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Oct. 8, 1946._
D. BLITZ
2,408,727
MEANS'FOR CI‘RCUIT TIME CONSTANT MEASUREMENT‘ ,
Filed July 11, 1944
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2,408,727
Patented Oct. 8, 1946
‘UNITED STATES PATENT OFFICE
2,408,727
MEAN S FOR CIRCUIT TIME CONSTANT
MEASUREMENT
Daniel Blitz, Princeton, N. J., assignor to Radio
Corporation of America, a corporation of Dela
ware
Application July 11, 1944, Serial No. ‘544,448
8 Claims.
1
(Cl. 161-15)
.
This invention relates generally to the testing
and -measuring ‘of operating characteristics of
electrical circuits and more particularly to an
2
electrical network wherein said capacitor and said
network are deenergized simultaneously until
said network attains a predetermined electrical
condition, and wherein the time constant of said
improved method of and means for measuring
network is indicated as a function of the residual
the time constant or delay time of electrical net
charge on said capacitor.
,
works.
The invention will be described in greater de
In the design, manufacture and testing of com
tail by reference to the accompanying drawing
plex electrical systems such as are employed for
of which Figure l is a schematic circuit diagram
remote control, telemetering, and radar, for ex
ample, it frequently is necessary to determine and 10 of one embodiment of the invention adapted to
the measurement of the eiiective time constants
maintain within predetermined limits the effec
of an electrical network which includes an elec
tive time constants or delay times of predeter
tromechanical device, Figure 2 is a schematic
mined circuit components. While the time con
circuit diagram of a second embodiment of the
stant of simple reactive circuits may be cal
invention, and Figure 3 is a schematic circuit
culated from the known circuit parameters, a
diagram of a third embodiment of the invention.
simple and reasonably accurate method of de
Similar reference characters are applied to simi
termining the effective time constants or delay
lar elements throughout the drawing.
times of more complex networks is extremely ad
Figure l of the drawing shows a complex elec
vantageous.
trical network X which, for example, may in
The present invention provides several embodi
ments of an improved method of and means for
employing the known discharging characteristics
of a capacitor for measuring the time constant
or delay time of an independent electrical net
work which may include electro-mechanical com
ponents.
The invention is particularly advan
tageous for testing and matching the time con
stants or delay times of complex electrical net
clude a capacitor 3 and a resistor 5 connected
in parallel across the input circuit of a conven
tional relay ampli?er ‘I which is connected to
energize the winding 9 of a relay II. The relay
25 H, for example, may include a movable contact
[3 and two ?xed contacts [5, l1 arranged to pro
vide a single-pole double-throw switch actuated
by the relay armature.
The positive terminal of a source of voltage,
works in conventional quantity production. For
the purpose of simplifying the description of the 30 not shown, is connected through a ?rst switch
19 to the ungrounded input terminal of the net
instant invention, ‘the term “time constant” is
work X. The negative terminal of the voltage
employed herein as inclusive of the more generic
source is grounded. The positive terminal of the
term “delay time” for complex circuits.
Among the objects of the invention are to pro
vide an improved method of and means for
measuring the operating characteristics of an
electrical network. Another object of the in
vention is to provide an improved method of and
means for testing and matching the time con
stant or delay time characteristics of a plurality
of electrical devices. A further object of the in~
vention is to provide an improved method of and
means for measuring the time constant or delay
time of an electrical network as a function of
the discharging characteristics of an independent
reactive measuring network. An additional ob
ject of the invention is to ‘provide an improved
method of and means for measuring the effective
time constant or delay time of an electrical net
work which includes an electromechanical de
, vice.
Another object of the invention is to provide an
improved method of and means for employing
the discharging characteristics of a capacitor for
voltage source also is connected through a
variable resistor 2| and a second switch 23 to the
common terminals of a storage capacitor 25, a
discharge resistor 21 and an indicating meter 29.
The ?rst and second switches l9 and 23 prefer
ably should be ganged for simultaneous opera
tion.
