Energia Statica

5/27/2018 Energia Statica

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CERCETRI ASUPRA NCRCRII ELECTROSTATICE N NCPERILEDE LUCRU DIN ELECTRONICI CALCULATOARE

RESEARCHES REGARDING THE ELECTROSTATIC CHARGE INELECTRONIC INDUSTRY'S WORKING ROOMS

Angela ANTONIUUniversity of Alberta, Canada

[email protected]

Mihai ANTOIUTechnical University of Iasi, Romania

Bd. D.Mangeron 53 Iasi, [email protected]

Critian FOALUTechnical University of Iasi, Romania


Liviu MATEITechnical University of Iasi, Romania


Arhon FORINTechnical University of Iasi, Romania


Rezumat: n lucrare se analizeaznivelul ncrcrii electrostaticee operatorul uman (P) pentru 3 secvene de bazpe care P learcurgentr-oncperedelucrudinindustriaelectronic:mersul peardosealelectroizolant, dezbrcarea unei piese de vestimentaie

(flanel), i la lucru stnd pe un scaun tapetat cuesturi sintetice.Msurrile, efectuate n condiii normale de lucru (22 Ci RH =50 %), aratcenergia electrostaticacumulatn cele 3 secveneeste important(i nociv), mergnd de la 1 mJ pnla 12,5 mJ,ceea ce impune luarea unor precauii (descrcarea lui P la masa delucru etc.), ce sunt analizate pentru fiecare din cele 3 activiti.

Keywords: operator uman, ncrcare electrostatic

Abstract:The paper analyzes human operator's electrostaticcharging for 3 basic activities in electronic industry work area:walking on insulator carpet, taking clothes off or on and sittingon a synthetic textile covered chair. Our measurements, in normalconditions (22 C, RH = 50 %), indicate that the electrostaticenergy accumulated on these 3 activities is important (andharmful), starting from 1 mJ to 12.5 mJ. This implies somecautions to be taken (personnel grounding, etc.). These cautionswill be analyzed for each of those 3 activities.

Keywords:human operator, electrostatic charging

1. IntroducereIndustria electronicdedicatinstrumentaiei i calculatoa-

relor, fiind bazatpe circuite integrate (IC) de tip CMOS, nre-gistreazpierderi importante att la fabricarea ct i n exploatarea

produselor respective, pierderi cauzate de sarcinile electrice (q) cese acumuleazn timpul lucrului pe operatorul uman precum i pemobilierul din ncperea de lucru [1, 6, 8]. Aceste sarcini (q) pot

provoca efecte nocive, att direct (strpungerea etajului de intrarela IC, etc.), ct i indirecte (bascularea falsla IC numerice).Primele se numesc defecte de tip hard, iar ultimele defectede tip soft [3, 4, 11]. n lucrarea de fase au n vedere numaidefectele de tip hard, cele mai frecvente i mai costisitoare.

Defectele de tip hard se datoresc, n principal, descrcrilorelectrostatice (ESD) care pot aprea cnd, de exemplu, persoana

operator uman (P) apropie un deget de un element electronic

sensibil (integrat CMOS, microprocesor etc.). Dei nocivitateasarcinilor electrostatice (q) este tot mai insistent cercetat, n ulti-mul timp [1, 4, 6, 7, 8, 11], se constatcmijloacele de proteciempotriva lui q (ce pot fi luate de fabricant i utilizator) rmnmereu n urma progresului rapid n domeniul circuitelor LSI(reducerea grosimii la cile de curent i la izolaia dintre ele etc.)

precum i n domeniul carcaselor de aparate i al mobilierului(generalizarea maselor plastice, materiale puternic electrizabile).

Plecnd de la aceste constatri i innd seama cn industriaelectronici n cea a calculatoarelor principalul generatorde qeste P, autorii au ntreprins unele cercetri legate de ncrca-rea electrostatica lui P n condiiile concrete ale unei ncperin care se lucreazcu componente electronice: mersul lui P, nncpere, spre masa de lucru, dezechiparea de hainele obinuitei lucrul la mas. Rezultatele sunt consemnate n lucrare.

1. IntroductionThe electronic industry dedicated for instrumentation and

computers, being based on CMOS type integrated circuits(IC) records important losses both in fabrication process and

products handling. These losses are caused by electrostaticcharge (q) that is accumulated during the work process both onhuman operator and on workspace furniture. These charges (q)can produce both direct damage (breakdown of input circuit,etc.) and indirect failure (false flip-flopping on digital IC,etc.). First ones are named hard damage, and the other softdamage. [3, 4, 11]. Our paper presents only hard damagesthat are most frequent and more expansive.

The hard damage are caused, usually, by electrostaticdischarge (ESD) that can occur when the human operatorcome to touch a sensitive electronic component (CMOS IC,

microprocessor, etc.). Although, the research in electrostaticcharge harmfulness is developing [1, 4, 6, 7, 8, 11], it can benoted that the protection methods against ESD (at manufactureror user) seem to be a step behind of faster LSI circuits developing(which means thinner current paths and smaller distance

between them, etc.) as well as of using of plastic materialsfor apparatus case and furniture that are easy chargeable.

Starting from these considerations, and considering thatin the electronic industry, the main q generator is thehuman operator (P), the authors have made some researcheson human operator electrostatic charging using real conditionsof a work space where are invloved ESD senitive components,as: Ps walking to the working table, taking off clothesaction, and common work at the table. The results of theseresearches are presented in this work.


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The 5thInternational Power Systems Conference28

S-a cercetat i nivelul de electrizare al mobilierului precumi al carcasei aparatelor (instrumentaie, PC-uri etc.). Rezultatelecercetrilor vor fi comunicate ntr-o lucrare viitoare.

The authors also, researched the charging level on furnitureand apparatus case (instrumentation, PC, etc.). The results oour research will be presented in a future paper.

2. Despre electrizarea operatorului uman2.1. Fenomene fizice de baz

n industria electronic, principalele fenomene care ducla ncrcarea electrostatic a operatorului uman (P) sunt:electrizarea prin contact i electrizarea prin frecare.

2.1.1. Electrizarea prin contactCnd doucorpuri electroizolante A i B (talpa, T, a ncl-

mintei lui P i un covor din PVC, de ex.) sunt puse n contact(fig.1a) are loc un schimb de electroni pncnd se ajunge laechilibru. DacA pierde electroni el se ncarcpozitiv (+),iar B (primind electroni) se ncarcnegativ (-). DacA esteseparat rapid de B (fig.1b), A rmne ncrcat +, iar B -.

n fine, situaia nu se schimbdacA mai pstreaz(saurevine) un punct de contact (fig.1c). Fazele prezentate n fig.1aratelectrizarea lui P la mersul pe o pardoseal electroizolant(PVC, de ex.). ns trebuie de reinut c electrizarea princontact nu e un fenomen pur, ci este asociat ntotdeauna cuelectrizarea prin frecare (aspect mai evident n fig.1c).

