Mark J. Nixon

Reliable and Real-Time Communication in Industrial Wireless Mesh Networks

Industrial wireless mesh networks are deployed in harsh and noisy environments for process measurement and control applications. Compared with wireless community networks, they have more stringent requirements on communication reliability and real-time performance. Missing or delaying of the process data by the network may severely degrade the overall control performance. In this paper, we abstract the primary reliability requirements in typical industrial wireless mesh networks and define three types of reliable routing graphs for different communication purposes. We present efficient algorithms to construct them and describe the recovery mechanisms in the event of component failures. Based on these graphs, data link layer communication schedules are generated to achieve end-to-end real-time performance. We demonstrate through extensive experimental results that our algorithms can achieve highly reliable routing, improved communication latency and stable real-time communication in large-scale networks at the cost of modest overhead in device configuration.

Control over WirelessHART network

It has been observed that the history of industrial process control development is also a history of reducing the number of wires necessary for effecting the control. Control over wireless is the end of this evolution. Wireless control faces a lot of challenges such as security, reliability, feedback latency, battery longevity, etc. In this paper we report some experience with implementing control over wireless. The platform we use is the WirelessHART mesh network, the first international industrial wireless control standard. We describe a full implementation of the standard and study the issues and solutions in its application. Our data suggest that WirelessHART technology is up to the challenge of wireless control.

Hypergraph-based data link layer scheduling for reliable packet delivery in wireless sensing and control networks with end-to-end delay constraints

Abstract Many mission-critical and safety-critical applications in networked wireless sensing and control systems have stringent reliability requirements and timing constraints on end-to-end ( E2E ) packet delivery. Late arrivals of packets could severely degrade overall system performance and cause serious problems in system operation. In this paper, we study the data link layer scheduling problem to maximize the reliability of E2E packet delivery in TDMA-based wireless sensing and control networks ( WSCNs ) subject to specified delay constraints. We propose to organize the physical network nodes into logical hypernodes and form a hypergraph for improved scheduling flexibility. Based on the hypergraph, we introduce two data link layer scheduling schemes to maximize the E2E reliability in packet delivery without violating any delay constraints of the packets. The first scheme, named dedicated scheduling , decides how many time slots (TSs) for each hypernode along the path to the destination should be allocated to transmit a packet, and the packets are only transmitted in their scheduled TSs. The second scheme, named shared scheduling , allows the packets to share their scheduled TSs, and thus further improve the E2E reliability. We apply these two schemes in both single-path routing and any-path routing in WSCNs. Asymptotic analysis of the proposed schemes is provided and extensive simulation experiments are performed to illustrate their effectiveness in improving the E2E reliability of packet delivery under different network settings.

PID control using wireless measurements

This paper presents a wireless PID controller, known as PIDPlus. The same quality control as wired PID can be provided by PIDPlus using a wireless measurement, despite slower wireless measurement update and communication interruptions. The PIDPlus novel algorithm is based on a modification of the PID reset and rate calculation to account for non-periodic measurement updates. The paper presents and evaluates an alternate approach of PID control accounting for non-periodic measurements with a Kalman filter observer that has been modified for use with a wireless measurement. A second alternative shows how the Smith Predictor may be modified to work with a wireless measurement. Test results are presented that compare the PIDPlus performance to that achieved using these alternate approaches for a variety of operating conditions that may be encountered when using wireless transmitters.

Data cleaning in the process industries

Abstract In the past decades, process engineers are facing increasingly more data analytics challenges and having difficulties obtaining valuable information from a wealth of process variable data trends. The raw data of different formats stored in databases are not useful until they are cleaned and transformed. Generally, data cleaning consists of four steps: missing data imputation, outlier detection, noise removal, and time alignment and delay estimation. This paper discusses available data cleaning methods that can be used in data pre-processing and help overcome challenges of “Big Data”.

Process Control over Real-Time Wireless Sensor and Actuator Networks

Wireless technologies have been successfully applied in the process industry since the creation of the first international standard IEC62591 WirelessHART. Applications started in areas where wireless sensors provide rich process information to the automation systems. Although real and demonstrated control applications are advertised, wireless-for-control is still in the initial stage and faces a lot of challenges. In particular, feedback latency and battery longevity, which are also problems for wireless-for-sensing, are even more critical when wireless actuators are applied. There are additional challenges in using wireless actuators because they actively affect the process. This paper lays the foundation for control using a wireless actuator. It demonstrates how traditional control methodologies can be modified to effectively work with general wireless communication. The innovations are tested with simulations and experimentations, both on commercial distributed control systems.

