Dec. 14, 1954
H. OTZMANN, JR
2,697,204
CALIBRATABLE ELECTRICAL INSTRUMENT
Filed April 7, 1951
29
37b
37a
31
37d
37c
37d '
Fig.3.
INVENTOR
Henry Ofzmonn, Jr.
BY
I
ATTORNEY
United States Patent Of?ce
2,597,204
Patented Dec. 14, 19542
1
2
Fig. 2 is a view in bottom plan of a spring retainer em
ployed in the instrument of Fig. 1; and
2,697,204
Fig. 3 is a view in elevation of an auxiliary perma~
nent-magnet assembly employed as a calibrator in the
CALIBRATABLE ELECTRICAL INSTRUMENT
instrument of Fig. 1.
Henry Otzmann, Jr., Roselle Park, N. J., assignor to West
Referring to the drawing, Fig. 1 shows an electro
inghouse Electric Corporation, East Pittsburgh, Pa., a
magnetic instrument having an airgap within which a
corporation of Pennsylvania
magnetic ?eld is produced. This instrument takes the
Appiication April 7, 1951, Serial No. 219,817
10hform of a permanent-magnet moving-coil instrument
aving a stator including a magnetic structure which
de?nines two airgaps 1
6 Claims. (Cl. 324-151)
Any portion of ‘
the airgaps 1 and 3. In the speci?c embodiment of Fig.
l, the magnetic structure includes a U-shaped perma
nent magnet 5 having pole pieces 7 and 9 secured in
This invention relates to electromagnetic instruments,
ble-coil electrical measuring instruments.
The invention is suitable for electrical instruments
and it has particular relation to permanent-magnet mova
20
Q
a
a
suitable for permanent-magnet movable-coil instruments
and will be described with reference to such an instru
The
25
strument
ment.
30
cured thereto. The free end of this
with a pivot for receptlon in a suitable bearing screw
13 towards a predetermined
stator and it also may be
owing its manufacture.
employed for establishing an electrical connection be
The calibration of an instrument also may be depend
ent on the speci?c application of the instrument follow~ 40 tween one end of the core 13 and an external circuit.
A similar stub shaft, spring and bearing screw assembly
ing its manufacture. For example, a steel panel on which
mav be provided for the lower end of the coil 13.
The shaft 15 also has secured thereto a pointer 21
which cooperates with a scale 23 to indicate the value
of the quantity which is measured by the measuring in
45
.
str'ument.
a shunt will
In accordance
with the invention, an auxiliary perma
'
'
'
stator. Such
The portions of
been speci?cally described are
Since the construction and opera
a1. Patent 2,179,305.
nent
'
'
instruments of
sary.
a magnetic ?eld employed
In order to adjust the strength of the magnetic ?eld
As applied to a permanent-magnet 60 in the airgaos 1 and 3, an auxiliarv permanent magnet
moving-coil instrument, this calibrator is
produce an auxiliary magnetomotive force across the
or ‘calibrator 29 _is incorporated in the i
airgap of the instrument. The magnitude and polarity
of the auxiliary magnetomotive force are adjusted by
rotation of the calibrator.
It is, therefore, an object of the
spouse to adinstment of the calibrator 29.
Convenientlv, the calibrator 29
tween, two polar extensions 31 and
strength of the magnetic ?eld.
It is a further object of the invention to provide a
permanent-magnet moving-coil instrument with an aux
iliary permanent magnet which is adjustable for the pur
pose of adjusting the strength of the magnetic ?eld with
in which the moving coil is positioned.
Other objects of the invention will be apparent from
the following description taken in conjunction with the
accompanying drawing, in which:
igure'l is a view in perspective with parts broken
away of a permanent-magnet moving-coil instrument em
bodying the invention;
709
The calibrator 29 is mounted. for rotation on the bridge
35 in anv suitable manner. For example, the calibrator
29 may be secured to a support 37 (Fig. 3).
port has a cylindrical body 37a which has
'
k.
enlarged
head 37b at one end and a screwdriver slot 376 at its
remaining end. - A peripheral groove 37a’ is formed
in the body to de?ne a neck 372 which has a diameter
2,697,204.
A
erence. to, certain. speci?c, embodiments thereof, nu
merous modi?cations falling within the spirit and the
scope of the invention are possible.
