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Àug- 28, 1952
J. U. l-:YNoN
3,051,898
MEASURING AND INTEGRATING SYSTEM
Filed sept. 28, 1959
k26
United States Patent
tice
3,051,898
Patented Aug. 28, 1962
2
1
in conjunction with the accompanying drawing in which
3 051,898
MEASURING AND’INTEGRATING SYSTEM
James U. Eynon, Willow Grove, Pa., assignor to Leeds
and Northrop Company, Philadelphia, Pa., a corpora
tion of Pennsylvania
Filed Sept. 28, 1959, Ser. No. 842,879
17 Claims. (Cl. 324--100)
there has been diagrammatically illustrated a system em
bodying the invention.
Referring to the drawing, there is applied to input termi
nais 1€) and 11 a voltage EX representative of, that is
proportional to, the magnitude of a condition to be
measured and integrated Values of which are desired.
Though as indicated above, 'there are many condi
This invention relates to measuring and integrating
tions Where there may be desired measurements of the
systems and has for an object the provision of such a 10 magnitudes as well as the determination of quantities
system which is reliable in operation and which per
representative of integrals of such conditions, reference
forms the required multiple functions of measuring and
may be had to gas chromatography as one field where
integrating with a minimum of components.
such measurements are particularly useful. For eX
In many industrial processes it is frequently desirable
ample, it has been found that with gas chromatograms a
to integrate with respect to time the magnitude of a 15 better correlation with concentration is achieved if area
condition or a measured variable and to produce an in
measurements beneath peak values are utilized instead
dication and/ or a record of the integrated magitude of
of measurements alone of the peak heights of the out
such a condition. In order to integrate the magnitude
of a condition, there must be provided a measuring sys
put of the chromatograph detector.
Thus it may be as
sumed that the voltage EX is that produced by the detector
tem arranged to produce a measured output of magnitude 20 in a gas chromatograph.
at all times proportional to that of the condition. This
The magnitude of the voltage Ex is determined by a
measured output is then applied to an integrating means
measuring system which includes a detector 12 and a
for producing a second output proportional to the integral
potentiometer comprising a slidewire resistor 13 energized
with respect to time of the measured output.
from a suitable source of supply, such as a battery 14
‘ In accordance with the present invention, the measuring 25 by Way of a rheostat 1S. The detector 12 is preferably
system which is utilized to produce the measured output
of the electronic type and such as shown in Williams
proportional to the magnitude of the condition is like
Patent 2,113,164. This detector operates to adjust the
wise utilized for measuring the second output proportional
movable contact 13a of slidewire 13 to maintain in bal
to the integral of the first output. This is accomplished
ance the measuring circuit. Thus as the magnitude of
by providing a means of disconnecting the integrating 30 the voltage EX changes, so does the position of contact
means from the measuring system and for then applying
13a on slidewire 13. Besides the mechanical connec
the second output as the input to that measuring system
tion to the contact 13a as indicated by the broken line,
for producing therefrom an indication of the magnitude of
there is also a mechanical connection, as indicated by
the integral with respect to time of the magnitude of the
the broken line 16, to a pen-index 17 of an exhibiting
35
condition. Thus the system as a whole operates periodi~
means which includes a scale 18 and a chart 19 arranged
cally to measure and to integrate the magnitude of a
to be periodically driven by a chart-driving motor 20.
condition and periodically to provide indications and/or
As the magnitude of the voltage Ex changes'in one direc
records of the integral with respect to time of the mag
tion or the other, the pen-index 17 -Will be driven in one
nitude of the condition.
direction or the other to- indicate on the scale 18 its in
40
In a preferred form of the invention there is utilized
stantaneous magnitude and to record that magnitude on
a measuring circuit for producing a voltage output pro
the chart 19.
portional to the magnitude of the condition. This voltage
The detector 12, through a mechanical connection 22,
output is applied to an integrating system including an
relatively adjusts a slidewire 23 and its associated con
ampliñer, an integrating capacitor, and an integrating re
tact 23a energized from a constant voltage source 24
sistor. The arrangement is such that the magnitude of 45 to produce, for an integrating system now to be described,
the charge on the capacitor is proportional to the integral
an input voltage EI, proportional to the voltage Ex. Thus
with respect to time of the voltage representative of the
the measuring system produces a first Voltage output which
magnitude of the condition. Periodically the integrating
is the input to the integrating system.
