[PPT] - Introduction of WirelessHART CSE 521S, Fall 2019 Yehan Ma PowerPoint Presentation

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Introduction of WirelessHART

CSE 521S, Fall 2019

Yehan Ma

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Applications in Process Industry

Ø Process industry

q Automotive production process q Chemical segments q Food and Beverage q Power generation

Ø Optimize process, enhance safety, protect environment

q Monitor the status of manually operated valves q Monitor safety relief valves to detect venting to avoid accidents q Detect leaks before they lead to environmental problems q Health, Safety, and the Environment (HSE) regulations

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pr pressure va valve ve Sensor Actuator control command Controller

Process Control

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11/13/19

sensor data

Ø Feedback control loop controls physical plants

q

Example: regulate pressure of a gas container

Controller State Observer Actuators Plant Sensors Reference ( ) u t ˆ( ) u t

( ) y t

ˆ( ) y t

ˆ( ) x t

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Why Wireless

Ø Cost reduction: wiring is economically infeasible Ø Easier installation: inaccessible locations Ø Easier maintenance

q Wired networks cannot handle severe heat or exposure of chemicals q A wireless infrastructure can remain in place for many years.

Ø Flexibilities and mobilities for sensor placement

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Challenges in Wireless

Ø Strict timing requirement Ø Reliable communication despite wireless deficiencies Ø Plant environments are inherently unreliable

q Interference, power failures, lightening, storms…

Ø High security concerns

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Wireless Technologies

Ø Existing standards fail in industrial environments

q ZigBee: static channel q Bluetooth: quasi-static star network

star network mesh network

Ø WirelessHART

q For process measurement and control applications q First open and interoperable wireless standard to address the critical

needs of real-world industrial applications

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Coordinator End Devices

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History

Ø HART (Highway Addressable Remote Transducer Protocol)

q Most widely used field communication protocol q 30 million devices worldwide

Ø WirelessHART released in Sep 2007 (as a part of HART 7)

q Adds wireless capabilities to the HART protocol while maintaining

compatibility with existing devices, commands and tools.

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Ø World-wide adoption of wireless in process industries

Wireless for Process Automation

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16.9+ billion hours
perating experience

[Emerson]

50,016+ wireless field

networks

Courtesy: Emerson Process Management

Offshore Onshore Killer App of Sensor Networks!

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WirelessHART Use Cases

Ø Monitor and control pressure and temperature of process fluids and gases Ø Improved control of plant steam supply by detecting “cool spots” in cross plant steam lines Ø Reducing risk of overfilling tanks by adding redundant level measurements (in oil and petroleum refineries) Ø Monitor and control safety valves

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What is special?

Ø Reliable: 99.9% Ø Secure Ø Self-organizing, self-healing Ø Interoperable Ø Supports both star and mesh topologies Ø Built-in time synchronization

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Network Architecture

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Network Manager

Ø Centralized brain Ø Manages the network and its devices

q Collect topology information q Routing, scheduling q Generates network management packets to devices q Change when devices/links break q User/administrator interacts with the Network Manager

Ø Redundant Network Managers supported (only one active)

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Field Devices

Ø Sensor/actuator/both Ø Connected to the process or plant equipment Ø Combines wireless communication with traditional HART field device capabilities Ø May be line or battery-powered

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WirelessHART Adapter

Ø Enables communication with a non-native device through a WirelessHART Network. .

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Gateway

Ø One gateway can support up to 80 devices Ø A Gateway provides

q One or more Host Interfaces connecting the Gateway to backbone

networks (e.g., the plant automation network)

q One or more Access Points providing the physical connection into the

WirelessHART network

q A connection to the Network Manager q Buffering and local storage for publishing data, event notification, and

common commands

q Time synchronization sourcing

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Other Devices

Ø Handheld devices

q Portable applications used to configure, maintain or control plant assets. q Typically belong to networks of different standards

Ø Plant Automation Network

q Connects client applications to the gateway

Ø Security Manager

q Industry standard AES-128 ciphers/keys

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WirelessHART PHY

Ø Adopts IEEE 802.15.4

q Same 16 mutually orthogonal channels q Operates in the 2.4GHz ISM band q Data rate of up to 250 Kbps

Ø Radio transceivers

q Omni-directional q Half-duplex q 100 meters LOS @ 0 dB q Time to switch between channels: 0.192 ms q Radio turn-on time: 4 ms

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How to achieve reliability?

