Machinery Condition Monitoring Using Wireless Self-Powered Sensor Nodes

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1 Machnery Condton Montorng Usng Wreless Self-Powered Sensor Nodes Fred M. Dscenzo, Ph.D. Rockwell Automaton, Inc. Allen-Bradley Dr Mayfeld Hts, OH 444 Kenneth A. Loparo Case Western Reserve Unversty 0900 Eucld Ave. Cleveland, OH Harry Cassar BP p.l.c. St. James Square London, SWY 4PD Unted Kngdom Dukk Chung, Ph.D. Rockwell Automaton, Inc. Allen-Bradley Dr Mayfeld Hts, OH 444 ABSTRACT There s rapd growth n the development of ultra-low power processors, rados, memory, and archtectures that form the bass for wreless sensor nodes. Smart dstrbuted wreless sensor nodes, orgnally developed for mltary applcatons over 0 years ago, are fndng ncreased use for wreless machnery condton montorng for ndustral and commercal applcatons. The major drawback to low-cost wreless sensor nodes s the need to regularly replace batteres. Ths paper descrbes a prototype self-powered wreless sensor system deployed n a shpboard applcaton. The sensor node scavenges energy from machnery vbraton and uses ths energy to power an embedded processor, sensors, and rado. Vbraton data and energy harvestng effcency data s perodcally transmtted to a data collecton server on the shp. Important ssues are presented ncludng the effcent desgn of the energy harvestng module, power converson and power storage, communcatons, power management, embedded dagnostc algorthms, ste survey and wreless sensor node nstallaton, and the need for a systems-level approach for self-powered wreless sensor nodes. Extensons to ths core work are presented that nclude adaptve power scavengng and self-powered sensor nodes embedded n machnery. Introducton There s a growng prolferaton of wreless devces for many ndustral and commercal applcatons such as for securty, safety, survellance, and machnery condton montorng. Although the wrng costs for communcatons and power cables are elmnated wth wreless devces, these costs are replaced wth the ongong cost of battery mantenance (e.g. battery cost, manpower, logstcs, envronmentally conscous dsposal, protecton from potental leakage, and potental equpment downtme due to unexpected battery falure). A crtcal technology s the ablty to scavenge energy from the envronment and use ths energy to power remote, dstrbuted sensors, rados, actuators, processors, memores, and dsplay elements. Ths technology s enablng and permts power-scavengng sensor nodes to never requre servcng and to be deployed n naccessble locatons or embedded nto machnery. Rockwell Automaton, n collaboraton wth BP s Chef Technology Offce n the U.K., has developed and deployed two self-powered wreless sensor nodes on the BP tanker Loch Rannoch. These sensor nodes were deployed as part of a technology evaluaton program to establsh the vablty of wreless sensor nodes operatng n a harsh shpboard envronment for machnery condton montorng. The shpboard tral of self-powered sensor nodes was done n parallel wth a larger scope test of wreless sensor nodes on the tanker. Background There are mportant technology changes occurrng that promse to change the character of machnery montorng. These changes wll affect future machnery condton montorng, safety, control, re-confguraton, and securty. New developments n dagnostc and prognostcs algorthms, emergng CBM archtectures and standards (e.g. OSA-CBM, MIMOSA Open O&M, and OPC/ISA), and new, low-power wreless communcatons standards and components (e.g. Bluetooth and IEEE ) enable the deployment of many low-cost dstrbuted sensors. An array of dstrbuted sensors can provde superor capabltes for msson-crtcal applcatons and can drectly reduce mantenance cost and total lfe-cycle cost. Wreless sensor nodes often employ energy effcent processors, memory, rados, and energy-management logc. These systems have been under development for over 0 years and are targeted for applcatons such as survellance, target acquston, and machnery montorng

2 [][]. In spte of ther energy effcency, the need for a relable, long-term energy source remans a roadblock to the broadscale deployment of thousands of dstrbuted sensor nodes. For many dstrbuted sensor applcatons t s not practcal to provde wre-lne power due to factors such as cost, weght, relablty, safety, or envronmental hazards (e.g. explosve envronments). For example, n many ndustral applcatons the cost of wrng may be $40 USD per foot or more and often exceeds the cost of the remote sensor. The need for costly wrng can be elmnated f the dstrbuted sensor node s self-contaned and s self-powered. Optons for self-powerng sensor nodes nclude batteres, mcro-fuel cells, mcro-generators, and power-scavengng technologes. A self-powered sensor node utlzng mcro-generators or fuel cells provde lmted beneft and s currently not consdered a vable soluton. Utlzng storage batteres for remote sensors s also not consdered