Sebastian Schriegel

Investigation of Industrial Environmental Influences on Clock Sources and their Effect on the Synchronization Accuracy of IEEE 1588

Networked Industrial Devices must fulfill requirements regarding temperature ranges, noise immunities, and mechanical loads (e.g. DIN EN 60068-2-6). The effects of these environmental conditions on the stability of the frequency of clock sources are well studied [1, 2]. However the influence on the synchronization characteristics of IEEE 1588 can be derived only partly from these investigations. The dependency between the frequency drift (df/dt) and the transmission period of the synchronization frames T is very important for the achievable accuracy of IEEE 1588-based networks. In order to examine these effects, a novel measuring method is proposed in this paper. The results of exemplary measurements at a crystal oscillator with different temperature and mechanical loads will be discussed. These results are compared with the existing requirements for industrial communication systems, especially for the Industrial Ethernet system PROFINET. The objective is to derive coherences and rules for the implementation of functional components of the synchronization procedure.

An FPGA based HSR architecture for seamless PROFINET redundancy

This paper presents the mapping of the High-Availability Seamless Redundancy (HSR) protocol to PROFINET RT. Whereas common PROFINET RT components that implement the Media Redundancy Protocol (MRP) are requiring up to 200 ms for recovery after link failures, HSR provides seamless redundancy. In order to overcome the incompatibilities between PROFINET and HSR a configurable HSR RedBox is implemented. The hardware architecture, running at 100 MHz, is mapped onto an Altera Stratix IV FPGA and is capable of processing up to 100 Mbps per port. Using several RedBoxes in a ring, a seamless redundancy is demonstrated for a PROFINET RT test network, using 1 ms cycle time with 3 ms watchdog. The presented architecture is highly configurable and can be mapped both to high-end and low-end FPGAs and therefore fulfills industrial requirements.

Fast and simple scheduling algorithm for PROFINET IRT networks

Scheduling of the communication in industrial networks takes time. Since it has to be carried out every time a new network is brought to work, the time necessary to perform scheduling becomes a prominent factor. The approach presented in this paper, simplifies the scheduling problem of PROFINET IRT by resolving communication conflicts by utilization of the dynamic frame packing (DFP) mechanism.

System modeling based on machine learning for anomaly detection and predictive maintenance in industrial plants

Electricity, water or air are some Industrial energy carriers which are struggling under the prices of primary energy carriers. The European Union for example used more 20.000.000 GWh electricity in 2011 based on the IEA Report [1]. Cyber Physical Production Systems (CPPS) are able to reduce this amount, but they also help to increase the efficiency of machines above expectations which results in a more cost efficient production. Especially in the field of improving industrial plants, one of the challenges is the implementation of anomaly detection systems. For example as wear-level detection, which improves maintenance cycles and thus leads to a better energy usage. This paper presents an approach that uses timed hybrid automata of the machines normal behavior for a predictive maintenance of industrial plants. This hybrid model reduces discrete and continuous signals (e.g. energy data) to individual states, which refer to either the present condition of the machines. This allows an effective anomaly detection by implementing a combined data acquisition and anomaly detection approach, and the outlook for other applications, such as a predictive maintenance planning. Finally, this methodology is verified by three different industrial applications.

A Survey of Ethernet Redundancy Methods for Real-Time Ethernet Networks and its Possible Improvements

Abstract Industrial Ethernet switches, form the network backbone in automotive production, substation automation systems, intelligent transport systems, and other major industrial automation projects. In the operation of industrial switches, the recovery time of a switch is vital for its applicability. In the last few years, a large number of solutions have emerged among the switch manufacturers which have been accompanied by standardisation activities in IEC. This paper gives a brief introduction of the industrial requirements for network redundancy and discusses details of existing solutions with a special focus on the ring topology. A possible optimisation of existing Ethernet based industrial switches is also discussed.

A proposal to integrate process data communication to IEEE 802.1 Audio Video Bridging (AVB)

This paper investigates prospects of the emerging IEEE 802.1 Audio Video Bridging (AVB) Ethernet standard in industrial automation applications. The notion of a small and predictable latency is common for both industrial and multimedia (audio, video) applications. The inbuilt characteristics of 802.1 AVB that includes synchronization, real-time traffic scheduling & shaping and resource reservation makes it a real-time capable Ethernet solution, which can be used for the process control applications as well. This paper presents a way to integrate the industrial process data communication to the lower layer services of IEEE 802.1 AVB, and describes a demonstrator implemented for a proof of concept.