system, having a voltage output representative of the
The integrating means may be of the type disclosed in
charge on the integrating capacitor, is disconnected from
Davis et al. Patent 2,830,245. As shown, the integrating
the measuring circuit. This output is then applied to the
system comprises an integrating resistor 25 (which cor
input of the measuring circuit, 'which input is then disresponds With the reset resistor of said patent) and an
connected from the condition under measurement, for
,amplifier 26 having a modulating means shown in the
measurement of the output, and thus the integral with
form of a vibrator 27 included in its input circuit. The
55
respect to tim-e of the magnitude of the condition over
movable contacts of the vibrator 27 is driven by an
the preceding time interval. Preferably, the measuring
operating coil 28 alternately to engage iirst one stationary
system includesv an exhibiting means for indicating not
contact and then to engage the other stationary Contact
only instantaneous variations in the- magnitude of the
of the vibrator. The amplifier 26 includes in its output
condition, but also for indicating and recording the afore 60 circuit a converter 29, such for example, as illustrated
said integral with respect to timev of that condition.
,
in FIG. 4 of said -Davis et al.> patent, in order to produce
For further objects and advantages of the invention
across output conductors 30 and 31 a direct current out
and for a discussion of a typical embodiment thereof,
put which increases when the alternating current input
reference is to be had to the following description taken
l(produced by vibrator 27) is of one phase and decreases
3,051,898
3
A.
when that input is of opposite phase. The conductors
seen that the potential difference at balance across the re
30 and 31 correspond with the connection in FIG. 4 of
sistor 36 will be equal and opposite to the potential dif
said Davis et al. patent leading to the cathode of the ,
ference across the capacitor 32.
The resistance means
tube 91 and to the conductor 50 of that patent. Phase
including the resistor 37 and the slidewire 38 is provided
sensitive converters which produce direct current outputs 5 in order that there may be derived therefrom a fractional
may take various forms, and a further example of a
part of a voltage equal to that across capacitor 32 for ap
suitable system may be found in FIG. 1 of McAdam et
plication to the input of the measuring system. This
al. Patent 2,901,563.
fractional voltage El is proportional lto the integral with
With slidewire contact 23a in its illustrated position, it
respect to time of the applied input signal EX. The man
will be understood there is an output from amplifier 26
ner in which the magnitude of the integrated output signal
and its converter 29. The polarity is such that current
is measured and recorded will now be described.
flows from one side of converter 29 by way of conductor
During the operations which have just been described,
30, an integrating capacitor 32, an integrating resistor 25,
contacts 33, the lower fractional part of the slidewire 23,
and by way of conductors 34 and 31 to the other side of
the converter 29. The potential difference developed by
the current fiowing through integrating resistor 25 op
poses the potential difference Ep. If these two voltages or
potential differences be of unequal value, there will be an
input signal to the amplifier 2.6 which will produce a 20
change in the output in a direction to reduce the difference,
approaching zero as a limit. 'Ihat the described opera
tion takes place will be evident by considering that the
movable Contact of vibrator 27 first engages its left-hand
a timing motor 41 energized from a suitable source of sup
ply has been effective in rotating a series of control cams
42-45 inclusive in a counterclockwise direction. After
a predetermined time interval and corresponding with the
time over which the magnitude of the condition EX is to
be integrated, a trough of cam 42 arrives in registry with
a cam follower 46 for operation of switch contacts 47 and
45 from their uppermost to their lowermost positions to
interrupt the circuit from the input terminals 10 and 11
and to complete a circuit from output conductors 49 and
Si) from the integrator to the input conductors 51 and 52
of the measuring system.
stationary contact. There will then be applied to the in 25
Concurrently with, and preferably just in advance of,
put of amplifier 26 an input signal of polarity and mag
the operation of the switch contacts 47 and 48, »the trough
nitude depending upon the direction and magnitude of the
of cam 44 arrives in registry with a cam follower 53 for
difference between the voltage Ep and the potential dif
the opening of switch contacts 33 an instant ahead of the
ference developed across the integrating resistor 25. Thus,
operation of the contacts 47 and 48. The effect of open
this input signal will be of one polarity or of an opposite
ing the switch contacts 33 is to disconnect the output of
polarity. When the movable contact 27 engages its right
the measuring means from the input circuit of the integrat
hand stationary contact, it will be seen the input to the
amplifier is shorted, meaning that there is zero signal ap
plied thereto. 'Ihus, zero or ground potential is utilized
as a reference signal with which the aforesaid difference
signal is at all times compared.
