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3,077,858
Feb. 19, 1963
M. E. ULUG
APPARATUS FOR CONTROLLING AND MEASURING THE THICKNESS
OF THIN ELECTRICALLY CONDUCTIVE FILMS
3 Sheets-Sheet l
Filed March 17, 196,0
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MEHMET EsIN ULUG,
BY ñGw-L
Hl ATTORNEY.
Feb. 19, 1963
M. E. ULUG
3,077,858
APPARATUS FOR CONTROLLING AND MEASURING THE THICKNESS
OF THIN ELECTRICALLY CONDUCTIVE FILMS
Filed March 17, 1960
5 Sheets-Sheet 2
INVENTORZ
MEHMET ESIN ULUG,
BY XîîäToRNEY. Q
Feb. 19, 1963
M. E. ULUG
y 3,077,858
APPARATUS FOR CONTROLLING AND MEASURING THE THICKNESS
OF' THIN ELECTRICALLY CONDUCTIVE FILMS
3 Sheets-Sheet I5
Filed March l7,_ 1960
FIG.4.
F|G.5.
zoo-
coMPENsATme VOLTAGE
leo -
(CBURMIADEGN)T
|40 -
VD.C.OLTS
|20 -
MEASURING CIRCUIT VOLTAGE
|00 -
B0
O
o
O
l
l
l
I
l0
2O
30
40
DISTANCE-FARADÀY SHIELD T0 TUBE FACE (INCHES)
FIG.6.
VOLTAGE
|
FREQUENCY
RESONANT
FREQUENCY
INVENTOR:
MEHMET ESIN ULUG ,
BY @A
. lfm?
Hl S
TORNEY.
3,077,858
3
num film deposited on the interior surface of lfaceplate 3
of cathode ray tube 4 and variations in the thickness of
glass faceplate 3 cause changes in the Q of a coil mounted
in probe unit 2. An output representative of the thick
ness of both the aluminum film and glass faceplate 3 is
thus fed into a cathode follower bridge circuit 5. A sec
ond oscillator 6 is also connected to probe unit 2. As
probe unit 2 is moved over glass faceplate 3 of cathode
ray tube 4, variations in capacitance between a probe grid
connected to the cathodes 23 and 24 of triodcs 20 and 22
respectively. Variable bias is supplied to triodes 2t) and
22 yby resistors R15 and R26* and variable resistors R16
and R21. The plate electrode of triode 20 is connected
to B+ through a plate supply resistor R13 and relay 25.
The plate electrode of triode 22 is connected to B+
through plate supply resistor R18. Relay 25 operates
contact arm 26 which contacts either terminal 27 or ter
minal 28. Terminal 27 is connected to a unidirection
located in probe unit 2 and the aluminum film, which is 10 Calibrating input voltage. Terminal 28 is connected to
the plate electrode circuit of triode 22. Contact arm 26
grounded through a lead connected to the anode button
is connected to grid electrode 29 of a triode 30.
in the cathode ray tube, cause an output which is repre
The cathode follower bridge circuit 5, which performs
sentative of the thickness of glass faceplate 3 to be fed
the function of indicating and/or controlling, comprises
into a D.C. amplifier 7. D.C. amplifier 7 and the auto
triodes 12 land 30 and associated circuitry. The plate elec
matic compensating circuit 8 are intrinsically related and
trodes of triodes 12 and 30 are directly connected to B+.
provide an output to the cathode follower bridge circuit 5
Equal resistors R9 and R12 are connected in the cathode
which is representative of the thickness of glass faceplate
circuit. The upper terminals of the resistors are connected
3. By means of D.C. amplifier 7 and automatic compen
through a milliammeter 31, a relay 32, a Calibrating re
sating circuit 8 the change in input to cathode follower
bridge circuit 5 from automatic compensating circuit 8 20 sistor R11 and a current limiting resistor R19.
Terminals 33 and 45 are the power input terminals to
caused by variations in the thickness of faceplate 3 is
a control circuit, visual indicating circuit or the like.
made exactly the same as that part of the change in the
Contact arm 34 is operated by relay 32 to contact either
input from the side of oscillator »1 to cathode follower
terminals 35 or 36. Terminals 45 and 35 are connected
`bridge circuit 5 which is caused by the same glass thick
to a lamp 37, but may be connected to means to control
ness variations. An indicator placed in the cathode fol
the apparatus which is applying the aluminum film to the
lower bridge circuit thereby provides a reading which is
interior of cathode ray tube 4. For example, the circuit
directly proportional to aluminum thickness regardless of
may be modified as shown in FIG. 2a to substitute an
glass thickness variations. D.C. ampliñer 9 is used for
on-ofr” switch represented at 37a for controlling the ma
switching purposes to be hereinafter set forth.
