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Патент USA US3090922

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May 21, 1963
M. L. BOYER
IMPEDANCE MEASURING APPARATUS
Filed July 15, 1959
N62
F\G.4
3,090,913
United States Patent 0 "
1
3,090,913
Ill/IPEDANCE MEASURING APPARATUS
Marcel Louis Boyer, Chatillon-sous-Bagneux, France, as
signor to L’Electronique Appliquee, Paris, France
Filed July 15, 1959, Ser. No. 827,340
Claims priority, application France July 17, 1958
7 Claims. (Cl. 324—57)
weenie
Patented May 21, 1953
2.
Each one of the ampli?cation channels then includes
a clipper-limiter stage, E1 from A1 and E2 from A2. As
seen from FIG. 3, the circuitry of such a clipper-limiter
arrangement may be quite conventional. The sine sig
nals shown at (a) and (e) in FIG. 4 are thus converted
into substantially rectangular signals. The shaping how
ever is not suf?cient for their ?nal use.
Consequently,
the output of the clipper-limiter circuit E1 drives a Schmitt
bistable circuit B1 and the output of the circuit E2 sim
The present invention concerns improvements in or
relating to impedance measuring apparatus giving direct 10 ilarly drives a Schmitt bistable circuit B2. The waveforms
from such Schmitt circuits are then purely rectangular,
ly displayed readings of the values of the modulus or
as shown in graphs (b) and (f) of FIG. 4.
amplitude and argument, or angle of phaseshift, of any
These waveforms are differentiated producing the wave
electrical impedance component or device connected
forms as shown in graphs (0) and (g) of FIG. 4 before
thereto.
being applied to separate control inputs of a ?ip-?op
An object of the invention is to provide an impedance
device B,” as shown in FIGS. 1 and 3, the derivated pulses
measuring apparatus which may operate over a broad
of a predetermined polarity or direction being short
range of impedance values and an extended band of fre
circuited as shown by the diodes inserted in the said in
quencies, without taring in a wide portion at least of the
puts
of the ?ip-?op device 13,. The control of B, is
frequency band, and with a single meter scale on the
ensured by the two series of pulses shown in graphs (d)
modulus indicator in the device.
and (h) of FIG. 4. This control actuates the ?ip-?op
A further object of the invention is to provide this
which
delivers plate voltages such as (i) and (j) of FIG.
apparatus with the additional view of using it for also
4. In these rectangular waveforms, of opposite direc
measuring such parameters as relative phaseshifts of sig
tions of variations, the signals vary between two constant
nals, attenuation characteristics of networks and fre
value levels, a lower one, +V1 and a higher one, +V2.
quency responses of quadripoles.
A voltmeter M, is connected across the plates of the flip
An impedance measuring apparatus according to the
?op. This voltmeter will be submitted to an AC. drive
invention is mainly characterised in that it comprises the
the half-cycles of which have widths varying in accord
combination of a signal forming head or input network
ance to the recurrence periods of the control pulses, viz.
supplied with ‘a reference oscillation processed therein in
to the relative phaseshift between the pulses of the two
accordance with the value of an impedance under study
actuating series. Consequently, the change of ampli
and the value of an impedance of reference for deriving
tude-modulated signals into pulse position modulated sig
from said oscillation two signals respectively proportional
nals enables the direct reading on M,7 of the value of
to the said impedance values, two identical ampli?cation
channels receiving said processed signals, a modulus or
argument or phase shift of the impedance to study, as is
amplitude meter connected between symmetrical points 35 apparent since M, measures the value of the DC. com
ponent (reinforced line in graph (k) of FIG. 4) which is
of the said channels and further means in the said chan
representative of the said phase shift.
nels for further processing the signals and to actuate
therefrom a relative phase-shift measurement.
It must be noted that when this phaseshift is zero or
180°, the DC. component V is zero.
Further, when the
This and further features will be described wvith respect
to an example of a practical embodiment according to 40 direction of phaseshift changes, so changes the direction
of the said D.C. component. The device then enables
the invention with reference to the accompanying draw
a direct indication of the “sign” of the phaseshift, which
is important since it demonstrates the character either
capacitive or inductive of the impedance under study.
embodiment;
FIG. 2 shows two circuit diagrams relating to the signal 45 There is, however, a di?iculty because in practice such
a phase metering arrangement does not operate for zero
forming head in this embodiment;
value or for values neighbouring zero. The signals in
FIG. 3 shows an illustrative circuit diagram of part
the channels are coincident or nearly coincident in time.
of the embodiment of FIG. 1; and,
The ?ipe?op is not stable in such a case. However, this
FIG. 4 shows graphs to be used in the explanation of
50 may be remedied by introducing a 180° systematic phase
the operation of part of the said embodiment.
shift in one only of the channels, for instance at the level
Referring to FIG. 1, two symmetrical and actually
of the Schmitt bistable device. A switch 031 enables the
identical ampli?cation channels start from the terminals
operator to produce such a reversal when required, by
1 and 2. Each channel includes ?rst an ampli?er, A1
from terminal 1, A2 from terminal 2. The outputs of said 55 permitting the signal to one input of the ?ip-?op to be
selected from the one or the other of the plate outputs
ampli?ers are connected to respective inputs of a meter
Of B1.
