Industrial wireless infrastructure goes beyond a hand full of WSN in the field sending back information to a localised host system, the broader picture of a truly industrial wireless infrastructure envisages a system where the entire oil and gas facility is integrated wirelessly and all arms of the organisation can wirelessly access data from approved wireless devices from any location in the world. This provides a wireless platform for more efficient management, operation and maintenance of the oil and gas facility.
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This review focuses on WSN in the oil and gas industry, WSN resides in level zero of the ISA 95.01 hierarchy model. The oil and gas industry have utilised WSN for a number of years, up until the release of industry specific wireless technologies i.e. Wireless HART and ISA 100.11a, all of the oil and gas WSN install base were based on vendor proprietary technology, as a result there several operability issues with other vendors device and host systems . Oil and gas facility operators and maintenance teams found themselves requiring multiple vendor devices and systems to meet the process application needs, resulting in high maintenance and operational costs defeating the purpose for having WSNs.
The vast majority of the first generation WSN were based on basic office wireless technologies, as a result the first generation WSN where plagued with a number of issues namely; signal reliability, power usage, device processing capabilities, coverage area, suitability for use in hazardous areas, security and data latency issues. All these issues were a cause of major concern in the oil and gas industry towards the deployment of WSN. 
Communication in the oil and gas industry demands the selected technology provides high availability, reliability, can coexistence with other networks on the plant, conform to an international standard, can operate in hazardous area, can transmit data in real time, is easily interoperable and is secure to outside intrusion and is cost effective . All these requirements plus the ever changing RF environment and high levels electromagnetic noise from heavy duty machinery on an oil and gas facility has made it difficult over the years for WSN to prove successful and be considered the norm when considering communication technologies.
The release of process industry specific WSN technologies like WirelessHART and ISA 100.11a, has significantly increased the interest in WSN in the oil and gas industry, it is estimated that investment in wireless infrastructure in the oil and gas industry will more than double from 1.2 million devices to over 3 million device between 2009 to 2015 . With the advances in WSN technology, the potential of WSN to deliver a reduced CAPEX and OPEX cost savings, and possible health and safety and environmental benefits , is proving too attractive to be overlooked by oil and gas industry looking to reduce cost and improve plant safety.
WSN are primarily based on the IEEE 802.15 family of technologies, which are designated as WPAN, WPAN typically consist of low data rates and a short coverage area . WSN utilise a range of frequencies in the ISM band of frequencies i.e. 900 MHz, 2.4 GHz and 5.8 GHz, these frequencies propagate through office cubicles, drywall, wood and other materials found in homes and offices but tend to bounce of large object like steel and concrete. Due to the high density of steel structures in an oil and gas facility, the first generation of WSN where plague by signal echo or multi path fading , high levels of signal echo and multipath fading lead to transmissions been cancelled .
Some of the wireless technologies used in Industrial applications include; Bluetooth, ZigBee, WirelessHART, ISA 100.11a etc. IEEE 802.15.1 AKA Bluetooth is a short range radio technology which operates in 2.4 GHz ISM frequency band; it was first introduced by the telecom vendor Ericsson in 1994 as a wireless alternative for RS232 communication . Bluetooth is relatively low-power, low-rate wireless network technology, intended for point-to-point communications . Bluetooth operates with three different classes of devices namely Class 1 devices which have a range of about 100meters, class 2 devices which have a range of about 10 meters, and class 3 devices with a range of 1m .
Bluetooth operates based on the features of Adaptive Frequency Hopping (AFH) and Forward Error Correction (FEC), AFH detects the potential for channel interference and blacklists channels found to have interference, to handle temporary interference the scheme re-tries the blacklisted channels and if the interference is no longer present channel can be used . For security and authentication purposes an acknowledgement is sent by the receiver to the transmitter before a connection can be made between devices, Bluetooth also uses FHSS which adds an inherent level of security, the hop sequence switches channels 1,600 times per second making capturing a single hop extremely difficult. Data transmitted using Bluetooth is encoded before transmission increasing the security of the transmission also password protection ensures only devices with identical passwords can participate on the network. Bluetooth also utilises a controlled device pairing process to determine which products can communicate, making devices invincible so they cannot be discovered by other devices .
Bluetooth is limited to eight devices per network and also has a limitation on the packet sizes . This limitation in the number of device per network makes the Bluetooth technology an impractical solution for WSN in the Oil and gas industry. Typically the quantity of nodes in an oil and gas application would be in the hundreds which would mean have several Bluetooth networks on the facility.
