Last year, in July 2015, the Journal South African Instrumentation & Control, published by Technews.co.za, released a new title in their ‘Industry Guide’ series, this time covering wireless applications of instruments in control systems. With 44 pages of ideas and applications, and background to the application of wireless comms for the instrument engineer, this gave a really useful source document – in the long tradition of these industry guides on relevant topics. This wireless guide is still available as a pdf on-line from Technews.
I was lucky enough to be asked to submit a review article covering some of the more recent applications of wireless that had caught my attention at the time. All of these are still topical, and relevant, so the review is now published here, with thanks to Technews. The reason for resurrecting the article is mainly because more information has just emerged about the application for the vibration powered sensors originating from Cambridge University research, now in use on the Forth Road Bridge. The new info, from a recent article in The Engineer is added at the end.
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The Forth Road Bridge, in Scotland, with the suspension cables being monitored by wireless vibration sensors, powered by harvesting energy from those same bridge vibrations!
Industrial wireless communications for sensor data and plant information is now available, proven on site, and built into Internationally accepted standards. Wireless links should now be seen as just another family of techniques for the plant manager or engineer to consider alongside 4-20mA loops, fieldbus networks, and data links. Most would accept that plant data can be ‘monitored’ over wireless as effectively as from these other networks: but the action resulting from the monitoring can also create a control loop.
To those who say that wireless links should never be used within control loops, it is appropriate to remind them that sludge blanket levels on settlement tanks have been monitored, and the data transmitted over a wireless link to control the de-sludging operations, for well over 30 years. Add to that a comment about the latest North Sea offshore gas platforms, where Fire and Gas Shutdown systems are now offered by Yokogawa, using wireless gas detectors, with a dual redundant wireless network to reliably transmit all crucial alarm data back to the logic system, alongside sensor health and battery status information.
So how else can the phrase ‘wireless sensor network’ cause a misapprehension?
That internet hype and Process Plants…?
The adoption of wireless as a plant tool has probably even been held back…. by the apparent hype and emphasis on the Internet, the ‘Internet of Things’, and ‘Big data’ networks monitoring lots of sensors – Sensors Everywhere. Financial Directors suddenly see enormous expenditure, hundreds of USD1000 sensors, mushrooming recruitment for expanded IT departments – and then they pick up the latest management articles forecasting major impacts from hacking and data breaches. No wonder they are sceptical even before starting to read a proposal.
From reports about many of the application examples quoted by the enthusiastic suppliers over the last few years, it appears that success in the application of a wireless based system has come to plant engineers who had a specific and defined requirement, a problem for which the engineer’s assessment showed that a wireless system provided the most logical and cost effective answer. But then, would you expect anything less from an engineer? The typical number of wireless sensors installed initially might be quite low, say a dozen or less: usually the cost justification is based on the problems of new wiring to these extra sensors on an existing plant.
Plant networks from the major suppliers
Inevitably in this competitive field, with many vested interests, it is difficult to find a non-partisan authoritative spokesman: so Ted Masters, President and CEO of the HART Communications Foundation, says (in a video shown on the Emerson website, entitled “WirelessHART: An Executive Perspective”)
“WirelessHART ….. gives users the opportunity to bring in valuable data that can be used in systems to help decision support, particularly in plants that are already installed and already wired. Now the ability to put a point anywhere and bring it easily into the system …… will ultimately yield better performing plants for users”
The video quoted above also features Peter Zornio, Chief Strategic Officer from Emerson Process Management, who paints their stance as totally devoted to ‘Pervasive Sensors’, ie sensors everywhere, monitoring the standard process plant parameters, but also gas leaks, steam leaks, corrosion/erosion, vibration, flames and valve activation, for example on safety showers. This is logical, from a sensor manufacturing company: and Emerson has been collecting a whole range of new sensors to create a family of, typically, add-on plant monitoring sensors. The clue then is in the name, WirelessHART: the network provides all the data you would get from a 4-20mA HART sensor, plus the battery status in the ‘wire-less’ sensor. Other suppliers have joined Emerson as WirelessHART enthusiasts and promoters: these are mainly from the wired-HART sensor manufacturers – like Endress+Hauser, Pepperl+Fuchs – but also include ABB and Siemens.
