Applicatio' filed August 9 1918. Serial No. 249 169.
rTE STATES PATENT OFFICE.
=KW 033 OP EAST ORANGE NEW JERSEY ASSIGNOR TO AMERICAN TELEPHONE AND TELEGRAPH COMPA.NY A CORPORATION OP NEW YORK. .
To all whom it may concern:
Be it known that I MACLEAN KniKwoon
residing at East Orange in the county of Essex and State of New Jersey have M
5 vented certain Improvements in Electrical
-. Measuring Apparatus of which the following is a specification.
This invention relates to improvements m electrical measuring apparatus and more
10 particularly to improvements in apparatus for determining the magnitude of currents induced in a telephone circuit by power transmission lines or other foreign elec--:trical circuits which extend parallel and in
15 close proximity to the telephone circuit.
The practice heretofore followed to determine the magnitude of the induced cur-rent consisted in connecting a telephone receiver to the telephone circuit bridging a
20 shunt across said circuit and varying the resistance until the receiver gave no audible sound. The shunt used for this purpose consisted in some instances of a variable resistance and in other instances of artificial
25 cable made-up of resistances and capacity.. In using this method with either type of shunt it has been found difficult to deter-mine exactly when the point of silence was reached. Experience has shown that the
30 results obtained from tests made upon the same circuit by two different observers some-times varied widely. To avoid this difficulty in determining the point of silence a method was devised which. consists in corn-
35 paring the tone produced in a telephone receiver by the induced current in a telephone circuit with the tone produced in the same receiver by a standard source of alternating current and varying the current from the
40 said source until it produces the same volume of tone as is produced by the current in the telephone circuit. Experience has shown that this method is productive of greater accuracy than any ordinarily used
45 in measuring the amount of tone or noise induced in a telephone circuit. My invention consists in improvements in. the apparatus by means of which the foregoing method of measurement may be most effec-
50 tively carried out.
This invention will be more fully under-
stood from the following description of the
apparatus together with the attached draw-
ing forming part of the specification the
55 figure of which viewed best from the right
hand side is a circuit diagram of one embodiment of the applicant's invention embracing a source of tone and a current controlling and switching mechanism.
In the drawing A represents the stand- 60 and source of alternating current hereinafter referred to as the tone source; B indicates the current controlling and switching apparatus; C indicates the telephone circuit in which has been induced an alternating cur- 65 rent; and D indicates the receiver used in determining when the balance has been attained. The tone source A consists of a vibrator 1 having a primary winding 2 and a secondary winding 3. The battery 4 is 70 connected to a reversing switch 5. One side of the reversing switch is connected directly to one end of the primary winding 2 and the other side of said switch is connected to the other side of the winding through contact 75 6 of switch 7 the function of which will be described later. A condenser 8 is bridged across the contact points of the vibrating element to decrease sparking. The switch 5 has been inserted in the primai'y circuit 80 in order that the polarity of the connections may be changed after definite intervals of time so as to increase the length of time that the vibrator will run without causing pitting of the buzzer contacts. 85
The secondary winding 3 is connected to binding posts 9 and 9' having the current limiting resistances. R R and R inserted between the ends of the winding and the binding posts resistance R being bridged 90 across and the resistances R and R being in series with said winding. The buzzer is designed to have a wave form that will create a tone in the receiver which is substantially of the same quality as that pro- 95 duced by the induced current in the telephone circuit.
The current controlling and switching apparatus B consists in a variable resistance shunt 10 and switches 7 and 11. The re-''100 sistance elements of the shunt 10 are bridged across the conductors 16 which are connected with the secondary winding of the vibrator 1. Intermediate between the points where the resistance elements are bridged across 105 the circuit and the secondary winding of the vibrator current limiting resistance R „ and 14 are in circuit. One side of said circuit is connected with the middle back• contact of switch 7 and the movable arm of shunt 110
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10 is connected with the left hand back con-tact of switch 7. Current limiting resistances RB and RT are inserted between the point where said shunt is bridged across
5 the circuit and switch 7. Resistances R4 R5 R and R are large compared with the variable resistance 10 and the impedance of the circuit containing said resistances looked at from the direction of the arrow X is sub-
10 stantially the same for all settings of the variable resistance 10 in consequence where-of the current output of the secondary winding and the frequency and tone of the vibrator remain substantially the same
15 throughout the entire range of the variable resistance 10. The right hand back con-tact and the right hand swinging contact of switch 7 are connected by conductors 12 with the primary winding of vibrator 1 in
20 order to close the circuit through the primary winding and thereby start the vibrator to operate whenever switch 7 is closed. A receiver D is connected by means of conductors attached to binding posts 13 and
25 13' to the left hand and middle swinging contacts of the switch 7. It will be seen therefore that whenever the switch 7 is operated the receiver D is bridged across the circuit that embraces the secondary
30 winding of the vibrator and the variable resistance shunt 10 and at the same time the primary circuit is closed through the contact 6. The left hand normal and middle normal contacts of switch 7 are connected
35 with the corresponding contacts of switch. 11. The telephone circuit C which has an alternating current induced in it is connected through binding posts 14 and 14' to the left hand and middle swinging contacts
40 of the switch 11.