a generally effectve soluton snce the batteres requred to power each sensor adds sgnfcant cost, weght, relablty and mantenance problems, partcularly when the sensors are located n dffcult to reach areas. These problems are multpled when hundreds of thousands of battery-powered sensor nodes are deployed. Furthermore, batteres have an uncertan lfe and t s dffcult to accurately predct the battery charge depleton profle. Batteres encapsulate caustc chemcals and heavy metals that may, n tme, leak causng damage to equpment, njury to workers, and may affect other nearby equpment and the envronment. Batteres also suffer from low power densty and rapd deteroraton and agng especally n hostle envronments. For these reasons batteres are not consdered a generally vable method to power remote wreless sensor nodes. Batteres may be effectve for targeted applcatons requrng low duty cycle and low power requrements n readly accessble locatons. Harvestng power from stray energy for remote sensors s well-suted for CBM sensor applcatons. CBM systems often requre perodc samplng from sensors whch may be dstrbuted across a machne, vessel, or faclty. Remote sensor processng can typcally be performed perodcally and at a frequency consstent wth the rate of local power generaton. Newer materals such as certan pezo-electrc materals exhbt hgh couplng effcences and can operate at elevated temperatures (>5 F). These materals are already beng used for vbraton and ultrasonc sensng and are well-suted for power scavengng devces for CBM applcatons. A remote self-powered sensng devce may be composed of four core elements not ncludng the machne or communcatons (Fgure ). The frst element s a sensng element such as temperature, pressure, vbraton, or magnetc feld. The second element s a parastc energy transducer capable of transformng stray energy nto an electrcal potental. The thrd element s a power storage devce such as a rechargeable battery or a capactor bank. And the fourth element s a processor and algorthms for nterpretng the sensor data. There are often addtonal elements such as local memory, dgtal output, or communcatons such as a wreless data lnk. The communcatons lnk may not be requred f the self-powered sensor node s used to locally store nformaton and operate as a black-box system or f only a local dsplay such as blnkng LED s used to sgnal a machne fault. Fgure Components of a Self-powered Sensor Node A more complete confguraton may nclude multple power storage elements wth dfferent electrcal characterstcs, multple sensor elements, multple energy harvestng modules wth dfferent electrcal and mechancal characterstcs, actuator elements, and adaptve hardware and software elements to optmze system performance.

3 The core elements descrbed above can provde valuable machnery condton montorng capabltes. The ablty to perform machnery condton montorng wthout the cost of wrng and the burden of perodc battery replacement provdes attractve benefts for many ndustral, commercal, and marne montorng applcatons. Establshed power scavengng technques such as pezo-electrc devces and photovoltac cells can provde the power needed for machnery condton montorng for reasonable envronmental condtons and provde perodc machnery montorng. Regular machnery montorng s partcularly valuable for shpboard systems. Routng power and sgnal cables on shps s frequently very dffcult due the presence of thck compartment walls, lmted free space for cable trays and conduts, and watertght compartment requrements. Smlarly, manually capturng data at machnes below deck s tme consumng for the shp s crew and can be dangerous durng hgh seas or n the presence of water, power cables, or petrochemcal fluds or gases. A program was defned to evaluate the capablty of exstng energy harvestng technologes and to establsh the deployment ssues and operatonal benefts afforded by wreless, self-powered machnery condton montorng. A set of prelmnary specfcatons were developed and a shpboard target applcaton was establshed. BP Shppng has supported ths project by provdng techncal nformaton and access to the FPSO tanker Loch Rannoch (Fgure BP Shp Loch Rannoch) [3][4]. Shpboard Tral Fgure BP Shp Loch Rannoch. Objectves The objectve of ths program s to establsh the vablty of an energy harvestng system comprsed of sensors, power generator, power converson electroncs, and power storage components. These components are assembled nto a system to be evaluated n the context of machnery condton montorng n a harsh envronment (e.g. a shp machne room).. Devce Desgn Several ntegrated self-powered sensor nodes were desgned and constructed for ths program. The self-powered sensor nodes contnuously scavenge energy from the envronment, convert and store the scavenged energy, and use the stored energy to perodcally power sensors, operate analog to dgtal converters (ADC), operate a mcroprocessor, llumnate local LED s, and perform rado