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Dec. 7, 1948.
Filed Aug. 20. 1947
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Dec. 7, 1948.
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Dec. 7, 1948.
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Filed Aug. 20. 1947
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Dec. 7, 1948.
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Dec. 7, 1948.
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Patented Dec. 7, 1948
Alan C. Williams, Minneapolis, Minn., assignor to
Franklin‘ Transformer Manufacturing Com
pany, Minneapolis, Minn, a copartnersliip
Application August 20, 1947, Serial No. 769,633
4 Claims. (Cl.
impedance at the commencement of any charging
This invention relates to instruments for test
period is that due to the resistance only, and,
ing electrostatic capacitors and has to do more
therefore, given a constant voltage, the resulting
speci?cally with an instrument designed for the
current will have an initial peak value, the mag
three-fold purpose of measuring capacity, series
nitude of which is independent of electrostatic
resistance, and leakage resistance.
capacity—which current will diminish as the
One of the objects of my invention is to pro
capacitor or capacitors in the circuit become
vide an instrument which will afford direct and
charged. If the capacity of the circuit is large,
accurate electrostatic capacity readings on a
the current ?ow will diminish slowly, but if the
meter scale.
Another object is to provide a capacitor test 10 capacity is small, the current ?ow will diminish
very rapidly. But, in either case, the capacltative
ing instrument which will afford direct indica
reactance of the circuit is zero at the outset of
tions of series resistance in the capacitor.
each charging period, and, consequently, the
A further object is to provide a compact, port
starting current is the same, whether the capacity
able instrument for measuring electrostatic ca
pacity, series resistance and leakage resistance, 15 is large or small, and depends entirely upon the
non-capacitative impedance of the circuit. By
wherein a single meter serves all three purposes.
utilizing only the peak values of current as a
means of producing indications, I am able to ob
tain direct measurements of series resistance, the
A further object is to provide an instrument
of the aforementioned character, which is espe
cially well adapted for testing ignition capacitors,
and which is further adapted to utilize an auto
mobile battery or the like, as a source of operat
20 accuracy of which is substantially una?ected by
the electrostatic capacity of the capacitor under
test. This renders the instrument immediately
available for making series resistance tests with
out the necessity for making adjustments to com
One of the features of my invention consists 25 pensate for capacity di?erences.
With these and other objects in view, my in
in a novel system and method for measuring elec
vention consists in the construction, arrangement
trostatic capacity, and contemplates an arrange
and combination of the various parts‘of my device
ment wherein the capacitor under test is alter
whereby the objects contemplated are attained,
nately charged and discharged from a current
source of constant voltage and at a ?xed periodic 30 as hereinafter more fully set forth, pointed out in
my claims and illustrated in the accompanying
rate, so that the quantum of charging current
drawings, wherein:
during a given unit of time is directly propor
Figs. 1 to 7, inclusive, are simple circuit dia
tional to the capacity of the capacitor under
grams, illustrating the basic principle underlying,
test-wherefore a measurement of current flow
during either charge or discharge periods, or both, 35 certain aspects of this invention;
Fig. 8 is a face view of the panel of a testing
is either translatable into a capacity value or may
ing current-thus avoiding the need for a special
battery or other voltage source, which would add
to the weight and bulk of the instrument.
- be directly readable as such, depending upon
whether the meter forming a part of the instru
ment is calibrated to read in terms of capacity or
in terms of voltage or current. According to the 40
preferred practice, the meter is calibrated to read
directly in capacity units.
Fig. 9 is a circuit diagram of the complete in
Fig. 10 is a fragmentary circuit diagram show
ing only those parts of the network of Fig. 9
which are employed in the making of capacity
Another feature of my invention resides in the
novel method of measuring series resistance in
zero at the instant of commencement of any
the switches are so positioned.