The ISA100 viewpoint
The alternative wireless sensor data network for process plants, primarily on offer from Yokogawa and Honeywell Process Solutions, is built according to the ISA100 US standard. Suffice it to say that the ISA100 and WirelessHART systems are incompatible, but very much the same as each other, same frequency 2400MHz, similar principles of networking between sensors. Yokogawa concentrate on collecting process sensor information, in the same way as WirelessHART, and have made their ISA100 sensor interface electronics available for any other manufacturer who wishes to incorporate it into their own sensors.
ISA100 has additional capabilities, in that systems can be configured to have a defined time response, and the network messaging can also “package” up electronic message data from the sensor, transmit it over the network, and reconstitute it in the original format at the control room end. So this is useful for sending rotating equipment vibration signatures, and other waveforms from sensor systems for analysis by proprietary electronic units. Yokogawa has progressed this so that they can attach an ISA100 transmitter to a standard HART sensor, even power it from their wireless transmitter battery if needed, and send the HART data back over the ISA100 system: a similar RS485 Modbus unit is also planned.
The Honeywell approach does seem to be defined by their wireless product family tradename, “OneWireless”: it presents a wireless network infrastructure for a process plant that can deal with all potential requirements, using ISA100 for sensors, wifi systems for on plant access and control by laptop type systems, phones and tablets, and the capability to incorporate security cameras and video streaming from engineer’s devices.
After understanding all this diversity, the whole lot, WirelessHART, ISA100, wifi and video transmission, all seems to go through on-site wireless access points and aerials that use Cisco hardware and technology.
The second wireless project
The first wireless project is a major step, and is likely to be driven by a pressing need, which justifies the initial investment – or is restricted in plant area coverage so is cost effective.
Possibly the plant engineer’s subsequent enthusiasm for any further wireless network technology comes when he then discovers that the wireless infrastructure created makes the next project easier, and more cost effective. However, this only happens when the network used suits the developing requirements for data collection and wireless communications on the plant, so hopefully the choice of the network adopted took this into account.
It does seem that many engineers who try wireless once are then converted, and go on to invest in further, expanded installations!
On-plant network examples
The amazing thing is, the examples quoted are all unique, driven by specific site requirements. Straight sensor monitoring is typically via WirelessHART. A simple justification project where the network avoided new hard wired connections across the plant for Health and Safety rule updates that required alarm monitoring of safety shower usage was maybe the first of many new applications. Leak detection on storage tank farms using sensors for hydrocarbons within bund walls was justified in a similar way, to meet environmental legislation. Other areas where hard-wired links are a hassle are rotating and transportable equipment, and construction sites: temperature sensors in rotating lime/cement kilns are ideal for wireless monitoring.
An application in the UK from Emerson Process Management illustrates the progressive adoption success with wireless techniques in an existing plant that initially appeared to present installation challenges. Barking Power is a relatively mature 1000MW CCGT power station near London, suffering from steam losses. A wireless project used Rosemount wireless acoustic transmitters to monitor steam traps for leakage, on a rolling basis round the plant. Quickly, a leak from a high pressure super heater steam trap was identified, which itself could have wasted GBP1400 of steam a day. A further 15 acoustic detectors were added to monitor vent valves that can stick during start-up, and also for relief valves that may not seat correctly. There were few problems with wireless communications even in the enclosed environment around the turbine hall. The battery powered wireless devices were easy to move around the plant to test new locations.
Emerson WirelessHART acoustic monitor installed on a relatively inaccessible steam trap discharge line at Barking Power
Then, high vibration levels were observed manually on the gas turbine starter motor, indicating a major problem. New parts were ordered but the motor needed constant monitoring to nurse the plant through to the next maintenance window. A motor failure would have caused damage in excess of GBP200,000, but keeping the plant running for a further two days could accrue revenue of over GBP50,000. So an Emerson CSI 9420 wireless vibration transmitter was added to the network, and the motor instantly monitored for potential failure. Travis Culham, a Rotating Machinery Engineer at Barking Power, commented: “We concluded that if Emerson’s Smart Wireless Technology could be successfully applied on this challenging application, then it could be applied pretty much anywhere on the plant”.