communcatons. A pcture of the self-power sensor node s shown n Fgure 3 Self-powered Sensor Node. The connector shown at the top s used to temporarly provde DC power to ntally charge the array of storage capactors. After the capactor bank s charged, the energy scavenged need only be enough to replace the depleted power from the operaton of the sensor node. Fgure 3 Self-powered Sensor Node There are seven core elements that comprse the self-powered sensor node. These elements are: ) Processor ) Rado 3) Sensors 4) Power Generator 5) Power Storage 6) Electronc power crcut 7) Software Two self-powered sensor nodes wth embedded processor, rado, sensor, and generator have been constructed. Each devce s programmed to sample three analog nputs. The frst analog nput s the sampled data from an accelerometer. The accelerometer s a sngle-axs sensor mounted on the nsde of the sensor node enclosure. Vbraton data s sampled for one second at khz. The second analog nput s the voltage generated from the

4 pezo-electrc generator. The thrd analog nput s the state of charge of the capactor bank. The generator voltage and the capactor state of charge are sampled to provde an RMS or DC voltage level. Each of these three nputs are stored n the local processor memory and also transmtted to a thrd processor. The thrd module receves the data transmtted from the two self-powered sensor nodes and sends the data through the seral port to a PDA wth a memory card. Software on the PDA dsplays the tme waveform data receved from the two remote sensor nodes on an LCD and also archves the data to a memory stck n the PDA. The confguraton of the sensor nodes s shown n Fgure 4 The objectve s to scavenge enough energy from the envronment to replace the power needed to support the machnery montorng and data transmsson functons. Prevous work conducted by the authors and publshed results from others ndcates that pezo-electrc materal s the most approprate generator technology for ths applcaton. Studes have ndcated that whle photovoltac cells may provde the greatest power-generaton densty, the most versatle, power-dense generators are based on pezo-electrc materals[5][6][7]. Fgure 4 Self-Powered Sensor Node System Pezo-electrc materals convert mechancal stran such as nduced by machnery vbraton to a voltage. When mplemented as a cantlever desgn wth one end fxed and the other end free to bend, a snusodal voltage s generated that corresponds to the harmonc moton of the beam. The power generated s a functon of the ampltude and frequency of the moton of the pezo-electrc beam. Maxmum stran s obtaned, and maxmum power obtaned when the resonant frequency of the pezo-electrc beam matches the vbraton frequency wth the most energy (.e. hghest ampltude) on the target machne. An ol pump was dentfed as the canddate machne for montorng snce t operates contnuously wth a relatvely hgh rotatonal speed. The target frequency where most of the vbratonal energy exsts for ths ol pump s 7800 cps (30 Hz). A cantlever beam desgn was used for the pezo-electrc generator element. The constrants for the generator s that t must ft wthn a three nch footprnt and have a resonant frequency of roughly 30 cps. Fgure 5 shows the pezo-electrc generator developed for ths program. The small threaded bolt at the narrow end of the generator can be extended or retracted as needed to provde fne tunng adjustment of the resonant frequency of the beam. Commercally avalable pezo-electrc b-morph materal was used to construct the generator element. Ths materal conssts of two layers of the pezo-electrc materal surroundng a brass metallc nner layer and a seres bender connecton s used. A narrow strp of composte materal s mounted just above the tmng screw to lmt the deflecton of the beam and prevent over-stranng the pezo-electrc element. Fgure 5 Pezo-electrc Generator Power converson electroncs were developed to rectfy the snusodal voltage from the pezo-electrc generator, scale ths voltage for chargng the super-capactor bank, convert power from batteres for pre-chargng the capactor bank, provde a voltage sgnal for montorng the generated power and the capactor state of charge, and regulate the power gong to the processor and rado. An array of nne super-capactors was used to store the generated power. The super-capactors provde excellent power densty and neglgble leakage current. The sensor node components descrbed above are housed n a small plastc enclosure attached to a stff mountng bracket. Fgure 6 shows the arrangement of the components n the enclosure. The box has a removable cover secured wth four screws to permt mountng devces on the nsde of the box and on the box cover. The power converson crcutry s assembled on one sde of a small perf-board and the array of supercapactors are mounted on the other sde. The assembled perfboard wth electroncs and capactors s mounted Materal used s T0-A4 from Pezo Systems Inc.