If it is desired to make a test across the
two wires of the pair a resistance R8 the
magnitude of which depends upon the elec-
trical characteristics of the circuit C is
45 bridged across the end of the circuit farthest
removed from the point at which the test
is being made. If it is desired on the other
hand to measure the current between the
circuit and ground the distant end of the
50 circuit is grounded as shown by the dotted
lines of the circuit C'. A current limiting
resistance R9 is arranged so as to be con-
nected in series with the receiver D when-
ever a measurement to ground is being made.
55 The right hand back contact of switch 11
is grounded so that whenever said switch
is operated contact 15 is closed thus ground-
ing one side af. receiver D which is neces-
sary for making the grounded circuit test.
60 Having in mind this description of the
parts of this apparatus and of the func-
tion that each part performs the method
of making a measurement of the magni-
tude of induced current on a telephone line
65 may be readily understood. If it is de-
sired to make a test on the circuit C the said circuit is connected as shown to binding posts 14 and 14' the receiver D is connected to binding posts 13 and 13' and the tone standard A is connected with the cur- 70 rent controlling and switching apparatus B by means of conductors 12 and 16. With the switches 7 and 11 in their normal positions the receiver D is bridged 'across the two sides of circuit C and an observer lis- 75 tens and notes the magnitude of the tone. Then switch 7 is operated disconnecting the receiver from the circuit and connecting it with the tone source A. If the tone there-from is found to be greater than that pro- s0 duced by the circuit the shunt 10 is adjusted so as to decrease it. The receiver is alternately bridged across the circuit and the tone source and the shunt is varied until the volume of tone created by the ch.- 85 cuit and by the tone source is substantially the same. It will be seen that by control-ling the flow of current through the primary circuit of the vibrator by means of the right hand contacts of switch 7 the vibrator operates only when the receiver is bridged across the tone source which increases the life of the batteries and thereby renders it possible to maintain the tone uniform during a considerable period of time.
If it is desired to make a measurement between the telephone circuit and ground the circuit is arranged as indicated by C' and switch 11 is operated which sets up a circuit from ground through contact 15 and conductor 17 receiver D resistance R9 through the two wires in parallel of circuit C' to ground. Alter noting the magnitude of the tone in the receiver D switch 7 is operated and a comparison is made with the tone from the tone source A. By alternately connecting the receiver with said source and said circuit and operating the. shunt 10 in the same manner in which it is operated when making the "metallic circuit test" a balance no is definitely reached between the tones
created in the receiver. The shunt 10 is calibrated so as to indicate the number of units of current sent through the receiver D.
It will be readily seen that by means of 115 this apparatus which is sufficiently small to be readily transported measurement may be made in the field by persons who are relatively unskilled in electrical testing and greater accuracy is attainable than wes here- 120 tofore practicable with the apparatus then known in the art.
Although the invention has been disclosed as embodied in a particular form it is evident that it is not restricted to such form 125 that it may be embodied in a variety of different forms without departing from the spirit and the scope of the claims herewith.
What is claimed is:
1. In electrical measuring apparatus the 130
90 95 100 105
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combination of a source of alternating cur-rent controlling means therefor a circuit having induced therein an alternating cur-rent indicating means and switching means
5 whereby said indicating means may be alternately connected with said source and said circuit.
2. In electrical measuring apparatus the combination of a source of alternating cur-
10 rent a circuit having induced therein an alternating current indicating means switching means to connect said indicating means with either said source or said circuit and a shunt across said source whereby
15 the current from said source to said indicating means may be varied.
3. In electrical measuring apparatus .the combination of a source of alternating cur-rent a second source of alternating current
20 indicating means switching means to connect said indicating means alternately with said first and said second source and means to substantially equalize the magnitude of
25 the signal given by said indicating means.
4. In electrical measuring apparatus the combination of a source of alternating current a circuit having induced therein an alternating current indicating means
S® switching means to connect said indicating means alternately with said- source of said circuit and to render said source operative only when connected with said indicating means.
35 5. In electrical measuring apparatus the combination of a circuit having induced therein an alternating current a buzzer de-
signed to produce an alternating current the wave form of which simulates that of the current induced in said telephone circuit a telephone receiver and means to connect 40 said receiver alternately with said circuit and said buzzer and a variable shunt whereby the magnitude of current transmitted from said buzzer to said receiver may be varied until the tones given by said receiver when 45 connected with said circuit and with said buzzer are substantially equalized.
6. In electrical measuring apparatus the combination of a buzzer having an output circuit a pair of conductors having an impedance coil bridged across one end indicating means and switching means adapted to bridge said indicating means alternately across said output circuit and other end of said conductors.
7. In electrical measuring apparatus the combination of a buzzer having an output circuit a pair of conductors having one end short circuited and grounded indicating means and switching means adapted to connect said indicating means alternately with said output circuit and with said conductors and a second switching means adapted to short circuit the other end of said conductors and to connect in series therewith an impedance coil and to ground one side of said indicating means.
In testimony whereof I have signed my name to this specification this 8th day of August 1918.

MACLEAN KIRKWOOD.
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