State of Data Communications for Process Control

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15 Νοε 2013 (πριν από 3 χρόνια και 9 μήνες)

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State of Data Communications for

Process Control


Presentation to the

North Texas ISA Section

October 23, 2012


By Dick Caro, CMC Associates

2

Dick Caro


Principle of CMC Associates, Arlington, Mass


Author of


Wireless Networks for Industrial Automation


Automation Network Selection


User Guide to Fieldbus Network Equipment for Process Control

3

The Problem With Standards

Too many wireless instrumentation standards:

1.

ISA100 Wireless (ISA100.11a
-
2011, IEC 62734)

2.

WirelessHART (IEC 62591)

3.

WIA
-
PA (IEC 62601)


Too many wired Fieldbuses

4.

Foundation Fieldbus H1 and HSE (IEC 61158 (1 & 5))

5.

Profibus
-
PA (IEC 61158 (3))


All directed at the same application:

Process control field instrumentation

4

Standards Are Incompatible



Networks may co
-
exist


Messages are not coordinated, they may collide


Positive acknowledgment requires
retransmission


Some probability message will be delayed



Cannot share messages between networks


Data sharing must be processed by store &
forward at the host level


Message travels on its own network to the
host


A host function is required to deliver the
message to the target device

5

Wireless Networks First

ISA100 Wireless

ISA 100.11a
-
2011 (IEC 62734)


WirelessHART

IEC 62591


WIA
-
PA

IEC 62601

6

Problem For the User

DCS suppliers support only one of the wireless networks




ISA100 Wireless

Honeywell, Yokogawa, Invensys, General Electric,
Masoneilan, Yamataki, Fuji, S3




WirelessHART

Emerson, ABB, Siemens, Endress+Hauser




WIA
-
PA

Unannounced Chinese supplier


7

Data communications is defined in formal layers.









Standards organizations:

ISO


International Standards Organization

IEC


International Electrotechnical Commission

IETF/RFC


Internet Engineering Task Force / Request For Comments


ISO/IEC 61850 Open Systems Layer Model

Layer

Name

Function

7

Application

Process Control Application

6

Presentation

Data Conversion

5

Session

Connections

4

Transport

Data Flow Control

3

Network

Logical Address

2

Data Link

Physical Address and Mastership

1

Physical

Media, Encoding

8

Compatible Physical Layer

ISA100 Wireless

WirelessHART

WIA
-
PA


All use IEEE 802.15.4


2006 chips with it's Medium
Access Control and a 16
-
channel direct sequence
spread spectrum radio with 128
-
bit AES security
encryption.


All use the same channel hopping logic

WirelessHART uses a fixed channel hopping table

ISA100 Wireless and WIA
-
PA have multiple channel hopping tables
including the one used by WirelessHART.


9

Slot Time

Wireless instruments are off 97% of the time and “wake up”
to send/receive. The “awake” period is called the Slot Time.


WirelessHART slot time is fixed at 10ms


ISA100 Wireless uses variable slot time, but defaults to
10ms


WIA
-
PA uses a variable slot time, but defaults to 10ms


Identical slot timing is necessary for networks
to interoperate

10

Meshing



Mesh networks use multiple paths and relay messages
from one node to another


overcome obstacles


reach longer distances


create resilient paths for increased reliability








11

Meshing Protocol


ISA100 Wireless: meshing protocol of IEEE 802.15.4e


WirelessHART: proprietary meshing protocol


WIA
-
PA: proprietary meshing protocol



Mesh protocol must be identical for nodes to
communicate.

12

Time Synchronization

Time slots must be synchronized between nodes to
schedule awake time data communications.


ISA100 Wireless: same method as IEEE 802.15.4e

Method defined by IEEE 1588

Distributed network time


WirelessHART: Derives network time by counting time slots


WIA
-
PA: Proprietary protocol

13

Network Addressing

Each network node must have a unique address:


ISA100 Wireless

Each node has an IPv6 address

Uses RFC 4944 6LowPAN protocol

Nodes are Internet addressable


WirelessHART

Proprietary address in the HART domain


WIA
-
PA

Proprietary

14

Transport Layer

Protocol to assure end
-
to
-
end delivery of messages


ISA100 Wireless

Confirmed service using UDP/IP (RFC 768) protocol

Network is capable of running TCP/IP but not used for real
-
time
communications


WirelessHART

Proprietary confirmed service


WIA
-
PA

Proprietary confirmed service

15

Will Wireless Standards Ever Converge?

Convergence would require agreement among all parties to
adopt the same protocols for:



Slot timing


Meshing protocol


Clock synchronization


Slot timing


Addressing


Transport protocol


Unlikely to occur due to lack of compatibility with the
installed base of instruments.

16

Wired Process Control Networks

Foundation Fieldbus H1


Supported by ALL major process control suppliers

Foundation Fieldbus HSE


Supported only by SMAR, ABB, & Yokogawa

Profibus
-
PA and DP, ProfiNET


Supported only by Endress+Hauser, Siemens

EtherNet/IP


Supported by Endress+Hauser, Rockwell

17

Foundation Fieldbus H1

Replace 4
-
20ma analog with a digital data stream

Can use old analog wiring to a junction box

31.25 kbps

Supports intrinsic safety

Supplies power to field instruments

Defines function blocks to compute in the field
instruments

Signal conditioning (smoothing, linearizing, engineering
units)

Control loop processing

Distributed DCS model

Currently used in 80% of new plant construction
worldwide

18

Foundation Fieldbus HSE

Aggregate and share H1 data across network

HSE Linking Device

Terminate 4
-
8 H1 networks in the field

Commercial Off
-
The
-
Shelf Ethernet hardware

Supply Link Active Scheduler across H1 networks

Specified as UDP/IP protocol on IEEE 802.3 (Ethernet)
networks

Any HSE segment may use any wireless protocol based
on UDP/IP

Wi
-
Fi (IEEE 802.11)

ISA100 Wireless

Currently supported only by SMAR, ABB, and Yokogawa

19

Profibus, ProfiNET

Replace 4
-
20ma analog with a digital data stream

Can use old analog wiring to a junction box

31.25 kbps

Supports intrinsic safety

Supplies power to field instruments

Does not provide any function block logic

Coupler required to link Profibus
-
PA segment with

Profibus
-
DP aggregation link

Currently, no ProfiNET couplers are available

20

EtherNet/IP

Developed by Rockwell, assigned to ODVA

Uses CIP (Common Industrial Protocol)

Physical Layer is IEEE 802.3 (Ethernet)

Endress+Hauser offers EtherNet/IP connection to
several of their process control field instruments

First Ethernet devices for process control

Intrinsic Safety is not possible with Ethernet

21

Trends in Process Control

Emerging use of CiF (Control in the Field)

Only for Foundation Fieldbus

Beginning of market for wireless field instruments

WirelessHART is market leader; ISA100 Wireless
emerging

Most installations are for safety applications

Used where wiring is prohibitive

Profibus, ProfiNet, EtherNet/IP mostly used for factory
automation

Continued brownfield modernizations

Control room consolidation

Replacement of pneumatic instrumentation

Awareness of benefits of VFD to replace control valves

22

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