Improvements in Electrical Measuring Apparatus for use in Regulating Electric Currents.
Year: 1898

page_text: Improvements in Electrical Measuring Apparatus for use in
Regulating Electric Currents.
We, ROOKES EVELYN BELL CROMPTON and SIDNEY WALTER ASHLEY, Electrical
Engineers, of Arc Works, Chelmsford, in the County of Essex, do hereby declare
the nature of this invention to be as follows:-
Our improvements consist in an arrangement for coupling up and using volt-
meters and ammeters on electric circuits by which a simple voltmeter can be so
arranged as to indicate the electrical pressure at any desired point in an electric
circuit and also indicate the current in that circuit.
We are aware that in Letters Patent No. 3576 of 1882 granted to John Hopkin-
son he states that "when the electricity is to be used at a distance from the
dynamo and conductors of a sensible resistance are used it is proper to maintain
constant the difference of potential at the end of such conductors where the
electricity is used and not at the dynamo itself" and he then describes a means of
indicating the difference of potential at the end of the circuit by a special
differential arrangement applied to a voltmeter or similar instruments.
By our improved methods we avoid this differential arrangement and in place
of it we use a low resistance galvonometer which can be shunted by a portion
of the main conductor in order to act as a shunted ammeter and we connect
this up by suitable conductors and by a special form of switch so that we can
indicate on this one instrument the potential difference on the circuit at a point
close to the instrument and by a movement of the switch the potential difference
at a distant point on the circuit and by a third movement can read the amperes
passing through the circuit. We can best describe our arrangement by taking
the simple case of an electric circuit consisting of a pair of feeders proceeding
from the omnibus bar of a generating station. When the instrument is to be
used as a voltmeter to indicate the potential difference at a point on the circuit
close to the instrument the switch is so arranged that the leads connect this point
with certain terminals on this instrument and thence through a suitable high
resistance placed in series with 'the instrument itself so as to make it act as a
voltmeter.
Again when the instrument is to be used as a voltmeter for reading the
potential difference at a distant point on the circuit a movement of the switch
attaches one of the voltmeter terminals to a point on the ammeter shunt at a
suitable position intermediate between its terminals, the other voltmeter terminals
of the instrument being attached to a suitable high resistance which bridges the
circuit from positive to negative at the same point where the potential difference
is measured when the switch is in its first position.
A third movement of the switch will bring the terminals of the galvonometer
into connection with the two ends of the ammeter shunt and thus the galvonometer

page_text: will act as an ammeter. It will be seen that by suitable proportions of resistance
aud by varying the point of attachment of the terminals the three desired readings
are obtained.
Sometimes it may be convenient to use three separate instruments permanently
connected as above indicated so that the whole three readings, home volts, distant
volts, and amperes, can be read simultaneously or two instruments may be used
one to read the amperes and the other provided with a switch to read home volts
and distant volts.
Improvements in Electrical Measuring Apparatus for use in
Regulating Electric Currents.
We, ROOKES EVELYN BELL CROMPTON and SIDNEY WALTER ASHLEY, Electrical
Engineers, of Arc Works, Chelmsford, in the County of Essex, 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 improvements consist in an arrangement for coupling up and using volt-
meters and ammeters on electric circuits by which a simple indicator can be so
arranged so as to indicate the electrical pressure at any desired point in an electric
circuit and also indicate the current in that circuit.
We are aware that in Letters Patent No. 3576 of 1882 granted to John Hopkin-
son he states that when the electricity is to be used at a distance from the
dynamo and conductors of a sensible resistance are used it is proper to maintain
constant the difference of potential at the end of such conductors where the
electricity is used and not at the dynamo itself" and he then describes a means of
indicating the difference of potential at the end of the circuit by a special
differential arrangement applied to a voltmeter or similar instruments.
By our improved methods we avoid this differential arrangement and in place
of it we use an indicator or galvanometer which can be shunted by a portion
of the main conductor in order to act as a shunted ammeter and we connect
this up by suitable conductors and by a suitable form of switch such as is known
as a double pole voltmeter switch so that we can indicate on this one instrument
the potential difference on the circuit at a point close to the instrument and by a
movement of the switch the potential difference at a distant point on the circuit
and by a third movement can read the amperes passing through the circuit. We
can best describe our arrangement by taking the simple case of an electric circuit
consisting of a pair of feeders proceeding from the omnibus bar of a generating
station.
When the instrument is to be used as a voltmeter to indicate the potential
difference at a point on the circuit close to the instrument the switch is so
arranged that the leads connect this point to certain terminals on this instrument
and thence through a suitable resistance placed in series with the instrument
itself so as to make it act as a voltmeter. Again when the instrument is to be
used as a voltmeter for reading the potential difference at a distant point on the
circuit a movement of the switch attaches one of the voltmeter terminals to a
point on the ammeter shunt at a suitable position intermediate between its