In FIG. 2 I have shown a circuit diagram of one em 30 chine for applying the aluminum film. This may be in
the form of a heater for Vaporizing aluminum in a man
bodiment of my invention. In that figure, a probe coil
ner well known in the art.
L3 having a high Q is shunted by capacitors C5 and C6
to form a parallel resonant circuit.
One side of the par
As shown in FIG. 2, a common B+ is used for all vacu
um tubes. The B+ may be derived from any suitable
allel resonant circuit is grounded at 9 and the other side
regulated power supply. Ground connections are made
is electron coupled in the plate circuit and forms part of
as shown.
a Miller-type crystal oscillator 1 which has high fre
As will be further described hereinafter, probe coil L3
quency stability characteristics. Such oscillators are well~
and probe grid or Faraday shield 16 are mounted in a
known in the art land will not be described further. The
output of oscillator 1 is connected to a rectifier circuit 40 single probe unit 2 (FIG. 3). The numeral 38 is used to
designate a grounded shielding can and contains com
comprising diode -10 and the parallel combination of ca
ponents 13, 15, 18, C12, C13 and R24. Can 38 is also
pacitor C7 with series connected resistors R6, R8 and
mounted in probe unit 2. As shown in FIGS. 2 and 3
potentiometer R7. Potentiometer R7 is connected to a
the input and output connections into can 38 are made
low-pass filter comprising capacitors C8 and C9 and in
by grounded shielded cables 39 and 40. A shielded
ductance L4. The output of the filter is applied to grid
grounded cable 41 is also used in connection with probe
electrode 11 of a triode vacuum tube 12. The previously
coil L3.
described circuitry may be called the measuring circuit.
FIG. 3 shows the construction of a suitable probe unit 2
What may be called the compensating circuit will now
for use with my invention. In FIG. 3, 38 is the grounded
be described. Oscillator 6 is another Miller-type crystal
shielding can schematically shown in FIG. 2. L3 is the
oscillator. A resonant tank circuit comprising the pri
mary coil 13 of air core transformer 14 and a variable 50 probe coil and `16 is the Faraday shield or probe grid.
capacitor C14 is electron coupled in the plate circuit and
forms part of oscillator 6. The parallel combination of
capacitor C13 and coil 15 form part of the secondary
circuit of transformer 14. A Faraday shield or probe
grid 16 is connected in the secondary circuit as shown
thereby introducing a variable capacitance C20 between
grid 16 and the aluminum film deposited on the interior
surface of the faceplate 3 of cathode ray tube 4. The
aluminum film is grounded at 17 by a ground connection
39, 40 and 41 designated the shielded grounded cables
schematically shown in FIG. 2. The main body of probe
unit 2 may be constructed of a suitable dielectric material
such as acrylic plastic.
The operation of the embodiment of my invention
shown in FIG. 2 will now be described with particular
A reference to that figure.
In operation, the tuned circuit comprising capacitors
C5 and C6 and probe coil L3 is tuned to resonance by
60 variable capacitor C6. It is to be understood that probe
to the anode button of cathode ray tube 4. It can be seen
coil L3 should have a high Q value at the frequency of
that capacitor C20 effectively shunts capacitor C13 and
operation. A Q of the order of 150 is suitable, but in
introduces into the secondary circuit of transformer 14
general the higher the Q the more sensitive the measure
a capacitance which is variable in accordance wit-h the
ment. Probe unit 2 is moved over faceplate 3 of cathode
distance between grid 16 and the aluminum film. The
ray tube 4. The resistance of the aluminum film depos
output of the secondary circuit is rectiñed in the rectifier
ited on the interior 4surface of faceplate 3 is coupled into
circuit comprising rectifier 18 and the parallel combina
the tuned circuit and lowers the Q value of the coil.