2. On human operator charging2.1. Basic phenomena

The main phenomena in electronic industry due tohuman operator charging are: contact charging and frictionalcharging (tribocharging).

2.1.1. The contact chargingWhen two insulator materials A and B (operators shoe-

sole and a PVC carpet) come to contact (fig. 1a), an electronschanging process occur until the electrical balance is done. IA loses electrons it will be positive charged (+) and B (thatreceives these electrons) will be negative charged (-). If A is fastseparated from B, A remains positive charged and B negative.

Finally, if A keeps a contact point (or touch again) with B(fig.1c), the charging will be the same. Fig. 1 presents thesteps of charging for a human operator walking on PVCinsulator carpet. We have to notice that contact charging isnta real pure phenomenon but it is always accompanied with atribocharging (fig. 1c)

a)

A

B

T

PVC

A

B

b)

AB

c)

Fig. 1. Electrizarea tlpii nclmintei (T):a, b) prin contact c)prin frecareFig. 1. The shoe-sole charging: a,b) by contact c) tribocharging

2.1.2. Electri zarea pri n f recare

Dacdoucorpurielectroizolante(AiB)sefreacntreele,unul pierde electroni (deci se ncarcpozitiv), iar altul acceptelectroni (deci se ncarcnegativ). Electrizarea prin frecareconstituie cea mai importantsursde sarcini electrice (q) nociven industria electronic. n afarde mersul lui P pe o pardoseal

(fig. 1) triboelec-trizarea n acest domeniu mai apare la:dezechipatul i mbrcatul hainelor (sacouri i flanele dinfibre sintetice, etc.) la locul de lucru

tergerea de praf cu o crp uscat a mobilierului i acarcasei la aparatele i calculatoarele din ncperea de lucru.

Nocivitatea sarcinilor triboelectrice constn aceea c, maiales n cazul lui P, pot genera tensiuni mari (5-15 kV), periculoase

pentru componentele electronice sensibile (IC CMOS, micropro-cesoare etc.). Nnivelul de ncrcare triboelectricdepinde i dedistana dintre A i B n seria triboelectric[8, 11, 14].

Observaie.Triboelectrizarea se produce i cnd unul dincorpuri(deex.Bfig.1)estemetalic.Aceastsituaiesentl-nete,deexemplu,cndPtergepensetacuocrpuscat.

Exemplede triboelectrizaren fig. 2a se aratmodul tipic de electrizare a unui P care

pete pe un covor electroizolant (EP) spre locul de lucru. Seobservcpe vestimentaia acestuia pot saparsarcini attpozitivectinegativenfunciedematerialeleprilorcevinncontact (vestimentaie, nclri, pardoseal). De reinut cla un P,sarcinile se acumuleaznumai pe mbrcmintea i nclri,iar corpul propriu-zis (mediu conductor) servete numai latransmiterea (spre degete) a sarcinilor respective (fig. 2b).

Fig. 2b prezintmodul tipic de triboelectrizare a lui P la loculde lucru. Aici electrizarea se produce din cauza micilor frecrifade scaun, precum i a tlpilor nclmintei pe pardosealaelectroizolant(CP). La aceastncrcare se poate aduga i cea

primitla mersul spre locul de lucru (fig. 2a) aa nct ntre dege-tele operatorului i o borna aparatului de msur (AM) poateaprea o descrcare prin scnteie (ESD), neplcutpentru P i(posibil) destruc-tivpentru obiectul de lucru (AM, PC etc.).

2.1.2. Tribocharging

When two insulator materials (A and B) are rubbing, onelosses electrons (becoming positive charged) and the otheraccepts these electrons (becoming negative charged). Thetribocharging represents the most harmful electric chargesource in electronic industry. In this realm the tribocharging

may occur: Walking on insulator floor-coverings Taking on or off clothes with synthetical fibers Wipe furniture or apparatus case using dry duster

The harmfulness of tribocharges resides in that,especially for human operator, it may generate high voltage(5-15 kV), which are very dangerous for sensitive electroniccomponents (CMOS IC, micro-processors, etc). It has to benoted that tribocharging amount depends on distance

between A and B in triboelectric seria [8, 11, 14].ote. A tribocharging will also occur when B is metallic

(when P wipes a metallic tool with a dry duster).Examples of P's tribocharging

Fig.2 presents the P's typical charging manner when he iswalking on an insulator floor-covering in his way to the

working place. It can be noted that on his clothes may appearcharges both positive and negative depending on the fabricparts that came in touch (clothes, shoes, floor). Here isimportant to keep in mind that for a person P the charges areaccumulated only on its shoes and clothes, and Ps body(conductive area) serves only for the charge transmission

process (through the fingers) (fig.2b).Fig.2b shows the P's tribocharging typical way at working

place. Here the charging occurs due the robs with the chair, aswell as shoes-soles on the insulator floor-covering (CP). Thischarge is added by the one received walking to the working area(fig.2a),sobetweenhumanoperator'sfingerandameasuringappa-ratus terminal may occur an electrostatic discharge (ESD), un-

pleasantforPanddamagingfortheworkingobject(AM,PCetc.).


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06-07.11.2003, Timioara, Romania 29

100-200pF

1-2 k

c)a)

5-10 kV

Rp

Up

Cpqp

EAM

C P

PP

C PG

T

b )

Fig. 2. Moduri tipice de electrizare aunei persoane (P): a) la mers b) la

masa de lucru c) modelul electrostatic

Fig.2. Typical way for operator'scharging: a) walking b) at workplace

c) human body model

n fine, trebuie de subliniat co triboelectrizare puternic(peste 5-15 kV) a lui P poate aprea la dezechiparea i echiparean haine de lucru, nivelul ncrcrii depinznd de viteza de echi-

pare i de poziia materialelor din haine n seria triboelectric.

2.1.3. Alte situaii de electrizare n tehnologia electronicn afarde electrizarea prin contact i frecare, n industria

electronici ce a calculatoarelor pot aprea sarcini electrice:prin inducie, prin ionizare i mai rar prin ncrcare direct.a) Electrizarea prin inducie (influen)

Cnduncorp(A)ncrcatcusarcin+seapropiedeuncorpmetalic (B), izolat fade pmnt (fig. 3a), atunci pe partea (B1)situatspre A apar sarcini de semn contrar (adic-), iar pe ceaopus(B2) sarcini de acelai semn (adic+). La ndeprtarea lui

A fade B sarcinile induse n B se micoreazpnla dispariie.n electronic, inducia electrostaticapare cnd, de exemplu,P (electrizat fiind) apropie un deget, F, (sau o sculmetalic)de un integrat (IC, fig. 3b). Cnd intensitatea cmpului electric(U - tensiunea dintre A i B, d distana dintre A i B):

d

UE= (1)

este mare (500-1000 kV/m) i daccellalt terminal a lui Beste legat la pmnt, ntre A i B se poate amorsa o descrcare

prin scnteie (ESD) carepoate cauza strpungerea integratului(prin tensiune induspe terminal sau prin curentul de descrcare).