An Emerson wireless acoustic monitor on a vent valve at Barking Power
A major application for wireless sensors from Honeywell Process Solutions will be the new Shah Gas project near Abu Dhabi. Because of a high percentage of hydrogen sulphide (23.5%), the project is unique, and needs significant worker protection and monitoring of this poisonous gas. This has led to the development of wireless H2S monitoring sensors by Honeywell Analytics, which will incorporate a ‘worker’ location and communication system: this actually uses a triangulation system on the wifi network to provide location data. At the perimeter of the plant there was a requirement for further H2S detectors to protect the local offices, and provide a klaxon warning in the event of a gas escape. Again wireless communication was specified for each gas detection pole, with a 1 second response time guaranteed. Here by choosing star topology for the network communications and with the time determinism defined within the messaging, only the ISA100 system was able to meet this specification.
Wireless Data links
Data links to connect typically a single remote outstation unit back to a control centre offer a different set of applications for wireless. Many are associated with the oil industry, in terms of oil and gas fields, and pipeline monitoring. Others are for agriculture, or environmental monitoring, or water resource management. Founded in 1993, Freewave Technologies in Boulder, Colorado, claim to be a specialist in reliable wireless machine to machine (M2M) and IOT communications solutions, now having supplied over a million systems. It does appear that they have developed the industrial side of this US based business in parallel with a lot of defence/military work on UAV (unmanned aerial vehicle) data transmission, and now have 2400MHz systems available for markets which cannot use the US 900MHz frequency band systems. The product range can replace wired systems for Ethernet or serial data transmission, or collection, transmission and repeating of SCADA system data, or multiple I/O circuits, over a wireless link.
In agriculture, the use of unmanned autonomous machinery is growing for practices such as harvesting, mowing and spraying. In a citrus fruit grove in Florida, Freewave M2M systems allowed an operator to supervise several autonomous mowing and spraying machines, only intervening when the machine meets an obstacle it cannot handle. Transmitted images show the operator what the machine is doing, and hopefully what the problem is: he can then use the wireless link to take control and direct the tractor around and away, presumably re-programming the route to be used in future. In this test the tractor used GPS Real-Time Kinetics location systems to provide the basic navigation (with centimetric accuracy) of the orchard, and one base wireless tower enabled reasonable coverage of a 3000 acre site: small repeater towers were used to provide coverage behind areas of denser foliage and trees. Simpler Freewave wireless SCADA transmission for a wide-spread water supply and sewage network has been installed for Parker Water and Sanitation across parts of Colorado. Here the major advantage is that the remote outstation can be re-programmed remotely, over the wireless link, avoiding the need for and delay caused by a site visit.
The use of wireless around the site on remote oil and gas well systems is quoted by Emerson and Honeywell, to save on site wiring, complexity and power. These use the WirelessHART or ISA100 systems quoted previously. But there are also packages for collecting data from such remote operation sites, supplied by Honeywell and others, with integrated solar panels trickle charging battery systems, then providing remote wireless data links.
The Big Battery question
What about the power supply for these wireless sensors? That has been the biggest question, and the current batteries are big too, making a fairly large sensor housing necessary. But this is the main area where technology is moving fast to catch up.
After five years of operation in Emerson sensors, the answer to this question is still that they are not seeing a significant demand for replacement battery packs. Yokogawa offer a two cell battery pack that is suitable for exchange in the field, even in a hazardous area. The pack, with enclosed lithium/thionyl chloride batteries that are available from standard suppliers, allows cell replacement by the user. But battery packs still seem to have a 7-10 year life expectancy: the life actually depends on the sensor response time the user requires. By the time the battery pack needs replacement, the current growth of battery technology will have provided a better cell.