Fig. 11 is a circuit diagram showing the net
electrostatic capacitors, and which is operative 45 work of Fig. 9 adjusted for the making of series
resistance measurements and omitting those parts
independently of the capacity of the capacitor
of Fig. 9 which are not utilized in connection with
under test. In making use of this method, I capi
the series resistance tests; and
talize upon the fact that the impedance of any
Fig. 12 is a circuit diagram showing the net
capacitor is, within practical limits, negligible, by
comparison with its series resistance, at the out 50 work of Fig. 9 with the switches set to the “ad
Just” positions and omitting those parts of the
set of each charging period. That is to say, the
network of Fig. 9 which perform no function when
counter E. M. F. of any uncharged capacitor is
The network shown schematically in Fig. 1 is
charging period. Thus, in any circuit compris
ing onlycapacity and resistance in series, the sole 55 for. the purpose of measuring electrostatic ca
paclty and includes a capacitor C, the capacity of
which is to be determined. Included in the net
reciprocating device.
The resistance or imped- .
ance of source E should be comparable to the
series resistance Rx. Also included in the circuit
work is a source of D. C. voltage E, a meter, and
a two-way switch having a movable contact mem
ber J and a pair of ?xed contacts A and B. The
of Fig. 4 is a resistor Ra, across which is connected
an alternating current meter M. The ohmic
value of resistor Rn is preferably of the same order
as the probable series resistance Rx- The alter
source E may be a 6~volt storage battery. The
meter M may be an ordinary D. C. ammeter or
milliammeter, and the two-way switch S may be
an electromagnetic vibrator wherein the member
nating or pulsating current ?owing in the net
work is a function of its series impedance, and
J is a vibrating reed making contact alternately 10 since any variation in the value of Rx introduces
with ?xed contacts A and B. Each time member
a similar variation in the total series impedance,
J engages contact A, a circuit is completed from
it will be apparent that the current ?ow through
source E through capacitor C, and the latter is
resistance R9. and the voltage drop thereacross
fully charged at the voltage of source‘ E, which is
will vary correspondingly. Hence, the de?ection
of constant value. It will be apparent that the 15 of meter M provides a measure of the value of Rx.
quantum of the charge thus imparted to capaci
Fig. 5 illustrates schematically an arrange
tor C is directly proportional to the capacity of
that element, provided, of course, that the contact
ment similar to that of Figure 4 for measuring
series resistance wherein a D. C. source is em
time is su?icient to permit the capacitor to be
come fully charged; and it will be evident that 20
when member J thereafter engages contact B, a
de?nite quantum of electricity, proportionate in
magnitude to the capacity of capacitor C, will be
discharged through meter M, and that the latter
will be de?ected correspondingly. If the two 25
way switch is operated at .a fairly rapid rate, the
meter M will show a steady reading which is pro
portionate to the capacity of the capacitor under
test. It is preferable that the contact time be
ployed in place of the alternating or pulsating
source E of Fig. 4. In this case, there is provided
a two-way switch S having ?xed contacts A and
B and a moving contact member J, which alter
nately and periodically engages contacts A and
B. When member J engages contact A, a charg
ing circuit is completed from D. C. source E
through capacitor C including its series resist
ance Rx and resistor Ra, across which is connected
an A. C. volt meter M. When, on the other band,
member J engages contact B, a discharge path is
su?icient to allow for fully charging the largest 30 provided for capacitor C, which path includes
capacitor for which the instrument is designed;
resistor Ra and the series resistance Rx. The
and where that may involve such a slow rate of
principle of operation is otherwise the same as
operation of the two-way switch as to tend to
that Of Fig. 4.
cause the meter to ?uctuate, it may be necessary
In Fig. 6 there -is shown an arrangement very
to provide for damping the meter in order to 35 similar to that of Fig. 5, but involving a modi?ca
counteract the ?uctuation.