tion of resistor R24 and capacitor C12 which in turn isv
connected to a low-pass filter comprising capacitors C10
Since the magnitude of the resistance coupled into the
and C11 and inductance L5. The output of the filter is
tuned circuit is proportional to the thickness of the alu~
applied to the grid electrode 19 of a triode 26 by means
minum, the variations in the Q of coil L3 are representa
of resistor R17 and also to grid electrode 21 of triode 22
tive of the thickness of the aluminum film. Another fac
by means of potentiometer R22 and resistor R23. Tri
tor must be considered, however. The Q of the coil also
odes 20 and 22 and their associated circuitry form a pair
varies in accordance with the thickness of' glass faceplate
of D.C. amplifiers. A pair of resistors R14 and R19 are
3. If there were no variation in glass thickness the Q of
aomeee
the coilvvould at all. times .be solely representative of .fthe-Yl ;
180.?> fphase .shift circuitI between oscillatçni` 6 andígrid- 29,..
aluminum thickness. if,"` however, as is generally the case, l
of triode 30 in order that the changeinyoltage ouv-gridV .n
the glassthickness varies,'.the~Q of the coil -:is :reign-esente.y
29 .be in the proper direction _for _correct compensation.
As probe unit 2 containing probe grid 16 is moved over
tive of .-both‘the glass thicknessand, the aluminumïthick- _
,L the exterior surface of `faceplateß, .theVcapacitance,C20:.»¿
ness. . Mathematically
between grid 16 and the aluminum filmdepositedcn-the¿i
’
interior surface of faceplate 3 of cathode ray `tuberi ¿v
where ]‘(X)` andvgOf) are’fpfunctions yof Xl-andy, which,
varieslin accordance «with the variationsin thicknessofthe f
Q,=Í(X)Äaf1.<ì sbt). Y
(1)
glass face ,plate which ¿formspart of the dielectric- _of _
thickness. 1 As- the `Q factor of probe' .coilrLíi is _’reducedg. y' 10 i capacitor C20.: CapacitorCZûeffectively _shuntscapaç?-v _
thevoltage youtput from oscillatorl is reducedximdircct.;
torv C13. since theanode;l button ofcathode ray .tube ,4 isf,
connected to both 1the.l aluminumA film and groundat 17. .~
proportion. Mathematically ~are respectively'the..aluminum thickness; and the glass` ,
V‘=KQ .
Variations >in- capacitor ,C20,detune the secondarycircuit;
of transformer~14 and. alsoL affect. the vprimary ,tuned cir-vv
cuit. The net result is that vtheoutput voltage- _0f thesec-„H
ondary circuit is representativecfthe value „ofpcapacitor
(2) `
where Vv is the voltageoutput of,.oscillato_r-- 1,\ K hisa
constant of proportionality and Q istheQtactor of coil-1,
L3.v Substituting `Equation-2 in Equationtl, vthe equation.;
C20 which in. itselfis proportional to thelthickness of glass4
faceplate 3 since ,
Corán
20
where f’(X) and g’(y) -`are-functionsof Xgand y equal...
respectively to KÍO() and.Kg(y);
The output-ot“ oscillator -1 is rectifiedby fthe circuit
the plates of the-capacitor..v The out-put voltage `varies up l
comprising-diode .16 and capacitor C7, resistorsiRó and.
A in FIGURE 6. As the distancefbetweennthe probe`
R8` and potentiometerv R7.> Potentiometer R7 can be«._
varied to increaseor decrease the D.C. output~from the¿
rectifier circuit. Therectifier circuit output `is. filtered byy
thickness variation),> the secondary v¿voltage output l def»
where- C isthe capacitance-and d is the distanceìbetween
andv down along that portion ,of the> curve> designated by
grid and vthe aluminum film? increases (due Yto a glass
creases.
a low-pass filter comprising capacitors »C8tandC9zand 30. The outputof `the secondary circuit is rectified by the>`
inductance L4. The filter output voltage `is then «applied-1
circuit ycomprising _diode 18,-presistor AR24 „and »capacitor
C12. The rectified output -is appliedto a low-pass „filter
to grid 11 of triode` 12. The -voltage that is applied {to
grid 11 may therefore» be expressed as
V1=Í”(X)+o "(y)
comprising capacitors C10 andmCll> and inductance L5.'
The filtered D.C. output is then applied -to .grids 19 and
21 of triodes 2() and 22 respectively.
(5)9
where f”(X) and g”(y) equal K1Í’(X) and K1g’(y) re
spectively; Ki, it will be understoocLfis simply-a constant
As noted previously, the output voltage of the second»
ary circuit is a function of the glass’thicknessof .face-A
plate 3,1and'therefore theDC. input'voltagelon, grids'19¿
to take care of the effects ofA rectir‘ication and voltage. di-v
vision. Thus the voltageV Whichis applied `to grid 11V isV
representative off‘both the aluminum thickness »and-the:
glass thickness.
