Trade.Information

Topic Name: EtherNet/IP Performance Test Tool Enables Manufacturers to Predict the Performance of Data Communication System Machines

Category: Computer science & technology

Research persons: NIST Research Team

Location: National Institute of Standards and Technology (NIST), United States

Details

Electronic commands passed from machine to machine over data networks increasingly drive today’s precisely timed and sequenced manufacturing production lines. However timing irregularities in the signals from even one machine—a difference of only a tenth of a second from the expected—can result in havoc for manufacturing processes on the plant floor. The timing glitches, called “cyclic jitters,” can cause real jitters, making production machines jump or shake, damaging products, even shutting down assembly lines. National Institute of Standards and Technology (NIST) engineers have created a software program to help avoid that problem.

The NIST “EtherNet/Industrial Protocol (IP) Performance Test Tool” enables manufacturers to anticipate how certain machines will perform as part of their data communication system. Data from the tool also can provide vendors with information need to better tune the performance of their equipment.

Individual vendors often define the performance characteristics of network devices in different ways. These documentation differences make it difficult for manufacturers or plant engineers to compare high-speed data transmission characteristics of similar devices. To determine how different performance characteristics relate, they have to make time-consuming searches through vendor manuals or spend hours contacting vendor company engineers. Although standardized tests can indicate how well devices conform to communication specifications, until now manufacturers never could be sure how well the device actually would work under normal or abnormally heavy transmission conditions on the factory floor.

The EtherNet/IP Performance Test Tool collects device information from the user, generates a set of test scripts based on that information, analyses the performance data and reports the results to the user. The software package provides device transmission data for three different conditions: with no background electronic traffic; with small background traffic; and with more than 240 devices on the network.

NIST began working on the project at the urging of U.S. Council for Automotive Research (USCAR)’s Plant Floor Controllers Task Force and developed the program in conjunction with the Open DeviceNet Vendor Association (ODVA) under a Cooperative Research and Development Agreement (CRADA). ODVA, a vendor organization that maintains the DeviceNet and EtherNet/IP standards used extensively by the U.S. automotive industry, plans to begin using the test tool as part of a new performance testing laboratory service later this year.

Note for Jitter
Jitter is an unwanted variation of one or more signal characteristics in electronics and telecommunications. Jitter may be seen in characteristics such as the interval between successive pulses, or the amplitude, frequency, or phase of successive cycles. Jitter is a significant factor in the design of almost all communications links (e.g. USB, PCI-e, SATA, OC-48).

Jitter can apply to a number of signal qualities (e.g. amplitude, phase, pulse width or pulse position), and can be quantified in the same terms as all time-varying signals (e.g. RMS, or peak-to-peak displacement). Also like other time-varying signals, jitter can be expressed in terms of spectral density (frequency content). Jitter period is the interval between two times of maximum effect (or between two times of minimum effect) of a jitter characteristic, for a jitter that varies regularly with time. Jitter frequency, the more commonly quoted figure, is its inverse. Generally, very low jitter frequency is not of interest in designing systems, and the low-frequency cutoff for jitter is typically specified at 1 Hz.

In the context of digital audio extraction from Compact Discs, seek jitter causes extracted audio samples to be doubled-up or skipped entirely if the Compact Disc drive re-seeks. The problem occurs during seeking because the Red Book (audio CD standard) doesn't require block-accurate addressing. As a result, the extraction process may restart a few samples early or late, resulting in doubled or omitted samples. These glitches often sound like tiny repeating clicks during playback. An approach that has produced good results is to do jitter correction in software involves performing overlapping reads, and then sliding the data around to find overlaps at the edges. Most extraction programs will perform seek jitter correction. CD manufacturers avoid seek jitter by extracting the entire disc in one continuous read using specific CD drive models at slower speeds so the drive will not re-seek.

Random Jitter, also called Gaussian jitter, is unpredictable electronic timing noise. An example of random jitter is the white noise heard over the radio or seen on a TV screen. Random jitter typically follows a Gaussian distribution or Normal distribution. It is believed to follow this pattern because most noise or jitter in a electrical circuit is caused by thermal noise, which does have a Gaussian distribution. Another reason for random jitter to have a distribution like this is due to the Central limit theorem. The central limit theorem states that composite effect of many uncorrelated noise sources, regardless of the distributions, approaches a Gaussian distribution. One of the main differences between random and deterministic jitter is that deterministic jitter is bounded and random jitter is unbounded.

Deterministic jitter is a type of clock timing jitter or data signal jitter that is predictable and reproducible. The peak-to-peak value of this jitter is bounded, and the bounds can easily be observed and predicted. Periodic Jitter, Data-Dependent Jitter, and Duty-Cycle Dependent Jitter are all types of Deterministic Jitter.

Note for Ethernet Industrial Protocol
EtherNet/IP (Ethernet Industrial Protocol) is an open industrial application layer protocol for industrial automation applications. It is supported by ODVA.

Built on the standard TCP/IP protocols, it utilizes long established Ethernet hardware and software to define an application layer protocol for configuring, accessing and controlling industrial automation devices.

EtherNet/IP™ classifies Ethernet nodes as predefined device types with specific behaviors.

The EtherNet/IP application layer protocol is based on the Common Industrial Protocol (CIP) layer used in both DeviceNet™, CompoNet™ and ControlNet™. Building on these protocols, Ethernet/IP provides a seam-less integrated system from the Industrial floor to the enterprise network.

ODVA is the organization that supports network technologies built on the Common Industrial Protocol (CIP™). These currently include the network adaptations of CIP—EtherNet/IP™, DeviceNet™ and CompoNet™—and major application extensions to CIP: CIP Safety™, CIP Motion™ and CIP Sync™.
In 2000, the ODVA and CI introduced EtherNet/IP. Here “IP” stands for “Industrial Protocol”. The EtherNet/IP protocol was however originally created by Rockwell Automation, with little or no inputs taken from other ODVA member companies.

Subsequently, additional CIP profiles have been developed that also operate with EtherNet/IP, these include CIP Safety, CIP Sync (this embodies IEEE 1588) and CIP Motion. EtherNet/IP was intended to be opened to the public, and at once it was suggested to publish the Level 2 source codes in sourceforge.net, but failed.

In figure, The points on this graph from the EtherNet/IP Performance Test Tool represent data packets. Those points pictured away from the centerline reflect timing errors in the network communications of the device being analyzed.