5 to the nsde of the cover. The processor and rado are components n a commercally avalable devce called a mote. The mote s mounted to the sde of the enclosure and s shown next to the cantlever generator. The pezo-electrc generator s shown mounted to the bottom of the enclosure. The battery holder s mounted to the sde of the enclosure and s shown wth two lthum batteres nstalled n Fgure 6. The batteres are used to charge the Capactor capactor bank pror to deployng the Batteres for pre-charge system. It s not essental to pre-charge pre-chargng connector crcut the storage capactors however startng wth a charged capactor bank elmnates Accelerometer the need to wat days or weeks for the generator to buld up a suffcent stored Pezo-electrc charge to power the processor, sensors, cantlever generator and rado. Battery power may be provded usng the battery holder as Telos Mote shown n Fgure 6 or provded by a DC supply through the capactor pre-charge connector on the sde of the case. Fgure 6 Assembled Self-Powered Sensor Node. Installaton & Operaton There were many uncertantes n ths experment ncludng the relablty and effcency of the energy harvestng devce durng prolonged unattended operaton at sea. Other uncertantes nclude not knowng the expected duty cycle or operatng characterstcs of the machnery provdng our source of power. Even f the machne operates contnuously t must operate wth an approprate level of vbraton near our targeted, tuned frequency. Other shpboard uncertantes nclude the weather and ambent vbraton caused by other shpboard machnes, sea state, clmate, and shp operaton. Research has been done n each of these areas and t s expected that harsh weather condtons and hgh seas are lkely durng the sea tral [8]. Movement of shps crew, closng of compartment hatch doors, and rado nterference are also consderatons for ths tral. Work was done pror to the nstallaton of the self-powered sensor nodes to mnmze these rsks and nsure a successful sea tral. Background work ncluded laboratory testng of components and system level testng of the self-powered sensor nodes. A ste survey was conducted aboard the shp pror to nstallng the equpment that ncluded montorng rado transmsson performance at the planned rado frequences whle operatng varous shpboard machnes such as motors and radar. Detaled documents were developed defnng the procedures for the ste survey, equpment testng, shpboard nstallaton, and equpment decommssonng. To reduce the rsk of falure due to a devce fault or due to nadequate power generaton capablty, two dentcal self-powered wreless sensor nodes were constructed. One node was deployed usng batteres plus power scavengng. Ths permts prolonged montorng of power generaton and energy utlzaton even f nsuffcent energy for operaton s generated. The second self-powered sensor node was deployed wthout batteres and reles solely on power scavengng for contnued operaton. Both sensor nodes were nstalled on the same ol pump n the machne room. Each sensor node s programmed to hbernate for one hour. Each hour the sensor node wakes up, turns on the accelerometer and after an approprate settlng tme samples vbraton. The accelerometer s turned off and voltages are then sampled from the pezo-electrc generator and from the capactor bank. The rado s then cycled on. After a sutable delay to permt the rado to power up and synchronze the sampled data values are transmtted to a thrd mote connected to a PDA as shown n Fgure 4 above. The self-powered sensor node then turns off the rado and returns to hbernate mode. The thrd mote receves the sampled data and send the values to a PDA through the seral port. The PDA dsplays the tme waveform data from both sensor nodes and logs the sampled data to a memory stck. The thrd mote and PDA are powered from the shp s power supply. The Telos mote from Motev Corporaton was used for ths prototype system