The arrangement depicted in Fig. 2 is equiva
tion which enables the use of a D. 0. meter.
this case, the discharge path includes only capac
lent to that of Fig. 1 but differs therefrom in that
itor C, wherefore current flows in one direction
meter M is inserted in the charge path instead of
only through resistor Ra.
the discharge path. It will be observed that in 40 The networks of Figs. 4-6, inclusive, can be
Fig. 1 the meter is actuated by the discharge from
made to effect accurate direct readings of series
capacitor C, whereas in Fig. 2 it is actuated by
resistance where the magnitude of capacitor C
the charging current. The end results are iden
is ?xed; and it can also be made to give readings
from which series resistance values can be com
The arrangements of Figs. 1 and 2 both per 45 puted, where the capacity value is known but not
mit of the use of direct current meters; but in
?xed. But in order to be able to achieve direct
Fig. 3 I have shown a modi?cation which utilizes
readings of series resistance, where the capacity
an alternating current meter. In this instance,
of capacitor C is not a ?xed'value, it is necessary
the meter M is interposed between the contact
to resort to a more elaborate arrangement as
member J and one terminal of capacitor C, and
hereinafter described, which, however, is pre
is traversed by both the charging and discharging
dicated fundamentally upon the same basic prin
current. Aside from entailing the use of an A. C.
ciple as that of Figs. 4-6.
meter, the arrangement of Fig. 3 is equivalent to
In Fig. 7 there is illustrated the method em
the arrangements of Figs. 1 and 2.
ployed for measuring the so-called leakage re
In Fig. 4, I have illustrated the basic method
sistance of a capacitor. Here the leakage resist
which I employ in measuring the series resistance
ance or, more accurately, the leakage conduct
of a capacitor. In this instance, the capacitor
ance is symbolized by a resistor Rb in shunt to
has an unknown series resistance, which is iden
capacitor C-which latter is connected in series
ti?ed by a symbolic‘ resistor element RX. It will
with a D. C. source E and a D. C. ammeter M.
be understood that the resistance Rx is incor
The meter will respond to any substantial leak
porated in the capacitor and is not external
age current and thus serve to detect any capaci
thereof as might be supposed from the diagram.
tor which is faulty in that respect;
Its effect, however, is equivalent to an external
Mounted on panel l0, Fig. 8, is a meter II,
series resistance, and it may, therefore, properly
which, as will be observed, has a scale l2 cali
be represented in the diagram as an added ele
brated for capacity readings from .1 to .5 micro
ment. But since it is not, in fact, such an ele
farad, and in addition is provided with self
ment, it is not possible to determine its ohmic
value by directly measuring voltage drop there
Connected in series with capacitor C is
a source E of alternating or pulsating direct cur
rent, which source may be a relaxation oscillator,
a trigger type oscillating circuit, a capacitor
charge-discharge circuit, or a circuit deriving its
alternating or pulsating nature from a mechani
cal action, such as a vibrating or rotating or
explanatory indicia respecting series resistance
and leakage resistance, and a further indicla
marked “Adi,” which is utilized in adjusting the
instrument preparatory to the making of series
resistance measurements. Mounted on panel Ill,
below meter I I, is a rotatable knob I3, which op
erates a gang of rotary multi-contact switches
whereby the instrument may be conditioned,
selectively, for making the various tests, and a
second rotatable knob‘v l4, which is connected to
the movable contactor of a potentiometer and is
used in making certain voltage bias adjustments,
as hereinafter described.
Referring now to the circuit diagram of Fig. 9,
a pair of conductors i5 and I8 are connected, re
spectively, to the terminals of a suitable current
source 81, such, for example, as a 6-volt storage
battery. Conductor l5 extends to the mid-point
tap ll of the primary winding l8 of a transformer 10
I 8; and conductor l8 extends to the moving con
tact member 20 of a vibrator 2 I, having fixed con
tacts 22 and 28 connected, respectively, to the two
end terminals of said primary winding l8. The
vibrator 2| may be electromagnetically. driven.
The moving contact member or reed 20 alternate
ly engages ?xed contacts 22 and 23; and it will
be apparent that with the vibrator in operation
ity), "L” (for leakage resistance), and “Adj."
