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Oct. 15, 1946.
P. s. CHRISTALDI
2,409,419 “
DEVICE FOR MEASURING 'IM'PEDANCES
Filed June 8, 1943‘
PH)
4
7' ‘.5
INVENTOR.
‘
-
KM Z/MW
Patented Oct. 15, 1946
2,409,419
UNITED STATES PATENT OFFICE '
Peter S. Christaldi, Upper Montclair, N. J., as
signer to Allen B. Du Mont Laboratories, Inc.,
‘Passaic, N. J ., a corporation of Delaware
Application June 8, 1943, Serial No. 490,032 ‘
6 Claims. (01. 175-183)
1
2
This invention relates to a device for measur
end I‘! of resistance R1 and the other input ter
minal I8 of the vertical beam de?ection system
of the oscillograph I4.
The operation is as follows when a capacitance,
for example, is to be measured.
A steep Wave front signal such as the square
wave signal indicated in Fig. 3 is applied to the
input terminals I and 2 With the condenser C‘x
between terminals 1 and Ill. The condenser C1
ing electrical impedances whether they are re
sistances, inductances or capacitances. Where
the term impedance is used herein, it will be
understood to mean either resistance or induct
ance or capacitance or a series or parallel com
bination of two or more of the same sort of im
pedances.
By this invention impedances can be easily and
readily measured very quickly without requiring 10 is adjusted until a square wave 2llappears upon
high skill on the part of the operator, simply by
the face 2| of the cathode-ray tube of the oscil
turning a knob or otherwise varying an adjust
lograph I4, thus showing a balance of the im
able known impedance.
pedance. The relationship is then:
In carrying out the invention a balance is ob
tained by applying a signal to a combination of 15
four impedances, three of which are known and
where C is the capacitance of the condenser C1
the fourth is the one to be measured. At least
one of the three known impedances is variable.
plus the distributed capacitance C3 of the wiring
The signal that is used in the inputto the de
and the input to the oscillograph I4, or,
vice is attenuated, and an analyzer of the at
tenuated signal, such as an oscillograph, is used
The value of the unknown capacitance Cx can
to determine when a, balance is obtained. From
be obtained.
this the value of the unknown impedance can be
When an unknown resistance is to be measured
ascertained as will be explained below.
The invention will be understood from the de 25 it may be put in the place where R1 is and a
known condenser C2 put where Cx is, and then
scription in connection with the accompanying
0.: 0%
when balance is obtained by varying condenser
C1 the resistance is:
drawing, in which:
Fig. 1 is a diagram of the device;
_
Fig. 2 shows a modi?cation of a part of Fig. 1;
and
Figs. 3, 4 and 5 are types of signals that may
appear upon the oscillograph and enable the op
erator to know when a balance is obtained so that
the value of the unknown impedance can be as
certained.
Reference characters I and 2 indicate the input
terminals of leads 3 and 4 to the device. Known
resistances R and R1, one of which may be var
iable, are connected in series across the leads 3
and 4. The lead 3 ends in the terminal ‘I.
The unknown impedance, which is shown on
the drawing as a, condenser Cx, is an example of
what can be measured. It is connected between
the terminals 1 and 9. The terminal 9 is con
nected at In to the lead II which extends from a
point I2 between resistances R and R1 to the in
put terminal I3 for the commonly known ver
tical beam de?ection system of the oscillograph
30
R1: 02
A pair of inductances Lx and L maybe used
instead of the condensers Cx and C1, as indicated
in Fig. 2. When balance is obtained:
35
The device operates as a balanced attenuator,‘
the balanced condition being shown by the oscil
lograph. When balance obtains:
40
With the resistances alone, all signals applied
at terminals I and 2 are transmitted with attenu
ation proportional to:
.
45
independent of frequency, and the signals are
I4. A horizontal beam de?ection system of the
applied to the terminals I3 and I8 of the oscillo
known sort using a. sawtooth wave which is syn 50 graph I4.
chronized in the usual way and is used for hori
When the device is out of balance due to the
zontal de?ection of the beam of the oscillator I 4.
reactance between the leads 4 and II being too
A condenser C1, which is indicated as being a
large, the signal on the face 2| will become more
variable condenser, is connected from the lead
like Fig. 4 ; and when the device is out of balance
.II to a point I6 on the lead 4 between the lower 55 due to the reactance between the leads 4 and II
2,409,419
3
4
being too small, the signal on the face 2| will
become more like Fig. 5.
What is claimed is:
1. In a device of the character described means
for measuring impedances which comprises a
nected to opposite ends of said parallel connected
three terminal network made up of a parallel
connected pair of known impedances, one of
pair of impedances and a wave form indicating
device to which said output terminals are con
nected.
2. The device of claim 1 in which said third
known impedance is resistive.
3. The device of claim 1 in which said third
known impedance is capacitive.
which is resistive and the other is reactive, con
4c The device: of claim I in which said third
nected in series with a third known impedance
which is of the same type as one of said known 10 known impedance is inductive.
5. The device of claim 1 in which the known
impedances, at least one of said impedances being
reactive impedance of said parallel connected
adjustable, said third impedance being connected
pair is capacitive and variable.
to terminals at opposite ends of this third im
6. The device of claim 1 in which the known
pedance which are adapted to be connected to, the
reactive impedance of said parallel connected
ends of an impedance to be measured, input ter~
pair is inductive and variable.
minals for a signal of complex wave form ,con
nected to opposite ends of said series connected
PETER S. CHRISTALDI.
three terminal network, output terminals con
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