ZigBee is based on the IEEE 802.15.4 and originally developed for home automation. It is a low-cost, low-power, short range, wireless, mesh network technology which operates in the 2.4 GHz ISM band and uses DSSS modulation. All nodes in a ZigBee network share the same channel and frequency hopping is not permitted, at start-up of a ZigBee network scans are carried to establish a channel with little or no interference, this channel is then used for its data transmission . A ZigBee network is capable of supporting hundreds of devices, the network architecture can be star, tree or mesh topologies. The technology uses three different types of devices namely ZigBee end devices, ZigBee router and a ZigBee coordinator.
ZigBee supports both non beacon and beacon enabled networks, non-beacon networks are allowed to transmit any time that the radio channel is open and idle. This creates a ‘free-for-all’ environment in which collisions occur regularly when two or more devices try to transmit at the same time. In this mode, the co-ordinator and routers must be active at all times, and so it is best suited to mains powered devices . A beacon enabled network can transmit only in its designated time slot; this regulates transmissions making collisions less likely. All nodes in the network are expected to synchronize their on-board clocks to this frame. Each node is allocated a specific time-slot within this super-frame during which it, and only it, is allowed to transmit and receive its data .
ZigBee utilizes the security mechanisms defined by IEEE 802.15.4, it using counter with cipher block chaining message authentication code (CCM) and AES-128 encryption, giving the option to use encryption-only or integrity-only . The technology permits the use of three keys namely Network key, Link key and Master key. To join the network the master key is required, for end-to-end data encryption the link key is required and provides the highest level of security, the network key is shared between all devices on the network and provides a lower level of security .
ZigBee networks offer no diversity in frequency since the whole network shares a single static channel, this makes the network highly susceptible to signal jamming. Frequency selective fading due to the high density of concrete and steel structures present in an oil and gas facility is also a major concern as this can stop all ZigBee communication. The use of a single static channel increases the chance of interference from other systems and increases delay as the network size grows. In non-beacon enabled networks collisions forces retransmissions and this increase latency time making the technology unsuitable for critical monitor or control applications .
ZigBee has existed for some time now and has been updated a number of times to improve features like reliability, latency and security which are of uttermost importance but ZigBee has still not been able to cope with the stringent requirements needed for reliable and secure data transmission on an oil and gas facility.
Wireless HART is one of only two released open wireless technology specific for process measurement and control applications . It is modelled on the OSI model with its physical layer bases on the IEEE 802.15.4 for low rate WPAN, it operates in the 2.4 GHz ISM frequency band. The application layer is based on the oil and gas industry wide accepted HART protocol. The technology was released in 2007, and was developed on a set of fundamental requirements namely: it must be easy to use and deploy, it should be a self- organising and self- healing network and it should be scalable, reliable and secure . Wireless HART employs TDMA where all devices on the network are time synchronised and communicate in a prescheduled 10ms fixed time slot, this reduces data collision on the network and also reduces the power consumption of network devices .
The Wireless HART network is made up of different devices which include field devices, network gateways which include network and security managers. Field devices are organized in either mesh or star topology with the gateway acting as a bridge between the field device network and the host system . Mechanisms like DSSS, FHSS, CSMA/CA, channel hopping, channel black listing are adopted by the technology to improve coexistence with other wireless networks in the environs.
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WirelessHART adopts two routing mechanisms to ensure data reliability and availability these routing mechanisms are called graph and source routing. During graph routing the network manager establishes the different routes which form the graph, each device on the network stores these routes and uses the predefined routes to identify the next device to forward data to during data transmission. During source routing a definitive list of the devices from the source device through to the destination which the data is to be routed is included the data packet header . Graph routing gives the WirelessHART the ability to self-heal if predetermined routes on the graph is unavailable an alternate route can be taken. WirelessHART adopts a mandatory security requirement, both the sending device and receiving device uses counter with cipher block chaining message authentication code (CCM) together with AES-128 as the underlining encryption methods. Session keys, joint keys and network keys are generated by the security manager and network manager to prevent intrusion and attacks against the network .
WirelessHART since its release has proven to be a reliable technology, it is well researched in both the academic and industrial fields with reputable instrumentation suppliers investing heavily the production and continued research and development of devices operating on the technology. The features and capabilities of the technology are addressed in more detail in section 4.1 of this report.
