An Improved Form of Voltmeter.
Year: 1891

page_text: Date of Application, 16th Oct., 1891
Complete Specification Left, 16th July, 1892-Accepted, 15th Oct., 1892
PROVISIONAL SPECIFICATION.
An Improved Form of Voltmeter.
We FRANCIS HENRY NALDER, HERBERT NALDER, CHARLES WILLIAMSOоTT
CRAWLEY, and ALFRED SOAMES, all of 16 Red Lion Street, Clerkenwell, in the
County of Middlesex Electrical Engineers do hereby declare the nature of this
invention to be as follows:-
Our invention is on the principle of a potentiometer working automatically.
The volts to be measured are applied to the ends of a resistance; and a standard
cell in series with a relay of any convenient form is applied to a part of it.
When the drop of the volts over this part to the ends of which the cell and
relay are applied is equal and opposite to that of the standard cell, no current
passes through the relay, but when this drop is less than the electro motive
force of the standard, a current passes and the relay tongue or its equivalent
makes contact with one stop; and vice versa when the drop is greater than the
electro motive,force of the standard cell with the other stop. These contacts
set in motion, or cause to set in motion, or to act suitable motive power by
which either the total resistance is altered or the points on the resistance, to
which the cell and relay circuit is applied are varied in such a way that the
drop of volts over the latter portion is increased or diminished to its former
value. At the same,time the motive power works a pointer backward or forward
according to the changes made in the resistances and by suitably marking a
dial this pointer may be made to indicate the volts at the terminals of the
resistance, and if desired a continuous record of them may be obtained on a
paper on a moving drum or other, equivalent means. In the event of the volts
at the terminals of the resistance getting either too high or too low and beyond
the range of the instrument the mechanism may be so arranged that the volts are
then automatically cut off the instrument, and an alarm given. As a check on
the accuracy of the standard cell it may from time to time be automatically cut
off the main circuit and joined in opposition to another similar cell when if the
two are not.equal, a bell may be caused to ring. or other warning given.
Dated this 16th day of October 1891.
FRAS. H. NALDER.
HERBERT NALDER.
C. W. S. CRAWLEY.
ALFRED SOAMES.
COMPLETE SPECIFICATION.
An Improved Form of Voltmeter.
4
"We FRANCIS HENRY NALDER, HERBERT NALDER, CHARLES WILLIAM SCOTT
CRAWLEY, and ALFRED SOAMES, all of 16 Red Lion Street Clerkenwell, in the
County of Middlesex, Electrical Engineers 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.:—
Our invention consists of a sensitive relay in series with a resistance, to the
ends of which the volts to be measured are applied or in shunt on a portion of
such resistance. When the volts are at some particular value the action on the
relay is such that the tongue or its equivalent makes no contact. When the
volts rise or fall to any prearranged amount above or below this value, the relay
makes a contact with one or another stop respectively and sets in motion or
D01