(for adjust). Said switches, together with two
additional rotary switches BI and 62, are ganged
together and driveably connected to the knob 18
shown in Fig. 8. The ?xed contacts of switches
-BI and 82 bear the same notation-s 'as those .of
switches 58 and 80, and it is to be understood that
the four rotary contactors 58, 58, 83 and G4 ,
always engage correspondingly labeled ?xed
The capacitor under test, marked “C,” has one
terminal connected, via conductors 65, 8| and IE,
to the negative terminal of source 81; and the
other terminal of said capacitor is connected, via
conductor 68, to the “L” contact of switch 58.
Fixed contact “S” of switch 58 is tied to the
“Adj.” contact of the same switch and is con
nected, via conductor 55, to anode 52 of tube 48;
and the “S” and “Adj.” contacts of ‘switch 80 are
gized alternately, thus producing a symmetrical 20 tied together and connected, via connector 81, to
positive conductor 34.
alternating voltage across the terminals of the
the two halves of the primary winding are ener
secondary winding 24. Said terminals are shunt
ed by a buffer capacitor 25 and connected respect
ively to the anodes 28 and 21 of a full wave recti
The “L” contact of switch 60 is connected
through a SOD-ohm resistor 68 and conductor 58 to
the cathode terminal of recti?er 28. .
?er tube 28. The mid-point 28 of secondary 25 One terminal of the primary winding 10 of
transformer 46 is connected via conductor ‘H to
winding 24 is connected via conductor 30 to the
- the positive lead I5, and the other terminal of said
D. C. return conductor 8|. Recti?er 28 has a
primary winding is connected to a ?xed contact
cathode heater ?lament 82 and a cathode 33,
‘I2 of a vibrator 13. A lO-ohm variable resistor 14
which latter is connected via conductor 34‘ and
resistor 35 to the anode 85 of a triode detector tube 30 is connected across the terminals of the trans
former primary winding. A second ?xed contact
81. Resistor 35 may be of 10,000 ohms resistance
15 of vibrator 13 is connected via conductor ‘I6 to
and forms, in conjunction with ‘a capacitor 38, an
the “S” contact of switch ‘Bl, which is tied to the
R-C ?lter for smoothing the pulsating current
“Adj.” contact of the same switch and, via con
output of recti?er 28. Capacitor 38 may suitably
have a capacity of four microfara-ds. Connected 35 ductor ‘H, to the “C” contact of switch 60.
The positive terminal of capacitor C is connect
across the output side of the ?lter, between con
ed, via conductors 86 and 18 through a 500-ohm
ductors 8| and 84, is a voltage regulator tube 38,
resistor 18 to the “C” contact of rotary switch 62
which is shunted by a voltage divider 40, com'-"
and through a .1 mid. capacitor 88 to the rotary
prising resistors 40s and 40b. Resistor 40s may
have avalue of 20,000 ohms, while resistor 401» 40 contactor v63 of switch 6l—which contactor is
connected via conductor 8| to the negative lead l8
may conveniently have a value of 2,000 ohms.
and via conductor 82 and- a .3 mid. capacitor 83 to
As indicated in the diagram, resistor 40b is the re
the “Adj.” contact of switch 62.
sistance element oi.’ a potentiometer having a
The vibratory reed 84 of vibrator 13 is con
moving contactor 42.
~ .
Detector tube 31 has a control grid 43 and an 45 nected through a l-ohm resistor 85 to the mov
able contractor -64 of rotary switch 62.
indirectly heated cathode 44, which elements are
In Fig. 9, the rotary contactors 58, 58, 83 and
interconnected through an input circuit including
84 are all in engagement with their respectively
the secondary winding 45 of a transformer 48, in
associated “L” contacts-which is the adjustment
series with a grid capacitor 41 shunted by a high
resistance grid leak 48. Capacitor 41 may have a 60 for testing capacitor C for leakage resistance. It
will be understood that capacitor C is located
value of .5 mid. and ‘resistance 48 may have a
outside the instrument case and is temporarily
value of 15 megohms.
connected to conductors I55.v and 88, for test pur
A second triode 48 functions as a direct current
poses, through ?exible leads.