The remaining terminal of the storage capaci
tor 25 is grounded. The remaining terminal of
the discharging resistor 21 is connected to the
fixed contact 15 which normally is in contact
with the movable contact l3 of the relay I I when
the relay is deenergized. The remaining ter
minal of the indicating meter 29 is connected
to the remaining ?xed contact I‘! of the relay ll.
Energization of the relay winding 9 by current
50 derived from the relay ampli?er 1 opens the re
lay contacts l3, l5 and closes the relay contacts
l3, [1.
In operation, when the switches 49, 23 are
closed, the capacitors 3 and 25 are charged to
measuring thertime constant of an independent 55 the same or different voltages provided by the
3
2,408,727
4
input voltage source. When the switches I9, 23
battery 49 to ground. The positive terminal of
the input voltage source is connected through the
are opened simultaneously, the capacitor 3 dis
charges through the resistor 5, providing a
voltage change to a value which actuates the
relay ampli?er to energize the relay winding 9,
thereby opening the relay contacts I3, 15 and
closing the relay contacts i3, ll. Simultaneously,
the storage capacitor 25 discharges through the
discharging resistor 21 until such time as the
relay contacts l3, l5 are opened. At a slightly
later interval, the relay contacts "[3, I‘! are closed,
thereby discharging the residual charge on the
storage capacitor 25 through the indicating meter
29 and providing an indication thereon which is
a function of said residual charge.
If the time constant of the measuring circuit
variable resistor 21 and the second switch 23 to
the ungrounded terminals of the storage capaci
01
tor 25 and discharge resistor 21, and also is con
nected through the meter 29 to the anode of the
gaseous discharge ampli?er tube 41.
In operation, when the switches l9 and 23 are
closed, the input voltage charges the capacitors 33
and 25 and applies the input potential to the
control electrode of the ?rst ampli?er tube 39,
and through the meter 29 to the anode of the
gaseous discharge tube 41. The cathode battery
4| determines the cut-oil grid voltage for the
?rst ampli?er tube 39. Since the ?rst ampli?er
tube 39 is conducting, the grid of the gaseous
discharge tube 41 is maintained at cutoff poten
tial by means of the cathode battery 49 whereby
25, 21 is appreciably longer than the effective
time constant of the network X (as determined
between the instant that the switch I9 is opened
no anode current ?ows through the gaseous dis
and the instant that the relay contacts l3, [5 are
charge tube 41.
opened), the indication provided on the meter 20
When the switches I9, 23 are opened, the volt
29 will be a function of the operating interval
ages across the capacitors 33 and 25 drop at rates
of the network X.
dependent upon the relative time constants of
It should be understood that the particular
the network X and the measuring network 25, 21,
network X has been selected merely for the pur
thereby decreasing the voltage applied to the grid
pose of illustration, and that it may be varied as
of the ?rst ampli?er tube 39 until the tube anode
desired. In the particular arrangement dis
current is cut oil. When the ?rst ampli?er tube
closed herein, it should be understood that the
39 cuts o?", a positive potential is applied to the
relay ampli?er or relay armature may be self
locking in order that the contacts I3, I‘! may re- U grid of the gaseous discharge tube 41, causing the
tube to conduct and thereby to discharge the
main closed after the initial energization of the
residual charge upon the storage capacitor 25
relay winding. Either a gas tube relay ampli?er
through the meter 29. The resultant pulse of
or a polarized relay may be employed for this
purpose in any manner known in the art.
If the operating time of the relay H is negli
current through the meter 29 thereby provides
an indication of the time constant of the net
work X, as described heretofore in the circuit of
gible as compared to the time constant of the
Figure 1. When the meter receives the residual
remainder of the network X, the indications pro
charge upon the storage capacitor 25, the dis
vided by the meter 29 may be employed to indi
charge resistor 21 merely acts as a shunt across
cate directly the time constant of the non-me
the
chanical elements of the network. In any event, 40 tube.meter and the conducting gaseous discharge
however, the time constant of the measuring net
The circuit of Figure 3 is similar to the circuit
work 25, 21 should be longer than the longest
of
Figure 2 With the exception that a conventional
time constant to be measured. The variable re
thermionic tube 5| is substituted for the gaseous
sistor 2| may be adjusted, or a separate voltage
discharge tube 47 of the previous circuit, and
source may be employed, to provide variation of = the
?rst ampli?er tube 39 is effectively connected
the effective sensitivity of the indicating meter
in series with the discharge resistor 21.
