TECHNICAL WHITE PAPER PLANNING AND DEPLOYING...

TECHNICAL WHITE PAPER

PROCESS AUTOMATION

WirelessHART provides a common standard for wireless automation in the process automation industry and enables many new applications which will bring great benefit in operating process facilities.

WirelessHART is easy to use. Nevertheless, due to aspects concerning mesh networking, radio wave propagation, and coexistence issues among other wireless networks, new methods must be developed when constructing a WirelessHART network.

These methods are not complicated and can be described in a few simple steps.

This paper introduces the basics on how to plan and construct a WirelessHART network by using easy rules and tips. This information is directed to planners and technicians who are planning to install a WirelessHART system.

Prepared by: Gerrit LohmannProduct Portfolio ManagerPepperl+Fuchs

PLANNING AND DEPLOYING NETWORKS

Technical White Paper – Planning and Deploying Networks

Pepperl+Fuchs is the proven market leader for communication technology in the process automation market. The product portfolio ranges from conventional interface technology and remote I/O systems to fieldbus components.

Almost all communication in process automation has been realized with cable. Wireless communication is the latest innovation introduced to provide communication paths between the control room and the field.

As many have come to expect, Pepperl+Fuchs is an early adopter of new technologies. This is the case for WirelessHART. You can rely on the experience of Pepperl+Fuchs when dealing with new technology and concepts to provide high-quality products that are easy to install, commission, and maintain. As a result, you benefit from a great feature that increases the performance of your plant.

MESH NEtwork Gateway

Router

www.pepperl-fuchs.com


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Table of Contents

1 Introduction 4

2 Project Scope 4

3 Coexistence 5

4 Network Planning 7

4.1 Site Survey 7 4.2 Placing Devices 8 4.2.1 Placing Gateways 8 4.2.2 Placing Field Devices 9 4.2.3 Checking for Connectivity 9 4.2.4 Placing Repeaters 12 4.2.5 Extending a Network 13 4.3 Summary 13

5 Commisioning the Network 14

6 HOST Integration 15 7 Documentation 16



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1 Introduction

There are just a few considerations to take into account when planning a WirelessHART network. Employing a wireless network really isn’t that much different than what is done today for wired devices.

This WhitePaper provides an overview of the considerations to look at when planning and deploying a WirelessHART project.

Fig. 1: Scheme of Process Facility

2 Project Scope

The first thing to do is to define the area where the network will operate.

Many facilities consist of multiple process units. It just makes sense to organize the wireless network in a similar fashion to how the plant treats these units in other respects. Often these process units are independent and exclusively responsible for their area. When reflecting on how the process units are set up while planning

a WirelessHART Network, ensure that the same areas of responsibility and work practices are incorporated into the network.Most process units can fit in a 250 m x 250 m square, which happens to be the line-of-sight transmission distance of WirelessHART in an unobstructed area. When the process unit is an indoor facility, the line-of-sight transmission is shorter, but the area can still be covered easily due to the mesh network as shown later.

Process Unit

Process Unit

Process Unit

Process Unit

Process Unit

Process Unit

Process Unit

Process Unit

Process Unit

ProcESS FAcILItY



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By limiting the scope of the WirelessHART network to a dedicated process unit, flexibility for future expansion remains since the individual

Before planning a WirelessHART network, itshould be clarified as to whether any other wireless networks are around in nearby process units or even outside, but close to the process facility. The following questions must be answered in particular:

Do they use 2.4 GHz and if yes, which channels do they use?

Where are they located? For what applications are they installed? How much is the data load?

The goal is to enable network coexistence. Coexistence means that each of the networks can transmit their data packages without being interfered with or interrupted by the packages sent by other networks. Or in other words: the data packages of both networks should not collide. Collision of the data packages happens when they are sent at the same time on the same frequency in the same location.

3 Coexistence

network won’t be constrained by devices and wireless projects in other plant areas.

Fig. 2: Occasions for colliding messages

Fig. 3: Channel occupation in 2.4 GHz band

Collisions are avoided by decoupling at least one of these factors:

Frequency: Using different channels or groups of channels for each network – Blacklisting of channels and designation of certain channels for each system.

Location: Use them a certain amount of distance away – often not possible, depending on location.

Time: Reducing Data Throughput – Collided and destroyed messages have the chance to get repeated.

Frequency

Location

time

wLAN 1 wLAN 2HArt Network

2.412 GHz 2.484 GHz

1 2 3 4 5 6 7 8 9 10 11 12 13 14



It is easy to determine whether to perform a time-based or location-based decoupling. A situation where networks communicate at different times (e. g., one network during one second, another network during the following second, etc.) calls for time-based decoupling. For location-based decoupling, simply place the networks far apart from each other. Frequency-based decoupling involves determining when channels of different networks overlap. Frequency-based decoupling is more complex since WLAN channels are different than Bluetooth channels, which are different from WirelessHART channels, etc.

