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Патент USA US2132267

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Oct. 4, 1938.
H_ww_ LORD
2,132,267
HEAVY ALTERNATING CURRENT MEASUREMENT
Filed July 51, 1957
lmverwtor‘:
Harold W. Lord,
by
A/OMZa/M
Patented Oct. 4, 1938
‘ 2,132,267
UNITED ‘STATES’ PATENT ‘OFFICE.
2,132,287
‘HEAVY ALTEBNATING-CUBRENT MEASURE
MENT
-
Harold w. Lord, Schenectady, N. ‘1., assignor to
General Electric Company, a corporation of
New rel-k ,
"
Application July 31, 1937,'Serial No. 156,746
4
(01. 111-95)
My invention relates to the measurement of related to the welding circuit, and vconnecting'an
heavy alternating currents and its object is to instrument. such as an oscillograph element‘ I6,
avoid the, use oi the‘ expensive and massive cur» in circuit with this pick-up coil.' Thus'in Figs. 1
rent-transforming devices that are ordinarily and 2 the welding circuit comprises a single turn ~
5 employed in making such alterating-current loop with which the pick-up coil is in'loose in
measurements.
-
.
~
I
- The invention is particularly useiul ior meas
uring the current in a resistance welding circuit
where the momentary current values may be of
10 the order of from 50,000 to 200,000 amperes.
In carrying my invention into eiiect, I employ
a pick~up coil inductively associated with the
heavy-current circuit to be metered. This might
be consideredas an air core transiormer connected
ductive relation. The voltage e induced in the
pick-up coil is a function of the mutual induct
ance 3n between such coil and welding circuit and
the rate oi change 01' current
i.
_
in the welding circuit, thus
.
‘ 15 between the circuit to be metered and an instru
ment circuit. The instrument circuit includes an
inductance in order that the current therein will
have a wave shape which corresponds to the wave
shape oi the current to be measured. In some
no cases, I may combine the pick-up coil and wave
shape-correcting reactance into a single device.
The features oi my invention which are believed
to be novel and patentable will be pointed out in
the claims appended hereto.
For a better un
25 derstanding oi my invention, reierence is made
in the iollowing description to the accompanying
drawing in which I?g. 1 represents the circuit
connections vaccording to my invention ior ob
taining an oscillograph record of the current
‘ so ?owing in a resistance welding circuit; Fig. 2
_
ii
I
‘5mm
1°
It is necessary to include a reactor H in the
measuring circuit in order that the current there
in shall de?ect the oscillograph element It in ac
cordance with the wave shape oi the welding cur- . 2o
rent. The instrument circuit should be oi low
resistance as compared to its inductance. Neg
lecting the eiiect oi resistance the current 11 in
the oscillograph circuit'is then related to the
voltage e induced in the pick-up coil in accord- 25
ance with the expression
‘"5
_
°"
‘111
dt
where L is the inductance of the reactor l1. and 30
represents a circuit ior thesame purpose wherein
the pick-up coil and inductance are combined;
35
10
a:
di
and Fig.‘ 3 shows a perspective view oi a portion ' represents the rate oi change oi current in the
oi a resistance welder with mypick-up .coil in osciilosraph circuit.
measuring'positionthereon'.
>
1
We may combine the above two equations by
‘Referring ‘now to the drawing ior a, detail de
eliminating'the common iactor e, thus
scription, in Figs. 1 and 2, ll represents a trans
former having a primary II and secondary i2‘
i'_ £1
35
"'4:- qt
' connected between an alternating-current source
40 oi supply It and the electrodes ll oi a resistance
40
mv'and L are circuit constants and hence
welder. The transformer II is' designed to pro
duce a very large low-voltage secondary‘ current
suitable ior resistance welding purposes. The
' welding current-through the electrodes“ may,v where k_ is va constant depending upon the cir
45' ior enmple, reach momentarily values up to cuit constants. Thus,-the current 11. ?owing in ‘i5
I
v
'
‘=lik
‘
'
‘the oscillograph is proportional to the weldins
current Land‘these currents have substantially
sign oi current-measurement transiormer or the same wave shape and phase relation. The
200.000 amperes or more.
.
. -
It is impracticable to use theconventional de
hunt ‘in the welding 5circuit where such large
50 current magnitudes are involved. It is-.desirable,
however.toobtainaproportional instrumentcur
proportionality between i and 11 can be deter
mined by’ calibration. 'However, since the cali- so
bration depends upon the mutual inductance be
‘ rentoi the same wave shape aathatoi the weld-v tweenthe pick-upcoil and welding circuit, the
ing current. In accordance withmy invention, ‘ pick-up‘ coil should be/immovably placed in the
thisisaccomplishedbyplacingaplck-upcoil ll throat oi the welder before calibration and not
“.inthe throat oi the welder where itis inductively moved thereafter without recalibration. The 55
2
9,182,267
transformation ratio between i and i1 is of the
_ order of
50000
~
-~
1
and above.