The periodic operation of the movable contact of vibra
tor 27 in opening and closing the aforesaid circuits pro
duces an input to the amplifier 26 having an alternating
ing means. With the contacts 33 open, the point 40 is
still maintained at or very close to ground potential by
the action of the amplifier 26. This action will maintain
the voltage across resistor 36 equal and opposite to the
voltage across the capacitor 32 during the time that the
contacts 33 are open.
Thus the integrator can store an
integrated value for a period of time so that the value
can be read out at the operator’s convenience. There
current component of a frequency dependent upon that 40 after, or concurrently therewith, the contacts 47 and 48
of the alternating source used for energizing the driving
connect the output of the integrating means to the input
coil of the vibrator 27. As shown, that source has a fre
of the measuring system. Since the voltage El is propor
quency of sixty cycles per second. The phase of the al
tional to the charge on the integrating capacitor 32, the
ternating current will depend on the polarity of the poten
measuring system will now be effective to measure the
tial difference applied to the input circuit of amplifier 216.
time integral of the voltage Ex over the period of time
If it now be assumed that the voltage Ep is greater than
during which integration took place. Thus, the detector
that developed across the integrating resistor 25, then
12 responds to the voltage E1 andthe contact 13a is moved
there will be an increased output from amplifier 26 to in
to a circuit-balancing position, and through the driving
crease the unidirectional current flow through integrating
connection 16 the pen-index 17 is lmoved to a position
resistor 25 to restore the voltage balance in the input cir 50 corresponding with the integrated value, Ei, of the condi
cuit to the amplifier 26.
tion as represented by the voltage Ex. This integrated
The integrating action takes place by reason of the fol
value is exhibited on the scale 18.
lowing considerations. Inasmuch as the current path for
To provide a distinctive indication on the chart 19, a
the integrating resistor 2S is by way of the integrating
crest is provided on the cam 43 which is arranged to close
capacitor 32, it will be seen that the current flow to the 55 the motor control switch 21 shortly after the operation of
capacitor 32 must be maintained constant if there is to
the switches by cams 42 and 44, as above described.
be produced a constant potential difference across the in
tegrating resistor ‘25. Inasmuch as the capacitor 32 ac
quires a charge and potential difference of magnitude pro
portional to the integral with respect to time of the cur
rent flowing through it (and hence proportional to the
integral with respect to time of the magnitude of the in
put condition EX), to overcome the increasing charge on
capacitor 32, there is developed from the amplifier 26
and the converter 29 an increasing output, an output
which increases as long as the voltage Ep has a finite
value greater than zero and at a rate depending upon the
magnitude of ythe voltage Ep.
Included in the output circuit of the converter 29 are
branch circuits, one including a resistor 36 and the other
including a resistor 37 in series with a slidewire 38 hav
ing a manually adjustable contact 38a.
It will be recalled that at balance, the point 40 is
With motor 20 energized, the chart is rotated in a down
ward direction to produce, by the chart-marker or the pen
portion of the pen-index 17, a line in the direction of
60 travel of the chart.
Such a line is shown at 19a. Anoth
er such line is shown at 19h. It will be noted that the line
1% appears to the left of the end of the horizontal line
just beneath it and for the following reasons.
In the integration of the magnitude of a condition hav
ing the `characteristic of a high amplitude which lasts
for a short interval of time, the peak value of the voltage
EX will exceed the integrated value represented by the
voltage E1. Thus on the chart 19 there will be recorded
all peak values which exceed in magnitude the time in
tegral of the condition over the period of time during
which the integration takes place. In this connection,
it is to be understood that by increasing the magnitude
of Ei, as by suitable adjustment of the contact 38a, all
brought to the same potential (to a very close approx
integrated values may be made to exceed the peak values
imation) as the conductor 34. Accordingly, it will be 75 as appearing on the chart 19, but without the respective
apetece
Y
5
.
6
,
measurements departing from true proportionality in re
spect to the magnitudes of ‘the condition under meas
urement and with respect to the time integrals of such
conditions.