6 Expermental Results The equpment was nstalled on the ol tanker and was left operatng and unattended for four months from md- August 004 to md-december 004. Perodc readngs provded by the shps crew ndcated the system was contnung to operate. Followng the sea tral all equpment was removed from the shp and the data fles captured from the sensor nodes were coped to a server for analyss. Over 8,000 data fles were captured. Most of the captured data looks vald however some corrupt fle names and data values were observed. The cause for the data faults s currently beng nvestgated. Vbraton data was captured at khz wth bt resoluton. Ths nformaton can be used to compute the nput power to the energy harvestng devce. Ths output voltage form the pezo-electrc generator was also captured to permt computng the output power. The rato of the nput power to the output generated power provdes a measure of the converson effcency. One of the self-powered sensor nodes consstently generated very low power levels wth the maxmum power observed on the order of tenths of watts. The other selfpowered sensor node was able to relably generate hundreds of mcrowatts. Laboratory and analytcal results suggest ths devce s capable of generatng perhaps ten tmes ths amount of power under the expected operatng condtons. The lower level of power generaton observed s lkely due to the varaton n rotatonal speed of the motor-pump system and lower ampltude of vbraton. Fgure 7 shows the power generated for the more effcent self-powered sensor node. The above dagrams suggests the ol purfer runs perodcally. It s nstructve to vew the rato of the power generated to the nput power. The power generated s recorded at each sample nterval by the mote as the rectfed voltage from the pezoelectrc generator. The nput power to the devce may be approxmated by the vbraton sensed from the accelerometer attached to the nsde of the power scavengng enclosure. At each sample nterval, acceleraton data s recorded. The power converson effcency may be calculated as the rato of output power to nput power. The followng equaton s used to compute ths rato: Equaton : Power Rato = x 34.8kΩ 0 0 = V The average power generated and the power converson effcency s shown for several representatve data samples n Table I below. Watts 4.E E-0 3.E E-0.E-0.00E-0.E-0.00E E E Tme A Fgure 7 Plot of Average Power Versus Tme for Mote 7 Watts

7 Table Average Power Generated and Rato of Input Power to Generated Power for Mote 7 MOTE 7 V = x 34.8kΩ = x 34.8kΩ 0 A 0 = Data Collecton Data and Tme Average Genreated Power (Watt) Rato Rato 0_0_04 0_05_9_AM.6E E E-05 0_0_04 0_47_05_PM.57E E E-05 0_0_04 03_55_AM.6E E E-05 0_0_04 45_4_PM.58E E E-05 0_0_04 0_3_PM.60E E E-05 0_0_04 9 AM.66E E-05.0E-04 0_0_04 0_07_PM.58E E E-05 0_0_04 7_56_AM.63E E-05.0E-04 0_0_04 59_43_PM.57E E E-05 0_0_04 6_3_AM.65E E-05.03E _9_04 8_38_33_PM 4.4E-03.04E-07.94E-05 9_9_04 8_55 AM 4.4E-03.04E-07.94E-05 9_9_04 9_37_09_PM 4.4E-03.04E-07.94E-05 9_9_04 9_53_58_AM 4.4E-03.04E-07.94E-05 V = x 34.8kΩ 0 0 = V A The power rato captured roughly every hour s shown n Fgure 8. Durng operaton, the machnery vbraton s lkely at an adequate ampltude level for the energy harvestng devce but most lkely at a frequency dstant from the resonant frequency of the energy harvestng cantlever beam. The cantlever beam was tuned for a nomnal rotatonal frequency of 7800 cps or 30 Hz. The data plots obtaned from the onboard machnery database ndcate a frequency of 7968 cps. Ths results n a stmulus relatvely far from the 7800 cps target resonant frequency of the cantlever beam. Ths wll result n reduced ampltude of vbraton of the cantlever beam and a correspondng sgnfcant reducton n the amount of energy generated. Fgure 8 Power Converson Rato for Mote 7 Conclusons The functonal elements comprsng the self-powered wreless sensor nodes are tghtly coupled. Successful ntegraton of the component elements s crucal to successful operaton of the energy harvestng system. Furthermore, the desgn of the ntegrated energy harvestng module must be compatble wth the expected operatng envronment. The generator desgn employed was based on extractng maxmum energy from the relatvely low levels of vbraton observed. Ths caused to devce to provde reduced power levels when strayng from the targeted resonant frequency. Efforts are currently n progress to dynamcally change the frequency response of the energy harvestng devce n response to changes n the envronment and operatng equpment energy spectrum. A systems approach s essental for defnng the requrements of each of the system elements and how they ntegrate nto an operatonal system. A systems approach wll nsure that the needed power s stored and used n an effcent manner to accomplsh the sensor node functons. The power budget ncludes requrements for sensors, rado, processng duraton and frequency of operaton, power converson effcences and power losses and leakage.