Depending on the network type and the basic IEEE standard used in it, one channel can overlap other channels due to wide bandwidth. Channels in WLAN (IEEE802.11) have a bandwidth of 22 MHz, but a distance of center frequencies of only 5 MHz, so that the single channels overlap. In contrary, networks based on IEEE 802.15.4 have a distance of center frequencies of 5 MHz, but only a bandwidth of 2 MHz, so the single channels do not overlap. Combined, one WLAN channel occupies about 5 IEEE 802.15.4 channels.

When a WirelessHART network has less than15 channels, it works compatibly with the other networks around it. It must be noted that the performance of the WirelessHART network decreases as fewer channels are available. This performance decrease will not be an obstacle to using the network, but in some situations must be considered (e. g. when fast response and low latency are required).

When multiple WirelessHART networks are used in the same location, the following issues must be considered:

Each Network must have a different Network ID. Assign blocks of channels to each network. Blacklist (Block) channel which are used by

other networks.

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Fig. 5: Infrastructure density in vertical dimension

Fig. 4: Infrastructure density and possible communication ranges in horizontal dimension

4 Network Planning

4.1 Site Survey

The area of a process automation plant can in general be divided into 4 groups:

Unobstructed: Clear line of sight to the device with no obstructions

Low Obstructions: Some infrastructure but there are still open areas where you can see from one device to multiple other devices. Medium Obstructions: A denser environment

but there are still rather large areas that are not obstructed such that a truck could be driven through.

High Obstructions: Can not see from one device to the next, significant metal and structural material.

These areas can easily be identified even on satellite pictures or on floor plans. The graphic below shows an example including the rule of thumb ranges which are possible in these areas. The numbers are conservative, so better results could be achieved.

In the vertical dimension, the density of the environment can differ. For example, at the floor level the density can be very high, but above a certain elevation there is low or even no obstruction.

A walk around the plant will give the first hints on where devices should be placed for radio communication reasons and where issues could come up due to high density environment.

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Unobstructed: 250 m

High obstruction: 30 mMedium obstruction: 75 m

Low obstruction: 150 m

High obstruction

Line of Sight orLow obstructions



Fig. 6: Placing the GW in respect to the initially planned network

4.2 Placing Devices

Generally, the WirelessHART field devices can be placed as they would have been placed with a wired installation. The self-organizing network will take care of forming the mesh network and establishing communication and will adapt to the process plant environment without additional interaction by an operator or engineer.

But several conditions must be considered and could result in a relocation of the WirelessHART field device (or at least the antenna).

4.2.1 Placing Gateways

Usually, the WirelessHART gateway (GW) is placed first since this is the core element of a WirelessHART network. There are three basic options for placing a WirelessHART gateway:

Where it is easiest to integrate with the system or plant network. Usually, this is the control building or other structure. This results in shortest possible cable run for the wired interface(s) of the WirelessHART gateway(s).Central to the planned network. Placing the

WirelessHART gateway in the center provides the best position for most of the devices to

have a direct communication link with the WirelessHART gateway. This location ensures the highest reliability. 3 Central to the process unit. This placement provides the most flexibility for future expansion of the initially-planned network to other areas within the process unit. With this solution, the highest possible flexibility is achieved.

It is desirable and best practice to have at least 25 % of the field devices with a direct communication path to the gateway. This ensures an ample number of data communication paths for the devices farther away.

Ideally the antenna of the WirelessHART gateway will be located in the area where there is line of sight even if repeaters are not placed at this height. This gives both a horizontal and vertical component to the communication paths. Furthermore, as with repeaters (see 4.2.4), the antenna should reach above dense infrastructure to provide best coverage.

The gateway antenna should be mounted at least 1 m from any other antenna for best performance.

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ProcESS control Building

Planned Initial Network

center of Initial Network

Easiest for Integration

center of Process Unit



4.2.2 Placing Field Devices

Generally, the WirelessHART field devices canbe placed like any other wired devices in accordance with the needs for the measurement task. The self-organizing mesh network will adapt to the process environment without any human intervention.

Nevertheless, some aspects in the direct vicinity of each field device must be considered to ensure good wireless communication:

Mount the devices at least 0.5 m from any vertical surface (wall) to avoid near field reflections which can disturb the radio communication (the radio waves need some space in order to become established) Mount the devices at least 1.5 m off the ground

to minimize effects of the fresnel zone (the radio

4.2.3 Checking for Connectivity

After placing the devices, it should be checked to see whether each field device has enough neigh-bors with good radio reception. Best practice is to aim for a radio signal strength not worse than -60

Fig. 7: Placing devices in the planned network

waves needs some vertical space to provide good connection between communication partners).

