Rapid VI adoption

Industrial Computer Hardware

I/O sensor/computer interfacing suppliers

November 2005 Industrial Computer Hardware

Virtual instrumentation uses the latest advances in commercially available computer technology to make faster and higher-performance measurements at lower prices than traditional instruments. For example, while instrument communication interfaces such as serial and GPIB have remained virtually unchanged for decades, a new PC bus called PCI Express provides dramatic improvements in data bandwidth to PC memory.

PCI Express

The 32-bit, 33 MHz PCI bus present on most desktop PCs provides 132 MBps bandwidth. While this is still adequate for many measurement applications, there are certain devices, such as a Gigabit LAN card, that can monopolise the bus. PCI bus architecture requires the bus to share the 132 MBps with all devices on the bus, so high-bandwidth devices such as LAN cards can strangle other devices in the same system. PCI Express remedies these problems, and has started to ship as a standard option on new PCs. PCI Express maintains software compatibility with PCI but replaces the physical bus with a high-speed (2,5 Gbps) serial bus. The bus sends data packets through transmit and receive signal pairs called lanes, which offer approximately 200 MBps bandwidth per direction per lane. The user may group multiple into x1 ('by-one'), x2, x4, x8, x12, x16, and x32 lane widths, and, unlike PCI, which shares bandwidth with all devices on the bus, each PCI Express device gets dedicated bandwidth.

Virtual instrumentation benefits

Plug-ins such as data acquisition devices and frame grabbers can use the increased bandwidth for faster acquisitions and higher throughputs, and systems with multiple devices benefit from guaranteed bandwidth per slot. National Instruments has helped lead the adoption of PCI Express by releasing the world's first PCI Express image acquisition and GPIB devices. The NI PCIe-1429 image acquisition device performs at rates exceeding 1000 frames/s. With a four-lane (x4) connection and two Camera Link inputs, it can acquire images at the maximum Camera Link rate - 680 MBps (slightly more than a CD-ROM worth of data every second).

PCI Express today and tomorrow

PCI Express is emerging quickly as the next plug-in bus standard. However, it will likely coexist with traditional PCI for the next decade, preserving existing PC-based test and control system investments. Because the PCI Express software layer is completely backward-compatible with PCI, the user can use the two buses together in systems and upgrade older PCI devices to PCI Express models with no required software changes. And with new PCs already shipping with PCI Express slots and measurement devices now available for the new bus, virtual instrumentation is already reaping the benefits of dramatic test and control system speed improvements.

For more information contact Michael Hutton, National Instruments SA, 011 805 8197.

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