The timing cams 42 and 44 maintain the contacts 47
and 48 in their lowermost position and the switch con
tacts 33 open until the motor 20 has been energized for
a length of time adequate to produce the distinctive in
tor and a potentiometer adjustable by'said detector for
maintaining said measuring system in balance with change
in the magnitude of said condition, and means operable
by ‘said detector for indicating instantaneous magnitudes
of said condition.
3. The measuring and integrating apparatus of claim 2
in which there is provided a voltage-developing means,
means operable by said detector for adjusting said volt
age-developing means for producing as la voltage said
a switch 54 to short-circuit the capacitor 32 wholly to 10 ñrst output of magnitude proportional to the magnitude
of said condition, said integrating means including an
discharge it, a cam follower 55 being associated with
integrating resistor and an integrating capacitor for pro
cam 45 for the operation of switch 54. Thereafter, the
ducing as a voltage said second output proportional to
cams 42-45 operate to restore the parts to their illus«
the integral with respect to time of said first output volt
trated positions. The applied voltage EX is immediately
age.
detected by the detector l2 which functions through con
4. The measuring and integrating apparatus of claim 3
tact 13a to rebalance' the measuring circuit and to set
dications on the chart 19. Thereafter the cam 45 closes
in which said integrating means includes amplifying
the-contact 23a to develop the input voltage Ep for the
means having a direct current output for supplying cur
integrating means. The integrating means then operates
rent to said integrating capacitor through a circuit in
in the manner described above to initiate the charging
of the capacitor 32 and for the development of the out 20 cluding said integrating resistor for producing in the in
put to said amplifying means a voltage balance.
put signal Ei from the integrating means preparatory to
5. The measuring and integrating apparatus of claim 4
the next operation of the circuit controlling switches 21,
in which said amplifying means has an input circuit and
33, 47, 48 and 54.
in which said switching means for disconnecting said inte
lf it be desired to integrate the quantity EX over more
grating means includes a switch for interrupting the cir
than one cycle of operation as determined by the motor
cuit between said voltage-developing means and said
41 and its associated cams, a switch 56 in series with
capacitor without interrupting connections of said capaci
the switch 54 may be opened so that the capacitor 32
tor to said input circuit of said amplifying means, where
will not be discharged at the end of the first cycle. If
by said second output will be proportional to the magni
after the crest of cam 45 has passed the cam follower 55,
the switch 56 be closed, the output E1 of the integrating 30 tude of the potential difference across said integrating
capacitor.
means will then be representative of the integrated quan
6. The measuring and integrating apparatus of claim l
tity EX over two time cycles. Obviously, the integration
may take place over any -selected number of consecutive
time cycles. By timed opening and closing of switch 6l
integrations over selected time cycles may be omitted.
For convenience, the integration interval has been de
scribed as taken in respect to time, the timing motor 41
providing the time-parameter. If the integration interval
be desired in respect -to a different quantity, the cams
in which there is provided means for modifying the opera
tion of said switching means for varying the time interval
over which integration of said first output takes place.
7. The measuring and integrating apparatus of claim l
in which there is provided means for resetting to zero said
integrating means after operation of said switching means
to apply said second output -as the input to said measur
¿i2-45 will be operated by a driving means energized
under the control of that quantity. For example, a
switch 57 in series with the motor 41 will be opened and
closed by a control means 58 responsive to the quantity
in respect’to which the integration interval is to take
ing system.
place.
ing system for relatively moving said marker and said
With the above understanding of the invention, it is
to be understood that modifications may be made in
various parts of >the system and that some features may
8. The measuring and integrating apparatus of claim 1
in which there is associated with said measuring system
an exhibiting instrument having a chart, a marker for said
chart, means operable under the control of said measur
chart for producing a record on said chart of the magni
tude of said condition, and means operable in timed re
lation with said switching means for relatively moving
said chart and said marker in a different direction for
to cover such modifications and reasonable equivalents 50 producing a distinctive mark on said chart in position
be utilized without other features, it being the intent
by the appended claims.
What is claimed is:
l. A measuring and integrating apparatus comprising
a measuring system having an output circuit and an in
put circuit, switching means for applying an input signal
to said input circuit proportional to the magnitude of a
condition for producing at said output circuit a ñrst out
put of magnitude proportional to the magnitude of said
indicative of the magnitude of said second output.
