Simplify Ethernet I/O for Measurement and Control

Ethernet has established itself as a standard for network communication in the business and IT sectors, and its ease of use, low-cost wiring, and widespread adoption has made it an attractive solution for measurement and automation as well. For engineers and scientists designing data acquisition systems, Ethernet extends the reach of their measurements to meet new distributed application challenges. Control and automation engineers also can use real-time Ethernet to add distributed I/O to an existing control system without losing determinism. National Instruments simplifies distributed measurements and real-time control applications with Ethernet data acquisition and deterministic Ethernet technology. 

Ethernet Data Acquisition

The use of PC-based technology for sensor measurements has continued to evolve over the last 20 years from early desktop bus architectures, such as Industry-Standard Architecture (ISA), to high-bandwidth, parallel systems with PCI Express and PXI Express. More recently, external buses for instrumentation, such as USB, have shown significant adoption in industry. The force behind this trend is the portability and flexibility that USB brings to measurement applications. Ethernet takes that flexibility one step further by offering measurements in remote or highly distributed applications.

NI Ethernet data acquisition (DAQ) devices combine Ethernet communication, direct sensor connectivity, and the flexibility of NI LabVIEW software for remote monitoring of electrical, physical, mechanical, and acoustical signals. The NI ENET-9xxx family of devices includes five Ethernet DAQ devices for the most common sensor measurements, from thermocouples to accelerometers. Each of the devices is also available as an NI WLS-9xxx device, which integrates an IEEE 802.11b/g wireless radio in addition to wired Ethernet.

Table 1. NI offers Ethernet DAQ devices for the most common sensor measurements.

A common challenge with Ethernet is the ability to stream waveform data continuously from an Ethernet-based device without significant software development effort. Using technology based on patent-pending NI signal streaming technology for USB, NI Ethernet DAQ devices can stream data on each channel at more than 50 kS/s with 24 bits of resolution. This translates to more than 6 Mb/s of real-time bandwidth per device for high-performance acceleration, strain, and sound measurements. Ethernet DAQ also uses the TCP/IP protocol for highly reliable network communication. TCP can automatically correct for the most common network issues, such as out-of-order or lost data packets.

Further enhancing the reliability, flexibility, and ease of use for Ethernet DAQ is NI-DAQmx driver and measurement services software. NI-DAQmx delivers time-saving features, such as the configuration-based NI DAQ Assistant with code generation for both LabVIEW and text-based languages; more than 3,000 measurement examples; device simulation; connection diagrams; and compatibility with LabVIEW, ANSI C/C++, C#, Visual Basic .NET, and Visual Basic 6.0. The DAQ Assistant is an intuitive, configuration-based interface that provides a step-by-step guide for configuring measurements with an NI data acquisition device.

Figure 1. The DAQ Assistant can generate code for LabVIEW, LabWindows^™/CVI, and Measurement Studio.

You can use the same NI-DAQmx driver across multiple programming languages and device families. For example, you can use a strain application developed for the NI USB-9237 with the NI ENET-9237 with no software changes. NI Ethernet DAQ facilitates the addition of remote measurements to new or existing data acquisition and data-logging systems. 

Deterministic Ethernet

Ethernet not only plays a significant role in measurements and data logging, it is also important in industrial control and automation. Many of these applications demand microsecond response times and real-time performance, which the standard TCP/IP protocol cannot provide. Considering its low-cost nature and existing infrastructure, considerable effort has been poured into creating Ethernet-based systems with deterministic capabilities. Today’s deterministic Ethernet technology presents an attractive solution for adding distributed I/O in time-critical systems.

NI offers a high-performance 8-slot chassis that brings deterministic Ethernet I/O to the LabVIEW graphical development platform. The NI 9144 expansion chassis uses standard CAT5 Ethernet cabling to deterministically communicate with NI real-time controllers containing two Ethernet ports, including NI CompactRIO programmable automation controllers and PXI hardware. The expansion chassis also features two Ethernet ports, so you can daisy chain multiple NI 9144 chassis (up to 100 m in between) from a single controller to expand your time-critical applications while maintaining hard determinism. With a temperature range from -40 to 70 °C and 50 g shock ratings, the rugged chassis is designed for industrial applications.

[+] Enlarge Image

Figure 2. This NI real-time system includes deterministic Ethernet I/O.

More than 30 analog and digital NI C Series modules are supported for high-accuracy measurement quality and direct connectivity to a wide variety of sensors. The NI 9144 works out of the box with minimal configuration because the LabVIEW Real-Time Module 8.6 automatically recognizes all connected chassis and modules. LabVIEW offers easy access to the physical channels using the click-and-drag I/O Variable, live test panels, and I/O forcing for troubleshooting.

The NI 9144 deterministic Ethernet chassis integrates with existing NI platforms such as field-programmable gate arrays (FPGAs) you can program with LabVIEW, industrial communications, and modular instruments, making the chassis ideal for applications such as machine building, large distributed systems, big physics, and hardware in the loop.

Figure 3. The NI 9144 expansion chassis for C Series modules integrates with existing NI platforms.

Whether you are taking temperature measurements in the lab or controlling a real-time system, NI Ethernet-based technologies simplify distributed I/O applications.

– Charles Stiernberg

Charles Stiernberg is an NI data acquisition product engineer. He received his bachelor’s degree in electrical engineering, with a focus on embedded systems and VLSI design, from The University of Texas at Austin.

– Irene Bearly

Irene Bearly is an NI Compact FieldPoint and remote I/O product engineer. She received her bachelor's and master's degrees in Electrical Engineering from Georgia Tech.

View additional resources on distributed Ethernet I/O.

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.

1 ratings | 5.00 out of 5

Print

Reader Comments | Submit a comment »