page_text: causes to be set in motion or to act a source of motive power whereby either
the total resistance is altered or the points on the resistance to which the relay
is applied are varied in such a way that the drop of volts over the latter
portion is increased or diminished to its former value. At the same time the
motive power works a pointer backward or forward according to the changes
made in the resistances and by suitably marking a dial this pointer may be
made to indicate the volts at the terminals of the resistance, and if desired a
continuous record of them may be obtained on a paper, on a moving drum, or
other equivalent means. In the event of the volts at the terminals of the
resistance getting either too high or too low and beyond the range of the
instrument the mechanism may be so arranged that the volts, are then auto-
matically cut off the instrument, and an alarm given.
Having described the nature of our said invention we will proceed to describe
with reference to the accompanying drawings the manner in which the same is to
be performed.
In Fig. 1 A is a sensitive "relay" one side of which is joined to one terminal
of the instrument, and the resistance in series with it is wound on the bobbins r₁₂,
etc. S is a spring holding the tongue T against the stop L when the volts on
the relay are below 90. B is a spindle carrying a pointer C which indicates
on the dial D, and an arm E which when the pointer is at the lowest reading
joins the ring F (which is in metallic connection with the other side of the
relay) short on to the terminal G and which when rotated clockwise joins the
ring on to the terminal successively through the resistance bobbins r₁ r, etc.
by making contact with the pins m₁ m, etc. one after the other, always making
the next contact before breaking the one before. In the instrument as shewn,
the tongue of the relay stands midway between the stops when the volts on the
relay terminals are 90, but makes contact with the stops H or L respectively
when the volts on its terminals are a small amount above or below 90. To.
prevent "hunting" the variation of volts necessary to just move the tongue
from one stop to the other should slightly exceed the steps by which the instru-
ment works, or 5 volt. If the volts on the relay are too high, the tongue
makes contact with the stop H making the circuit of the motor N through the
field magnet circuit P & the armature Q causing it to revolve; the source of
power is shewn as a battery at K but the power may equally well be derived
from the same source as that whose volts it is desired to measure. The spindle
of the motor being connected to the spindle B carrying the contact arm E &
pointer C by the worm U gearing on to the wheel W causes it to rotate
clockwise and add resistance to the circuit of the relay. The resistances on the
bobbins r₁r, etc. are so adjusted that each bobbin required to be introduced
into the circuit of the relay, to restore the tongue to the centre implies an
excess at the main terminals of 5 volts over 90 v. and the dial being divided corre-
sponding to the number of coils in circuit the pointer on it reads direct in half
volts from 90 upwards. If the main volts fall those in the relay fall also &
the tongue makes contact with the other stop L. The circuit of the motor is
again made but the current from L passes through a second field magnet
winding p. p. in the opposite direction to the first so that the motor runs
backwards till it has cut out sufficient resistance to raise the volts, on the relay
to 90 again, when the motor stops and the pointer indicates the volts at the main
terminals as before. When the arm reaches the upper limit of the reading the
pin V on the wheel W presses against the spring X and opens the forward:
circuit of the motor thus preventing the arm going too far. In the same way..
when the arm gets to the lower limit of its range the pin V presses against
the spring Y & opens the backward circuit. The arm may of course be
arranged to move clockwise as the volts fall & vice versa ; the connections &
numbering being reversed. The "relay may be of the dynamometer, current
weigher, hot wire, multicellular or any other electro dynamic or electro static type.
In the case of using an electro static type we may shunt it with a resistance.
"

page_text: Fig. 2. is a vertical section through Fig. 1. the same letters referring to the
same parts, a is an insulating piece on the arm E carrying the spindle b & c
which rub on the ring F, and pin M etc. respectively. d is the glass front.
Although we have described the instrument as working from 90 to 110 volts
by 5 volts at a time we do not confine ourselves to these values but may make
it to work for other ranges, & with other even or uneven steps. We do not
confine ourselves to any particular form of driving gear but may use any well
known motion thrown into gear or started & controlled by the relay.
Fig. 3 shows diagramatically another method of joining up. Here a standard
cell or cells e is joined in series with a delicate polarized relay A in shunt across the
resistance R. in the main circuit the cell thus taking the place of the spring s.
When the volts on R, due to the current passed through it by the volts to be
measured are equal & opposite to the volts of the cell no current passes through the
relay circuit. When they are above or below that value the relay touches the H
or L stop & works as before. If desired that the instrument should not begin to
read till it reaches an E.M.F. in excess of that of the cell or cells a further
resistance R, may be introduced as shewn.
Fig. 4 shows diagramatically an arrangement for obtaining a continuous record on
a moving drum or other equivalent arrangement. The rack f. gearing into the
wheel W. and moving the pencil point g. on the drum h. This form of voltmeter
may conveniently be used for measuring the fall of potential over a resistance in the
main circuit & thus measure the main current flowing; in which case the dial or
drum may be marked to show the ampères corresponding to the volts measured.
CLAIMS.
1) In an electrical measuring instrument the combination of a relay acted on by
the volts to be measured or a part thereof with mechanism controlled thereby to
keep the volts on the relay itself practically constant and at the same time to
indicate the volts to be measured visually or to give a continuous or other record.
2) An electrical measuring instrument automatically measuring in terms of excess
over a fixed value.
3) An electrical measuring instrument in which the power requisite to move the
indicating pointer or pencil is controlled by, but does not affect the measuring part
itself.
4) The instrument substantially as described.
FRAS. H. NALDER.
HERBERT NALDER.
C. W. S. CRAWLEY.
ALFRED SOAMES.