29.
When the switches I 9 and 23 are closed, the
If neither relay ampli?er or relay are polarized
capacitors 33 and 25 are charged to the input
to provide self-locking of the relay armature
after the relay winding 9 is energized in response v O potential and ‘a positive 'bias is applied to the
grid of the ?rst ampli?er tube to provide a con
to the voltage change in the input circuit of the
ducting path therethrough for the storage capac
relay amplifier, the movable contact 13 should
itor discharge circuit which includes the dis
make contact with the ?xed contact I‘! for an
interval sufficiently long to permit complete dis
sipation of the residual charge on the storage
capacitor 25 through the indicating meter 29.
charge resistor 21. Since the?rst ampli?er tube
39 is conducting, the grid of the second ampli?er
is maintained at cuto?' potential due to
the biasing action "of the cathode battery 49 con
nected between the cathode of the second am
In Figure 2 the network X, of which the time
constant is to be determined, is shown, by way of
pli?er tube and ground. Since the second am
illustration, as comprising a parallel-connected
capacitor 33 and resistor 35. The positive ter (D a pli?er tube 5| is cut o?, no current ?ows through
the meter 29.
minal of the voltage source is connectedithrough
When the switches l9 and 23 are opened, the
the switch Hi to the ungrounded terminals of the
capacitors 33 and 25 discharge through the ‘re
capacitor 33 and resistor 35, and also is con
sistors 35 and 21, respectively, until such time as
nected through a high isolating resistor 37 to
the control electrode of a ?rst ampli?er tube 39‘. C; V. the voltage on the ?rst ampli?er tube 39 drops
The cathode of the ampli?er tube 39 is connected = below cuto?‘ value as determined ‘by the ?rst cath
ode battery 4! connected between the cathode of
through a. first battery 4| which biases the cath~
said tube and ground. When the anode current
ode positively with respect to ground. The anode
through the ?rst ampli?er tube 39 cuts off, the
of the ampli?er tube 39 is connected through an
discharge path for ‘the storage capacitor 25
anode resistor 43 to a source of anode voltage,
through the discharge resistor 21 is opened, and a
not shown. The anode of the ?rst ampli?er tube
positive potential is applied to the grid of the
39 also is connected through a second isolating
second ampli?er tube, causing it to conduct and
resistor 45 to the control electrode of a gaseous
to discharge the residual charge upon the storage
discharge second ampli?er tubev 41, the cathode
of which is connected through a second ‘biasing 75 capacitor 25 through the meter‘29, to provide an
indication of the time constant or delay time o!
2,408,727
6
of an electrical network comprising a capacitor,
the network X as described heretofore in the
connection means for a source of charging po
circuits of Figures 1 and 2. It is noted that the
tential, means for selectively applying said poten
circuit of Figure 3 does not require a separate
tial to and for simultaneously removing said po
anode voltage source for the ?rst ampli?er tube,
tential from said network and said capacitor, a
and the discharge resistor 21 is effectively discon
thermionic discharge circuit for said capacitor,
nected from the storage capacitor 25 during the
means for indicating directly the electrical charge
interval when the meter indicates the residual
on said capacitor, and thermionic tube switching
means responsive to the removal of said potential
charge thereon.
Thus the invention described comprises several
from said network for selectively disconnecting
10
embodiments of an improved method of and
said discharge circuit from and for alternately
means for measuring, over a relatively wide range,
connecting said indicating means in shunt with
the effective time constant or delay time of an
said capacitor to indicate said network time con
electrical network which may, if desired, include
electromechanical devices. The circuits described
stant as a function of the residual charge on said
provide convenient, rapid, and relative accurate
5. Apparatus for measuring the time constant
of an electrical network comprising a capacitor,
connection means for a source of charging poten
indications of the time constant of a network
under measurement. The indicating meter in
each circuit may be calibrated in any desired
manner, or if desired, an alarm or other device
capacitor.
tial, means for selectively applying said potential
to and for simultaneously removing said potential
may be substituted for the indicating meter to 20 from said network and said capacitor, a resistive
indicate predetermined time constant values.