8 The followng summarzes the conclusons from ths study.. There s a need for adaptve self-powered systems, Energy Harvestng s a vable technology for wreless sensor nodes the benefts are sgnfcant for applcatons such as shpboard machnery montorng 3. It s mportant to establsh hardened devces that operate relably, and requre mnmum set-up and nstallaton effort. The remote operaton of sensor nodes n partcularly harsh shp engne rooms requres an addtonal level of ntegrated desgn, testng, and valdaton before deployment. 4. Data analyss requres more than sampled data from the sensor node. It s mportant to nterpret sampled data n context wth shp operaton, other machnery operaton, sea state, and wth hstorcal data. 5. Collaboratve development and n-feld technology evaluaton can accelerate development the complexty of hghly dstrbuted, remote technology development and deployment has been addressed by the sgnfcant up-front laboratory testng, data analyss, documented feld procedures, ste surveys, and traned staff members. The shpboard tral has demonstrated the sgnfcant benefts provded by wreless sensor nodes for shpboard machnery montorng. The potental benefts that nclude ncreased machnery relablty, reduced mantenance cost, reduced mantenance effort, and enhanced safety have been recognzed by a recent trade publcaton award [9]. These benefts are further expanded by mplementng self-powered systems desgned to never requre mantenance. Ths s an enablng technology that not only mproves the economcs of deployng sensor nodes but also permts devces to be located n naccessble locatons and embedded nsde un-powered rotatng machnery. The fundamental technologes demonstrated n ths lmted scope shpboard tral promse to change the way machnery wll be montored n the future. Acknowledgement The BP CTO organzaton s to be commended for provdng the vson, the leadershp, and the commtment to ths nnovatve program. Specal recognton goes to BP Shppng ncludng the captan and crew of the Loch Rannoch for supportng ths mportant feld evaluaton program. Rockwell Automaton Marne Management and GMS staff under the leadershp of Mr. John Zubak provded nvaluable support to ths program through weekly communcatons and nstallaton servces provded throughout the sea trals. References [] "Wreless Integrated Mcrosensors", presentaton gven at The Seventh IEEE Sold State Sensor and Actuator Workshop on June -6, 996 at Hlton Head, South Carolna. [] Dscenzo, F.M., Loparo, K.A., Cheng, D., Twarowsk, A., Intellgent Sensor Nodes Enable a New Generaton of Machnery Dagnostcs and Prognostcs, Machnery Falure Preventon Technologes, MFPT 00, Vrgna Beach, VA, 00. [3] In Dust We Trust, The Economst, Technology Quarterly, Vol.37, No.8379, pp.0- [4] Mghty Motes, Plant Servces, November 004 [5] Ghand, K., Compact Pezoelectrc Based Power Generaton, Power Pont presentaton by Contnuum Control Corporaton to DARPA/USAAMC, 3-4 Aprl 000, Bllerca, MA, USA, [6] Roundy, S. J., Energy Scavengng for Wreless Sensor Nodes wth a Focus on Vbraton to Electrcty Converson, Ph.D. Thess, Unversty of Calforna at Berkeley, Berkeley CA, USA, May 003, [7] Roundy, S. J., Energy Scavengng for Wreless Sensor Nodes wth a Focus on Vbraton to Electrcty Converson, Power Pont presentaton, Unversty of Calforna at Berkeley, Berkeley CA, USA, 9 February 003, [8] Economc Development Unt, Shetland Islands Councl, Shetland n Statstcs, Shetland Ltho, ISBN , 003, Green Head, Lerwck, Shetland, ZE 0P, UK, pp. 7, [9] 00 Best IT projects n 004, Infoworld, November 004