.
A measurement of the oscillograph de?ection
for a known welding current provides a reason
ably accurate overall calibration. The welding
‘current for low heats with the electrodes short
10
circuited may be fairly accurately determined by
measuring the steady state current in the pri
mary of transformer I0 and multiplying this val
ue by the turn ratio of this transformer. The
pick-up coil may be provided with different taps,
such as indicated at I8, Fig. l, for convenience
in varying the calibration tosuit the different
operating currents for different welding condi
In order to give a practicable example
tions.
but not by way of limiting the invention, it has
been found that the pick-up coil may have eight
.
hundred turns of No. 25 enameled wire wound on.
a‘ two-inch diameter tube three inches long and
may have taps at two hundred and four hundred
.
.
1. In combination, a primary circuit in which
alternating current of from 50,000 to 200,000 am
peres may ?ow, apparatus for measuring such
currents in said circuit comprising, a'pick-up coil
loosely inductively related to said circuit, an in
strument supplied by said pick-up coil, and a re
actorv having an iron core‘ containing an air gap
connected in vseries with said instrument and
pick-up coil, said reactor serving to cause the
wave shape of the current induced in said instru 10
ment circuit through said pick-up coil to be simi
lar to the wave shape of the current in the pri
mary circuit, the ratio between the currents in
the primary and instrument circuits being not
less than
'
50,000
1
2. In combination, an alternating-current
welding machine having electrodes and electri 20
cal supply conductors leading to'the electrodes
and forming a single-turn conductor loop when
current flows through said conductors and be
tween said electrodes in a welding operation,
means for obtaining a record of the current ?ow 25
core reactor with a small air gap rated at one
in said conductors comprising, a coil inserted in
henry with .3 ampere direct current through its - such loop so ‘as to form therewith a loosely cou-"
winding and weigh about one pound. The plac- ‘ pled mutual inductance coupling, an electrical
ing of the pick-up coil on a resistance welding recording device of the oscillograph type con-'
machine is represented in Fig. 3."
nected to be energized from said coil, and a re-, 30
As shown in Fig. 2, the pick-up coil l5 and re
actance included in the energizing circuit of said
actor " of Fig. 1 may be combined by using a recording device for causing the wave vshape of
reactor I9 as both pick-up coil and reactor. Such the current induced therein through said mu
pick-up reactor must be placed relative to the tual inductance coupling to conform to the wave
welding circuit so that the current ?owing in the ‘shape of the current ?ow in the welder supply 35
K oscillograph vibrator circuitis just su?cient for conductors.
a good deflection. Too strong a ?eld in the pick
3. In combination, a heavy-current alternat
up reactor will saturate the iron thereof and ing-current circuit forming a single-turn loop,
cause distortion in the recording.
,
_
i
means for measuring the current ?ow in said _
turns. This coil ‘Weighs about ten ounces. The
reactor used at I‘! with this pick-up coil is an iron
40
If the pick-up reactor is used and the welding
current varies over a considerable range, it will
' be'advisable to mount the pick-up reactor so that
it may be turned through an arc of ninety de
grees by means such as indicated in Fig. 2 at 20
and thus vary its inductive relation with respect
to the welding vcircuit for di?erent “ranges of
circuit comprising, a coil placed within said loop 40
so as to have a voltage induced therein when
currentl?ows in said circuit, which voltage is
proportional to the rate of change of current'in '
said circuit and the mutual inductance between
said loop and coil, ‘and a measuring circuit con 45
taining a current-measuring ‘device upon which
the voltage induced in said coil is impressed, said
welding current. ‘ The calibration of the instru
- ment circuit current will, of course, vary with measuring circuit icontaining su?lcient inductance .
_ the position of the pick-up reactor and, after to cause the wave shape of, the current in the
60
being calibrated, different rotary positions of the
reactor may be marked with the proper calibra
tion
constants.
~
'
I
-
instrument circuit to 'be siinilar [to the wave 50
shape of the current in‘ the heavy-current circuit.
4. In (combination, a heavy-current alternat- .
The instrument at l6 instead of being ‘of the ' ing-current circuit in which currents of the or
‘ recording type may obviously be of the indicat
der of 100,000 amperes may ?ow, means where
ing type.
by the value and wave form of the current in 55
In accordance with the provisions of the pat
suchvcircuit may be recorded comprising, a coil
ent statutes, I have described the principle of op
mutually inductively related to said “circuit, an
eration of my invention together with the appa
iron corencontaining an air gap for said coil, said
ratus which I now consider to represent the best
60 embodiment thereof but I desire to have it un
derstood that the apparatus shown is only illus
trative and that the invention may be carried out
. by other means.
core and ' '1 being mounted for relative move
ment withv respect to said circuit, whereby the 60
mutual inductive relation may be varied, and an
oscillograph recording element energized from
said coil.
‘
/
‘
What I claim as new and desire to secure by
65
Letters Patent of the United States is:
HAROLD w.‘ Loan.
05
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