The voltageapplied to grid `11 controls .the-plate; cur-~
rent of-triode 12 and avvoltage »is developed across resis
and 21 is `also a function of glassvthicknessv. Mathemati~
40.
V3=g2 (y.)
(7)
WhereVa is the DLC. voltageon gridm21vandvg2(y) ispa`A
function of y, .y being the glass thickness.
tor R9 of the same generalform _as Equation 5 . In other
both aluminum thickness and glass thickness.V The volt@
age applied to grid 11 is shown in PIG. 5.V lt can be seen
l
V2=g Pl (y)
on grid 29 of triode 30.' In other Words, the` compensat_-.
ing circuit mu-st produce a voltage on grid 291t-he varia
tions of which due to varying glass thickness are equal to
the variations of that partîofsthe voltage applied to grid
11 of triode 12 caused .by the sameglassthickness Avaria
tions.v
"
it is the purpose `of’triode 22, _which With/ritsl associated..
circuitry isa D.C. amplifier, to providear-Dß. voltage on'.
grid29 of triode 30 which may be expressed -I'nat_heflîn'atpi->
cally asV
words‘the voltage across resistor R9 is representative of »
that this voltage is very closelya linear v'function-ofthel
aluminum and glass thickness..
The basic function of;the_ compensating circuitv is_ftoproduce a voltage
cally
V2=s'.’(y) n.
This result-may .be achieved by. varying potentiometerRZZy
which controls the magnitude of’the change >in-D.C. in-v
put voltage on grid 2.1 for a given change in glass thick
ness,Y andby adjusting variable> resistor R21-»which con
trols- the bias. Potentiometer RZZand resistor R21canV
be adjustedso that the change in.outputvoltageîrom the
55
D.C. amplifier, i.e. the input voltage Ito1grid-29-,~lvil-hen con
tact arm26 touches terminal 28,-. caused byvariationsinl
the »glass thickness of«faceplate_f3ïis exactly .the same as.
The operation . of the . compensating. circuit y to
the change in thatpartcf theÃnput-voltageio grid-.11;
achieve this result will now be described.
rThe tuned circuit comprising. primary, coil .13.oftrans 60 caused by the ,.same,` glass .thicknessvariations Mathe
matic‘ally, the D.C. voltage on `grid v29V‘c`a'n, Àby the previ
for-mer 14 andvaria‘ble capacitor C14 is detuncdfrom
ously noted- adjustment, be represented «by
u
resonance to a point‘where the voltage acrossthetuned.
circuit is .approximately *oneY half vthat .when the circuit is
V2.=g.'_'(r)~,
(6.).k
in resonance. Detuning, of course, is achieved I'oy-vary
ing .capacitor C14.` Thetuned circuit is detuned approxi~
65
mately tothe point 42 shoWn.in.FIG.-6 since .operation
must bezconñned to oneside of~ the .unsymmetrical resonf>
ance curve and not. permitted to slip over the'pealgcoitheA
curve otherwise oscillation would cease as shownvby the
The voltage ongridll.. Onthecthcr, han@ iacutea by.
Vr=ff’(X-)+g"(y)
(5)
Assumingßcontact v arm .26.to be closed; .on 4termin/alr` 28.,._as
will be.hereinafter..discussed,-v the cathodeìollower'.bridge,
sharp fall off in. voltage at frequencies abovethe resonant 70 circuit .5 ¿ operates in such ya vmannerLas, to etîectively, sub?
value. if an oscillator were used‘which. hada sym
metrical characteristic, Operation would be permissible on
either side of the curve but notover the lspeak. Opera;
tion on the high frequencyV sideY of a symmetrical reson-v
ance curve would necessitate, however, the addition of 75
tract .the `voltage , applied Lto... grid -2j9foflftrîëëdß.'~«.0È„fro" , _
the ¿voltage .appliedtoÍ grid
_of triode, 12py ' Theßvoltïage.
across,resistorliwl maybeeiçpressed as
`
'
"
3,077,858
8
7
not yet connected to grid 29. Probe unit 2 is then
placed on the center part of faceplate 3 of cathode ray
tube 4 and a reading, say A, on meter 31 is obtained.
