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OSCILLOGRAPH

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Originally appearing in Volume V20, Page 349 of the 1911 Encyclopedia Britannica.

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OSCILLOGRAPH . In connexion with the study of alternating or varying electric current, appliances are required for determining the mode in which the current varies. An See also:

INSTRUMENT (Lat. instrumentum, from insincere, to build up, furnish, arrange, prepare)

instrument for exhibiting optically or graphically these See also:

variations is called an oscillograph, or sometimes an ondograph. Several methods have been employed for making observations of the See also:

FORM (Lat. forma)

form of alternating current curves—(I) the point-by-point method, ascribed generally to Jules See also:

Joubert; (2) the stroboscopic methods, of which the See also:

WAVE

wave transmitter of H. L. Callendar, E. B. See also:

Rosa, and E, Hospitalier are examples; (3) methods employing a high-See also:

FREE

free quency See also:

GALVANOMETER

galvanometer or oscillograph, which originated with A. E. See also:

Blondel, and are exemplified by his oscillograph and that of W. Duddell; and (4) purely See also:

OPTICAL

optical methods, such as those of I. See also:

FROHLICH, ABRAHAM EMANUEL (1796-1865)

Frohlich and K.

F. Braun. In the point-by-point method the See also:

shaft of an alternator, or an alternating current motor driven in step with it, is furnished with an insulating disk having a metallic slip inserted in its edge. Against this disk See also:

PRESS (through Fr. presse from Lat. pressare, frequentative of premere, to crush, squeeze, press)

press two springs which are connected together at each revolution by the contact of the slip at an assigned instant during the phase of the alternating current. This contact may be made to See also:

close the See also:

CIRCUIT (Lat. circuitus, from circum, round, and ire, to go)

circuit of a suitable See also:

VOLTMETER

voltmeter, or to See also:

charge a See also:

CONDENSER

condenser in connexion with it, and the See also:

READING

reading of the voltmeter will therefore not be the See also:

AVERAGE

average or effective voltage of the alternator, but the instantaneous value of the electromotive force corresponding to that instant during the phase, determined by the position of the rotating contact slip with reference to the poles of the alternator. If the contact springs can be moved See also:

ROUND (O. Fr. rond, Lat. rotundus, the Fr. is the source also of Du. rond; Ger., Swed., Dan. and Nor. rond)

round the disk so as to vary the instant of contact, we can See also:

plot out the value of the observed instantaneous voltage of the See also:

machine or circuit in a wavy See also:

CURVE (Lat. curvus, bent)

curve, showing the wave form of the electromotive force of the alternator. This See also:

PROCESS

process is a tedious one, and necessarily only gives the average form of thousands of different alternations. In the Hospitalier ondograph,' a synchronous electric motor driven in step with the periodic current in the circuit being tested drives a See also:

CYLINDER (Gr. KvAwSpos, from KvXivaety, to roll)

cylinder of insulating material having a metallic slip let into its edge. This cylinder is driven at a slightly See also:

LOWER

lower See also:

SPEED, JOHN (1552–1629)

speed than that of synchronism. Three springs press against the cylinder and make contact for a See also:

SHORT, FRANCIS JOB (1857– )

short See also:

time during each revolution, so that a condenser is charged by the circuit at an assigned instant during the alternating current phase, and then subsequently connected to a voltmeter. This process, so to speak, samples or tests the varying electromotive force of the alternating current at one particular instant during the phase and See also:

MEASURES

measures it on a voltmeter. Owing to the fact that the cylinder is losing or gaining slightly in speed on the circuit periodicity, the voltmeter goes slowly, say in one See also:

minute, through all the phases 1 E.

