A high efficiency passive neutralizer system

Journal of Electrostatics, 10 (1981) 2 1 7 - - 2 2 2

217

Elsevier ~¢cientific Publishing Company, Amsterdam -- Printed in The Netherlands

A HIGH EFFICIENCY PASSIVE NEUTRALIZER

SYSTE~'I

D. I~ITCI{LL ~ AND P.E. SECHER+ School of Electronic

Engineering

Science, University College of Norsh Wales, Bangor,

United I(ingdom.

ABSTRACT An e;~erimental

study wss made of the improved neu
could be obtained from a f~ne wire passive neutralizer by heating it. ment re~ulted from a decrease

This improve-

in the critical field for onset of corona at the hot

wire due to the locally reduced ambient air density. It was possible


neutralLry for a significant

range of operating conditions.

INTRODUCTIOH The industrial use of passive neutralizers significantly

in recent years.

driven neutralizers, simple,

- grounded points or wires - has grown

Compared with radioactive bars, or electrically

operating at high voltage,

passive devices are seductively

of relatively low cost and appear to be ir~herently safer.

Comparisons

of

(L) radioactive,

electrically powered,

neutralizing

ability of the three classes of device is not greatly different,

radioactive

and passive neutralizers

bars can give a slightly lower residual

suggest

~hat the

surface charge density.

although

(2)

If the surface charge density on a web before and after it passes under a passive neutralizer

(3) plotted

is measured,

a characteristic

of the form shown in figure i can be

Three distinct operating zones can be distinguished.

In zone A, the

neutralLzer has no effect since the field set up by
This threshold

is just exceeded at conditions

field

corresponding

to

the boundary between zones A and B. In zone B the corona current builds up rapidly with increasing charge

Jensi~y and progressively more efficient neutralization

zone C, corresponding ing occurs,

to high input surface charge densities,

giving rise to the phenomenon k n o ~

* Now at i~otorola,

East Kilbride.

0304-3886/81/0000--0000/$02.50

+

input surface

is observed.

~or

limited reverse charg-

as overcompensation.

This is

Now, at Royal Doulton Tableware Limited, Stoke-on-Trent.

© 1981 Elsevier Scientific Publishing Company

218

+~ Residual surface charge density - ;0I Figure I.

!./

:

Zone C

M ~~Input

surface charg~

TypLcal performance characteristic of passive neutralizer.

observed when strong corona current generation results in neutralization significantly upstream of the corona source.

Reverse web charging below the neutraliz!r-{{

device results from the effect of the emission-associated electric wind from [on trajectories following field lines which cross the web surface. f= has been found (4,5) that when a corona source f
This enhancement

hea~ed source. devices,

is heated,

arid that for a given f[eld~heat!ng

(i)

and

(8)

t.he <-lectr[c field Lncreases the corona

is due to the local decrease in air density around Lh{'

With the aim of improving the performance of passive neutralizing

the authors have explolted the healing effect to reduce bo~,h the maximum

residual surface charge density (corresponding

co point }) in figurx~ i) &~s well a~

(6) ~he overcompensatLon effect.

The system which has been ew31ved

appears

to out-

perform existing neutralizers and to offer a satisfactory solution to many moving web static problems

in tnduszry.

E)G)ERIIvLENTAI, TEST ARRANGEIv~ENTS The corona source used

[n the series of experimenEs reported here consisted of a

small diameter taut wire mounted at the required height over the charged moving surface Co be neutralLzed. variable DC power supply. of a wattmeter

Incorporation

[n the corona wire circuit enabled Che power input ~o the wire (les~

than 20W) to be monitored. was possible

The two ends of the corona wire were connected to a One end of the corona wire was grounded.

From resistance measurements and simple calculations

i!,

to correlate wire temperature with power input.

14easuremen= of neutralizing performance was effected using a moving insulatingsurface test rig (7) consisting of a metre disc of perspex 2 cm ~hick, mounted horizon~ally on the shaft of a variable speed motor.

The :',urfacc of the disc could

be charged by means of a corona source coupled to a high voltage unipolar power supply (I .D.B. model 320) which was remotely controllable.

The neutralizing devi{:(:

219 under test was positioned above the disc diametrically

opposite

the charging source.

Surface charge density upstream and downstream of the neutralizing monitored as the associated quasi-~lifonn Rotating vane field mills field,

device was

electric field above the disc surface.

(I.D.B. model iO7 Mk II) were used to measure electric

the measured values being output both as analogue readings on the instruments

display meters,

and digitized fop subsequent data processing.