This last reading should be read when no compensation
is being used, so it is necessary to prevent contact arm
where K4 is a constant, and the voltage across resistor
R12 may be expressed as V
since triodes 12 and 30 are identical as are resistors R9
and R12. Therefore the difference in potential between
points 43 and 44 is equal to K4[Í”(X)]. In other words
the difference in potential between points 43 and 44 is di
rectly proportional to the thickness of the aluminum film.
A milliammeter 31 connected between points ¿53 and 44 10
26 from switching to terminal 28 as it will do as soon as
probe unit 2 is in proximity to faceplate 3 of cathode ray
tube 4. This may be achieved by disconnecting the ground
connection to the anode button of the cathode ray tube.
For the remainder of the calibrating process, compensa
tion is used, i.e. the ground lead is reconnected. Probe
unit 2 is placed on the center part of faceplate 3 and
will therefore provide indications directly proportional to
aluminum thickness, and may be calibrated directly in
terms of aluminum thickness. Variable resistor R11 is
meter 31 is made to read A again, but this time with
used to vary the sensitivity of meter 31 and resistor R10
is simply a current limiting resistor.
compensation. Pieces of glass are added between probe
unit 2 and faceplate 3, but the probe unit is not moved
Relay 32 is used to control contact arm 34.
laterally on faceplate 3. The apparatus must be adjusted
The re
so that no deflection of meter 31 takes place. The con
lay contracts and spring tension can be adjusted so that
for any value of current flowing vbetween points 43 and
44, and therefore for any value of aluminum thickness,
trols for the latter two adjustments are potentiometer
R22, variable resistor R21 and variable capacitor C14.
Once meter 31 has been calibrated in the aforemen
tioned manner, probe unit 2 may be moved over faceplate
3 and the current indicated by meter 31 is directly pro
portional to the aluminum thickness. Meter variations
contact arm 34 will close on terminal 35 to turn on light
37.
It should be particularly noted that light 37 may bc
replaced by a control mechanism, such as lan on-off switch
37a as shown in FIG. 2a, to actually control the machine
applying the aluminum film and shut it oí when a pre
then indicate relative aluminum thickness.
:If it is desired that meter 31 be calibrated directly in
determined thickness of alumnium has been applied to the
units of thickness, the following method may be used.
interior surface of cathode ray tube 4.
All the previous steps are repeated. Thin uniform alu
A second D.C. amplifier comprising triode 20 and its
minum films of varying thicknesses are formed by conven
associated circuitry is used to effect automatic switching.
tional methods on glass plates comparable in thickness
When meter 31 is being calibrated and no compensation
is being used, grid 29 of triode 30 is connected to a D.C. 30 to the faceplate thickness of a cathode ray tube. Probe
unit 2 is then placed on the glass surface of each plate
calibrating voltage source through terminal 27 and con
and the meter reading noted. Each aluminum film may
tact arm 26. In this case the current passing through re
then be etched off its glass plate and weighed. Since
lay 25 is of such a magnitude to maintain contact arm 25
the length, width, weight and density of the ñlm is known,
connected to terminal 27. However, when probe unit 2
is placed on faceplate 3 of cathode ray tube 4, the voltage 35 the thickness may be easily calculated and the meter cali
brated accordingly.
applied to grid 19 of triode 2t) changes as previously dis
Since there are limits to the degree of variation of
cussed and varies the conduction of triode 20 so that re
lay 25 causes contact arm 26 to contact terminal 28 there
by applying the compensating voltage V2=g"(y) to grid
29 of triode 30.
,
faceplate thickness which may be compensated, it is pref
erable that in the calibration operations previously de
40 scribed a “bogie tube” be used. In this particular in
FIGURE 5 is a graph showing the compensating volt
age applied to grid 29, the measuring circuit voltage
applied to grid 11 and the bridge current between points
43 and 44 against the distance from the Faraday shield
16 to the tube face. The plots were obtained by insert
ing pieces of glass between the tube face 3 and the probe
unit 2 to gradually build up the glass thickness. The
probe unit 2 was not moved laterally on the tube face
however, and therefor there was no actual variation in the
thickness of the aluminum nlm. Note that the bridge .
current remained very closely constant as the glass thick
ness was increased.
