The electromagnetic interference in case of onboard navy ships computers - a new approach

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1 The elecromagneic inerference in case of onboard navy ships compuers - a new approach Prof. dr. ing. Alexandru SOTIR Naval Academy Mircea cel Bărân, Fulgerului Sree, Consanţa, soiralexandru@yahoo.com Absrac. On a navy ship, like a complex elecromagneic sysem, he elecronic microcompuers(generally- he elecronic equipmen) are submied o a large ensemble of disurbances(50hz-0gz), ransmied by field and by conducion. Due o he complexiy of his phenomenon and he dynamic-random characer of he inerference process, he radiional mehods such a ess and measuremens becomes insufficienly. The proposed mehod offers boh he dynamic-saisical modelaion possibiliy of he inerference and he predicion, on a shor ime horizon, of he compuers sabiliy in a complex disurbing environmen; his being very imporan for he good managemen and operaion of a navy ship.. Inroducion A navy ship represens a complex elecromagneic sysem on wich he elecronic microcompuers are submied o a large scale a disurbing frequencies (50Hz-0Gz). Such disurbances are consiued by he dynamical-random combinaions of some signals, ransmied by conducion and by field. The radiional mehod used for he EMI evaluaion, based on ess and measuremens, becomes insufficienly, due o he complexiy of he dynamical-random characer of he disurbances. The proposed mehod-he mehodology for analyze and predicion of ime series (dynamic series), on a shor ime, named Box-Jenkins mehodology - offers he possibiliy o idenify he compuer evoluion and is sabiliy in presence of a grea number of disurbances. Even more, his one permis o predic his evoluion on a shor ime. I is imporan o emphasize ha his mehod is a complemenary one o he radiional mehods [].. The idea of he mehod The main idea of his mehod consiss in he fac ha a daa series, characerizing a dynamic-random process: Z, Z -, Z -, srongly dependen, could be considered as being generaed by filering of an independen saisic value series: a, a -, a -, having a fixed disribuion funcion (usually normal, wih null average and σ dispersion) (fig.)[]. a Θ Φ ( B) ( B) Z Fig.. The analyzed process such a linear filer

2 The sequence {a } represens a whie noise ype process. The {Z } values of he analyzed process- he answer of he microcompuers of he elecromagneic disurbances on heir whole picked up a equal ime inervals(ms, s, m, h ec.), represens a ime series (dynamic series); his series will be submied o a subsequen processing. Θ B Φ B he ransfer funcion of a linear filer, we can wrie: Z If we noe ( ) ( ) Θ () ( B) Θ = = Φ( B) Φ Θ Φ... Θ... Φ q p In according o he relaion() he ime series {Z } can be inerpreed as being he exi of he linear filer and he values {a } he inpu of he filer. Θ(B) represens an auoregressive operaor(ar), and Φ(B) a sliding average operaor(ma), in case of a parameric model of he process; B is a delay sep operaor, given by relaion: B Z = Z () The relaion () allows us o represen he curren values of he dynamic-random process by is previous values and by a curren and previous values of he whie noise. The problem is o deermine some parameric models, such as (), for he analyzed process, named ARMA models. Afer he sage of choosing he opimum model, i follows he sage of parameers esimaion. Then, he model is submied o a validaion procedure and, finally, o a predicion sage. The predicion procedure is a shor ime horizon and offers precious informaion abou he mos probable evoluion of he compuers sabiliy in he disurbing environmen. 3. The sages of he mehod Pracically, he main sages of his mehodology are he following: Sage. Model idenificaion In his sage i used wo measuring insrumens o analyze he saisic independence beween daa of series: he auocorrelaion esimaed funcion facr and he parial auocorrelaion esimaed funcion facrp. In order o express he saisic relaion beween he daa of series, Box and Jenkins suggesed a family of models ARMA (p, d, q)(p,d,q), where (p, d, q) refers he unseasonable characer of he model and (P, Q, D) he seasonable characer. These models are called Auoregresive and Sliding Average Models. The facr and facrp heoreical funcions are associaed o hese models. Finally, will be chosen ha model of he analyzed series for wich he esimaed funcions facr and facrp are closes o he heoreical funcions facr and facrp. The chosen of his model imposes o pass o he nex sages: esimaion of parameers and validaion of he model. Sage. Esimaion of he parameers We deermine, in his sage, he esimaed values for he parameers of he chosen model, in cerain condiions of saionariy and reversibiliy. If hese condiions are no fulfilled, he model will be rejeced. q p a ()