ampli?er and has a control grid 50 connected di
It will be observed that the "L” contacts of
rectly to cathode 44 of tube 41, a cathode 5| con 55
switches 62 and 63 are blanks and that the .1 mid.
nected through a resistor 53 and conductor 54 to
capacitor 80 is connected in shunt to capacitor
movable contactor 42, and an anode 52 connected
C; also that each of said capacitors is connected
via conductor 55 to a ?xed contact mark “Adj.” of
a multiple contact rotary switch 56. Cathode 44'
through conductor 88, meter ll, resistor 68 and
and grid 58 are connected via a resistor 51 to the 00 conductors 69 and 34, to the cathode terminal
negative end of voltage divider 48. Resistors 58
of diode 28—the other terminals of said capacitors
and 51 may have values of 10,000 ohms each. In
being connected to the negative lead [6. The
actual practice, I employ a double triode ‘tube of
capacitor 88, in shunt to capacitor 0, serves no
the GSL'IGT type instead of the two tubes 81 and
purpose in testing the latter for leakage re
48, but it is more convenient, for purposes of de
sistance, but it is useful for other tests and its
scription, to shown‘ two separate tubes in the
presence across the capacitor C, when testing
The meter l I, which may be a D. C. milliamme
ter, calibrated as shown in Fig. 8, has its negative
terminal connected to the movable contactor 58 of
rotary switch 58, and its positive terminal to the
movable contactor 58 of a second multiple contact
rotary switch 58. Each of the two rotary switches
58 and 88 has four ?xed contacts marked, respec
tively, “S’a' (for series resistance), "C” (for capac
for leakage resistance, is purely incidental and
harmless. Any leakage current ?owing through
capacitor C will cause a de?ection of meter II
and if this does not extend beyond the meter
scale area marked “Leak O. K.”-—see Fig. 8-—the
capacitor under test may be regarded as satis
factory. The function of resistor 58 is to limit the
current through meter II in event the capacitor
under test may prove to be shorted or in event
of the test leads being touched together.
For the purpose of describing the manner in
which the instrument operates for measuring
to the vibrator reed 84. When reed 84 engages
?xed contact 12, a circuit is completed through
shunt resistor 14 and conductor ‘I i to the positive
terminal of source 81, by virtue of which each
of said capacitors receives a charge. Immediately
electrostatic capacity, reference is now made to
the circuit diagram of Fig. 10, which ShOWs' only . thereafter, when reed 84 engages ?xed contact
those parts and circuit connections of Fig. 9 which
15, said capacitors are discharged through the
enter into the capacity measuring operation.
path which includes resistor 85, conductor 16 and
It will be seen that the capacitor C, under test,
contactor 63.
is shunted by the .1 mfd. capacitor 88 and that 10. The magnitude ‘of the initial current through
one terminal of each of said capacitors is con
the above-de?ned capacitor-charging ‘circuit is
nected to the negative terminal of source 81, while
the remaining terminals of said capacitors are
connected to the reed 84 through resistors 18 and
85 in series. The reed 84 is in continuous oscilla
tion, making contact alternately with ?xed con—
tacts ‘l2 and ‘I5.
When reed 84 engages contact ‘I2, a capacitor
charging circuit is established from the positive
terminal of source 81 through primary winding
10 of transformer 16, and through resistor 14
which is in shunt to said primary winding, said
circuit also including the resistors ‘I9 and 85 and
the movable contactor v64. This results in fully
charging both capacitors.
Immediately thereafter, when reed 84 engages
?xed contact 15, a circuit is established for dis
charging both capacitors through the meter Ii‘.