Reliable synchronization accuracy in ieee 1588 networks using device qualification with standard test patterns

This paper presents a device qualification approach for IEEE 1588 devices. Based on repetitive measurements within heterogeneous networks, standard stimulation data and device reaction values are defined for qualification of PTP bridges. According to these measurements, PTP bridges are classified into three classes basic, advanced, and high-performance. In order to execute the required device tests, a special IEEE 1588 Test Adapter is proposed, which operates as a hardware-in-the-loop tester. This Test Adapter, which is mapped onto a cost-efficient Altera Cyclone IV FPGA, is controlled by a standard PC and implements all time-critical PTP tasks in hardware. Within a case study, this Test Adapter is validated for analyzing and performance qualification of five exemplary PTP bridges. Overall, the proposed qualification approach in combination with the IEEE 1588 Test Adapter supports vendors and operators of PTP bridges to quantify the synchronization accuracy of a PTP bridge within a complex IEEE 1588 network without utilizing complex simulation models.

Node to node synchronization accuracy requirements of Dynamic Frame Packing

The evolution of industrial communication inexorably moves towards Ethernet based networks. One important reason for using Ethernet at the shop floor is to participate on the continuous advancements of standard Ethernet. In contradistinction to the star topology, used commonly in home and office networks, in the industrial automation most common network structure is line. It is due to the fact that it simply follows the architecture of plants (production line). Depending on the size of an automation facility the size of such a network structure may contain up to 100 nodes. Thus, the node to node synchronization jitter, with its cumulative behavior, becomes a relevant performance factor for high demanding applications such as motion control. This paper examines influence of the synchronization jitter on the industrial Ethernet networks by taking the example of PROFINET IO, a common representative of an industrial Ethernet based protocol. It uses a Time Division Multiple Access (TDMA) procedure together with the communication scheduling to fulfill hard real-time requirements. Additionally the protocol uses Dynamic Frame Packing (DFP) in order to optimize bandwidth utilization. The efficiency of both mechanisms strongly depends on the node to node synchronization accuracy.

Reproducible IEEE 1588-performance tests with emulated environmental influences

The IEEE 1588 standard is widely established and accepted for clock synchronization in Ethernet networks. High accuracy IEEE 1588 implementations require a well-coordinated hardware/software co-design. Processing of sophisticated control algorithms for the time speed of local clocks within synchronization slaves are particularly important. Hence, IEEE 1588 implementations should be tested with respect to certain performance indicators like control loop behavior and synchronization accuracy. Furthermore, interoperability with other devices and standard compliance also need to be considered. The achievable synchronization accuracy depends on environmental conditions, network load and network topology. A test system should be able to emulate these physical conditions. This requires a well-founded knowledge about influences on IEEE 1588 implementations caused by both, environmental conditions and network load. This could be a frequency drift of crystal caused by either temperature variations or mechanical stress. Unfortunately, the standard does not specify an expected behavior in such an environment. Due to lack of standardization and test methods, a system-wide guarantee for synchronization accuracy can only be given for proprietary closed systems. In this paper a reproducible test environment with the ability to emulate environmental conditions is presented, followed by an evaluation of two exemplary implementations. The possibility to guarantee synchronization accuracy with the help of appropriate certification tests in such a specific test environment will be demonstrated.

A descriptive engineering approach for cyber-physical systems

Plug and produce (PnP) aims at reducing system engineering effort. Therefore several PnP aspects have to be solved. This paper gives an overview and classifies process types and PnP aspects. Furthermore it identifies coupled processes as the most challenging ones and provides a new engineering approach for such systems. A new two-step descriptive engineering approach is applied to automatically synthesise control code from a given product specification. The main idea of the approach is to use a descriptive view rather than a prescriptive. This means that the engineer specifies what he wants to produce and no longer how he wants to produce it. Thus, it reduces engineering effort and releases more resources to optimize the process.