Hospitalier, " The Slow See also:

REGISTRATION

Registration of Rapid Phenomena by Stroboscopic Methods," Journ. Inst. Elec. Eng. (See also:

LONDON

London, 1904), 33, 175. In this See also:

paper the author describes the " Ondographe " and " Puissancegraphe." See also a description of the ondograph in the See also:

Electrical See also:

REVIEW (Fr. revue, from revoir, to see again, Lat. re and videre)

Review, (1902), 50, 969. of voltage which are performed rapidly during each See also:

period by the alternating current. The voltmeter See also:

NEEDLE (O. Eng. ncedl; the word appears in various forms in Teutonic languages, Ger. Nadel, Dutch naal, the root being ne-, to sew, cf. Ger. nahen, and probably Lat. nere, to spin, Gr. vi)ats, spinning)

needle may then be made to See also:

RECORD (Lat. recordari, to recall to mind, from cor, heart or mind)

record its variations graphically on a See also:

DRUM (early forms drome or dromme, a word common to many Teut. languages, cf. Dan. tromme, Ger. Trommel: the word is ultimately the same as " trumpet," and is probably onomatopoeic in origin; it appears late in Eng. about the middle of the 16th century)

drum covered with paper and so to delineate the wave form of the current. The process is analogous to the optical experiment of looking at a quickly rotating See also:

wheel or See also:

engine through slits in a disk, rotating slightly faster or slower than the See also:

OBJECT

object observed. We then see the engine going through all its motions but much more slowly, and can follow them easily. In another form devised by Callendar,' a revolving contact disk is placed on the shaft of an alternator, or of a synchronous motor driven by the alternating current under test. A pair of contact springs are slowly shifted over so as to close the circuit at successive assigned instants during a See also:

COMPLETE

complete phase.

The electromotive force so selected is balanced against the steady potential difference produced between a fixed and a sliding contact on a See also:

WIRE (A.S. wir, a wire; cf. Swed. vire, to twist, M.H.G. wiere, a gold ornament, Lat. viriae, armlets, ultimately from the root wi, to twist, bind)

wire traversed by another steady current, and if there is any difference between this last, the potential difference, and the instantaneous potential difference balanced against it, a relay is operated and sets in See also:

ACTION

action a motor which shifts the contact point along the See also:

POTENTIOMETER

potentiometer wire and so restores the See also:

BALANCE (derived through the Fr. from the Late Lat. bilantia, an apparatus for weighing, from bi, two, and lanx, a dish or scale)

balance. This contact point also carries a See also:

PEN (Lat. penna, a feather, pen)

pen which moves over a rotating drum covered with paper. As the brushes are slowly shifted over on the revolving contact so as to select different phases of the alternating electromotive force, the pen follows and draws a curve delineating the wave form of that electromotive force or current. An instrument devised by E. B. Rosa is not very different in construction.2 A commutator method has also been devised by T. R. Lyle (Phil. Mag., See also:

NOVEMBER (Lat. novem, nine)

November 1903, 6. 517) in which at an assigned instant during the phase a selection is made from the periodic current and measured on a galvanometer. The oscillographs of A. E.

Blondel' and W. Duddell operate on a different principle. They consist essentially of a galvanometer of which the needle or coil has such a short natural periodic time that it can follow all the variations of a current which runs through its See also:

cycle in say IA-0th second. This needle or coil must be so damped that when the current is cut off it returns to zero at once without overshooting the See also:

mark. By means of an attached See also:

MIRROR (through O. Fr. mirour, mod. miroir, from a sup-posed Late Lat. miratorium, from mirari, to admire)

mirror and reflected See also:

ray of See also:

LIGHT

light the See also:

motion of the movable See also:

SYSTEM

system can be indicated on a See also:

SCREEN (usually, but very doubtfully, connected with Lat. scrinium, a box for holding books, from scribere, to write; a connexion with Ger. Schranke, barrier, has been suggested)

screen. This ray is also given a periodic motion of the same frequency by reflection from a See also:

SEPARATE

separate oscillating mirror so as to make the two motions at right angles to one another, and thus we have depicted on the screen a See also:

bright See also:

LINE

line having the same form as the periodic current being tested. In W. Duddell's oscillograph' (fig. i) the galvanometer See also:

PART

part consists of an electromagnet in the See also:

field of which is stretched a See also:

