TECHNICAL WHITE PAPER PLANNING AND DEPLOYING NETWORKS

Transcription

1 PROCESS AUTOMATION TECHNICAL WHITE PAPER PLANNING AND DEPLOYING NETWORKS 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 Lohmann Product Portfolio Manager Pepperl+Fuchs

2 MESH Network Gateway Router 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.

3 Table of Contents 1 Introduction 4 2 Project Scope 4 3 Coexistence 5 4 Network Planning Site Survey Placing Devices Placing Gateways Placing Field Devices Checking for Connectivity Placing Repeaters Extending a Network Summary 13 5 Commisioning the Network 14 6 HOST Integration 15 7 Documentation / 17

4 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. 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 FACILITY Fig. 1: Scheme of Process Facility 04 / 17

5 By limiting the scope of the WirelessHART network to a dedicated process unit, flexibility for future expansion remains since the individual network won t be constrained by devices and wireless projects in other plant areas. 3 Coexistence Before planning a WirelessHART network, it should 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: Frequency Location 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. Collisions are avoided by decoupling at least one of these factors: Time Fig. 2: Occasions for colliding messages 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 GHz GHz WLAN 1 HArt Network WLAN 2 Fig. 3: Channel occupation in 2.4 GHz band 05 / 17

6 It is easy to determine whether to perform a timebased 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. When a WirelessHART network has less than 15 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: 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 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 channels. Each Network must have a different Network ID. Assign blocks of channels to each network. Blacklist (Block) channel which are used by other networks. 06 / 17

7 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. Unobstructed: 250 m Medium Obstruction: 75 m High Obstruction: 30 m Low Obstruction: 150 m Fig. 4: Infrastructure density and possible communication ranges in horizontal dimension 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. Line of Sight or Low Obstructions High Obstruction Fig. 5: Infrastructure density in vertical dimension 07 / 17

8 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) Placing Gateways 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. 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 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. ProcESS Control Building Easiest for Integration Center of Center of Initial Network Planned Initial Network Fig. 6: Placing the GW in respect to the initially planned network 08 / 17

9 4.2.2 Placing Field Devices Generally, the WirelessHART field devices can be 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 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. ProcESS Control Building Planned Initial Network Fig. 7: Placing devices in the planned network Checking for Connectivity After placing the devices, it should be checked to see whether each field device has enough neighbors with good radio reception. Best practice is to aim for a radio signal strength not worse than -60 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 09 / 17

10 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. ProcESS Fig. 8: Device 1 has good connectivity (four neighbors) 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. ProcESS Fig. 9: Questionable connectivity: Device 1 has only two neighbors. Device 2 is placed additionally to act as a repeater and third neighbor. 10 / 17

11 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. 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: UNOBStrUctED: 250 m HIGH OBStrUctIon: 30 m Fig. 10: The communication distances when reaching into areas of different infrastructure density 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. 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. acceptable perception no perception good perception Fig. 11: radio communication quality in reference to device location due to antenna pattern 11 / 17

12 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 highdensity 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. Line of Sight or Low Obstructions High Obstruction 2 m 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. 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 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. REPEATER OVER or AroUND OBSTACLES Repeater in canopy Repeater at lower level as canopy Fig. 13: Placing repeaters to provide detour around obstacles 12 / 17

13 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 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). ProcESS Initial Network Control Building Fig. 14: Extend the network through simply placing devices 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 13 / 17

14 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. 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. 14 / 17

15 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 SCADA ERP Network DCS Maintenance station Fieldbus WirelessHArt Gateway WirelessHArt Gateway Zone 1 Field Devices Fig. 15: Communication Structure of WirelessHART 15 / 17

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. YG 1945 Field Device with External Sensor GATEWAY 1 2 YG 1945 TT 2001 TT TT 1945 YR 1945 YA V RS485 Fig. 16: Symbols to document WirelessHART devices Field Device with Loop Powered Adapter If more information is desired, e. g. the connection to a control loop or mains power, the symbols can be upgraded (Fig. 16). 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 V + - YA 2010 Fig. 17: Upgrading the symbology YG 1234 Level TL 1945 YA 1945 GatewAY TT 2010 TEMPERATURE VALVE POSITION TT 2010 StorAGE TP 2000 VALVE POSITION PUMP 1 VALVE 1 VALVE 2 PUMP 2 Fig. 18: Documented WirelessHART installation 16 / 17

17 process AUTOMATION PROTECTINg your PROCESS Technical White Paper Planning and Deploying Networks 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 demanding 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 companies with the broadest line of proven components for a diverse range of applications Worldwide/German Headquarters Pepperl+Fuchs GmbH Mannheim Germany Tel pa-info@de.pepperl-fuchs.com Asia Pacific Headquarters Pepperl+Fuchs PTE Ltd. Singapore Company Registration No E Tel pa-info@sg.pepperl-fuchs.com 3 Western Europe & Africa Headquarters Pepperl+Fuchs N.V. Schoten/Antwerp Belgium Tel pa-info@be.pepperl-fuchs.com 6 Northern Europe Headquarters Pepperl+Fuchs GB Ltd. Oldham England Tel pa-info@gb.pepperl-fuchs.com 4 Middle East/India Headquarters Pepperl+Fuchs M.E (FZE) Dubai UAE Tel pa-info@ae.pepperl-fuchs.com 7 Southern/Eastern Europe Headquarters Pepperl+Fuchs Elcon srl Sulbiate Italy Tel pa-info@it.pepperl-fuchs.com 5 North/Central America Headquarters Pepperl+Fuchs Inc. Twinsburg Ohio USA Tel pa-info@us.pepperl-fuchs.com 8 Southern America Headquarters Pepperl+Fuchs Ltda. São Bernardo do Campo SP Brazil Tel pa-info@br.pepperl-fuchs.com Subject to modifications Copyright PEPPERL+FUCHS Printed in Germany Part. No /11 00