.
of the ratio-meter kind, MZ, which will give a reading of
With this additional switching arrangement, the phase
the value of the modulus or amplitude of any impedance
meter included in the impedance measuring apparatus
Z under study. In one of the input leads to My, is in
may then indicate small values of phaseshift neighbouring
serted a galvanometer G.
60
ings, wherein:
FIG. 1 shows a block schematic Earrangement of this
Ampli?ers A1 and A2 are identically provided and
each includes a high value current feedback so that their
response (output current vs. input voltage) is of great
linearity. FIG. 3, part A1, shows an example of circuitry
for such a high linear response ampli?er. It includes 65
two cascaded ampli?er stages, the ?rst of which uses a
pentode tube and comprises a current feedback loop
through a recti?er bridge. The other diagonal of the
bridge is connected across the corresponding winding
of the ratio-meter MZ so that this winding is supplied
with the average output current from the ampli?er, which
is proportional to the input voltage.
zero and the zero value itself without any loss of accuracy.
During the use of the apparatus, terminals 1 and 2 will
receive signals the voltage value of which is due to re
main within certain predetermined limits so that the out
put currents from the ampli?ers be neither too high nor
too low as applied to the windings of M2. If these cur
rents were of a too high value, from too high voltages
at 1 and 2, the response would become non-linear. If
these currents were too low, the accuracy of the measure
would be damaged. The provision of a galvanometer G
in one of the leads to the meter MZ enables the operator
to detect such undesirable conditions so that he could
3,090,913
4
remedy by adjusting the level~of the input signals atml
of Ve-and' has its value de?ned by the ratio of the ?xed
resistance divider, viz.:
and 2 and reinstate normal operating conditions for the
apparatus!
,
_
,.
V.
,
.
r.
The head of the apparatus, or the input network on
the left-hand side of terminals 1 and 2 in FIG. -1, has an
input terminal Ve, receiving an A.C. voltage from a ref
erence source (not shown), the frequency and voltage of
Q denoting the said divider ratio.
I
The meter MZ will display the value of the ratio of the
said input voltages _V,z, and VP; It will of course be scaled
which may be adjustable, and includes a pair of voltage
in ohms. The phasemeter will give the value of go. As
the input of the apparatus is asymmetrical, one terminal
dividers, Rii-Riz and R21—R2z respectively, a ?rstset of
resistors R3, a second set of resistors R4, a selection switch 10 to ‘ground, there is no stray effect from the capacity in
the head.
C1 for these sets ofresistors, and a combination switch
C5 having four banks of three terminals each.~ These
However, this arrangement, if used alone, could not
banks are noted cm, 02-2, c23, Q4, and the terminals are
give the accuracy of the measurement in any; range of re
noted a, b and c.
r
_7
sistance values, since for a high value of Z, R4 should be
Position a of the combination switch will be later _dis 15 made of a ‘practically unobtainable value.
_'
Y. ,
cussed. In such position a, however,‘ it must be'noted
_ When dealing withimpedances Z_ of high value, the
that the contacts of e22 and 6,, connected to the terminals
operator switches C2 to position b, circuit (b) of FIG}.
of the impedance Z to study, are unconnected to any cir
cuit in the head or input network.
All advantages are preserved and,’ further, aninterversion
of the ampli?cation channels from thesignals developed
7
The connections of the other terminals in C2 are as
follows: terminal 0 of bank 021i is connected to the in
in, the head is so ensured as to re-establish the, correct
termediary tap of voltage divider R11--R12, terminal b
direction of the phaseshift measuredby Mq‘o, (Otherwise,
the direction and value of this phaseshift would have been
of bank 024 is connected to the intermediary tap of voltage ,
divider R21—R22. Terminals b of banks 021 and (:23 are
on
“complemented”). This ‘enables a single scale to be set
Mga.
.
‘
I
i
v
v.
A
)
._.I
simultaneously connected to that armature of C1 relating 25 _ With C2 on position b, the input terminal 1 receives
to resistors R3. Terminals c of banks (:23 and 6,, are
a voltage:
,
simultaneously connected to the armature of contact C1
relating to resistors R4.
