Improvements in or relating to Alternate Current Meters.
Year: 1897

page_text: Date of Application, 8th Dec., 1897-Accepted, 12th Feb., 1898
COMPLETE SPECIFICATION.
Improvements in or relating to Alternate Current Meters.
We, CLARENCE PAUL FELDMANN, 35, Otto Strasse, Electrician, and HELIOS
ELEKTRICITATS AKTIENGESELLSCHAFT, 389, Venloer Strasse, Manufacturers, both in
the City of Köln Ehrenfeld, German Empire, do hereby declare the nature of this
invention and in what manner the same is to be performed, to be particularly
described and ascertained in and by the following statement: -
The present invention relates to a zero adjustment for alternate current meters.
In all meters for single or polyphase alternate currents, in which there are provided
a main current magnet H and a shunt magnet N (Figure 1), or generally in which
two or more fields H, which are excited from the main current I, or a portion thereof
or are induced, together with two or more fields N, which are induced or excited
by a branch current i having its phase displaced with regard to the main current I
(Figure 2) thereby effect the rotation of a revolving body or a disc M, there may easily
occur also undesirable rotary motion of the revolving body or of the disc M, which
motions are caused by a slight want of symmetry in the geometrical or magnetic
arrangement. These revolutions occur especially when the fields H are not excited
whilst the shunt fields N are excited, and they then cause a to and fro motion of the
meter in spite of the stoppage of the main current.
Several methods have been tried in order to obviate this difficulty. Thus for
instance the protective influence of a copper plate partially covering the whole of
the fields N, or the arrangement of a hole or slot in the disc N, may effect the
zero position, that is to say the disc will be held fast in a given position when the
fields N are excited and the fields H are without current, notwithstanding little
defects of symmetry in the mounting or other arrangements.
The object of the present invention consists of a new method of adjusting the
zero point in the above defined sense. The invention consists in the application of
a suitably formed and extremely thin magnetic layer A, under the influence of a
permanent magnet B, which apparatus can be attached to the revolving body M
of the meter itself or to a special brake disc M. As a rule meters of this kind
possess already for the checking and regulating of their motion one or more
permanent brake magnets B, which act either upon the meter body M itself or
upon a brake disc M', or the like connected with the said meter body. It is therefore
only necessary to cover a thin zone or a small sector or other suitably shaped piece,
of the itself unmagnetic body M or M¹ standing under the influence of the brake
magnet B, with so thin a layer of magnetic material by mechanical or galvanic
means that the resulting magnetic unsymmetrical checking suffices exactly for
the producing of a fixed zero position, without on the other hand taking off the
quickened action of the fields displaced in phase. There consequently occurs in
a meter provided with this new arrangement for the creation of the zero position
a differential effect between the quickening powers of the field groups displaced
in phase, and the delaying power of the magnetic and completely closed brake
magnets, which for instance can be so controlled by the galvanic production of the
spot or strips A, that the meter in spite of having a very sharply defined zero
position loses nothing of its sensitiveness even with regard to relatively weak

page_text: currents. Because even when the delaying spot or strip is brought upon the body
of the meter disc M the dimensions of the said strip or spot can be so finely
adjusted that the revolving currents in the meter disc M which really effect the
motion required to be registered will not be perceptibly disturbed in their course.
It is obvious that the invention can also be applied in a number of small modifi-
cations. Thus for instance several spots or strips might be used so that several
fixed zero positions will be created and so forth.
Having now particularly described and ascertained the nature of our said in-
vention, and in what manner the same is to be performed, we declare that what
we claim is:-
In alternate current meters having no direct supply of current to the movable
armature, the arrangement of one or more thin strips or layers of magnetic material
produced by mechanical or electrolytic means on the armature or the brake body
connected to the same for the purpose of creating a differential effect of such
dimensions that one or more fixed zero positions are produced the sensitiveness of
the meter remaining practically unaltered.
W. P. THOMPSON & Co.,
322, High Holborn, London, W.C., Patent Agents for the Applicants.