This circuit includes resistors 19 and 85, reed 84,
?xed contact ‘I5, conductors ‘I6 and ‘i1, movable
contactor 59 of rotary switch 60, meter ll, mov
able contactor 58 of rotary switch 56, conductor
88, movable contactor 63 of rotary switch 'BI and
governed principally, by the combined impedances
of resistors 14 and 85, plus the combined series
resistances of capacitors C and 80. The imped
ance of primary winding 10 is very high com-~
pared to that of ‘resistor ‘I4 and, therefore, does
not‘ materially alter the parallel impedance of
those two elements; but even if the primary wind
ing impedance were low, that fact would be of
no importance here. The important factor is
that the capacitative impedance of the charging
circuit, due to the reactance of the two capaci
tors, or either capacitor alone, is so exceedingly
small, at the instant when the charging circuit
is closed, that the initial current magnitude is
substantially independent of the capacity of those
capacitors. That is to say, irrespective of whether
the series capacity of the charging circuit is
large or small, the initial impedance due to said
capacity is negligible, and the only impedance
which need be considered in determining the peak
magnitude of the current flow during each charg
ing period is that due to resistors 14 and 85,- plus
the series resistance of the parallel-connected
conductors BI and 65.
The shunting capacitor 80 having a capacity : Li capacitors C and 80. But resistors 74 and 85 are
of .1 mfd. has, for its purpose, to produce a meter
set ‘at some ?xed values and are not altered by
deflection beyond that part of the scale marked
the operator of the instrument; and, therefore,
“Ser. Res. 0. K.” even when the capacitor under
since the supply voltage is constant, the only
test is as small as .1 mfd. Except for that factor,
factor which causes any substantial variation of
capacitor 80 could be omitted.
the peak current magnitude in the charging cir
The function of resistor 19 is that of a current
cuit is the series resistance of the‘parallel ca
limiter, serving to protect the meter against
heavy current surges.
The i-ohm resistor 85
Before proceeding further, it should be pointed
serves no purpose in the capacity test, but is use—
out that capacitor 80 performs no essential func
ful for another purpose which will be explained 45 tion in the circuit of Fig. 11. Its usefulness is
only in conjunction with the capacity test of Fig.
It will be evident that the quantum of capacitor
charging current per unit of time is proportional
10; but, on the other hand, it constitutes no im
pediment to the'serics resistance test because its
to the combined capacities of capacitors C and
series resistance has been ‘measured in advance
80 and, accordingly, that the quantum of current 50 of its inclusion in the instrument and ascertained
per unit of time discharged by said capacitors
to be very low, and the meter calibration takes
is, likewise, proportional to the combined capaci
into account its series resistance. Hence, there
ties of said capacitors. Hence, the meter de?ec
is no need to provide additional switching means
for cutting capacitor 80 out of circuit. Since the
tion is an accurate measure of the combined
capacities. The meter is calibrated to subtract 55 series resistances of two capacitors in parallel
from the scale reading the capacity of capacitor
have the same combined effect as do ordinary
resistors of corresponding magnitude connected
80 and, therefore, the actual scale reading cor
responds to the capacity of capacitor C only.
in series, the low series resistance of capacitor 80
does not have'the effect of reducing the total se
Series resistance test
60 ries resistance. In other words, the series resist;
ance of capacitor 88 does not constitute a low
With the four rotary switches adjusted so that
resistance shunt across the series resistance of
their movable contactors engage the “S” ?xed
contacts, the resulting effective network is that
capacitor C, but, instead, has the effect‘ of a
shown in Fig. 11. All elements and circuit con
corresponding low resistance in series with the
nections of Fig. 9 which do not participate in the
series resistance test have been omitted from
Fig. 11 in the interest of clarity.
Referring to Fig. 11, it will be seen that the
capacitor C, under test, is connected in shunt
to the .1 mfd. capacitor 80 and that said capaci 70
series resistance of capacitor C.
tors have a common terminal 88 connected to
the negative terminal of the D. C. source 81.
The other common terminal of said capacitors
(?xed contact “S” of switch 62) is connected
Now, for the sake of'simplicity, let us disregard
capacitor 80, for the time being, and assume that
it is cut out and that we are measuring only the
series resistance of capacitor C. Later on, I will
show the validity of this assumption.