Finnaly, it must be noted that a P's powerful tribocharging(over 5-15 kV) may occur at its taking clothes off and on, thetribocharging level depending on the speed of P's actions andits clothes fabrics position in the tribo- seria.

2.1.3 Others charging situations in electronic industryBesides the contact charging and tribocharging, in

electronic and PC's industry may occur also electric chargesdue: induction phenomenon, ionization and direct charging.a) Induction charging

When a body A, positive charged, comes near to a metallicnon-grounded body (B) (fig 3.1) then the B1side, positionednear to A, occurs negative charging and onto the other sideB2 occurs positive charging. If A is moved away from B, the

inducted charges on B decreases to 0.In electronic industry the induction charging phenomenonoccurs, for instance, when P (being charged) aproach hisforefinger, F, (or a metallic tool) to an integrated circuit (IC,fig.3b). When the electric field intensity (between A and B) :

d

UE= (1)

is big (5001000 kV/m) and the IC has a grounded pin (fig.3c)then between A and B may occur a sparkling ESD. Thisdischarge may cause the IC damage (due the voltage inducedon a pin or the discharge current).

B1

a)

B2

BA F

A B

IC

b)

F

AB

IC

c)

EId

Fig. 3. Electrizarea prin induciea) fenomen b) i c) situaii practice

Fig. 3. Induction charging a) phe-nomenon b) and c) practical examples

b) Electrizarea prin ionizare[1, 2, 14]n tehnologia electronic electrizarea obiectelor electro-

izolante prin ionizare are loc, de regul, la masa de montaj ncazul (aproape general) cnd se folosesc ionizatoare pentrureducerea nivelului de ncrcare electrostatica pieselor mnuiten timpul lucrului. Dacsarcinile electrice date de ionizator nusunt de semn contrar celor aflate pe piesele n discuie, atunciacestea se adaugcelor aflate pe piesele deja ncrcate i ncarc

piesele neutre. Tensiunile ce pot apare pe piesele (IC etc.)aflate pe masa de lucru, din cauza ionizrii pot depi uor100-200 V i deci nu trebuie ignorate.

c) Electrizarea prin ncrcare direct[1, 14]Fenomenul are loc cnd un obiect cu structurcapacitiv

(P, IC etc.) vine n contact cu o sursde sarcini electrice (con-densator ncrcat), sau cu o sursde tensiune continu. O astfelde ncrcare poate fi evitat(sau atenuat) prin precauiiadecvate (descrcarea prealabila sursei de sarcini i respectivcreterea impedanei fade sursa de tensiune).

b) Ionization charging [1, 2, 14]In electronic industry the insulated objects charging due

the ionization process occurs at the manufacturing area whereionisators are used for a charge level reduction onto the handled

parts during the work time. If the electric charges providedby ionisator do not have the opposite sign to the existing chargesthen the ionisator' s charges are added to the ones onto thecharged parts or uncharged parts that in this way becamecharged too. The drop voltages that may occur on the parts(IC, etc) from the working area due the ionization processhave big values (100-200 V) and can't be ignored.

c) Direct charging[1, 14]Thephenomenonoccurswhenacapacitancestructureobject

(P, IC) comes in touch with an electric charges source (chargedcapacitance) or a continuous voltage source. This type ocharging can be avoided (or lowered) taking right cautions (asan electric charge source emptying process or an increasedimpedance).

2.1.4. Modelarea operatorului umanPentrumodelareaelectricaoperatoruluiuman(P)standard,

adicnclatistndcutalpanclmintei(T)peuncovor(CP)aezat pe sol (G, fid. 2a) s-au propus diverse scheme [1, 4, 6, 7,8, 11, 12]. Dintre acestea cea mai simpl(i mai des folosit) esteceadinfig.2c[1,8].Pefigur,Rreprezintrezistenaechivalenta corpului propriu-zis (mediu conductor de tip electrolit), iar C -capacitateaechivalentaluiP.Aceastadinurmestecompusdincapacitatea dintre nclri i pmnt (CTG) i din capacitatea

2.1.4. On human body modelThere were proposed different diagram [1, 4, 6, 7, 8, 11, 12]

for electric model of the standard human operator (P). Standardhuman operator is the one who has his shoes on, is staying withhis shoe-sole (T) on an insulator floor-coverings (CP) placed onthe ground, (G .2a). The simplest diagram is the one illustratedin fig.2c [1, 8]. Here RP represents the equivalent resistance othe body (electrolyte type conductive medium) and CP the P'sequivalent capacitance. The last one contains the capacitance


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corpului lui P (mbrcat) fade pmnt, consideratdrept capa-citatea unei sfere avnd suprafaa egalcu cea a corpului lui P).

Cpvariazn limite largi (100-250 pF) n funcie de mate-rialul tlpilor (T) i al covorului (CP), precum i de greutatealui P [8, 10]. nsn calcule se considervaloarea standard:C = 200 pF (i R = 1,5 k), iar n testele experimentale,C se msoar. Cunoscnd pe C i pe q (sarcina acumulatn C ) se poate calcula tensiunea la "bornele" lui P cu ajutorulrelaiei cunoscute:

pp UCq = (2)precum i energia electrostaticacumulatn Cp:

22

2

1

2

1

2ppP

P

UCUqC

qW === (3)

n practic, se msoarUpi Cp, iar qse calculeaz.

between its shoes and ground (CTG) as well as P's (dressed)body capa-citance reported to the ground, (being assumed ascapacitance of a sphere with surface as big as P's body surface).

CP varies in large limits (100-250 pF) depending on solesmaterial (T) and floor-covering type (CP) as well as P's weight[8, 10]. But for theoretical calculus we will use the standard value:CP = 200 pF (RP = 1,5 K), and for the experimental tests CP ismeasured. Knowing CP and q (the accumulated charge in CP)it can be derived the voltage at P's "terminals" using the relation:

pp UCq = (2)as well as charging accumulated energy of CP:

22

2

1

2

1

2ppP

P

UCUqC

qW === (3)

In practice, firstly UP and CP is measured then q is computed.

Rv=1014

Cv=10pF

b)a) T

G

P

covor - carpet

tabl(IS)iron sheet

sol - base

ESVSL

G

ESV

SLRCP

RT

RP

CP

Sq

UP

P

q

UP

Fig. 4. Metodde msurare atensiunii UPpropusde autori:

a) aranjament b) schemechivalent

Fig.4. Proposed method for Upvoltage measurements: a) physical

setup b) equivalent diagram

3. Cercetri asupra electrizrii operatorului uman lamersul pe covor electroizolantDei q a lui P la mersul pe covor electroizolant (CP) poate fi

analizati teoretic [4, 5, 12], calculele respective sunt labori-oase, iar rezultatele nu sunt concludente, din cauza variabilitii

parametrilor (R, C etc.) ce intrn joc. O cale mai simpli maieconomicconstn abordarea pe cale experimental[6, 8, 9,10], pe care vom merge n cele ce urmeaz.