page_text: terminals, the other voltmeter terminals of the instrument being attached to a
suitable high resistance which bridges the circuit from positive to negative at the
same point where the potential difference is measured when the switch is in its
first position. A third movement of the switch will bring the terminals of the
galvanometer into connection with the two ends of the ampere shunt and thus
the galvanometer will act as an ammeter. It will be seen that by suitable propor-
tions of resistance and by varying the point of attachment of the terminals the
three desired readings are obtained.
Sometimes it may be convenient to use three separate instruments permanently
connected as above indicated so that the whole three readings, home volts, distant
volts, and amperes, can be read simultaneously or two instruments may be used
one to read the amperes and the other provided with a switch to read home volts
and distant volts.
Figure 1 shows diagramatically the indicator G arranged
1. To indicate the amperes passing through the conductor B.
2. The difference of potential between the conductors B and C.
3. The difference of potential between the same conductors B and C at the
distant point E.
A represents a source of electrical energy, B and C the two conductors going
to the distant point D¹, at D¹ the utilizing devices E E E are placed, G is an
indicator, which is a galvanometer of a suitable type, preferably one of the
D'Arsonval type having a moving coil. I and S are the terminals of this instru-
ment. R is a resistance box provided with three terminals D, S¹ and I¹. In this
box is fixed a resistance K P and the terminal I¹ is connected to a fixed point P
on this resistance.
The terminal D is connected to one end K of the resistance K P and the
terminal S is permanently connected to P. H is a portion of a conductor B
conveniently arranged to act as a shunt to the galvanometer G. It is fitted with
three potential points or terminals P2, P3 and P. Of these P2 and P4 are fixed
13 can be connected to P³. A switch is provided by which the various connections
described below can conveniently be made.
The terminal D of the resistance box R is permanently connected to a point F
on the conductor C near the source of electrical energy.
When it is desired to use the instrument G as an ammeter to indicate the current
passing through the conductor B the switch is moved so that P2 is connected
to I, the terminal S is also connected to P. G then acts as a shunted galvanometer
and if the shunt ratio is correct will give the current correctly in amperes.
Secondly when it is desired to read the voltage at the point F close to the
source of energy S and S¹ are both connected to P and I and I are connected
together.
Thirdly, when it is desired to read the voltage of the distant point D¹, P³ is
connected to S, P2 is connected to S¹ and I is connected to I¹. The potential
point P3 is so placed as to give a voltage opposed to that portion of the main
voltage which is used to work the voltmeter and bearing the same ratio to the
said portion of the main voltage which is used to work the voltmeter as the fall of
potential due to losses in the conductors B, C up to the point D' bears to the main
voltage between B and C.
In the apparatus modified as described above and illustrated diagrammatically
by Figure 2, the three readings which it is desired to note viz-potential
difference on the circuit at a point close to the instrument, the potential difference
at a distant point on the same circuit, and the amperes passing through that
circuit, are all indicated on one instrument, and they can only be read onc at
a time, as the switch mentioned above is placed in each of these respective positions.
If all three readings are required to be shown simultaneously then three separate
indicators must be used, one connected to points P and P Fig. 2 will indicate the
potential difference on the circuit at a point close to the instrument, the second
connected to points P and P¹ Fig. 2 will indicate the potential difference at a

page_text: distant point on the same circuit, and the third, connected to points P Fig. 2 and
P³ Fig. 2 will indicate the current passing through the circuit.
Two indicators may also be used instead of three, one connected to points P Fig. 2
and P3 Fig. 2 indicating the amperes passing through the circuit, the other being
used in conjunction with a suitable switch to indicate either the potential difference
at the point close to the instrument, or the potential difference at the distant
point on the circuit. When this indicator is required to show the potential
difference at a point on the circuit close to the instrument the switch handle H
is turned so that A is brought into contact with 1) Fig. 2 of the switch K.
When this same indicator is required to show the potential difference at a
distant point on the circuit, H (Fig. 1) is turned so that it (H) is brought into
contact with the point B Fig. 2 of the switch K.
Having now particularly described and ascertained the nature of our said
invention, and in what manner the same is to be performed, we declare that what
we claim is:-
1. The construction and use as an electrical measuring apparatus for use in
regulating electric current of an indicator or galvanometer which can be shunted
by a portion of the main conductor in order to act as a shunted ammeter, con-
nected by suitable conductors and a suitable form of switch adapted to indicate
on this one instrument the potential difference on the circuit at a point close to
the instrument and by a movement of the switch an indication of the potential
difference at a distant point in the circuit is obtained and by a third movement
the amperes passing through the circuit can be read, substantially as set forth.
2. The construction and use as an electrical measuring apparatus for use in
regulating electric currents of three separate instruments or two separate instru-
ments one provided with a suitable switch, permanently connected, substantially as
and for the purpose set forth in Claim 1.
3. The construction and use of electrical measuring apparatus for use in
regulating electric currents, substantially as and for the purpose set forth.
Dated the 19th day of January foɔɔ.
1093.
WM. BROOKES & SON,
55 and 56, Chancery Lane, London,
Agents for the Applicants.