The peak current pulses traversing the ca
pacitor~charging circuit ‘give rise to a correspond
ing series of recurrent peak voltage‘ pulses across
the terminals of secondary winding 45, which tere
through movable contractor 64 and resistor 85 75 minals are connected to vthe input electrodes of
detector tube 31; and since the latter is a grid
leak detector, a constant negative potential will
accrue on its control grid 43-which‘negative po
tential is determined almost entirely by the peak
values of potential across the terminals of sec
ondary winding 45. In other words, the average
‘or R. M. S. current in the capacitor-charging‘cir
cuit is not the determinant as respects the neg
the network which is utilized for adjusting the
cathode bias of tube 49, so that the instrument
will give a correct series resistance indication,
notwithstanding changed circuit conditions
which might otherwise impair the accuracy 01
the reading.
From an examination of Fig. 12, it will be seen
‘that the .3 mid. capacitor 83 is periodically
charged through resistors 14 and 85, and dis
ative potential accruing on grid 43, but rather
it is the peak current in that circuit—which peak 10 charged through resistor 85-capacitors 80 and
C being out of circuit. This produces a de?nite
current is not materially in?uenced by the mag
negative potential on grid 43 of tube 31 and a
nitude of the capacity of capacitor C, but is in
corresponding de?nite negative potential on grid
?uenced by the series resistance of that capac
50 of tube '48; and the plate-cathode current
The plate-cathode current through detector 15' through tube 49 is then determinable by the po
' tential of cathode 5|, which is adjustable by mov- ‘
tube 31 is, of course, dependent upon the poten
ing contactor 42 along potentiometer resistor 40b.
tial of grid 43--said current decreasing as the
Said contactor 42 is thus moved until the indica-.
grid becomes more negative and vice versa; and
tor of meter il registers with the meter scale seg
it will now be apparent that the greater the se
ries resistance of capacitor C, the greater will be 20 ment, marked “Adj.” By so adjusting the in-'
strument before making a series resistance test,
the plate-cathode current through tube 31. The
the operator can be assured that the capacitor
magnitude of plate-cathode current through de
under test is satisfactory from the standpoint of
tector tube 31 could be utilized directly as a meas
ure of series resistance by inserting a meter in
series resistance, if the indicator shows a reading
conductor 34, but it is preferable to provide an 25 within that part of the meter scale labeled “Ser.
arrangement wherein the current through the
' Res. 0. K.”
meter can be adjusted to produce a given scale
Some changes may be made in the construc
reading under a standard condition, and that can
tion and arrangement of the parts of my capaci
best be, done by utilizing a second tube, the bias
tor testing instrument without departing from
of which can be adjusted independently of tube 30 the real spirit and purpose of my invention, and
31. Thus, I have added tube 49, the grid 50 of
it is niy intention to cover by my claims any mod
which is connected directly to the cathode 44 of
i?ed forms of structure or use of mechanical
tube 31, and in the plate-cathode circuit of which
equivalents which may be reasonably included
is included the meter ll. Obviously, the plate
within their scope without sacri?cing any of the
cathode current through tube 48 varies in unison
advantages thereof.
with the plate-cathode current through tube 31,
but the grid-cathode bias potential of tube 48
can be regulated independently of tube 31 by rea
son of the fact that cathode 5| is connected to
the movable contactor 42 of the voltage divider.
The normal potential of cathode 5| can thus be
raised or lowered at will, and in that way, the
current through meter H can be adjusted to
produce a given scale reading in response to a
pre-established standard condition.
I claim as my invention:
1. In a system for measuring the series resist
ance of an electrostatic capacitor, a charging cir
cuit including a source of current of constant
voltage in series with said capacitor, a resistor in
cluded in said circuit in series with said capaci
tor. a discharge circuit for said capacitor, a two
' way switch continuously operating to open and
close said circuits alternately, a transformer hav- '
ing a primary winding and a secondary winding,
said primary winding being connected across said
resistor, a grid-leak triode detector having its
“Adj.,” and the purpose of this is ~vto enable
input electrodes connected across said secondary
the instrument to be adjusted in advance of a
winding, and a meter responsive to the plate
series resistance test, so as to compensate for 50 cathode current through said detector.