9. A measuring and integrating apparatus comprising
a measuring system having an output circuit and an input
circuit, switching means for applying an input signal to
said input circuit proportional to the magnitude of a
condition, said measuring system including a detector and
potentiometer means foi- producing at said output circuit
a first voltage output of magnitude proportional to the
magnitude of said condition, integrating means having
condition, integrating means having an output circuit and
an input circuit connected to said output circuit of said 60 an output circuit and an input circuit connected to said
output circuit of said measuring system for integrating
measuring system for integrating with respect to» time
with respect to time said first output and for producing
said iirst output and for producing at said -output circuit
at said output circuit of said integrating means a second
of said integrating means a second output proportional
output proportional to the integral with respect to time
to the integral with respect to time of said ñrst output, and
means for operating said switching means for discon 65 of said íirst output, said integrating means including an
integrating resistor, an integrating capacitor, voltage-di
necting said integrating means from said output circuit
viding resistance means and an amplifier of the chopper
of said measuring system and for connecting said output
type responsive to the difference between said iirst volt
circuit of said integrating means to said input circuit
age output and the potential difference developed across
of said measuring system in place of the input responsive
said integrating resistor, a phase-sensitive converter hav
to the magnitude of said condition for establishing a mag
ing an output circuit and an input circuit connected to the
nitude of the output from said measuring `system pro
output of said amplifier for producing a direct current
portional to the integral with respect to time of said
output, said integrating resistor and said integrating ca
magnitude of said condition.
pacitor being connected in series circuit relation with said
2. The measuring and integrating apparatus of claim l
output circuit of said converter and with said output
in which said measuring system includes a voltage detec
3,051,898
8
opposite polarity, an integrating capacitor connected
circuit of said measuring system, said resistance means
being connected across said output circuit of said integrat
in series-circuit relation in said output circuit of said
amplifier and in series-circuit relation with said integrat
ing means, and means for operating said switching means
for disconnecting lsaid integrating means from said out
ing resistor, the amplifier output current iiowing through
put circuit of said measuring system and for connecting 5 said integrating resistor having a magnitude which de
velops said potential difference balancing said measuring
the output circuit of said integrating means to said input
circuit of said measuring system in place of the input
system output voltage, voltage-dividing resistance means
responsive 'to the magnitude of said condition for apply
connected across said amplifier output circuit for develop
ing at least a fractional part of the voltage developed
ing a potential difference, switching means for connect
across said resistance means to the input of said detector 10 ing the input of said amplifier to be responsive solely to
for establishing a voltage output from said measuring
the difîerence in the potential acquired by said integrating
system proportional to the magnitude of the voltage de
capacitor and that developed by said voltage-dividing re
rived from said resistance means thereby to provide a
measurement of the integral with respect to time of said
sistance means, said amplifier regulating the current ñow
through said resistance means to produce a potential dif
ference equal and opposite to that across said integrating
capacitor whereby measurement of a potential difference
developed by said resistance means will `be proportional
magnitude of said condition.
10. A measuring and integrating apparatus comprising
a measuring circuit having input terminals for applica
tion thereto of a voltage which varies in accordance with
the magnitude of a condition, said measuring system in
cluding a detector and potentiometer means for produc
to the potential diiierence across said integrating capaci
tor, and means for applying at least a fraction of said
last-named potential difference as the sole input to said
ing a voltage balancing that of the applied voltage and
measuring system for the measurement of the magnitude
for producing a first output voltage of magnitude propor
of the integral with respect to time of said magnitude of
said condition.
tional to the magnitude `of said condition, integrating
means including an amplifier having an input circuit,
13. The combination of claim l2l in which said meas
modulating means included in said input circuit, a phase 25 uring system includes a Voltage detector and a potentiom
eter adjustable by said detector for maintaining said
sensitive converter connected to the output of said ampli
fier for producing a direct current output, an integrating
measuring system in balance with change in the magni
resistor and an integrating capacitor in series-circuit re
lation with said output of said converter, means including
said modulating means for applying to said amplifier the
difference between said first output voltage and the poten
tial diti’erence developed across said integrating resistor
for applying a signal having an alternating current com
tude of said condition.