3.1. Alegerea metodei de msurare3.1.1. Metoda clasic

Scurtprezentare n aceastmetod, P este puspusspeascpe un CP care la rndu-i este aezat pe o coalde tablde fier (IS) legatla pmnt (G), la fel ca n fig.4a. n timpultestului, P este conectat la un voltmetru electrostatic (ESV) cuajutorul unui cablu coaxial suplu (CX). Firul cald este legat laun electrod metalic inut n mnde ctre P, ceea ce permite catensiunea de la "bornele" lui P sfie transmisla ESV (CX iESV sunt omise din fig.4a; poziia lor poate fi gsitn [10]).

P pete pe CP cu o cadenconstant(tipic 2 pai /sec),iar ESV indic tensiunea U ce apare la bornele capacitiitotale: C = Cp+ Ccx+ Cv, deoarece capacitatea lui P (Cp), acoaxialului (Ccx) i a voltmetrului (Cv) se plaseazn paralel.

Neajunsuri. Principalul neajuns constn prezena lui CXntre P i ESV, prezence duce la douconsecine negative:a) CapacitateaCcx(500-600 F) este mult mai mare dect Cp

(200 pF) ceea ce face ca U, indicatde ctre ESV, sfiemult mai micdect U(mrimea cutat). Din (2) i (4) se

poate calcula U nsoperaia de msurare pierde din vitezade informare asupra evoluiei lui Upn timpul testului.

cxpvcxpp CCCCCUq ,


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Deosebirea constn faptul c, tensiunea U este msuratdirect la "bornele" lui P, cu un ESV, aa cum se aratn fig. 4a.Se observci aici e necesaro legtursupl, o srmliat(SL) ce conecteazla pmnt (G), borna de masa lui ESV.nsSL nu intervine n nici un fel n ecuaia msurrii lui U ,ceea ce constituie principalul avantaj al metodei propuse.

n fig. 4b se aratschema electricechivalenta aranjamen-tului din fig. 4a. Se observcCp, capacitatea proprie a lui P(fig. 2c) se ncarc, de la Sq, prin rezistena tlpilor lui P (RT),

nseriatcu rezistena lui P (Rp = 1,5 k), careeste neglijabilfadeRT

(109-1012),iarS sedescarc(la pmnt) prin rezistenacovorului (RCP), ce este de acelai ordin de mrime cu RT (daradesea superioaracesteia). n schemSqreprezintsursa desarcinelectric(q), ce ia natere la frecarea tlpii nclmintei(T) de covorul electroizolant (CP) n timpul pirii lui P.

Voltmetrul electrostatic (ESV) este de tip moric[3, 11, 14]i are urmtoarele caracteristici: tensiuni nominale: 0,2; 2 i 20 kV,rezistende intrareRv> 10

14, Cv= 10 pF, rezoluie 3 % (c.s.).

RezultcRv>>(RCP+RT)icCv> 10 pF, resolution3 % (EOS- the end of scale). Starting from here,RV>>Rcp +Rand CV


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apoi se trece K pe poziia b, cnd tensiunea cititla ESV scadela valoarea U. Capacitatea cutatse calculeazcu relaia:

10 =

UU

CCP (6)

S-au efectuat cte 3 msurri pentru ambele tipuri de covoare(CP1i CP2), lundu-se media citirilor. Rezultatele sunt trecuten tabelul 2. Datele din tabel aratcvaloarea cea mai marea lui Cpapare la combinaia talpde piele (T1) pe covor (CP1)

de PVC i cvaloarea cea mai micse obine pentru combinaiatalpde cauciuc (T2) pe covor pe polipropilen(CP2).

decreased voltage Uindicated by ESV. The searched capacitancecan be derived with:

10 =

UU

CCP (6)

It was performed 3 measurements for both carpet types(CP1 and CP2) and as result was taken the average. The resultsare shown in table 2. The table 2 data show that the CPgreatervalue occurs at the skin sole (T1) on PVC carpet (CP1)

combination and the CP smaller value can be attained at therubber sole (T2) on polypropylene carpet (CP2) combination.

Tabelul 1 Valorile rezistenei de izolaie la nclri i covoare de testTable 1 Insulation resistance of test shoes and floor-coverings

Material R T1 RT2 Rcp1 Rcp2Rezistance () 3 109 5 1011 5 1010 2 1012

Tabelul 2 Valorile capacitii om/covor (Cp) n situaiile de testTable 2 Person/floor-covering Capacitance (Cp)

Material R T1 RT2 Rcp1 Rcp2Resistance () 3 109 5 1011 5 1010 2 1012

U0 C

a

k

CP

1

2

RCP

U

ESV U0 C

a

k

U

ESV

P

CP

IS

G

Fig.5. Schema de msura rezistenei (RCP) a covoruluiESV - voltmetru electrostatic, C - condensator cunoscutFig.5. Diagram of carpet resistance (RCP) measurement

ESV - electrostatic voltmeter C - known capacitor

Fig.6. Msurarea capacitii (CP) a sistemului om (P) pe covor (CP)Fig.6. Measurement of capacitance (C ) between person (P) and

carpet (CP)

3.2.2. Msurarea ncrcrii electrostatice a operatoruluiuman la mersul pe covor electroizolant

3.2.2.1. Unele consideraii teoreticeAranjamentul utilizat pentru msurarea ncrcrii electro-

statice a lui P la mersul pe covor electroizolant (CP) este cel

din fig. 4a cruia i corespunde schema echivalentdin fig. 4b.La fiecare pas a lui P (dezlipirea tlpii de covor, fig. 1b),Cpse ncarcprin rezistena tlpii (RT) dupecuaia cunoscut:

)1( PTCRt

PmPi eUu

= (7)

n care

iPTCR = (8)

este constanta de timp, iar Upm valoarea maximce o poateatinge UP (fig.7). n intervalul dintre 2 pai (fig. 1b), CP sedescarcprin rezistena covorului (RCP) dupecuaia:

PCPCR

t

PmPd eUu

= (9)

n care

dPCPCR = (10)

este constanta de timp la descrcare.Din analiza ecuaiilor (7) i (9) rezultcdac:

CPT RR > (11)

P nu se poate ncrca (sau se ncarcmai puin dect n cazulRT< Rcp), deoarece viteza de descrcare a lui Cpeste mai maredect viteza de ncrcare a acestuia. Examinnd datele din tab. 1se constatcsituaia: tlpi de cauciuc (RT2) pe covor din PVC(Rcp1) ndeplinete condiia (11). Acest lucru aratc(teoretic)

pentru pardoseala din PVC, nclmintea cea mai adecvatestecea cu talpde cauciuc. Condiia (11) mai aratcsituaia ceamai defavorabil(ncrcarea cea mai mare) o constituie: mersulcu tlpi de piele artificial(RT1) pe un covor tip mochet(Rcp2).