'
»
and as R3 is far smaller than Z in this case,_concer_nirig
The switch C1 actually is a range commutator or selec
tor switch. All that may be notedconcerning this switch 30 the orders of values of Z and R3, this relation '(v) sub- ,
stanti-ally reduces to: _
as to'a pecularity thereof is that it includes aliposition
E which is to be used to e?ect an equilibrium of the chan
(vi)
nels before operation of the apparatus. The terminal E
in the set R3 is connected to the intermediary tap of di~
viderRzl-i-Rm. The terminal E in theset R4 is. con
nected to the intermediary tap of -R11—-R12. .Resistors
R11 and R21 may advantageously be provided asadjust
able resistors. The equilibrium or balancing of the chan
nels is effected by. an adjustment of. the feedbackratio
V,=V,.(R,/z)
v v
\
.Terminal 2 of the ampli?cation channelthen receives
avoltage:
it
I
t
_
,
V1‘: Ve-Raz/ (R2i-l-R22) :Ve-P
denoting
The meter
P theMz
ratio
gives
of this
the divider.
ratio of' the
v voltages
' on ter
in the ampli?ers A1 and A2; in this respect, an adjustable 40 minals 1 and 2. For position b, this'ratio d is:
resistance is shown in FIG. 3 in such a feedback circuit.
~(viii)
All terminals from resistances R3 oppositeto those co
operating with the armature of C1 are grounded. .All ter
minals from resistances R4,opposite to those cooperating
with the other armature of C1 are connectedto' the input 45
. reference terminal of the head.
Of course, the unshown
reference generator must. have a_~te‘rminal to the‘ ground,
as indicated in the drawing by, a ground at_the other termi
nal than the one to which are connected the circuitry
of the head or input-network.‘
,
_
'
, c
-
I
.
When switch C1 is in ‘any, other position than those
corresponding to E in sets Rsrand R4, one: of theresistors
R3 and a corresponding one of the resistors R4 are selected.
I
a=P.Z/R3
and for position '0, this ratio is:
For measuring with the same reading scaleon Mz
,values of Z one hundred times, for.:1inst'an'ce,_ higher in
a case than in the other one, it will su?ice to, provide that,
‘in thecircuitry of, the head, 100.2 according, to relation
50 (iv) is equal to Z according to relation (viii), viz.:
land,imore generally speaking, denoting, n asithe required
ratio of the value order of the impedances to study:
>When further switchyCz is onposition b withnan imped
Iance 2 connected as shown, the electric diagram of the 55
head is such as shown in (b); of FIG. 2. When, in ‘the
otherwise same conditionsswitch C2- is on position 0, the
.electric diagram of the head is such as shown at (c)
,)
NQW, as previously stated, thereis a vlrso'sitiona'for '
the switch C2 wherein theimpedance Z is disconnected
aswell as the sets of resistors and voltage dividers from
Considering ?rst the position l-c‘of C2‘, circuit diagram 60 :terminals
1_ and 2. .In this positionaathev terminals ..1
(0) in FIG. 2, the input voltage at 2 is: '
in 'FIG.
2.
.
.
,
, and 2 are merely connected to taps of attenuators el and
Vz=V.-'z/(Rr+Z)
e2. For instance these attenuators may be of the. ,kind
Z, for instance of. the order of .ahundred times Z or more,
thanfor measuring impedances. Two separate signals
(i)
.varying'by. degrees, and for instance arercalibrated to vary
and; provided R4 is of an order of value much higher than 65' from 5 vdecibleshetween each'tap. This. meanstthajt the
relation (i) is substantially equivalent to:
(ii)
'
V,'=V,z/R,
apparatus may as well be used foradditional purposes
. may be applied to theattenuators and Mlp willv give the
_ phase shift between these signals. A quadripole maybe
Z being a complex impedance, .viz. offthe form R-HX,
70 .connected across the attenuators and fed by a reference
the argument of the impedance, i.e. the phaseshift intro
duced with respect to Ve substantially is:
- pole. .MZ may have a decible scale too,,forj,su,ch a pur
voltage. '7 The change of‘frequency of this voltage, will
enable study of the response’v characteristic ,of said quadri
_
<p=arc tan X/R
pose. ‘_ {Xttenuationmeasurements may also be madeby
The input voltage on terminal 1 will preserve the phase 75 connecting the outputs of transmission circuits and de
vices to the inputs of the attenuators e; and e2; a.s.o.'
(iii) 7
3,090,913
5
I claim:
1. Apparatus for measuring the impedance value and
the phase angle of an unknown impedance comprising, in
combination, a source of oscillations comprising a genera
tor having one terminal thereof grounded, an input net—
work energized from the other terminal of said generator
and including two branch circuits, one branch circuit in
cluding a reference impedance embodied in a ?rst ?xed
resistance voltage divider and the other branch circuit in
cluding a second voltage divider formed of the unknown
impedance to be measured and a ?rst standard imped
ance, said branch circuits producing at the outputs of said
voltage dividers two signals proportional respectively to
the impedance values of said reference impedance and
said unknown impedance, two identical ampli?cation 15
6
means to connect the other end to a terminal of the said
range selection switch.