3 Sage 3.Validaion and diagnosis of he model The nex sage consiss of he validaion of he model. In oher erms, he chosen model mus o fulfill he qualiy procedure asked by Box-Jenkins mehodology. Sage 4. Predicion of he analyzed daa series The predicion problem assumes he obaining he fuure values (on a shor horizon of ime) of he iniial series, respecively {Z +, Z +, } values, condiioned by he daa of analyzed series ill he momen; his momen represens he origin of he predicion sage. 4. The implemenaion of he mehod In order o implemen he Box-Jenkins mehodology on board of he navy ship, he following sofware ools have been used: - he program-package TS-Sysem (Sysem idenificaion and parameers esimaion) [3]; - he program DAqS-DATA ACQUISITION SYSTEM [4], for daa acquisiion; - he program-package SELFTEST, for esing he suscepibiliy of he microcompuers(eut-equipmens Under Tes) a he complex elecromagneic disurbances [5]. Also, for acquisiion of he daa is used he process board ype IMP 3595 SOLARTRON INSTRUMENTS Ld., U.K.(0 channels, 0-0 µa, -V +V). The EUT (Equipmen under es) were consised of wo PC 486 compuers. The research was performed in wo sages. In he firs sage: he deerminaion of he suscepibiliy of he microcompuers a he global elecromagneic disurbances on board; in he second sage: he predicion of here suscepibiliy. Measuremens have been made for 0 operaing Modes of a navy ship, from saring he elecric generaors, up o he operaing he Navigaion Saions, Radar Saions, Radio Saions. The disribuion of daa for Mode 3 is presened in fig.. Fig.. Disribuion of daa for Mode 3 The values of auocorrelaion funcion for 0 values of he delay, as well as he value of he saisic es T show ha here is a correlaion in daa. The correlaion marix of he model coefficiens are presened in Table, for 5 Modes of operaion. 3

4 Table. Correlaion marix of he coefficiens No. mode Mode Mode Mode 3 Mode 4 Mode 5 Mode,000 Mode 0,9,000 Mode 3 0,94 0,863,000 Mode 4 0,96 0,860 0,988,000 Mode 5 0,96 0,880 0,987 0,976,000 I can see ha he raes of correlaion of daa have values beween 0,860 and 0,988, wha shows a srong correlaion of he signals in Mode 3. The some conclusions can be drawn if we analyze he specral densiy funcion (PSD). Table 3 shows he resul of model s parameers esimaion. Table 3. Coefficien Esimaed Sandard Value of Low limi Upp limi Value Error T-es Phi -0,3 0,088 -,63-0,407-0,055 Thea 0,79 0,06,0 0,608 0,850 Thea 0 0,700 0,056,777 0,590 0,809 Consequenly his signal can be pu in he form of some parameric models, such as (3): 0 0 ( Φ ) Z = ( B ) ( Θ )( Θ B ) a 0, (3) respecively: 0 0 ( 0,3B) Z = ( B ) ( 0,79B) ( 0,700B ) a + (4) The specral densiy funcion (fig. 3) shows ha he analyzed series can be pu in a Box- Jenkins model. Fig. 3. The specral densiy funcion 4

5 The resuls of validaion sage of he model poin ou ha i passes he es made on he bases of residues analysis. I can pass o he predicion of daa series. The predicion of daa evoluion, performed on he bases of he choused model was made on a 0 values horizon (ogeher wih 50 values of he iniial series) (fig. 4). Fig.4. The Predicion of daa series The rus limis (Upp and Low) are given wih 95% probabiliy. Noe. For his model have been used: 9 ieraions; number of available daa = 00 Conclusions During 0 experimens, he compuers under es have normally behaved. However i is possible ha oher regimes of working o affec heir behaviour. The obained resuls demonsraed ha he elecromagneic inerference in case of elecronic microcompuers can be pu in parameric models and can be predic by means of his mehodology; more of his, here are a qualiaive mehod and a sofware suppor o implemen is, wih favorable implicaions in he anidisurbance proecion sraegy of navy ship. References [] Soir Alexandru, A mehod for he analyse of he behavior a he elecromagneic disurbances on heir whole of he elecronic microcompuers, A paened invenion, OSIM, nr. 60/997, Buchares, [] Popescu Theodor, Time series. Applicaion in he sysems analyse, Technical Publishing House, Buchares, 00. [3] ***, TS-SYSTEM/D Pack-Program package: Sysem idenificaion and parameers esimaion, Research Insiue in Informaics, Buchares, 990. [4] *** Doq S-Daa Acquisiions Sysem-Program package for process boards ne S-NET, 5

6 Solarron Insrumens Ld., U.K., Research Insiue in Informaics, Buchares, 990. [5] Soir A., Balan T., SELFTEST-Program pacquage for compuers auoesing, Naval Academy in Research Insiue in Informaics, Buchares,