Din acest motiv situaia RT1/Rcp2 va fi examinat maiamnunit la partea experimental.

3.2.2. On human operator charging at walking on aninsulator carpet

3.2.2.1. Theoretical considerationsThe physical setup used for the P's charging measuring

process at his walking on an insulator floor-covering (CP) is

presented in fig.4a and its equivalent diagram is shown in fig.4b.At every P's step (the sole is lifted from the floor-covering)CPis charging via sole resistance (RT) using the known equation:

)1( PTCRt

PmPi eUu

= (7)

where

iPTCR = (8)

represents the time constant and UPm-the maximmum valueof UP (fig.7). Between two steps, CPis discharged via carpetresistanceRCPusing:

PCPCR

t

PmPd eUu

= (9)

where

dPCPCR = (10)

represents the discharging time constant.Using (7) and (9) we can derive that if

CPT RR > (11)

the human operator can not charge(or charging is smallerthan the case ofRT< Rc ). This is because the Cp dischargingspeed is greater than its charging speed. From table 1 it can benoted that the case: rubber sole (RT2) on PVC floor-covering(Rcp1) fulfill equation (11). These means that (theoretically)the most appropriate shoe for PVC floor-covering is the onewith rubber sole. Also, equation (11) reveals that the worstcase (the greatest charging) is to walk with artificial leathersole on moquette (Rcp2).

That is why the case RT1/Rcp2will be carefully analyzedin our experiments.


7/12


3.2.2.2. Condiii de experimentarea) Aranjamentul experimental

Aranjamentul experimental utilizat de ctre autori estecel din fig. 4a, iar experimentrile s-au efectuat n aceeaisali n aceleai condiii climatice ca la 3.1.2b. Lungimeacovoarelor de test a fost, la ambele tipuri (CP1i CP2), de 8 m.

n scopul de a micora rezistena de contact dintre pieleatlpiiluiPitalpanclmintei(T)s-arecurslaumezireauoara primei. n acelai scop s-a umezit uor i palma n careoperatorul ine electrodul de intrare la ESV. Operaia a maiavut ca scop i simularea situaiei cnd P este uor transpirat.

b) Cadena pailor persoanei de testDurata unui pas la mersul unei persoane este timpul (TP)scurs din momentul desprinderii tlpii de covor pn nmomentul revenirii acesteia pe covor.

Pentru ridicarea curbelor experimentale Up(t) este avantajosa se alege un Tastfel nct la captul acestuia, Cpsse descarcect mai puin. Acest deziderat poate fi exprimat prin condiia:

T


8/12


frecarea la mersul pe mocheteste mai mare dect la mersul pePVC. La mers cu pai trii(curba 2) tensiunea Up este multmaimare(dubl)fademersulnormal,ceeaceimpuneevitareaacestui stil de mers, prin instruirea corespunztoare a lui P.

friction that is greater in the carpet case. In lazy walking case(curve 2) UP is bigger compared with normal walking case, andis recommended to be avoided, by human operator's training.

Up(t)Upm

2,5

2

1,5

0

0,51

3 6 9 12 15 2118 24

t(sec)

Up(kV)

b

10

8

6

0

2

4

3 6 9 12 15 18

t(sec)

Up(kV)

a

Mers normal (normal walk)

Mers cu pai trii

(lazy walk)

Fig. 7. Curba tensiunii (Up) la mersul cu tlpide piele artificialpe covor de PVC

Fig. 7. Curve of Upvoltage for walking with soleof artificial leather on PVC floor-covering

Fig. 8. Curbele tensiunii (Up) la mersul cu tlpi depiele artificial. pe covor tip mochet

Fig. 8. Curves of Upvoltages for walking with soleof artificial leather on carpet

Observaii1. Testele au fost efectuate pe mochetde polipropilennetratat

antistatic, deoarece n comer se gsete numai aceastvariant. Mocheta antistatizat, dei se ncarc mult mai

puin, nu e preferatde cei care amenajeazncperi pentru

lucru cu calculatoare, deoarece este mai scump, se gsetemai greu i, n plus, antistatizarea se pierde n timp.2.ncrcrile la mersul pe mochet(fig. 8) sunt mari i pot duce

la descrcri electrostatice (prin operator) care sunt nocivepentru circuitele electronice sensibile. De exemplu, considerndCp= 200 pF, la mersul normal (Upm= 5 kV), conform cu (3),energia la descrcare este W= 2,5 mJ, iar la mersul cu paitrii (Upm10 kV) atinge 10 mJ, valori (mai ales ultima)suficiente pentru a provoca defecte de tip hard (strpungeride IC tip CMOS, microprocesoare) precum i erori de tip soft(basculrieronatealecircuitelornumerice).Acestedefectepotaprea i la mersul pe pardosealPVC, deoarece la Cp = 200 pFiUpm=3,2kV(fig.7)energiapusnjoc:1mJpoateprovocadefecte de tip hard i soft. n plus dacdescrcarea se face

prin scnteie, aceasta poate provoca aprinderea unor vapori

inflamabili (vapori de lac electroizolant etc.) deoarece pragulde inflamabilitate este 0,25 mJ [10, 11].

Notes:1. These tests were done using a polypropylene carpet, untreated

antistatic, because in romanian market this is the only typeavailable. Although antistatic treated carpet is less chargeable,it is not preferred by the PC workrooms designers due the

higher price and because it loose the antistatic features duringa period.2. The charging values at walking on the carpet (fig.8) are

important and may cause electrostatic discharge (via operator)that is harmfull for sensible electronic devices. For instance,assumingCP=200pFinthenormalwalkingcase(UPm5kV)according with (3) the charging energy is 2,5 mJ and in lazywalking case (UP 10 kV) increases to 10 mJ, values thatcouldgenerate(speciallyinthelastcase)harddamage(CMOSor P chips breakdown) and soft errors (false flip-flops atdigital circuits). These damages could occur for PVC floor-covering, too. In this case, if C= 200 pF and Up = 3.2 kV(fig. 7) the energy will be W= 1 mJ, enogh to generate harddamage or soft errors. If the discharge is sparkling, it couldgenerate explosion of flammable vapors (from electro-

insulating paint) because flammability minim value is0.25 mJ [10, 11].

ESV

BF

C U1

q1

ESC

ESV

CX

FC

C U2

q2

ESC

GP -q

GP

Fig. 9 Metoda directde msurare a ncrcrii la dezechipareFig.9. Direct method of charging measurement

Fig. 10 Metoda indirectde msurare a ncrcrii la dezechipareFig. 10. Indirect method of charging measurement

4. Msurri asupra ncrcrii electrostatice a operatoruluiuman la dezechipareDup cum s-a mai afirmat, la dezechiparea lui P poate

aprea o ncrcare electrostatic(q) sensibil mai mare dectla mersul acestuia pe o pardosealelectroizolant.

