Control Over WirelessHART Network S. Han, X. Zhu, Al Mok University of Texas at Austin M. Nixon, T. Blevins, D. Chen Emerson Process Management

Research Scope 2 WirelessHART Stack Development Standard-Compliance Verification Localization-aware Applications Network Management and Performance Measurement Sampling Reduction Techniques and Data Quality Maintenance Competition and Collaboration among Protocols in 2.4GHz Band Wireless Control

Outline Introduction Control over WirelessHART network – Control in the Host – Control in the Gateway – Control in the field Prototype System and Experiments Future Works 3

Introduction The history of controlling a process plant is also a history of reducing the number of wires in the industrial plant. Applications in process plants – Class C: applications for monitoring – Class B: applications for control – Class A: applications for safety 4 Auxiliary Critical The current wireless adoption is at the Class C level.

Introduction (Cont.) Control Spectrum in Industrial Plant Critical Issues when control goes wireless – Security: open air communication – Reliability: wireless is inherently unreliable – Safety: the topmost concern in a process plant – Speed: Is the speed of WirelessHART enough? – Battery Longevity: replace the battery is costly 5 SupervisoryOpen LoopClose LoopCritical

Control over WirelessHART Network 6 Control in the Host – the control module runs in the host’s Function Block Application Control in the Gateway – Gateway needs a function block application layer to allow configuration and execution of control modules. Control in the field – A device supports a set of function blocks.

Control in Host vs. Control in GW 7 Control in Host – No change to the gateway – Drawback: further communication delay between GW and the Host. The longer the loop delay is, the worse the control performance. Control in the Gateway – Gateway needs to be enhanced with the control modules. – A deterministic schedule is established for all communications by the network manager. – Function block execution may be fully synchronized with IO communication. – Gateways may be fully redundant.

Control in GW vs. FF Approach 8 Control implementation is independent of field device manufacturer. All function blocks are available for use in any control strategy. Field devices only need to address measurement/ actuation and communication – minimizing power consumption, simplifying design. Control strategy may be fully backed up using redundant gateways. The DCS interface to the function block application is simplified since all blocks reside in one device. The field devices EDD is very similar to that required for wired HART devices – making it easy for manufacturers to engineer.

What about Control-in-the-Field? 9 WirelessHART has all of the core features required to support control-in-the-field – Secure peer-to-peer communications – Publish/subscribe capability – Synchronized communications – Fully defined user layer WirelessHART is highly optimized and robust – Exception reporting – Mesh behavior

Peer-to-Peer Communications Devices are allocated a peer-to-peer session Network Manager allocates routes and communication resources to achieve reliable and real-time peer-to-peer communications

Cons of Control-in-the-Field 11 Force device manufactures to understand control Inconsistent implementations of function blocks Inconsistent sets of function blocks in devices Power Saving Concerns – running function blocks in devices increases battery usage by up to 3x – running function blocks in controller or GW + leveraging exception reporting techniques reduces battery usage in devices by up to 20x

WirelessHART Prototype System 12 Major Components in the prototype : Network Manager Gateway Host Application Access Point Field Device Sniffer PC Side Embedded Side

Overall Design of the System 13

Concrete Overview of the System 14 Network ManagerGatewayHost Application Sniffer Access Points

Design of the Gateway 15

Experiment Setup 16 Network Topology Gateway + Network Manager Access Point Sensor + Actuator Control Loop Sensor publishes the primary value every 4 seconds When gateway receives the sensor data, the Function Block Application issues command 79 to the actuator

Experiment Setup 17 Network ManagerGatewayHost Application Sniffer Sensor Actuator Access Point Publishing Control

Experiment Environment 18 Emerson Process Management Office Building – A lot of non-WirelessHART traffic such as Wi-Fi, Bluetooth. – Nine active WirelessHART networks around

Experimental Results 19 The test runs for almost 2 hours Gateway received 1651 burst messages from the sensor Not a single packet loss is recorded

Observations from Experiments 20 WirelessHART Supports Control – Experiment is built with actual WirelessHART device, gateway, and network manager – The environment is noisy – The communication is reliable Fastest Loop Achievable? – In theory, we can achieve a 20ms loop period – Two adjacent timeslots are used for publishing and control respectively

Conclusion 21 Challenges in introducing wireless into industrial process control Comparisons among three approaches for control over WirelessHART networks A prototype WirelessHART system for evaluating the performance of control in Gateway approach

Future Work 22 Measure the jitters in different setups Test the fastest loop supported in WirelessHART Build a real demo kit