Commercial batteries for an intrinsically safe battery pack, which can be fitted on site to a Yokogawa DP cell
There are also some really interesting developments in energy scavenging power sources already. In the UK, Perpetuum developed an energy harvester that could power an integrated wireless vibration monitoring sensor, creating the power from a moving magnet within a coil. Subsequently, the company have split their vibration-generator unit from the harvesting electronics, so that the latter can replace, for example, the battery in an Emerson wireless pressure transmitter, and the Harvester part is mounted on an adjacent motor or similar -that creates some vibration. Then the harvesting electronics can also be used to collect other inputs, for example from solar cells.
A Pepetuum Intelligent Power Module designed to fit the Emerson 3051S pressure transmitter
This could be the next area where further developments in technology will impact the design of wireless sensors. From ABB, the TSP300-W wireless temperature sensor has a micro-thermal electric generator (micro-TEG, a form of thermopile) that can generate power from the temperature difference (>20⁰C) between the ambient temperature, and that of the process being monitored, whether hot or cold. This is used to trickle charge a Lithium battery, which will operate for ten years at least.
A power module for a sensor chip, from Illinois
Research is coming up with even more novel power ideas like this. At the other end of the size spectrum, researchers at the University of Illinois have produced a lithium-ion micro-battery suitable for ‘on-chip’ integration, using 3D holographic lithography. New lighter batteries using sodium-ion technology are being developed by Faradion to replace conventional lithium-ion cells. Cambridge University researchers have taken the energy harvesting vibration sensor further, in order to produce small self-powered wireless sensors that can be stuck onto the Forth Road Bridge in Scotland, to monitor the effects of traffic vibrations in the suspension cables.
The next step
The recent big consumer technology changes have enabled the technology, with mobile phones producing the economically priced components, aerials etc. Better capacitors, energy scavenging, batteries will all emerge to make the sensors longer lasting. Standards and customers are making the suppliers work together, and they are chasing to satisfy the significant new market demand.
Probably the major limitation to further adoption of these wireless systems in any industry will be in terms of expertise – the knowledge and understanding needed to design and put the systems together. There will be a lot of opportunity for installers and engineers to develop expertise in these new and niche applications, and there should be plenty of new applications emerging! But for once, some of the easiest applications are on process plants, even in hazardous areas, as the products and packages available for these jobs are now established.
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2016 Update on the Forth Road Bridge:
The above text was written in July 2015. Since then new applications have been reported here on ProcessingTalk.info. But this month’s story in The Engineer gives more information on the Forth Road Bridge application: Jason Ford reported:
“Cambridge start-up 8power has signed a contract with Innovate UK to support the development of its vibration energy harvesting (VEH) technology, an advance with a range of money-saving sensor applications.
The contract funds a collaborative project led by 8power and supported by Costain and the Centre for Smart Infrastructure and Construction (CSIC) at Cambridge University. It aims to develop a sustainable, scalable business case for the deployment of sensors in a range of industrial, infrastructure and construction applications.
According to 8power, VEH employs parametric resonance to facilitate power generation from a variety of vibration sources including motors, moving vehicles, or traffic-induced movement in structures such as bridges.
In October 2016 8Power was named the winner of the 7th Discovering Start-ups competition, which is organised by Cambridge Wireless.
Speaking at the event, Dr Antony Rix, 8Power CEO said that advances in wireless technology are making it easier to monitor a range of variables but that the acquisition of data requires large batteries or regular battery replacement.
“Our team solved this problem by developing a fundamental, patented innovation and a technique called vibration energy harvesting, “ he said. “What we do is take vibration energy that’s naturally there in the environment and turn it into electrical power.”
He added that the conventional – and inefficient – way of doing this is to swing a mechanical resonator from side to side, moving a magnet through a coil to generate electricity.
“What we do instead is move the anchor point up and down and this creates massively more energy and that means much more power, about 10 times more than our competitors…as a result the 8Power technology can enable this technology to power sensors in a much wider range of applications where the batteries of our competitors simply can’t compete,” he said.
“Trials of the technology on the Forth Road Bridge have demonstrated that the solution works in live conditions.”