4.1. Metoda de msurutilizatDeoarece la dezbrcarea unei piese de vestimentaie (flanel,

bluzetc.) P trebuie saibambele mini libere, nu se poateutiliza metoda din fig. 4 (P nu poate ine n mnelectrodul deintrare la ESV). De aceea, s-a recurs la msurarea lui q. Dintremetodelecunoscute[3,4,14]s-aalesceaancrcriicondensato-rului, iar msurarea lui q s-a fcut direct (q1) i indirect (q2).

4. Measurements on electrostatic charging due the takingclothes offAs we said before, when P takes off his clothes (a sweater

etc.) it could occur an electrostatic charging (q) greater thanthe one at walking on an insulating floor-covering.

4.1. Measuring methodBecause taking clothes off involves both hands of human

operator (P), the method used on fig. 4 cannot be used (P cannot hold the ESV electrode). So, we decide to measure thecharge (q) from different knwon methods [3, 4, 14] it was

preffered condenser charging method. The charge wasmeasured directly (q1) and indirectly (q2).


9/12


4.1.1. Msurarea ncrcrii prin metoda direct(q1)Schema aranjamentului de test este prezentatn fig. 9.

Msurarea lui q1se desfoarntr-o incintecranatelectro-static (ESC) i decurge n felul urmtor: P i scoate piesa devestimentaie(GP,flanel,deex.)ioaruncrapidntr-unrecipi-ent (fig. 10) dupcare, cu degetul arttor (F) atinge borna deintrare (B) a unui condensator cunoscut (C). Astfel, sarcina q1 ceapare la scoaterea lui GP se scurge practic complet n condensa-torul C, ceea ce face ca bornele acestuia saparo tensiune U1.Cum C este n paralel cu C , precum i cu capacitatea Cv(capacitatea de intrare a ESV), rezultecuaia msurrii:

),(;)( 11 CCCUCCq PVP


10/12


mrime mai mari dect cele de la mersul pe pardosealelectro-izolant, deci mai periculoase, ce impune luarea unor precauii.Cea mai simpli sigur, dupprerea autorilor, este ca dupdezechipareinaintedeapunemnapeoricedispozitivelectronicsensibil,operatorulsatingcuambeleminiunelectrodmetaliclegat la pmnt, descrcndu-se astfel aproape complet.

floor hence more dangerous, so are required some cautions.The simplest based on authors opinion is after stripping andafter device touching, the operator should touch with his

both hands a grounded electrode so the discharge will becomplete.

b) La msurarea indirectPentru msurarea indirect(q2) rezultatele sunt trecute n

fig.12.Dinexaminareaacestorarezultc,exceptndpersoaneleD i E, sarcinile electrice (q2) msurate sunt sistematic mai micidectceledinfig.11.Acestaspectpoatefiexplicatprinneglijarea

capacitilor coaxialului i a voltmetrului la deducerea expresiei(14). Faptul cn cazurile D i E s-a obinut q2 > q1poate fiexplicat prin electrizarea suplimentar a flanelei n timpulcderii acesteia n cilindrul 1 al FC (frecarea de peretele lui 1).c) Comparaie ntre q1i q2

Comparnd diagrama din fig. 11 cu cea din fig. 12 seconstatcdiferena: )()( 222111 EBAEBA qqqqqqq ++++++= LL (15)este de 5 %, valoare obinuitla msurrile n electrostatic(unde, se tie, dispersia rezultatelor este mult mai mare dectn cazul msurrilor altor mrimi electrice sau magnetice).

O concluzie. Pe baza valorii lui qdecurge o concluzieimportant: Testarea ncrcrii la dezbrcarea unei piese devestimentaie se poate face i numai prin msurarea lui q2 ,

operaie mai simpli mai uor controlabildect cea de lamsurarea lui q1 .

b) Indirect measuring caseIn the situation of indirect measuring (q2) the results are

illustrated in fig.12. Analyzing them, we can say that, exceptingDandEcases,themeasuredcharges(q2)arelowerincomparisonwith the ones shown in fig.11. This aspect may be explained i

the coaxial and voltmeter's capacitance from (14) are neglected.In D and E case it was attained the relation q2 > q1 due the

pullover additional charging during its fall into the cylinder 1of FC device (due the friction with 1's wall).c) Comparation q1versus q2

Comparing fig.11 and fig.12 it can be noticed that thedifference q: )()( 222111 EBAEBA qqqqqqq ++++++= LL (15)is 5%, a common value in electrostatic field (where theresults' dispersion is bigger than in electric or magnetic fielddispersion).

A conclusion. Based on the values of qwe can derivean important conclusion: The test of charging at takingclothes off can be made only using the q2's measuring

method, a simpler and easy controllable operation comparedwith q1's measuring method.

5. Msurarea ncrcrii operatorului uman la masa de lucruDup cum s-a artat la 1.2 (fig. 2b), operatorul uman

(P) la masa de lucru se ncarc electrostatic datoritfrecrilor de scaunul pe care st precum i la o eventualridicare de pe scaunul respectiv n timpul lucrului.

5.1. Contextul experimentalS-a folosit un scaun tapetat, cu partea platacoperitcu o

folie de vinilin. Scopul acestei folii (folositdin ce in ce maimult pentru protecia mecanica tapetului) a fost de a simulasituaia cea mai defavorabil, tiut fiind faptul cea se electri-zeazmai puternic dect estura de tapet.

Ca persoane de test s-au folosit aceleai 5 persoaneA E (studeni) din 4.2.1. Aceste persoane au fost echipatecu acelai tip de pantaloni: blugi din fire sintetice tip bumbac(piesde vestimentaie tipicla personalul tnr).

Ca metod de msur s-a folosit metoda ncrcriicondensatorului, ca n fig. 9, cu deosebirea cde aceastdat

persoana de test este aezatpe scaun ca n fig. 2b.Mersul msurrii. Persoana de test (P), n prealabil des-

crcatelectrostatic, se aeazpe scaunul de test n faa unuiobiect(calculator)aflatpemasadelucru.Dupaceeaserotetepescaun de 3 ori la dreapta i la stnga (pentru a simula micrileobinuitedintimpullucrului),iarnfinalseridicnpicioareiatinge cu degetul arttor (F) borna de intrare a condensatoruluicunoscut (C)(la fel ca n fig. 9). Dacvoltmetrul (ESV) indictensiunea U, sarcina necunoscutqse calculeazcu relaia:

UCCq P )( += (16)n care C i Cpau semnificaia din (13).