3:
smaller than. the.
diameter. of. the. body.. The- supportv
may be constructed of a nonmagnetic material. such as
brass, and may be secured to the calibrator 29 in any
1 claim as my invention:
suitable‘manner; such‘ as1)by.
soldering.
. has an .opening proportioned '
The bridge 35 (Fig;
to ‘receive'snugly‘ the ibody~37arof'the:support. The head
37b oft'the‘support acts as a'spacenbetweenithe calibrator
29 and the bridge 35. The calibrator ‘is-retained in ‘P051; .
tion?by means-‘of a bow ‘spring 4'1iWhi'3h'h3S a'centrallv 10
disposed slot143 formed therein (Fig; 2). 37¢. (Fig. 3 ).
is proportioned to": receive. snugly ‘the? neck
a circular
In‘ addition; the'spr'ing has on its convex'side
diameter:
slightly
greater
than
depression‘ 45' having. a
the‘diameterlof'the body ‘37a '(Fig. 3). When'the spring . 15
41" isvin mounted position‘ as illustrated in' Fig.- 1, the
biased? downwardly‘ to urge" the
center of the spring‘ is
the bridge‘ 35;. Be:
head 37b into‘ ?rm engagement with
cause of the constant pressure exerted'by the spring" on.
the calibrator, the calibrator is held securely in mounted
1. In a permanent-magnet, moving-coil instrument,
a magnetic structure having‘ an; airgap arcuate about
an axis, said magnetic structure including a ?rst per
manent magnet for producingamagnetic» ?eld in- the
airgap, a coil having a coil side disposed in said air'gap,
means mounting: the- coili for-rotation’ relative to the
magnetic‘ structure about‘ said axis, said coil ‘side be
ing positioned to develop a' motor‘ action by'the reac
tion ofcurreut ?owing therethrough and said magnetic
?eld which urgesithelcoil about-'saidaxis relative to the
magnetic structure, a second permanent magnet co‘
operating with the magnetic- structure to shunt said
airgap, and means mounting the second permanent
magnetfor. adjustmentabout an _axis_to,vary the mag
netomotive force applied‘ thereby: across, said‘ airgap
said’motor-action operating-to move the coil relative to
thesecond permanent magnet.
osition‘andfyetmay'ib'e rotated as'desired. It’will be
2. An instrument as claimed inclaiml' in combina
tionwith a casing havinga base member, substantiallyv
transverse to said axes, said.sec0nd permanent magnet
noted’further 'that‘the calibrator mayrbe'readily ‘replaced. .
For example, the‘ calibrator of Fig. 1‘ but
mayhaving
be replaced
a. dif'by‘ a’ calibrator ‘ similar in construction
léeing. accessible for adjustmentthrough said base mem
ferent
coercivethe‘
force.
Preferably,
calibrator and" the associated casing
are so constructed‘ that the calibrator may- be adjusted
without disturbing thecasingin any. wa .
er..
3. An instrument as de?ned‘ in claim 1 wherein the
magnetic structure. includes a pair of_ spaced polepieces
Forrexamnle,
magnetically connectedirespectively to the poles of said
?rsbpermanentmagnet, the poles ofv saidfsecond per
manent magnetbeing positionedior movementrespec
the‘ base‘ 27 of the casing may-‘have an: opening 27a
_
I
formed
thereinv through which a‘. screwdriver‘ may be.
inserted for the-purpose of adjusting'the'calibrator: To
.
tively towards, and, away from said polepieces in 're
sponse to adjustment of, the second permanent magnet
prevent entry'of dust‘ into'the casing, the base 27a may
be‘ provided? with a- tubular extension 27b which snugly
embraces the end of‘ the body 3721 which containsthe
screwdriver
slot that
370. the‘ operatiom ofl'the‘ calibrator now
It is believed
may beset forth: Polarities
about the second‘axis.
'
4. An instrument as claimed in claim 3‘,|wherein_said‘
mounting; means includes a non-magnetic bridgemem
ber connecting said: pole, pieces, and means" mounting,
the second permanent magnet on said‘ bridge memberfor‘ rotation: relative tov the bridge. member about said.
for‘ the‘ calibrator arev rec»
resente‘dl in Fig. 1' by the‘oonventional' p‘olarityr'mark‘ N
for north-pole and S'ior' south pole; with the polarities
as’ illustrated inFig; 1", the‘ calibrator 29' assists’ the‘ per ~10
manent‘ magnet 5; in directing magnetic
?ux‘ through
the magnetic
?ux.
the‘ airg‘aps' 1' and 3} Consequently; that which would.
density in the airgaps- is greater‘ than
be provided'by the permanent magnet 5' alone.