An AIM 65 microcomputer was employed

to control

conduct of the tests, and the data logging.

the experimental

Specifically

speed and initial surface charge density could be automatically increments and the resultant ored.

residual surface charge density

Digitized values of rotor speed,

field were recorded on cassette data was subsequently

EXPERimENTAL

fc~' tunes.

the

increased in defined

(electric field) monit-

initial electric field and residual electric

tape, under microprocessor

control.

The recorded

analysed on a Systime model 5000 minicomputer.

RESULTS

a par,ge of corona-wire

residual

parameters,

in a given test, the rotor

to charged-surface

spacings,

characteristic

cupves of

field as a function of input field were recorded for different wire temperaFrom these characteristics

(E oUt)max, in figure i.

corresponding

were deduced the maximum values of residual field,

to the maximum residual

surface charge density - point R

The (E oUt)ma x values ape shown in figure 2 plotted as a function of

wipe temperature.

It will be seen that at most wire temperatures

above ambient,

fop

x105j,.81,t--Wire height above, surface-- mm. o positive web 1"4 t "-.%. / t,.. 6 " , . "-.--~-* ..... negative web 1"2 Figure 2.

$

k

I 1.0 X

"5 o

I..d

0.8

o. j I

0

,oo 260

I

4oo 560

Temperature of wire

°C

V a l u e s o f (E o u t ) max plotted as a function of wire ~empepature f o p p o s i t i v e and negative webs. Mean web speed i0 m/s. Wire diameter O.05mm.

220 a given wire to surface spacing

(E out) is lower for a positively charged surmax charged surface. This is in accord wi~h the prev[ou~

face than for a negatively (4)

observations of

bomperature

as

compared Effects

with due

[n.~:ignifi('ant In z o n e

a negative

a poe] rive

line

characterize

the

source

charged

surfacE,

the

threshold

field

field-creai:ing

wLth

charged

k~crcas:~ surI"a¢o~

~.u.

error

were

from

exceeding

the neutralizer performance

found

t{) I)e r ~ l a t . L v e l y

Ln t h J . s p a p e r .

characteristic

boundaries,

~[thout

corona

speed

further

neutralizer

zone

of

(positive

source.

be d~.scussed

Lhe p a s s i v e

between

by a straight

of

not

decrease

corona corona

to variation arid will

1~ o f

Lhe c u r v e

a greater

ind±cat':ng

for

(fLgure

points

])

it

b~ f ( ) u n d

]~ t o ~i, c<]n b e

a few percent.

]:

is

in Lermr of the 'gradient'--

tha

represEFltud

convenient ::o A (~ out)

A

(E in)

~'-. Wire height Q'~---~... " above surface ~ ' ~ ""'~-.~. - - mm. 0"5

~,isure

is

Oe,

o

p

,3. ~ r a d k . n r ,

- A(E

ouu)

A ( Z in )

itive web

as a fLlncLion tem[)( r a t u r e .

"~

o f v,'iP~

.... -~. . . . . . negative web

Gradient

/

50

. . . . ~---~'_ ~

-'e

81 0

'

0

i

100

200

I

I

I

300

400

500

Temperature '['he in

'gradient.' the

spacings

was measured

curves the

be exp<('ted migrat:on A] r h e a t i n g

for

sho%~] i n f : . g u r e var!azion in

thaL once

behavleur by

of

of wire

a range

3.

the

rather

b h e w:_re i s

of wire

I~ can

gradient

with

incideni3

°C

be


seen

that,

bemperatupe fLeld

exceeds

thaz] ion

generatfon

a purely

lo(;al

except

is the

corona

such

spacings

ab ;rnali

relat:.vely

deter~nines

phenomenon

surface

w[r(

~:mall. onse~

for

the

~,~{

t o s t ] r ' i ' ~ ,'

This

threshold,

neuzral[zation thaz

r~uit.

i! :.',r~

~I'fLol(~r~ y . larger

w! r(.

221 to surface spacings the ions are moving through air at quasi-ambient

temperature

for the major part of their trajectories. Figures 4(a) and 4(b) generated from the data used to plot figures 2 and 3 show the variation of (E oUt)ma x and gradient respectively separation.