ISA100.11a is the second of the two open wireless technology’s specific for process measurement and control applications, ISA 100.11a is a Low data rate wireless mesh network technology operating in the 2.4 GHz ISM frequency band, it is modelled on the OSI model and adopts IEEE 802. 15.4 as its Physical layer. The technology was released in 2009 and is suitable for process applications where delays of up to 100ms can be tolerated . ISA 100.11a technology aims to deliver Low energy consumption devices, easy scalable networks, interoperability with legacy infrastructure and applications, a secure and robust wireless network which is capable of coexisting with other wireless devices in the industrial work space .
An ISA-100.11a network is made up of non-routing and routing field devices, a system manager, a security manager, backbone routers and gateways. Non-routing devices are the field sensors / actuators, while routing devices could also act as field sensor/actuator or a router. Routing devices are important in the mesh network, data is transmitted from the source to the destination through a number of hops, with the routers responsible for routing the data to the right destination. They can also use alternative paths to improve reliability similar to WirelessHART network.
Data packets are routed from one subnet over the backbone network to its destination, the backbone router is responsible for this routing function, the routing destination can be another subnet or the gateway. Thegatewayis the physical interface between the field network and the plant host network. The system manager is responsible for the administrative functions and communication configuration of the network .
ISA 100.11a supports frequency hopping and channel blacklisting, this eliminates faulty frequency bands and improves robustness against interference. The technology also uses DSSS modulation technique which divides the signal into small fragments and spreads it over the available frequency channels, this disguises the signal making it appear as noise to the other wireless technologies with in the range as a result overcoming interference and increasing communication reliability . ISA.100.11a is a very robust technology, in addition to DSSS, the technology utilises three different diversity techniques, namely space diversity, frequency diversity and time diversity .
ISA100.11a utilises integrity checks and optional encryption to guarantee the security of the network, the technology also utilises AES-128 bits, message authentication and encryption codes. In addition to this a shared global key, a private symmetric key or certificate are required in order a for a sensor node to be permitted to join an ISA100.11a network .
The technology provides a synchronizing sampling mechanism, this mechanism provides reduction of reporting rates and transmissions can be configured to take place when the rate of change of the measured data exceeds a certain defined threshold. Adaptive transmission power control is also adopted by ISA 100.11a devices, this provides field devices the ability to dynamically select a transmit power level, thereby optimizing the power used by the device. Finally the routing capability of field devices can be turned on or off depending on the location of a device here by reducing the power demands of the device to suit the design requirements .
The application layer of ISA 100.11a is flexible and has tunnelling capabilities, this permits the user to maintain compatibility with oil and gas facility legacy protocols like Fieldbus Foundation, HART, Profibus, Modbus, and others . ISA.100.11a adopts 6LoWPAN protocol for its network and transport layers, this offers interoperability with internet based hosts and sensor nodes in other WSN networks with IPv6 compatibility .
ISA 100.11a has proven to be a reliable WSN in the oil and gas industry, monitoring and alerting, asset management, predictive maintenance, condition monitoring are the application areas which have specific requirements and performance characteristics that can be covered by ISA.100.11a technology.
ZigBee and Bluetooth are some of the technologies which have not really been accepted by the oil and gas industry as a means of wireless communication for process monitoring due to some shortfalls such as, ZigBee cannot provide the required QoS support for handling latency and message flow determinism required by industrial applications, ZigBee only utilizes DSSS hence its performance can easily degrade in case of continuous noise in the environs. Bluetooth on the other hand, isn’t sufficiently scalable to handle the vast number of measuring points on an oil and gas facility.
However, WirelessHART and ISA100.11a technologies have been adopted for industrial applications due to their ability to deterministic data transmission, reliability, security, reduced data latency and low-cost features. WirelessHART does not support multiple protocols as ISA100.11a does, the transmission of HART messages are the only information specified and supported by WirelessHART while ISA 100.11a support most of the oil and gas legacy communication protocols like Foundation fieldbus, MODBUS, Profibus, HART etc. .
The extreme environments experienced on an oil and gas facility i.e. high temperatures, high level of EMI, large steel and concrete structures and constant movement of heavy machinery makes wireless communication highly unreliable in this environment. The release of industry specific technologies i.e. Wireless HART and ISA 100.11a has somewhat addressed the concerns over reliability, security, signal latency of a WSN, compliancy to the standards by wireless device vendors has also lead to operability across multiple vendor devices.
Confidence has grown in the use of WSN since the release of industry specific technologies with a hand full of vendors and end users championing the way on WSN. The install base of WSN is continually increasing and this will aid the industry gain a better understand the technology. Till date majority of the install base are on purely monitoring only points due to latency concerns with WSN, further academic and industry based research is required in the use of WSN for fast acting closed loop control and safety critical applications with the aim resolving the latency issues associated with WSN.
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