Let it‘ be assumed‘ next that‘ the calibrator 29 is ro
tated 90°‘ from1theposition-illustratediin Fig. 1'. When
5'. In a i moving coil' instrument; a magnetic struck
ture de?ning‘ an airgap, said magnetic structure includ
ing, means for establishing a ?rst magnetomotive force
across said' ai'rgap, a permanent" magnet for establishing
a second magnetoinotive force across the airgap, a
coil having. a‘ coil side in the. airgap; means mounting‘
so located, the calibrator 29‘ has‘ negligible effect‘ on the
magnetic ?eld's present’ in the airgaps- 1' and‘ 3*. Conse
flux density '_ in‘ the airgaps is equalvv
quently,
the magnetic
substantially‘ to that which would be provided‘ by the
ermanent magnet 5:‘ alone.
Should the calibrator 291 be» rotated 180“ from the
axis;
hi)
the- coil for. movement relative to‘ the magnetic struc-f
ture and the. permanentv magnet“ in» response to the- re,
action'. between current passin through the coil and a
magnetic ?eld in the airgap, and‘ means‘ mounting the
permanent magnet for adjustment relative to- the mag
netic structure through a range su?i'cient to bring said
position illustrated in-Fig; 1', the poles of'the calibrator
would be adjacent, respectively, unlike poles of‘ the
riliiagnetomotive forces into opposing or aidingv relation
magnetv 5. Under‘ these. circumstances, the magnetic
ture de?ning an airgap, said' magnetic structure includ
flux density in they
airgaps 1- and' 3" would; be substan-'
. .
tially‘ less than the densities obtained by‘ provision of
the‘ permanent magnet 5" alone. Intermediate positions‘
of the calibrator would produce intermediate effects on
6. In a moving coil instrument, a- magnetic struc-
i'ng a ?rst permanent magnet for establishing a first‘
magnetomotive force across said ai'rgap, a second per
manent magnet for establishing a second magnetornotive
It‘
force across the airgap, a coil having‘ a coil side» in the
airgap, means mounting the coil‘ for‘movement relative
The calibrator can be
to'the magnetic structure and the permanent magnets’
?ux density‘ on. the airgaps: 1 and‘ 3.
the"
magnetic
shouldv
be noted that‘ the adjustment for the calibrator
29 is a continuous adjustment.
s ips.
rotated‘ continuously and does not require steps of any
type. Furthermore, it should be noted that the cali
brator 29 permits the‘ full strength of the permanent
magnet 5 to be utilized. For example, the tolerance
prescribed for manufacture ofv the instrument may be
such that with the calibrator displaced 90° from the
position illustated‘ in Fig. , the average instrument
measures correctly. This means that the entire strength
of the permanent magnet ‘5 is utilized in the average '
instrument. Inaccuracies in instruments which deviate
in. response to the reaction between current passing
through the coil and a magnetic ?eld in the airgap,
and means mounting" the second. permanent magnet for’
rotational adjustment relativev to; the» magnetic-- structure;
about an axis and- through a range’ sui?cient to bring,
’ said magnetomotive forces. into.‘ opposing: 0r.- aiding. re;
lationships.
from the average may be compensated by suitable ad
Number
justment of the calibrator 9. Toy illustrate the range
497,448
of adjustment which may be obtained by such a calibra -i Li
691,393
tor, _a variation of the order of 45% of’ the full-load
1,282,497
reading of the instrument may be obtained readily by
1,479,524
adjustment of the calibrator 29’. Since the adjustment
2,102,409
provided by the calibrator 29 is self-contained, the in
2,538,740
strument may be readily adjusted in the ?eld for use
on magnetic or non-magnetic panel's,,as desired.
Although the invention has been described with ref
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References Cited‘. in, the ?le of this, patent
UNITED STATES.- PATENTS
‘ Name
Date
I-loyt _______________ __ May 16', 1893
La Roche ____________ __ Jan. 21, 1902
Trent ______________ __ Oct. 22;, 1918
Van Guilder ________ __ Jan. 1, 1924
Fans _______________ __ Dec. 14; 1937
Wallace ______________ __ Jan. 16, 1951