14. The combination of claim l2 in which there is
provided means for modifying the operation of said`
switching means for varying the time interval over which
the amplifier output current iiows through said integrating
ponent of phase and of amplitude dependent upon the
direction and magnitude of said difference, resistance
capacitor.
l5. The combination of claim l2 in which there is
associated with said measuring system a recorder having
means connected across said output of said converter for
a chart, a marker and driving means for said chart, means
operable under the control of said measuring system for
developing a potential difference, an output circuit from
moving said marker for producing a record on said chart
said integrating means derived from said resistance means,
of the magnitude of said condition and of the magnitude
switching means for disconnecting said integrating means
from said measuring system, whereby said direct cur 40 of the integral with respect to time of said magnitude of
rent output produces a potential difference across said
said condition, and timing means for controlling the
operation of said switching means.
resistance means equal and opposite to that across said
integrating capacitor, and 4means for interrupting the
16. The combination of claim l5 in which means are
provided to control said driving means for said chart for
circuit from said input terminals to said detector and
movement of said chart only during the said production
for establishing connections from the output circuit of
said integrating means to said detector as the input to
said measuring system thereby to produce a magnitude
of said first output voltage proportional to the integral
with respect to time of the magnitude of said condition.
l‘l. The measuring and integrating apparatus of claim l0 ^
in which there is »associated with said detector an exhibit
ing means having a chart, driving means for the chart,
of one of said records on said chart.
17. A measuring and integrating yapparatus comprising
a measuring system responsive to the magnitude of a
condition for producing a first output of magnitude pro
portional to the magnitude of said condition, integrating
tion of the instantaneous magnitudes of said condition
means having an input circuit, means operable under the
control of said measuring system for developing across
said input circuit an input voltage proportional to the
magnitude of said condition, said integrating means com
during the period of integration thereof, and timing means
prising means including Áan `amplifier for producing in
for establishing the time over which said magnitude of
its output circuit a direct current of magnitude which
increases when the input to said amplifier is of one polar
a marker for producing a record on said chart for indica
said condition is integrated for controlling the operation
of said switching means and for controlling the operation
ity and decreases when the input to said amplifier is of
of said driving means for said chart to move said chart
opposite polarity, an integrating capacitor and an in
60 tegrating resistor in series-circuit relation with said out
relative to said marker.
12. The combination with a measuring system for
put circuit of rsaid amplifier and in said input circuit, a
measuring the magnitude of a condition and for produc
connection from one side of said input of said amplifier
ing an output voltage of magnitude proportional to the
Xtending to the junction between said integrating resis
magnitude of Aa condition, of integrating means having
tor and said integrating capacitor, and a second connec
an input circuit to wi‘hch said output voltage is applied,
tion for the other side of said input extending to the side
an integrating resistor in series-circuit relation in said
of the output circuit of said amplifier remote from said
input circuit, an amplifier having an output circuit and
integrating capacitor for application to said amplifier ot
an input including said input circuit for application there
the difference-potential between said input voltage and
to of the difference between said output voltage and the 70 the potential difference developed across said integrating
potential difference developed across said integrating re
resistor by reason of current iiow therethrough from said
sistor, said amplifier including output means for produc
amplifier by Way of said integrating capacitor whereby
ing flow of a direct current through said output circuit
said output current from said amplifier will charge said
which increases or decreases when said difference volt
integrating capacitor to a potential proportional to the
age applied to its input is of one polarity or of an
integral with respect to time of said magnitude of said
a î @51,898
Q
l@
condition, Voltage-dividing resistance means connected
References Cited in the file of this patent
UNITED STATES PATENTS
across the output of said ampliñer, switching means for
disconnecting from said input circuit said input Voltage
for development yin said input of said »amplifier of ya poten
2,359,767
Keinath _____________ __ Oct. 10, 1944
2,366,913
Le Clair ____ _1_ ________ __ Jan. 9, 1945
tial difference representing the difference between that
2,575,711
Hippie _____________ __ Nov. 20, 1951
across said integrating capacitor and that developed by
2,577,735
Broomell ___________ __ Dec. 11, 19‘51
said resistance means, and means including said switching
2,663,855
Beggs _______________ __ Dec. 22, 1953
means for applying as the sole input to said measuring
OTHER REFERENCES
system -a potential difference derived from said resistance
means for operation of said measuring system to produce 10
Publication: “A Combined Current Indicator and In
tegrator,” on pages 688490 of “The Review of Scientific
an output proportional to the magnitude of the integral
Instruments,” vol. 22, No. 9, Sept. 1951.
with respect to time of said magnitude of said condition.
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