It has been found that 2 megacycles is one suitable
frequency for oscillator 1 while 5 megacycles is a suit
able complementary frequency for oscillator 6. An op
erative thickness gauge constructed according to the em
bodiment of my invention illustrated in FIG. 2 has been
constructed and accurately compensates for glass thick
ness variations of as much as i‘ßt inch.
stance a “bogie tube” is one in which the faceplate thick
ness, at least at the center of the tube, corresponds to the
most probable value of the faceplate thickness of a num
ber of cathode ray tubes. Thus by calibrating the appa
ratus using the most probable value of faceplate thick
ness, one insures that compensation will be effective both
for thicknesses above and below the most probable thick
ness. On the other hand, if calibration were effected
using tubes with much lower or higher than average face
plate thicknesses, compensation may not be effective over
the whole range of values of possible thicknesses. As
noted hereinafter use of the components listed will enable
compensation for glass thicknesses of mißt". Improv
ing the linearity of the apparatus as known in the art
would enable compensation for larger variations.
Probe Unit
As noted previously, probe unit 2 comprises both probe
grid or Faraday shield 16 and probe coil L3. Since a
60 good probe unit is essential for the correct operation of
Calibration of the Apparatus
the embodiment of my invention hereinbefore described,
I shall comment in some detail on the construction of
In calibrating the apparatus, probe unit 2 is placed
on a slab of non-conductive material and meter 31 is
the probe unit shown in FIG. 3 which has been success
zeroed by varying potentiometer R7. Since there is no
capacitance between probe grid 16 and the slab of non
gilly used with the embodiment of my invention shown in
conductive material, the compensating circuit is inopera
tive and relay 25 maintains arm 25 in contact with
terminal 27 and a source of D.C. calibrating voltage input.
IG. 2.
Probe unit 2 shown in FIG. 3 comprises two concen
trically mounted cylinders 46 and 47 closed at their ends
by discs 4S, 49, 50 and 51. Disc 48 is circular in shape
-as is disc 51. Discs 5G and 49, however, are annular in
'Ihe meter 31 is obviously zeroed when potentiometer R7
is adjusted so that the voltage on grid 11 equals the 70 shape to accommodate disc 51 and cylinder 46 respec
tively. Another disc 52 is mounted as shown and con
calibrating voltage input on grid 29. Probe unit 2 is then
tains an annular trough to accommodate the bottom coil
placed directly on a sheet of aluminum at least greater
of probe coil L3. All parts 46 through 52 are made
in thickness than the maximum allowable aluminum film
from acrylic plastic, and with the exception of the joint
thickness and meter 31 is set for full scale deflection by
between disc 49 and cylinder 50` which is effected by
variable resistor R11. The compensating circuit is still
3,077,858@
l@ it
which> can bevused toïaccurately control! 4the thickness -
means of screws 53`and 54, al1 >plastic parts `are lasseni- l»
bled kusing chloroform.'
of the Vthin conductivefil'mîas it is beingïdepositedfon‘thev
Probe coi1'L3 is wound'on cylinder -46fand consists of '
dielectric
material.
What VI claim- asL newand ldesire 4to-secure 'by »Letters
16 turns‘of close wound' #l2 enameled copper wire'.`
Probe coil L3 is connectedl in the/plate circuit of oscil-V
lator 1 through' shieldedpcablev 41 and terminal 575g
Grounded can 3,8 contains'the components R24; 'C12Q
C13` and transformer 14'> shown kin FIG. 2. The'inputj
' Patent of the United Statesfi's: -'
l. In electrical apparatus for gauging the thicknessiof
a thin electrically-"conductive 'filn‘l portion of ía sandwich
consistingbfisaid-'fili?'ïfo?med on a non-conductive base; ‘
andoutput connections to" these" components are made,> /first sensingv means v adapted to sense »saidï 'sandwich»'ïand-Jl
by shielded cables 39 and 40 ‘and terminals 56' and 57; 10v “provide a firstfsig'n'al representative ïof' íthe»thickness of '
both said thin electrically conductive film and said non-“
Shielded cables 39, 4t) and 41 are, of course, used to f
conductive base, second’fsensing‘mèans'ï adapted" to 'lsense
minimize stray capacitance;
said sandwich and> provid'e‘ïfa `Asecond vsignal representative ‘i
Probe grid is is sandwieiied >between discs si; and s2'
of the thickness of said non-conductive base, and-'means'.
and is connected into the circuitry (see'FIG’,` 2) by wire ’
‘adapted to determine-the*diffërencef‘betweensaid first
58. yAs shown in FiGf. 4, probe grid 16 is generally
and second signals I¿to ~`thereby ¿pröduce'fa #third '-sign/al‘î
circular in shape, and’in this particular embodiment ‘com
representative A'solely 'of-`r the thickness `of` Ysaid = thin -elec-`
prises' fifteen loops of '#22 enamelled copper ywire var-`
trically conductive film-'_>`
ranged to cover a circular area of' 3%” diameter; It is '
2.~Apparatus` according to‘vclaim-v 1 'further-character
worthwhile noting that probe'grid '_16 should not be con-u
structed in the form of a conductive mesh 'of' screen- 20" ‘ize'd by means adapted‘to indie-'ate theîmagnitude'ï-offsaid
third signal representative solely of the thickness-‘ofA
since excessive loading is caused by current fiow in the
closed loops;
l
.