I claim as my invention:
1. Apparatus for measuring the time constant
of an electrical network comprising a capacitor,
connection means for a source of charging poten
tial, means for selectively applying said potential
to and for simultaneously removing said potential
discharge circuit for said capacitor, means selec
tively connected in shunt with said capacitor for
indicating the electrical charge on said capacitor,
and gaseous discharge tube switching means re
sponsive to the removal of said potential from
said network for selectively disconnecting said
discharge circuit from and for alternately con
from said network and said capacitor, a discharge
circuit for said capacitor, means selectively con
necting said indicating means to said capacitor
stant as a function of the residual charge on said
connection means for a source of charging poten
to indicate said network time constant as a func
nected in shunt with said capacitor for indicating 30 tion of the residual charge on said capacitor.
the electrical charge on said capacitor, and
6. Apparatus or the type described in claim 5
switching means responsive to the removal of said
including high gain polarity reversing amplifying
potential from said network for selectively dis
means interposed between said network and said
connecting said discharge circuit from and for
gaseous discharge tube.
35
alternately'connecting said indicating means to
'7. Apparatus for measuring the time constant
said capacitor to indicate said network time con
of an electrical network comprising a capacitor,
tial, switching means for selectively applying said
- 2. Apparatus for measuring the delay time of
potential to and for simultaneously removing said
an electrical network comprising a capacitor, con— 40 potential from said network and said capacitor,
capacitor.
nection means for a source of charging potential,
means comprising a resistive thermionic tube
means for selectively applying said potential to
discharge circuit responsive to predetermined
and for simultaneously removing said potential
energization of said network for selectively dis
from said network and said capacitor, a resistive as in charging said capacitor, means selectively con
discharge circuit for said capacitor, means selec
nected in shunt with said capacitor for indicating
the electrical charge on said capacitor, and ther
tively connected in shunt with said capacitor for
indicating the electrical charge on said capacitor,
mionic tube switching means responsive to said
discharge circuit for selectively connecting said
and switching means responsive to the removal of
said potential from said network for selectively 50 indicating means to said capacitor to indicate
disconnecting said discharge circuit from and for
said network time constant as a function of the
alternately connecting said indicating means to
residual charge on said capacitor.
8. Apparatus for measuring the time constant
said capacitor to indicate said network delay time
as a function of the residual charge on said ca
pacitor.
3. Apparatus for measuring the delay time of
an electrical network comprising a capacitor, con
nection means for a source of charging potential,
of an electrical network comprising a capacitor,
55 connection means for a source of charging poten
tial, switching means for selectively applying said
potential to and for simultaneously removing said
potential from said network and said capacitor,
means comprising a resistive thermionic tube
means for selectively applying said potential to
discharge circuit responsive to predetermined
and for simultaneously removing said potential
from said network and said capacitor, a resistive 60 energization of said network and supplied with
energizing potential from said capacitor for se
discharge circuit for said capacitor, means for in
lectively discharging said capacitor, means selec
dicating directly the electrical charge on said ca
tively connected in shunt with said capacitor
pacitor, and electromagnetic switching means
responsive to the removal of said potential from 65 for indicating the electrical charge on said
said network for selectively disconnecting said
capacitor, and thermionic tube switching means
discharge circuit from and for alternately con
responsive to said discharge circuit for selectively
necting said indicating means in shunt with said
connecting said indicating means to said capaci
capacitor to indicate the effective delay time of
tor to indicate said network time constant as a
said network and said electromagnetic switching
function of the residual charge on said capacitor.
70
means as a function of the residual charge on said
capacitor.
4. Apparatus for measuring the time constant
DANIEL BLITZ.
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