Over the air provisioning of industrial wireless devices using elliptic curve cryptography

Security has become a key consideration in industrial settings. Newer technologies, such as wireless sensor networks, have adopted the position that security is mandatory. For wireless sensor applications it is important to secure data in transit in the air, to authenticate data originating from, or arriving at the wireless devices and applications, and, most important, to protect the safety and integrity of the legacy process control and plant safeguarding systems that the new wireless world interconnects into. Current industrial wireless mesh networks, such as WirelessHART™, ISA100.11a, and WIA-PA, have adopted AES 128 bit encryption for both securing communications and data. To ensure that devices and applications are authenticated special join keys are used. The process of loading these keys is called provisioning. To ensure that join keys remain secret they are loaded offline through special wired interfaces or provisioned over the air using less secure mechanisms. What is needed is a low cost efficient public key mechanism that can be utilized over the air while not compromising security. This paper examines the use of elliptic curve cryptography for this purpose. We realize this technique on a WirelessHART mesh network. Efforts are underway to incorporate this approach as an addition to the WirelessHART standard.

ColLoc: A collaborative location and tracking system on WirelessHART

Localization in wireless sensor networks is an important functionality that is required for tracking personnel and assets in industrial environments, especially for emergency response. Current commercial localization systems such as GPS suffer from the limitations of either high cost or low availability in many situations (e.g., indoor environments that exclude direct line-of-sight signal reception). The development of industrial wireless sensor networks such as WirelessHART provides an alternative. In this article, we present the design and implementation of ColLoc: a collaborative location and tracking system on WirelessHART as an industrially viable solution. This solution is built upon several technological advances. First, ColLoc adds the roaming functionality to WirelessHART and thus provides a means for keeping mobile WirelessHART devices connected to the network. Second, ColLoc employs a collaborative framework to integrate different types of distance measurements into the location estimation algorithm by weighing them according to their precision levels. ColLoc adopts several novel techniques to improve distance estimation accuracy and decreases the RSSI presurvey cost. These techniques include introducing distance error range constraints to the measurements, judiciously selecting the initial point in location estimation and online updating the signal propagation models in the anchor nodes, integrating Extended Kalman Filter (EKF) with trilateration to track moving objects. Our implementation of ColLoc can be applied to any WirelessHART-conforming network because no modification is needed on the WirelessHART field devices. We have implemented a complete ColLoc system to validate both the design and the effectiveness of our localization algorithm. Our experiments show that the mobile device never drops out of the WirelessHART network while moving around; with the help of even one dependable anchor, using RSSI can yield at least 75p of distance errors below 5 meters, which is quite acceptable for many typical industrial automation applications.

Wi-HTest: compliance test suite for diagnosing devices in real-time WirelessHART mesh networks

Abstract WirelessHART™ was released in September 2007 and became IEC standard in April 2010 (IEC 62591). It is the first open wireless communication standard specifically designed for real-time process control applications. It is designed to the same standard as its wired counterpart for reliability and interoperability . To ensure the compliance with the HART™ communication protocol and the adherence to its strict timing requirements, all WirelessHART devices must be thoroughly tested and registered with the HART Communication Foundation (HCF). In this paper, we present Wi-HTest, the test suite developed to exercise WirelessHART devices, thus facilitating compliance assessment . We discuss the detailed architecture of Wi-HTest and highlight several critical features like packet handling with accurate timing control, fault data injection, and the virtual network approach for scalable test setup. We also describe a sniffer called Wi-Analys for capturing WirelessHART packets along with their timing information and a post process suite for analyzing the packets. These three tools together provide the complete compliance verification environment for WirelessHART. Based on the test specification developed by HCF, we presented several representative test cases for examining WirelessHART devices’ behaviors in different layers. These test cases in turn show that Wi-HTest is a novel and efficient test suite for verifying the compliance of WirelessHART devices .

Event based control applied to wireless throttling valves

This paper addresses the PID modifications and communication support that enable effective control using wireless throttling valves. To conserve the battery power used by a wireless positioner, the PID in a control system can be modified to minimize changes to the actuator position.. Effectively, a controllers output to an actuator is event-driven. It is not based on regular scan periods. A new WirelessHART command is proposed that allows the PID to compensate for communications delays from the control system to wireless throttling valve. This paper presents the performance achieved in a flow lab using an industrial size prototype wireless throttling valve in closed loop control of a liquid flow process. In this wireless control field trial, control performance using a wireless valve was evaluated using both a wired and wireless transmitter for the flow measurement.