Ø Time diversity Ø Channel diversity

q Channel hopping q Channel blacklisting

Ø Route diversity

q Graph routing

Ø Power Diversity

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TDMA Data Link Layer

Ø 10 ms time slot

q Transmission starts at a specified time after the beginning of a slot

Source & destination set channel
Allows receiver to begin listening

q Enough time for transmission + ACK

Ø Superframe: a series of time slots defining the communication schedule of a set of devices

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Access Point End Devices A B C D AàB BàC CàD Sleep Sleep Slot 1 Slot 2 Slot 3 Slot 4 Slot 5 Superframe

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Time Synchronization

Ø Gateway is the root source of time Ø When a device receives a packet from a time synch source

Δt = time of arrival – expected arrival time
sends Δt to the sender via ACK

Ø When a DLPDU from a time synch neighbor is received, time

f the receiving device should be adjusted.

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Shared vs. Dedicated Time Slots

Ø A time slot may be shared or dedicated Ø Dedicated slot: only one sender sends to a receiver Ø Shared slot: multiple senders attempt to send to a receiver

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Shared Time Slots

Ø Devices contest for access using a contention-based scheme.

q Behave similar to Slotted Aloha q Use collision-avoidance (backoff).

Ø Using shared links may be desirable when

q Throughput requirements of devices are low q Traffic is irregular or comes in bursts

Ø May reduce latency since devices do not need to wait for

dedicated slot

q True only when chances of collisions are low

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Channel Hopping

Ø Enhances reliability

q Avoid interferences q Reduce multi-path fading effects

Ø Blacklisting restricts hopping to some channels Ø Each device has a channel map (logical to physical) Ø ActiveChannel = (ChannelOffset + ASN) % #Channel

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Routing

Ø WirelessHART supports both Graph and Source routing Ø Graph routing: provides redundant paths Ø Routing graphs

q Uplink graph: upstream communication q Downlink graph: Downstream communication q Broadcast graph

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Scheduling

Ø Slots and channel assignment

q Each receiver uses a separate channel for reception q A transmission is followed by a retransmission on the same link on a

dedicated slot, then again on another link on a shared slot

Ø Each network contains exactly one overall schedule that is created and managed by the Network Manager. Ø The schedule is organized into Superframes

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Superframe

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Superframe

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Superframe

Ø All devices must support multiple superframes Ø At least one superframe is always enabled while additional superframes can be enabled or disabled Ø Slot sizes and the superframe length are fixed and form a network cycle with a fixed repetition rate

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Data Link Protocol Data Unit (DLPDU)

Ø Five DLPDU types:

q Data q ACK q Advertise (periodic) q Keep-Alive (periodic) q Disconnect

Ø Devices receiving a packet with an unknown packet type must not acknowledge the packet and shall immediately discard it.

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Network Initialization

Ø WirelessHART Network automatically starts up and self-organize. Ø Before a network can form, a Network Manager and a Gateway must exist. Ø The Network Manager activates the first Superframe. This establishes the system epoch – ASN 0. Ø Once the Network Access Point starts to advertise, devices can begin to join the network. Ø As devices join, the network forms.

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Network Maintenance

Ø Advertise and Keep-Alive DLPDUs assist in building and maintaining the device's neighbor list Ø A Keep-Alive must be transmitted to the neighbor if Last Time Communicated > Keep Alive Interval. Ø Keep-Alive transmissions are repeated until a new DLPDU is received from the neighbor Ø Keep-Alive no more often than once per 30 seconds (if temperature varies 2º C per minute or less).

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Network Maintenance

Ø Path failures are reported to the Network Manager when devices lose connectivity to neighbors. Ø After the Path Fail Interval lapses, a Path-Down Alarm is generated (by both the sender and the receiver). Ø As each device's Health Report Timer lapses, the devices generate health reports, which include indications of any problems the device is having with a neighbor. Ø Default period of each devices health report is 15 minutes.

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Network Maintenance

Ø Devices continue trying to reestablish communication until the links between them are deleted by the Network Manager. Ø It is common for broken paths to be restored after a temporary environmental effect passes. Ø If the disruption persists, additional Path-Down Alarms will be generated when the Path Fail Interval lapses again.

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Best Practices

Ø Each field device should have at least three neighbors

q The 3rd neighbor will act as a backup if one of the two primary paths is

bstructed or unavailable.

Ø Devices (antenna) mounted >0.5m from any vertical surface. Ø Devices mounted >1.5m off the ground. Ø 25% of the network devices should have a direct connection to the gateway in large networks.

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