The basic dimensions ‘of'probe unit 2 are as follows:
Component:
Cylinder 46 ______________ _. 9" long, 1%” O.D„
ï/s” walls;
Cylinder 47 ____________ __.__
4” long, 4%” O.D.,
ï/Zt’»Í walls.
Discs 48, 49,5@ __________ __ l/è” thick.
Disc 51 _________________ __ V16” thick.
Disc 52 _________________ __ 1/s” thick.`
As shown in FIG. 3,'probe grid ‘V1-6 and probe coil L3 are symmetrically mounted about the same vertical axis.
it is, of course, essential'that' probe grid 16 and probe
coil L3 _be mounted in such a configuration in‘order thatthe effects of each, in the circuit shown ‘in FIG. 2,l
caused by movingprobe unit 2 over faceplate o are a
result of the same variations in `glass thickness. lf`,'for
example, probe grid 16 and probe coil L3 were substan
tially laterally displaced from one another, the effects
of each in the circuit would be based on probably differ
ent glass thicknesses, and, as a result, the compensation
would beincorrect.
It is to be understood Vthat the probe unit hereinbefore 45
described in detail is to be in no way interpreted as
said> thin‘l electricallyconductive-film;v
3Q4 Apparatus -accordingfïto-claim »1 further ïcharacter-V ’
ized by means `responsive l»to said -third 'signalurep'resen-~
tative 'solelyï of Vtheßthickness of Vsaid lthin electricallyy
conductive film to control the thickness of said thin `ele'c- »
tricallyI conductive film "as‘ it is being`~deposited on said
nonlcondüctive base‘. Y
4. Apparatus according to’claim'l wherein said differ~
` encev determining means comprisesv a ‘cathode vfollower-
bridge circuit.
5. ln electrical apparatus for‘gauging the thickness fof
a thin electrically conductive film portion of a sandwich'
.consisting of said film-formedon a non-conductive base,
first sensing means-adapted to'sense `said `sandwich and
provide a first `unidirectionalsignal representative of they
thickness of both said _thin electrically conductive .-film
and said non-conductive base,- second sensing means
adapted yto sense said sandwich simultaneously with said`
first sensing means and provide a second unidirectional'
signal representative of ythe- thickness of'only said'non'
conductive baseportion of said sandwich, and meansj
adapted‘to determine the difference between said first
and second- signals to thereby produce a third- signal
representativel solelyïof' the thickness'of-’said'thin elec
trically conductive film.
6. In electrical apparatus for lgauging the thickness of
limiting the scope of my invention.
a thin electrically conductive film portion of a sandwich
General
consisting of said film deposited on a non-conductive
Those skilled in the art will realize that while I have 50 base, first sandwich sensing means adapted to provide
chosen to deal with unidirectional voltages and currents
a first signal representative of the thickness of both said
for measuring purposes, my invention is not limited
thin electrically conductive film and said non-conductive
thereto. While unidirectional currents and voltages are
base, means to rectify said first signal to thereby provide
much to be preferred, my invention could also be con
a second signal representative of the thickness of both
structed using alternating voltages and currents. lt is
said thin electrically conductive film and said non-conductive base, second sandwich sensing means adapted to
to be noted, however, that the stability .of measurement
at high frequencies is not as good as at low frequencies
provide a third signal representative of the thickness of
said non-conductive base, means to rectify said third
and D_C., and moreover, the use of A.C. would require
the construction of an expensive high frequency ampli
signal to produce a fourth signal representative of the
fier. lt is also to be noted that in the end rectification 60 thickness of said non-conductive base, means adapted to
alter said fourth signal to produce a fifth signal repre
of the A.C. is almost sure to be required in any case
sentative of the thickness of said non-conductive base
since almost all suitable high frequency A.C. measuring
instruments rectify before measuring. The net effect
would then be simply to place the rectification circuitry
in a different part of the whole circuit.
such that the variations in said fifth signal caused by
variations in the thickness of said non-conductive base
are substantially equal to the variations of that part of
said second signal caused by the same variations in thick
ness of said non-conductive base, and means .adapted to
determine the difference between said second and fifth
Oscillator frequencies of 2 and 5 megacycles have
been found particularly suitable for use in measuring
the orders of aluminum thickness to be found on the
signals to thereby produce an output signal representative
interior of cathode ray tubes. Those skilled in the art
will realize that greater thicknesses may -be measured by 70 îìtïlely of the thickness of said thin electrically conductive
decreasing the frequency of oscillation.