5. An impedance measuring apparatus according to
claim 2, including additional means on said range selec
tion switch to provide an additional position wherein to
disconnect the sets of standard resistors from the terminals
of the combination switch.
6. An impedance measuring apparatus according to
claim 1, including a pair of attenuators, means for direct
ly connecting said pair of attenuators to the output termi
nals of the said branch circuits of said input network and
simultaneously disconnecting therefrom all other circuits
of the input network.
7. Apparatus for measuring the impedance value and
the phase angle of an unknown impedance comprising, in
channels controlled by said signals of said branch circuits,
combination, an input terminal connected to a source of
respectively, a ratiometer connected to be energized be
tween symmetrical points on said two channels for indi
cating the ratio of the ampli?ed signals in said two chan
nels, a phase meter having two inputs energized respec 20
cuits connected to said terminal, one branch circuit in
cluding a reference impedance embodied in a ?rst ?xed
tively from the outputs of said ampli?cation channels
and indicating the relative phase shift between the signals
in said two channels produced by the unknown imped
oscillations, an input network comprising two branch cir
resistance voltage divider and the other branch circuit in
cluding a second voltage 'divider formed of the unknown
impedance to be measured and a ?rst standard imped
ance, said branch circuits producing at the outputs of
said voltage dividers two signals proportional respectively
ance connected in one of said branch circuits, ‘a third volt
age divider formed of ?xed-resistances of different resist 25 to the impedance values ‘of said reference impedance and
ance values from said ?rst ?xed-resistance divider, a sec
ond standard impedance of a different value from said
?rst standard impedance, and a multiple-contact switch
for establishing in one position thereof the connections of
said ?rst and second dividers in said branch circuits and, 30
said unknown impedance, two identical ampli?cation
channels controlled by said signals of said branch circuits,
respectively, a ratio-meter connected to be energized be
tween symmetrical Points on said two channels for indi- -
cating the ratio of the ampli?ed signals in said two chan
nels, a phase meter having two inputs energized respec
in another position thereof connecting said second ?xed
tively
from the outputs of said ampli?cation channels and
resistance divider in said other branch circuit instead of
indicating the relative phase shift between the signals in
said second voltage divider, and simultaneously connect
said two channels produced by the unknown impedance
ing said unknown impedance and said second standard
resistance in a fourth voltage divider connection in said 35 connected in one of said branch circuits, each channel in
cluding means for converting ‘amplitude-modulated and
one branch circuit, and disconnecting said ?rst ?xed-resist
phase-modulated signals into position-pulse-modulated
ance divider, said unknown impedance and said second
signals, each channel also including a Schmitt-type trig
standard resistance being reversed in positions in said
ger circuit for shaping and differentiating said position
fourth voltage-divider connection from the positions oc
modulated
pulses, a ?ip-?op device having inputs to
40
cupied by said unknown impedance and said ?rst stand
which are applied pulses from said Schmitt-type' trigger
ard impedance in said second voltage divider connection.
circuits, said phasemeter being connected across the ‘out
2. An impedance measuring apparatus according to
puts of said ?ip-?op for indicating the relative phase
claim 1 wherein said pair of standard resistors includes
shift between the two series ‘of input pulses, by the meas
further standard resistors to form sets of standard resis
tors and a range selecting switch connected to select a 45 urement of the dc. component of the voltage across said
?ip-?op outputs, and switching means for selectively ap
pair of corresponding standard resistors in said sets prior
plying
to one of the ?ip-?op inputs either the signal from
to the operation of the combination switch, the ratio of
one or the other of the respective plates of the correspond
values of corresponding standard resistors in the said sets
ing Schmitt-type ‘trigger circuits.
being maintained constant during the said range selection
switching.
References Cited in the ?le of this patent
3. An impedance measuring apparatus according to
UNITED STATES PATENTS
claim 2, wherein the ratio of the standard resistors in said
2,558,945
Fritzinger ____________ __ July 3, 1951
sets is propertional by a predetermined constant coe?i
2,622,127
Alsberg et ‘a1. ________ _._ Dec. 16, 1952
cient to the product of the ratios of the ?xed resistance
5 01
voltage dividers.
4. An impedance measuring apparatus according to
2,806,295
Ball ________________ __ Sept. 17, 1957
OTHER. REFERENCES
claim 2, including ‘a ground connection for one end of
Kretzmer, “Measuring Phase at Audio and Ultrasonic
the standard resistors of one set, means to connect the
Frequencies,” Electronics, October 1949, pp. 114-118.
other end to a terminal of the range selection switch,
Holtje et al., “Experimenter,” General Radio, April
means connecting one end of the standard resistors in the 60
‘other set to the input terminal of the input network and
1956, vol. 30, No. 11.
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