Pentru fiecare persoande test (A E) s-au efectuat cte3 msurri, considerndu-se ca rezultat media celor 3 msurri/

5.2. Rezultate obinuteDeoarece n acest caz ncrcarea electrostatica lui P este

influenati de greutatea corporala acestuia (BW), dispersiarezultatelor msurrii lui qeste mult mai mare dect n celelalte2 situaii anterioare (fig. 4 i 9). De aceea, rezultatele msurriiau fost prezentate n ordinea cresctoare a lui q. Sub indicele(A, ), la fiecare persoan, s-a menionat i BW-ul n kg.

5. On human operator charging at the working tableAs was shown in 1.2 (fig.2b), the human operator (P) at

his working place is charging due the frictions with the chairwhere he is sitting, as well as the lifting from his chair in hisactivity.

5.1 Experimental contextIt was used a textile tapestried chair with its plate side

covered by a vinyl foil. This foil, used for the tapestrymechanical protection, simulated the worst conditions becausethe vinyl foil is charging stronger than the textile tapestry.

As test persons (P) were used the same five persons A,

... E (students) as in 4.2.1. All the test personnel wereequipped with the same trousers type: synthetic fiber (cottontype) blue jeans (these are very common wear for the youngergeneration).

As measuring method was used the charging condensermethod as in fig.9, the main difference is the Ps position inthe chair, illustrated in fig.2b.

Measuring process . The test person (P), being staticallydischarged, sits on the test chair facing a PC from the workingtable. He rotates three times from left to right (simulatingusual moving on his chair during his ordinary activitity) andfinally stand up and his finger (F) touches the input terminalof the known condenser C (as it is shown in fig.9). If thevoltmeter (ESV) indicates the voltage U, the unknown chargeqcan be computed using:

UCCq P )( += (16)where Cand CPare the same as in (13).

For every test person (A, B, C, D, E) three measurementswas done and the final result was the average of them.

5.2 Final resultsAs long as the Ps charging is influenced by his body

weight (BW), the results dispersion of q measurements isgreater than the dispersion of previous two cases treated infig.4 and fig.9. That is why these results were ordered asincreasing values of q. Under the indicative A ... E the bodyweight (kg) was mentioned for each person.


11/12


Din examinarea datelor se desprind 2 constatri.1.ncrcarea q crete la creterea lui BW, cretere mai

pronunatn zona BW-urilor mici i mijlocii (50-70 kg)2. Nivelul ncrcrii q este mai redus dect la dezbrcatul

unei piese de vestimentaie, dar (dup cum se va arta)este mai mare dect la mersul pe pardoseal electroizo-lant. Aceste aspecte sunt prezentate n cele ce urmeaz.

5.3. Comparaie ntre ncrcri la cele 3 tipuri de activitiale lui P

Deoarece nivelul ncrcrii electrostatice la mersul pe par-

doseal electroizolant este exprimat prin tensiunea (Up) labornele operatorului, iar la dezechipare i la lucru stnd pescaun - prin sarcina electricacumulat(q), comparaia s-a fcutconvertind ambele mrimi n nivele de energie electrostatic(W), nivele calculabile cu relaii de forma (3), adic:

C

qWUCW

22

2

1;

2

1== (17)

La fiecare din cele trei tipuri de activiti efectuate dectre P s-a calculat nivelul maxim i cel minim al lui W. Lacalculul lui W pentru mersul pe mochets-a omis mersul cu

pai trii (fig. 8), ca fiind activitate anormala) Comparaie ntre nivelele minime ale energiei electrostatice

acumulaten fig. 14a se prezintnivelele minime ale energiei electro-

statice acumulate la efectuarea fiecrei din cele 3 secvene pecare operatorul le parcurge n timpul activitii ntr-o ncperede lucru: (1) mersul pe pardoseal electro-izolant (PVC),(2) - dezbrcarea unei piese de vestimentaie (flanel, n cazulanalizat) i (3) - lucrul obinuit stnd pe scaun.

Din examinarea acestor date rezultcnivelul cel mai micde ncrcare electrostatic(1 mJ) apare la mersul pe pardosealde PVC (1), iar cel mai mare (6,4 mJ) - dezbrcarea flanelei (2).La lucru stnd pe scaun (3), nivelul (2,4 mJ) ocupo poziieintermediar. Aceste date aratci n cazul cel mai favorabil(nivele minime de energie) energia acumulatpe operatoreste importanti poate produce defecte de tip hard i soft

precum i aprin-derea unor vapori inflamabili (pragul deinflamabilitate fiind 0,25 mJ).

De asemenea, din fig. 14a se poate observa csituaia cea

mai gravapare la dezbrcatul unei piese de vestimentaie (2),ceea ce impune tratarea cu atenia cuvenita acestei secvene(descrcarea lui P).b) Comparaie ntre nivelele maxime a energiei electrostatice

acumulateNivelele maxime ale energiei electrostatice ce se poate

acumula pe operatorul uman (P) la mersul pe mochet(1), ladezbrcarea unei flanele (2) i la lucru stnd pe scaun (3)sunt prezentate n fig. 14b.

Examining the data we have two conclusions:1.ThechargingqincreasesasBWincreases.Theincreasingrate

is more important for middle and small BW range (50-70 kg).2. The charging level is lower compared with the taking

sweater off case (as will be shown) and greater comparedwith the walking at an insulating floor-covering. Theseaspects will be analyzed in next paragraphes.

5.3. Comparation of charging due to the 3 activity of PAs the charging level of P walking on insulator floor-

covering was given as operator's "terminal"voltage (Up) and

the charging level of P taking clothes off or sitting on chairwas given as accumulated charge (q), we will convert bothof them into electrostatic energy levels. We will use the nextequations:

C

qWUCW

22

2

1;

2

1== (17)

For each of the three activity types of P a maximum andminimum value of W was obtained. We did not analyze thelazy walking charging case because it is an abnormal activityand it have to be avoided.

a) Comparation of minimum values of accumulated electrostaticenergyFig. 14a presents minimum levels of accumulated electro-

static energy for each of the three activities which P doesduring the ordinary working time in a normal work place: (1)walking on insulator floor-covering (PVC), (2) - taking agarment piece off (a sweater, in our analyzed case) and (3) -sitting on chair.

Anlyzing these data it could be noted that the lowest electro-static charging level (1 mJ) occurs at walking on PVC floor-covering (1), and the highest level (6.4 mJ) is for taking sweateroff (2). A midle level (2.4 mJ) was determined for sitting onchair. These learn us that also in the most favorable case(minimum level) the accumulated energy is important andcould generate hard damage or soft errors as well as explosionof flammable vapors ( the lowest flammable energy level is0.25 mJ).

From fig. 14a it could be also noted that the worst case is

for taking garment piece off (2). So, it have to be seriouslytreated this activity (operator have to discharge after takingclothes off).b) Comparation of maximum values of accumulated electro-

static energyThe maximum levels of electrostatic energy that may be

accumulated on the human operator (P) at walking on carpet (1),taking sweater off (2) and sitting on chair (3) are presentedin fig.14b.