LOOP

loop of very See also:

FINE

fine wire. To this is attached a mirror; hence, if a current goes up one See also:

side of a loop and down another, the wires are oppositely displaced in the field. The loop and mirror move in a cavity full of oil to render the system dead-See also:

BEAT (a word common in various forms to the Teutonic languages; it is connected with the similar Romanic words derived from the Late Lat. battere)

beat. A ray of light is reflected from this mirror and from another mirror which is rocked by a small motor driven off the same circuit, so that the ray has two vibratory motions imparted to it at right angles, one a See also:

SIMPLE

simple See also:

HARMONIC

harmonic motion and the other a motion imitating the variation of the current or electromotive force under test. This ray can be received on a screen or photographic See also:

PLATE

plate, and thus the wave form of the current is recorded.

In the Duddell oscillograph it is usual to See also:

PLACE (through Fr. from Lat. platea, street; Gr. IrAar6s, wide)

place a pair of loops in the magnetic field, each with its own mirror, so that a pair of curves can be delineated at the same time, and if there is any difference in phase between them, it will be detected. Thus we can take two curves, one showing the potential difference at the end of an inductive circuit, and the other the current flowing through the circuit. In one form of Blondel's oscillograph, the vibrating system is a small magnetic needle carrying a mirror, but the principle on which it operates is the same as that of the instrument above described. The oscillograph can be made to exhibit optically the form of the current curve in non-cyclical phenomena, such as the See also:

DISCHARGE (adapted from the O. Fr. discharge, modern decharge, from a med. Lat. discargare, to unload, dis- and earn care, to load, cf. " charge ")

discharge of a condenser. In this See also:

case the large vibrating mirror must be oscillated by a current from an alternator, on the shaft of which is a disk of non-conducting material with See also:

brass slips let into it and so arranged with contact brushes that in each period of the alternator a contact is made, charging say a condenser and discharging it through the oscillograph. In this way an optical See also:

REPRESENTATION

representation is obtained of the oscillatory discharge of the condenser. A form of thermal I the coils embracing the Braun See also:

TUBE (Lat. tuba)

tube. oscillograph has been devised by J. T. Irwin (Jour. Inst. Elec.

Eng. I References.—See J. A. See also:

Fleming, A Handbook for the Electrical Lond. 1907, 39. 617). In this instrument the periodic current, the Laboratory and Testing See also:

ROOM

Room, vol. i. (London, 1901), which contains time variation of which is being studied, passes through a pair of fine a See also:

list of See also:

ORIGINAL

original papers on the oscillograph ; Id., The Principles of wires or strips, going up one wire and down the other. These wires Electric Wave Telegraphy (London, 1906), which gives illustrations are also traversed in the same direction by a See also:

CONSTANT, BENJAMIN (1845-1902)

constant current from of the use of the oscillograph and the Braun See also:

CATHODE

cathode. ray tube in a See also:

BATTERY (Fr. batterie, from battles, to beat)

battery. The two currents are therefore added in one wire and depicting condenser discharges; also, for the development of the subtracted in the other, and produce a See also:

DIFFERENTIAL

differential See also:

HEATING

heating effect oscillograph, A. E. Blondel, " Oscillographs : New Apparatus for which causes unequal expansion, and this in turn is made to tilt a registering Electrical Oscillations " (a short description of the bifilar and soft See also:

IRON [symbol Fe, atomic weight 55.85 (0=16)]

iron oscillographs), Comptes rendus (1893), 116.

502; 1H. L. Callendar, " An Alternating Cycle Curve See also:

Recorder," I Id., " On the Determination and Photographic Registration of Electrician, 41. 582. Periodic Curves," La Lumibre eleclrique (See also:

AUGUST (originally Sextilis)

August 29th, 1901); Id., 2 E. B. Rosa, " An Electric Curve Tracer," Electrician, 40. 126. ' See Assoc. See also:

FRANC

Franc. pour l'Avanc. See also:

des Sciences (1898), for a paper I ' See K. F. Braun, Wied.

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