Ensure that the devices are at least 0.5 m apart from each other to avoid cross-talk (the radio waves of two close-by neighbors could disturb each other when too close).

The best practice is to use at least five devices in a WirelessHART network. Less will work, but with more devices the network becomes stronger and more reliable because more alternative paths are available. The network can be extended any time, either due to the need for more measurement signals or also with repeaters without measurement functionality to strengthen the network.

to -70 dBm. Of course, to have communication to the network at least one neighbor must be available. One neighbor is acceptable when the device is at the outer perimeter of a network and

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ProcESS control Building

Planned Initial Network



Fig. 8: Device 1 has good connectivity (four neighbors)

the data is not important. The problem is that, when the commu nication to this one and only neighbor is broken for whatever reason, the device is lost. To form a mesh network with redundant paths, each device must have two neighbors. If one neighbor fails, the second

one takes over and provides connection to the WirelessHART net work. But best practice for a really strong mesh network is to check that each device has three neighbors. This gives an extra level of redun dancy since network connection is still provided when two neighbors fail.

But not in all occasions will each device have two or three neighbors. When it becomes evident that this is the case, it is possible or necessary

to place additional repeaters to strengthen the network and provide good connectivity to each device.

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ProcESS

Fig. 9: Questionable connectivity: Device 1 has only two neighbors. Device 2 is placed additionally to act as a repeater and third neighbor.

ProcESS



When checking the connectivity, keep in mind that the radio propagation depends on the environment (see 4.1). So the radius of each device is different, depending on the infrastructure density in its vicinity.

Another aspect to consider when checking for connectivity is the third dimension. The antennas used in WirelessHART devices are dipole antennas. They do not radiate the radio wave equally in each direction, but mostly in the horizontal plane like a torus or donut. The opening angle of this torus is ≤ 45°, and devices can not communicate with each other when the vertical angle exceeds this.

Especially when the radius of communication cuts the border of a different environment, this must be considered. This deforms the theoretical circle to be either more flat or extended:

So, when placing devices over several levels, it must be ensured that the vertical angle between those devices is less than 45°. When the angle is more than 45°, but the elevation between the devices is less than 15 m, there should not be a problem unless the devices are directly over each other.

Fig. 10: The communication distances when reaching into areas of different infrastructure density

Fig. 11: radio communication quality in reference to device location due to antenna pattern

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UNoBStrUctED: 250 m

HIGH oBStrUctIoN: 30 m

acceptableperception

good perception

no perception



Fig. 13: Placing repeaters to provide detour around obstacles

4.2.4 Placing Repeaters

Most WirelessHART field devices are placed in a highly obstructed area where the range is limited. Repeaters can be placed strategically in order to provide best coverage.

Placing the repeaters in the area above the dense infrastructure provides maximum range between the repeaters, serving as a kind of “repeater layer network”. While the repeaters might have direct access even to the GW with a single hop, their communication reaches down into the high-density area, providing a communication path to the devices placed there. For communication “downwards” to the field devices, it must be considered that the dipole antennas have an opening angle of ≤ 45°. Place the repeaters such that the devices are within the respective antenna opening angle. Repeaters can also be used to circumvent obstacles or extend the reach of the network. They allow communication over or around obstacles and allow devices to be placed farther from the gateway.

It is best practice to place repeaters elevated from the ground, e. g. on chimneys or support structures. The reason is that the physical infrastructure at higher elevations is usually less

Fig. 12: LOS above high density infrastructure

dense, providing a better communication path for the radio signal. This better path allows the repeater to communicate with more devices, which means that the repeater has more neighbors. The more neighbors the single devices have, the stronger the network is.

However, in some cases it may be more practical to go around an object such as a building by placing a repeater or secondary device at a lower elevation.

A repeater is not only an investment to strengthen and extend the network. It can turn out that the repeater can also – even if not planned at the initial network – provide useful measurement and serve as “secondary” instrumentation.

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rEPEAtEr oVEr or AroUND oBStAcLES

repeater in canopy

repeater at lower level as canopy

Line of Sight orLow obstructions

High obstruction2 m



4.2.5 Extending a Network

The WirelessHART network is not a static installation. The self-adapting mesh will allow a device to be added anywhere that it has a line of communication to another device. This can be within the perimeter of the existing network or expanding the network outward.

The network’s ability to self-organize allows the communication paths for the new device to be created without human intervention. The network is continually “groomed” by the network manager to constantly evaluate the data paths and make

Fig. 14: Extend the network through simply placing devices

any needed adjustments to ensure the reliability of the data transmissions.

The reach of a WirelessHART network is not restricted to “line of sight” to the gateway.