Clearly minimization

surface spacings while attainment possible

of minimum gradien: to put off to Lhe highes~

input fields the onset of overcompensation

ate at large wire-surface

as a function of wire-surface

of (E oUt)ma x dictates operation at minimum wire-

indicates a requirement

~o oper-

spacings.

xlC~ . . . . empirical 1.4 characteristic _/ .derived from/f ref (8)//,/~20o 1.2

.,

0'5 l! + ~'~i

C')¢~

pos.web neg.web

,'

(EoUt)max


I.0

/

v/m

//.

,,Y ,y./.Yooo

,/e

/

(>(

;'/ Z / 7"

Figur~ 4(a) Figure 4(b)

Yi

i

I

I

~ 0.2

~

Q

E 0.1

~--,

"~

i

20 40 60 80 Wire height- mm.

0

I

I

I

20 40 60 ~0 Wire height -- mm.

Variation of (E out) max as a function of w~re-surface Variation of gradient values averaged over temperature function of wire-surface separation.

separation range, as a

Implementation

It seemed possible

that an optimized practical passLve neutralizer

realized by combining an essentially distance

I

L

-e- pos.web .... neg.web

'J 0

IN

/;/'_/

o.,

Practical

, /

conventional

system could be

passive device separated some

from The web, %'ith a downstream heated wire placed close to the web.

5 shows the physical disposition characteristics

of the two neutralizers

Figure

and the measured performance

of ~he individual and combined neutralizers.

If boLh neutralLzers upstream of the other, of the first uniT.

are, in use simultaneously,

with the wide-separation

unit

the close-spaced unit merely operaLes on the residual field

With no heating of the wire of the second neutralizer

reduction of Lhe residual field is relatively small. gives a very low final residual

Lhe further

Heating of the wire, however,

fLeld over a major part of the input field range.

222

xlO 5

primary neutralizer

}0"5 (Eout)

7

O

-primary -,,..

"~&.primary neutralizer}o 08 ~ + heated secondary "

ne r i er

~,nhe=~,~

neutralizer] ~ -;1[-- ~ (heatedwi~,,1 . . mm. . . ~. _mm. _ ~ ~ [v-4_.t12 4(J

Figure 5.

V/m

(lSW)

secondary IOF~1-~--~ ~

-" movement

5 x 105V/m. I( E: in)'*"

~

~o~nn,4=~, ............. ~ "-.<.~-" n e u t r a l i z e r alone

hea te d secondaw ,~ ~neutralizer alone (15W)

of web

Performance characteristics and when combined.

for tm,o passive neutralizers

individually,

CONC] .US IONS It is clear that the principal problem asset Lated w:, ~h passive neutralizers, the significant heating

threshold field for corona onset,

the corona source.

The resulting worsening of ~he overcompensat[on

ca~l be countered by mounting a conventional web upstream of the heated uni~. neutralizer

is not dissimilar

The combination

c~lq be partially allieviated

The overall per±'or~nance of the

use of the combination passive neutralizer,

bar

par~sLve

(2)

cheaper" than a combination

the urlfounded but very real disqui~ t

often associated with the latter t~rpe of device.

e×ception of situations where ar~ inflammable

specified where previously

'combination'

to that of a combination passive/radioactive

bar and would not generate

among operating porsonn(l

effect

passive neutralizer well spaced from Lh{~

passive bar should be signif[cangly

passive/radioactive

n&mt(ly by

With th~

vapour atrnosphere~or' space prohibit

th~

zhe system might wiuh advantage be

a combination passive/radioactive

bar would have been zhc

normal choice. R e f e r e e ' s note:

In a d d i t i o n clouds.

there m a y be h a z a r d in the p r e s e n c e

of f l a m m a b l e d u s t

REFERENCES

~. 2. 3. 4. 5. 6. 7. 8.

P.E. Socket (Ed), 'Static Elec~rification; Fundamental Concepts, Hazards and Applications', University College of North Wales, 1976. The Radiochemical Centre, 'Eliminate Static', 1980. K.G. Lovstrand, inst. Phys, Conf. Sop. No. 2'7, (1975), 246-255. lJ.i~. Awad and G.S.P. Castle, Prec. 1973 Annual lqeeting of I.A.S., lJ[lwaukee, (1973), 3 7 3 - 3 8 0 . B. ~ a k i n a n d I . I . Inculer, Lbid, 381-389. British Patent Appl:ieatton filed. P.E. Secker, Inst. Phys. Conf. Set. No. 48 (1979), 115-123. M. Kawasaki and T. Adach[, Prec. Abstracts 1977 Annual Lieet[ng of the ]nst]tute of Electrostatics 3apan, (]977) 3a.