(C)

0

0,1

0,2

0,3

0,4

0,5 AD

BC E

q1

Persoane testate

5060

7080 85

(mJ)

0

1

2

3

4

5

W

1

2

3

6(mJ)

0

2

4

6

8

10

W

1

2

3

12

a) b)

Fig. 13. ncrcarea electrostatic(q) la lucru pe scaun.n parantezgreutatea a persoanelor de test

Fig.13. Electrostatic charging (q) for sitting on chairIt's also noted the personal weight

Fig. 14. Comparaie ntre energiile electrostatice la mers (1), ladezechipare (2) i la lucru pe scaun (3) a) valori minime b) maxime

Fig. 14. Comparation of electrostatic energy for walking (1), taking clothesoff (2) and sitting on chair (3): a) minimal b) maximum values


12/12


Din comparaie cu datele din fig. 14.a rezultc:1. Nivelele maxime ale energiei electrostatice acumulate de

ctre P n timpul celor 3 secvene sunt aproximativ dublefade nivelele minime, ceea ce impune tratarea (precauiide descrcare) cu mai multatenie a acestora din urm.

2. Ierarhizarea nivelelor maxime la cele 3 secvene rmnecam aceeai ca la nivelele minime (fig. 14a).

Comparing to data of fig.14a, it could be noted that:1. The maximum levels of electrostatic energy accumulated

during the three sequences are twice of the minimum levels.So the latest should be carefully treated (the dischargingcautions).

2. The maximum levels order for the three sequences remainsthe same as in the minimum levels case (fig.14a).

6. Concluziin aceast lucrare s-au prezentat rezultatele testrii la

ncrcare electrostatic a operatorului uman (P), ntr-o

ncpere de lucru obinuit i n condiii normale de clim:22oC i RH = 50 %. ncrcarea acumulat a fost testatpentru fiecare din cele 3 secvene pe care P le parcurge ntimpul lucrului: mersul pe pardoseal electro-izolant,dezbrcarea unei piese de vestimentaie i la lucru stnd pescaun tapetat.

Din examinarea acestor date rezulturmtoarele concluzii:1. Nivelul energiei electrostatice (W) acumulate pe operator

(P) variaz n limite largi, nivelul minim (1 mJ) fiind lamersul pe pardosealdin PVC, iar cel maxim (12,5 mJ) la dezbrcarea unei flanele, o situaie de mijloc (4 mJ)fiind la lucrul aezat pe un scaun tapetat.

2. Aceste nivele sunt importante i deci nocive pentru obiectulde lucru (integrat COMS, P) deoarece pot produce defectede tip hard (strpungeri, etc.) i de tip soft (basculri false laintegrate numerice) i de ceea trebuie luate precauii cores-

punztoare:descrcareaoperatoruluinaintedeancepelucrul,sau conectarea acestuia n permanenla pmnt [2, 11]. n altordine de idei, dacdescrcarea energiei acumulate se face prinscnteie atunci chiar la nivelul minim menionat (1 mJ) exist

pericolulaprinderiiunorvaporiinflamabili,tiutfiindfaptulcpragul de inflamabilitate n asemenea cazuri este de 0,25 mJ.

3.Contribuiile autorilor la aceastlucrare constau n: efectuarea msurtorilor n cele 3 situaii menionate, ameliorarea metodei clasice de msur a ncrcrii

electrostatice la mersul pe pardosealelectroizolant; sugerarea unei noi metode de msurare a ncrcrii

electrostatice la dezbrcatul unei piese de vestimentaie.

6. ConclusionsIn this paper it was presented the testing results of human

operator (P) electrostatic charging, in a usual working room

with normal climatic conditions: 22o

C and RH = 50%. Theaccumulated charge was tested for each of three sequencesthat P does during the ordinary working time: walking oninsulator floor-covering (PVC), taking a garment piece ofand sitting on tapestried chair.

Examinig our experimental data it could be conclude:1. The level of Ps accumulated charge varies in large range

from the lowest level (1 mJ) recorded at walking on a PVCfloor, to the highest (12.5 mJ) at taking a sweater off. Amiddle situation was obtained at sitting on a tapestriedchair (4 mJ).

2. These levels are important and harmfully for the workingobject (CMOS integrated circuit, microprocesors, etc) andmay generate hard damage (breakdown, etc.) or soft errors(false flip-flops of digital circuits). That is why it have todo precautions: operator's discharging before every activityor his permanent connection to ground [2, 11]. In otherside, if he accidentally discharge by spark it could be generatean explosion of flammable vapors, even for lowest level oaccumulated energy (1 mJ). It is known that the flammabilitythreshold is 0.25 mJ.

3. The authors contribution is: experimental measurements for each of the three cases; improvement of classical method for electrostatic charge

measurement; suggesting a new method for measurements of charging

due to taking clothes off;

Bibliografie (References)1. Amerasekera, A. and Duvvury, C.,ESD in Silicon Integrated circuits, J. Wiley, New York, 20032. Antoniu, M.Msurri electronice, (ElectronicMeasurements) vol. 1 i 3 , Satya, Iasi, 2001 i 20023. Daniel, F. .a.: Triboelectrification of house flies walking on syntetic dielectric surfaces, Journal of Electrostatics, nr. 54, 2002, p. 167-1774. Greason, W.D.:Electrostatic Discharge in Electronics, J. Willey, New York, 19925. Greason, W.D.:Analysis of the Charge Transfer of Models for Electrostatic Discharge (ESD) and Semiconductor Devices, IEEE Trans.

on Industry Applications, nr. 3 (May/June) 19966. Kolyer, J.M. .a.:ESD from A to Z, Van Nostrand Reinhold, New York, 19907. Lacy, E.A.:Protecting Electronic Equipment from Electrostatic Discharge, TAB Books Inc., Blue Ridge Summit, 19848. Mardiguian, M.:Electrostatic Discharge, ICT, Gainsville, 19859. Osei, K.N.:Measurement of Electrostatic Charge on Protective Clothing on Low Hummidity, Tez de Master of Science (Thesis of

Master of Science), University of Alberta, Edmonton, CANADA, 199210. Oxe, J. .a.:Die Prufung und Beurteilung des electrostatichen Verhaltens textiler Bodenbelage (Testing and Evaluation of electrostatic

behavior for textile floor-coverings), Der 11 Internationalen Chemiefasertagung, Dornbirn, 21: 23 06 197211. Sclatter, N.:Electrostatic Discharge Protection for Electronics, TAB Books, Blue Ridge Summit, 199012. Seaver, A.E.: A Mathematical Justification for the Simple HBC Model, Proceedings of ESA 2001, Michigan State University, East

Lansing, USA, June 200113. Sharma, R. .a.:Effects of Plasma Treatment on surface Resistivity of Polymers, Proceedings of ESA 2001, Michigan State University,

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