WirelessHART networks can extend many hundreds of meters due to the mesh technology used. Any field device employed in the network only needs to see at the very least one, but preferably two or more other network devices (see 4.2.3).

4.3 Summary

In summary, the following steps should be taken when planning a WirelessHART network:

Plan your network around the process unit just as you would a traditional instrument installation.

Use a scaled drawing and the estimated

density of the infrastructure to plan your device placement.

Locate the gateway based on any requirements of the connection to the system and anticipated expansion of the network.

Place the devices as needed for your

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ProcESS

Initial Network

control Building



5 Commisioning the Network

After it has been decided where to place the devices, the next step is the commissioning of the network.

As the access point and core element of WirelessHART, the gateway should be installed and started up first. The minimum setup the gateway must have is the network ID and join key for the network.

The first field device which should be commissioned is the field device closest to the gateway. The parameters can either be preset in the maintenance shop or online in the field. The

minimum parameters are the network ID and join key. Additionally, it is best practice also to set at least the long tag to network ID and join key. If possible, it is advisable that a device be preset in the maintenance shop with all necessary parameters including application-related ones (e. g. burst rate) and then switched on in the field. After the first field device has joined the network, proceed with the second-closest field device to the gateway, then with the third-closest and so on until the whole network is initiated. whole network is initiated.

application, taking into account the direct vicinity for radio communication performance.

Use repeaters or secondary instruments to fill any gaps in network coverage or circumvent large obstacles.

Use directional or long distance antennas if needed to reach remote areas.

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6 HOST Integration

In principle, a WirelessHART network replaces a remote I/O system. The only difference is that the backhaul bus of a remote I/O system is exchanged to a wireless backhaul bus and that “cards” from any supplier can be attached to it and these “cards” must not be located in a switchgear cabinet or box.

As a remote I/O system, multiple different options for bus connection to the plant network are available. Either RS485 or Ethernet are mostly available as physical connection. Gateways offer different protocols to be transmitted over the busses, e. g. Modbus.

The data can be used by different systems

DCS: Data can monitor additional parameters which could influence the process and must be taken into account for process control.

Scada Systems: Collecting Data for process supervision, e. g. for process optimization and quality assurance. Asset Management: Monitoring the status and

managing parameter sets of field devices. ERP: planning supply chain management based

on data directly taken from the factory floor

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Fig. 15: Communication Structure of WirelessHART

ScADA ErP

DcS

WirelessHArtGateway

WirelessHArtGateway

Maintenance station

Zone 1

Field Devices

Network

Fieldbus



If more information is desired, e. g. the connection to a control loop or mains power, the symbols can be upgraded (Fig. 16).

7 Documentation

Plants are in general documented in accordance to EN62424 or ISA 5.1. These standards both have a set of symbols to represent measurement devices (circles) and generic computational devices (hexagons). Since repeaters, adapters, and gateways are – in a wider sense – computational devices, the hexagon can be used to represent them, identified by “user-defined” letters. They can be upgraded with a sign for “unguided radiated signal”, taken from ISA 5.1.

With these symbols, it is quite easy and comfortable to document a PA plant. Most symbols are known and used already in wired installation, the wire is just replaced by the sign for an unguided radio signal.

Fig. 16: Symbols to document WirelessHART devices

Fig. 18: Documented WirelessHART installation

Fig. 17: Upgrading the symbology

YG1945

TT1945

YR1945

YA1945

TT1945

GAtEwAY

FIELD DEVIcE wItH LooP PowErED ADAPtEr

YG1945

-+24V RS485

1 32 4

YA2010

-

+

24V

1

3

2

4

1

2

FIELD DEVIcE wItH ExtErNAL SENSor

TT2001

1

2

GAtEwAY

LEVEL

PUMP 1 PUMP 2VALVE 1 VALVE 2

StorAGE

tEMPErAtUrE

VALVE PoSItIoN VALVE PoSItIoN

YA1945

TL1945

YG1234

TT2010

TT2010

TP2000

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8

4

2

6

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3

Subject to modifications • Copyright PEPPERL+FUCHS • Printed in Germany • Part. No. 240110 07/11 00

For over a half century, Pepperl+Fuchs has been continually providing new concepts for the world of process automation. Our company sets standards in quality and innovative technology. We develop, produce and distribute electronic interface modules, Human-Machine Interfaces and hazardous location protection equipment on a global scale, meeting the most deman-ding needs of industry. Resulting from our world-wide presence and our high flexibility in production and customer service, we are able to individually offer complete solutions – wherever and whenever you need us. We are the recognized experts in our technologies – Pepperl+Fuchs has earned a strong reputation by supplying the world’s largest process industry com-panies with the broadest line of proven components for a diverse range of applications.


PROCESS AUTOMATION – PROTECTINg yOUR PROCESS

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