It can be seen that by my invention I have produced
a gauge not only useful for accurately measuring the
m.
7. Apparatus according to claim 6 in which said means
adapted to provide said first signal comprises a high fre
quency signal source containing an inductive probe in
thickness of a thin conductive film deposited on a di
electric material of variable thickness, but also a gauge 75 the output circuit thereof, and said means adapted to
3,077,858
11
provide said third signal comprises a high frequency
signal source containing a capacitive probe in the output
circuit thereof.
8. Apparatus according to claim 6 further character
ized by means adapted to indicate the magnitude of said Cl
12
means adapted to alter said fourth signal comprises a
D.C. amplifier, said apparatus being further character
ized by switching means adapted to apply a constant uni
directional signal to said difference determining means
i in place of said fifth signal when no compensation is
9. Apparatus according to claim 6 further character
ized 'by means adapted to utilize said output signal to
control the thickness of said thin electrically conductive
film while it is being deposited on said non-conductive
desired and adapted to apply said fifth signal to said
difference determining means when compensation is de
sired, and means adapted to utilize said output signal
to control the thickness of said thin electrically conduc
tive ñlm while it is being deposited on said non-conduc
base.
tive base.
output signal.
l0. Apparatus according to claim 6 wherein said
means adapted to alter said fourth signal comprises a
16. Apparatus according to claim 6 wherein said
difference determining means comprises a cathode fol
lower bridge circuit.
D.C. amplifier.
17. Apparatus according to claim 6 wherein said
1l. Apparatus according to claim 6 further character 15
means adapted to alter said fourth signal comprises a
ized by switching means adapted to apply a constant
.C. amplifier, said difference determining means corn
unidirectional signal to said difference determining means
prises a cathode follower bridge circuit, said apparatus
in place of said fifth signal when no compensation is
lbeing further characterized by switching means adapted
desired and adapted to apply said ñfth signal to said
difference determining means when compensation is 20 to automatically apply a constant unidirectional signal
to said difference determining means in place of said
desired.
fifth signal when no compensation is desired and adapted
1.2. Apparatus according to claim 6 wherein said
to automatically apply said fifth signal to said difference
means adapted to alter said fourth signal comprises a
determining means when compensation is desired, and
D.C. amplifier, said apparatus being further character
means adapted to indicate the magnitude of said output
ized by means adapted to indicate the magnitude of said
output signal.
signal.
13. Apparatus according to claim 6 wherein said
18. Apparatus according to claim 6 wherein said
means adapted to alter said fourth signal comprises a
means adapted to alter said fourth signal comprises a
D.C. amplifier, said difference determining means com
D.C. amplifier, said apparatus being further character
ized by means adapted to utilize said output signal to 30 prises a cathode follower bridge circuit, said apparatus
being further characterized by switching means adapted
control the thickness of said thin electrically conductive
to automatically apply a constant unidirectional signal
film While it is being deposited on said non-conductive
to said difference determining means in place of said fifth
base.
signal when no compensation is desired and adapted to
14. Apparatus according to claim 6 wherein said 35 automatically apply said fifth signal to said difference
means adapted to alter said fourth signal comprises a
determining means when compensation is desired, and
D.C. amplifier, said apparatus being further character
means adapted to utilize said output signal to control
ized by switching means adapted to apply a constant uni
the thickness of said thin electrically conductive film
directional signal to said difference determining means
while it is being deposited on said non-conductive base.
in place of said fifth signal when no compensation is 40
desired and adapted to apply said fifth signal to said
References Cited in the file of this patent
difference determining means when compensation is
UNITED STATES PATENTS
desired, and means adapted to indicate the magnitude of
said output signal.
15. Apparatus according to claim 6 wherein said 4
2,793,345
2,806,204
Hags _______________ __ May 2l, 1957
Rothacker ___________ __ Sept. l0, 1957
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