Gunnar Prytz

A performance analysis of EtherCAT and PROFINET IRT

Ethernet is emerging as the preferred industrial communication platform upon which a multitude of protocols and solutions specially targeted at industrial communication requirements have been developed. This paper concentrates on a set of protocols popularly referred to as the Real-time Ethernet protocols and analyses two key technologies, namely PROFINET IRT and EtherCAT. The real-time performance characteristics of PROFINET IRT and EtherCAT is compared by looking into what factors affect their performance in a set of realistic scenarios. The goal is to provide a scientifically solid study on this subject where many presentations are seriously flawed by basic mistakes, misunderstandings or biased views. The detailed analysis presented here shows that EtherCAT has a performance advantage over PROFINET IRT and the reasons for this are discussed.

Evaluation of Time Gateways for Synchronization of Substation Automation Systems

The International Electrotechnical Commission (IEC) 61850 standard is widely used in substation automation system (SAS), even if some aspects related to the network-based time synchronization are still under investigation. The latest version of the IEC 61850 standard introduces IEEE 1588 Precision Time Protocol (PTP) for distributing time in the station and process buses, in addition to the previously used Simple Network Time Protocol (SNTP). Some time synchronization problems may arise when mixing old and new IEC 61850 devices in the same system; the IEEE 1588 PTP and SNTP technologies have somewhat different time representations and synchronization schemes, requiring time gateways for smooth integration. This paper introduces and compares the performance of some compact time gateways with different implementation architectures. All the examined gateways have the same external structure: They are transparent two-port devices which are inserted in the last network link between the switch and the end device, in order to perform the time conversion from IEEE 1588 PTP to SNTP. The time gateways are built using the same hardware platform based on a Field Programmable Gate Array that enables the creation of real embedded prototypes. The experimental results show that all the considered time gateways are applicable to SAS, but some of them have better performance than others in terms of synchronization accuracy. Moreover, the authors identify the bottleneck in the SNTP implementation of the time gateway architecture. A careful analysis of the behavior of SNTP is proposed, and useful suggestions for trading off between synchronization accuracy and time gateway complexity are given.

Network recovery time measurements of RSTP in an ethernet ring topology

There is currently high activity in the area of redundancy for Ethernet networks. A large number of solutions have emerged among the switch manufacturers during the last few years. This has been accompanied by standardization activities in the IEC. This paper looks briefly into industrial requirements on network redundancy and existing solutions with special focus on ring redundancy solutions. The Rapid Spanning Tree protocol (RSTP) is currently the best-performing Ethernet redundancy standard. RSTP is commonly used in meshed topology networks but performance data from use in ring topology networks is very limited. This paper therefore presents new results from experiments with this protocol in a ring network. This helps in determining where RSTP can be used in industrial networks where the ring topology is common.

QoS in switched Industrial Ethernet

As Industrial Ethernet evolves it will increasingly include integration with the “IT network” in order to utilize the benefits which the use of Ethernet provides. This will result in a mixed protocol environment also in the industrial networks, which in turn will require proper usage of QoS in order to maintain the demanding requirements of latency, jitter and packet loss in the Industrial Ethernet protocols. This paper highlights the emerging need for using QoS as well as some other related technologies in Industrial Ethernet networks and outlines some guidelines to achieve well-performing networks and efficient communication both for real-time control data and other less time critical data.

Characterization of Accelerometers Using Nonlinear Kalman Filters and Position Feedback

In this paper, we describe a method to test and characterize accelerometers using an accurate position sensor and nonlinear Kalman filters. The method is designed to estimate parameters in nonlinear accelerometers and could be a simpler alternative to methods using centrifuges or vibrational testing. The method makes it possible to do real-time parameter estimation. In addition, the method can be integrated into an inertial tracking or navigation system with sufficiently accurate position measurements. The estimation filters have been implemented and successfully tested using Monte Carlo simulations. An experimental setup has been built, and its functionality has been verified.

Mixing Real Time Ethernet traffic on the IEC 61850 Process bus

The introduction of the IEC 61850 standard represents a milestone for the Substation Automation System (SAS): the network based control system simplifies the architecture, increasing the interoperability and decreasing the development cost. Looking at the network structure, IEC 61850 defines the Process bus that is used to connect the equipment and sensors which operate close to the power lines. This paper investigates the case in which the Process Bus is opened to other real-time systems that use Real-Time Ethernet protocols. A simulation environment has been used to analyze the Process bus behavior when non IEC 61850 devices are connected (in particular, PROFINET IO devices). The preliminary results suggest the possibility to mix different real-time data streams on the Process Bus, with tolerable variations of the performance of the IEC 61850 applications.

Redundant and synchronized EtherCAT network

Communication redundancy and time synchronization are two important requirements commonly found in industrial systems. However, achieving high redundancy performance in combination with highly accurate time synchronization at all times is a challenging task. EtherCAT is a high performance, functionality rich communication technology offering both advanced redundancy features and accurate time synchronization. This paper will describe a robust solution where an EtherCAT system offers high redundancy performance in combination with accurate time synchronization. The solutions is based on using Ether-CAT slaves integrated into the EtherCAT master nodes. In the redundant case there is a need for two of these integrated slaves and they need to be configured appropriately to offer a robust solution.

Time synchronization concerns in substation automation system

One of the main problems in mixing old and new IEC 61850 devices in the same substation automation system is related to the network-based time synchronization. The IEC61850 defines two different protocols for distributing time in Station and Process Bus: SNTP and IEEE1588 PTP. The two protocols have almost different time representations and synchronization schemes. When an old IEC61850 device with SNTP has to be integrated into new substations with PTP-compliant network infrastructure, time gateways may be required. The paper discusses the time synchronization concerns in a typical Substation Automation System and analyzes the performance of a compact Time Gateway; it is a transparent, two-ports, device which is inserted in the last network link between the switch and the end device. The tests have been carried out by means of an embedded prototype based on FPGA. The experimental results show the applicability of the Time Gateway concepts, giving useful hints on the trade off between synchronization accuracy and device complexity.

Architecture of an embedded time gateway between PTP and SNTP

This paper deals with time synchronization in mixed network infrastructures for automation of industrial and electric plants, where old devices, which retrieve time information with the well-known NTP, must coexist with new IEEE1588 PTP compliant devices. Since PTP and NTP use very different time representations and synchronization strategies, an easy integration is quite difficult and requires additional hardware. The paper describes a transparent Time Gateway that is able to interface SNTP devices with a PTP synchronization domain (PTP devices and PTP switches). The Time Gateway has been realized with an embedded system based on an FPGA with a soft processor and an open source operating system. Preliminary experimental results show the feasibility of the proposed architecture, even if some improvements may be needed to match the time synchronization accuracy required by the legacy SNTP devices.

Multicast filtering in industrial Ethernet networks

The need for efficient multicast filtering in Industrial Ethernet networks will most likely rise as a result of its increased usage of multicast protocols and its increasing network capacity. The current support for multicast filtering in industrial Ethernet networks is somewhat limited since the available functionality for handling of L2 multicast is poorly supported both in switches and device stacks. This paper proposes a way to use the widely supported L3 multicast protocol IGMP as a possible means to mitigate this problem until better L2 protocol support is available.