any condition in the circuit which might give rise
2. In a system for measuring the series resist
to erroneous series resistance indications, which,
ance of an electrostatic capacitor, a charging cir
in turn, might result in either passing bad capac~
cuit including a source of current of constant
itors or rejecting good ones.
voltage and a D. C. impedance, both in series
When the instrument has been adjusted in the 65 with said capacitor, switching means for periodi
manner hereinafter described and a capacitor is
cally opening and closing said charging circuit, a
under test, the series resistance of which is low,
discharge circuit for said capacitor, means for
the meter reading will fall within the limits of
closingv said discharge circuit each time said
’ that portion of the meter scale marked “Ser. Res.
charging circuit is opened, a detector associated
0. K.,” but if the series resistance is excessive, the
.with said D. C. impedance, a meter and a circuit
meter-indicator will de?ect beyond that portion.
for said meter including a source of current for
If, when capacitor C is disconnected, a series
actuating the meter, said detector being opera
resistance reading is made on capacitor 80, there
tive to vary the current in said meter circuit in
will be some de?ection of the meter. indicator due
conformity with the magnitude of the peak volt
to the series resistance of capacitor 80; but the 65 age across said D. C. impedance so that the de
meter scale portion, marked “Ser. Res. 0. K.” is
?ection of said meter is a measure of the series
made large enough to allow for that amount of
resistance of said capacitor.
series resistance, plus the permissible series re
3. In a system for measuring the series resist
Referring now to Fig. 8, it will be seen that
the meter scale includes a segment labeled
sistance in the capacitor under test.
10 ance of an electrostatic capacitor, a charging cir
cuit including a source of current of constant
voltage and a D. C. impedance, both in series
Prior to each series resistance test, the knob
with said capacitor, switching means for periodi
I3 is turned to the “Adj.” position and, as a re
cally opening and closing said charging circuit,
sult, the four rotary switches are set as shown
in Fig. 12. That ?gure portrays, schematically, 76 a discharge circuit for said capacitor, means for
Preliminary adjustment
closing said discharge circuit each time said
charging circuit is opened, a triode detector hav
ing a grid-cathode circuit including a grid-leak
eluding a grid-leak resistor shunted by a grid
capacitor, an anode-cathode circuit for said de
tector including a source of current, a triode am
' pli?er having its grid connected to the cathode
of said detector, a source of anode-cathode cur
rent for said amplifier, a voltage divider con
nected across said source of current, a movable
resistor shunted by a grid capacitor, said detec
tor being operatively associated with said imped
ance so that its grid bias is proportional to the
peak voltage developed across said impedance, an
anode-cathode circuit for said detector, means
connection between the cathode of said ampli?er
and said voltage divider, whereby to vary the nor
said ampli?er tube, a meter, and an anode-cath 10 mal potential of said cathode, and a meter in
ode circuit for said ampli?er tube including said
cluded 'in series in the anode-cathode circuit of
for varying the usual grid-cathode potential of
meter and a source of current, the arrangement
said ampli?er.
being such that the current through said meter
is proportional to the peak voltage across said
4. In a. system for measuring the series resist
ance of an electrostatic capacitor, a charging cir
cuit including a source of current of constant
voltage and a resistor, both in series with said ca
pacitor, a discharge circuit for said capacitor, a 20
continuously operating switch operative periodi
cally and alternately to open and close said cir
cuits whereby to recurrently charge and dis
charge said capacitor', a transformer having a
primary winding and a secondary winding, said 25
primary winding being connected across said re
sistor, a triode detector having a grid-cathode
circuit including the secondary winding of said
transformer, said grid-cathode circuit also in
The following references are of record in the
?le of this patent:
Jones ________ _'_____ Dec. 30, 1930
Houck __________ __ Sept.
McCarty ________ __ Feb.
Triplett ________ __ Sept.
Baumzweiger ____ __ June
France ____ __'____ __ May 12, 19.30
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