a PXI trigger bus.

The cards deliver two 12bit, 1MSps analogue output, 24-channel programmable DIO and two 16bit timers/counters that provide flexibility for multitasking. They also come with a WDM driver for C/C++, VB, Delphi, C++ Builder and .Net programming languages for MATLAB and LabView.

Microstar Laboratories unveiled the DAP 5380a, a PCI-based DAQ board with up to 16 channels. The board acquires 14bit data at 800KSps on each of four channels, and 625KSps on each of eight channels. The DAP 5380a can transfer data to the host PC at 3200KSps. It incorporates a 233MHz Intel Pentium processor and 128Mbytes of on-board DRAM.

According to Measurement Computing's Stevens, DAQ boards offer more bang for the buck by incorporating a higher level of functional integration, driven primarily by the chip vendors. "On the converter front, signal conditioning functions [bridge excitation, DAC deglitching] that have traditionally required discrete circuit design are now readily available and allow direct connection to sensors and field electronics," he said.

Diamond Systems' DMM-32X-AT has autocalibration and an operating temperature range of -40°C to 85°C.

Stevens added, "The current generation of MCUs is rich with peripheral interfaces—Ethernet Web servers, USB, CAN, UART, among others. These high levels of connectivity are integrated with ever-improving analogue features—PGAs, ADCs and DACs—some of which approach the parametric performance of traditional 14-16bit monolithic devices."

"You're getting more functionality for a similar price," added Charlie Stiernberg, a product marketing manager for NI. "For instance, ADCs were far more expensive in the 1980s and 1990s. But recent trends in ADCs, such as fitting more channels on a single chip, are helping to keep prices down."

Board makers are also helping engineers speed setup for their DAQ systems. Diamond Systems Corp. introduced an embedded DAQ board in the PC/104 form factor with advanced automatic autocalibration. The DMM-32X-AT has 32 A/D input channels with 16bit resolution, a 250kHz maximum sampling rate, programmable input ranges, and user-selectable single-ended/differential configuration.

The board's 24 digital I/O has bit-by-bit direction programmability and buffers for enhanced output current of -15mA/64mA. On-board programmable counter/timer circuitry includes a 32bit counter/timer for A/D and D/A sample timing, as well as a 16bit counter/timer.

The DMM-32X-AT offers an extended operating temperature range of -40°C to 85°C. It has Universal Driver software that provides a programming library to simplify control of all the board's features and enable programmers to develop application software quickly.

NI, which develops advanced instrumentation software as well as hardware, ships its USB-6221 and USB-6229 boards with free data-logging software to help users leverage USB's plug-and-play capabilities, thus helping shorten time to measurement. The boards also interface with NI's LabView Signal Express interactive measurement software and TestStand test management software.

- Spencer Chin
EE Times

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