An interrupter in electrical engineering is a device used to interrupt the flow of a steady

direct current Direct current (DC) is one-directional electric current, flow of electric charge. An electrochemical cell is a prime example of DC power. Direct current may flow through a conductor (material), conductor such as a wire, but can also flow throug ...

for the purpose of converting a steady current into a changing one. Frequently, the interrupter is used in conjunction with an

inductor An inductor, also called a coil, choke, or reactor, is a Passivity (engineering), passive two-terminal electronic component, electrical component that stores energy in a magnetic field when an electric current flows through it. An inductor typic ...

(coil of wire) to produce increased voltages either by a

back emf Counter-electromotive force (counter EMF, CEMF, back EMF),Graf, "counterelectromotive force", Dictionary of Electronics is the electromotive force (EMF) manifesting as a voltage that opposes the change in current which induced it. CEMF is the EM ...

effect or through

transformer In electrical engineering, a transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple Electrical network, circuits. A varying current in any coil of the transformer produces ...

action. The largest industrial use of the interrupter was in the

induction coil An induction coil or "spark coil" ( archaically known as an inductorium or Ruhmkorff coil after Heinrich Rühmkorff) is a type of transformer used to produce high-voltage pulses from a low-voltage direct current (DC) supply. p.98 To create the ...

, the first transformer, which was used to produce high voltage pulses in scientific experiments and to power

arc lamp An arc lamp or arc light is a lamp that produces light by an electric arc (also called a voltaic arc). The carbon arc light, which consists of an arc between carbon electrodes in air, invented by Humphry Davy in the first decade of the 1800s, ...

s, spark gap radio transmitters, and the first

X-ray tube An X-ray tube is a vacuum tube that converts electrical input power into X-rays. The availability of this controllable source of X-rays created the field of radiography, the imaging of partly opaque objects with penetrating radiation. In contras ...

s, around the turn of the 20th century. Its largest use was the

contact breaker A contact breaker (or "points") is a type of electrical switch, found in the ignition systems of spark-ignition internal combustion engines. The switch is automatically operated by a cam driven by the engine. The timing of operation of the switch ...

or "points" in the

distributor A distributor is an electric and mechanical device used in the ignition system of older spark-ignition engines. The distributor's main function is to route electricity from the ignition coil to each spark plug at the correct time. Design ...

of the

ignition system Ignition systems are used by heat engines to initiate combustion by igniting the fuel-air mixture. In a spark ignition versions of the internal combustion engine (such as petrol engines), the ignition system creates a spark to ignite the fuel-ai ...

of gasoline engines, which served to periodically interrupt the current to the

ignition coil An ignition coil is used in the ignition system of a spark-ignition engine to transform the battery voltage to the much higher voltages required to operate the spark plug(s). The spark plugs then use this burst of high-voltage electricity to ig ...

producing high voltage pulses which create sparks in the

spark plug A spark plug (sometimes, in British English, a sparking plug, and, colloquially, a plug) is a device for delivering electric current from an ignition system to the combustion chamber of a spark-ignition engine to ignite the compressed fuel/air ...

s. It is still used in this application.

Medical use

Bird's interrupter

The physician

Golding Bird Golding Bird (9 December 1814 – 27 October 1854) was a British medical doctor and a Fellow of the Royal College of Physicians. He became a great authority on kidney diseases and published a comprehensive paper on urinary deposits in 1 ...

designed his own interrupter circuit for delivering shocks to patients from a voltaic cell through an induction coil. Previously, the interrupter had been a mechanical device requiring the physician to manually turn a cog wheel, or else employ an assistant to do this. Bird wished to free his hands to better apply the electricity to the required part of the patient. His interrupter worked automatically by magnetic induction and achieved a switching rate of around (five times per second).Bird (1838), pp. 18–22 The faster the interrupter switches, the more frequently an electric shock is delivered to the patient and the aim is to make this as high as possible.

Page's interrupter

A rather more cumbersome interrupter was constructed by the American Charles Page slightly earlier in 1838 but Bird's work was entirely independent. Although there is little in common between the two interrupter designs, Page takes the credit for being the first to use permanent magnets in an automatic interrupter circuit. Bird's (and Page's) interrupter had the medically disadvantageous feature that current was supplied in opposite directions during the make and break operations, although the current was substantially less during the make operation than the break (current is only supplied at all while the switch is dynamically changing). Treatment often required that current was supplied in one specified direction only.

Letheby's interrupter

A modified version of the interrupter was produced by

Henry Letheby Henry Letheby (1816 – 28 March 1876) was an English analytical chemist and public health officer. Early life Letheby was born at Plymouth, England, in 1816, and studied chemistry at the Royal Cornwall Polytechnic Society. In 1837 he commenced ...

which could output only the make, or only the break currents by a mechanism consisting of two spoked wheels. Bird also produced a uni-directional interrupter using a mechanism we would now call split-rings. The date of Bird's design is uncertain but may predate Letheby's. Both designs suffered from the disadvantage that automatic operation was lost and the interrupter had to once again be hand-cranked. Nevertheless, this arrangement remained a cheaper option than electromagnetic generators for some time.

Other designs

Other early interrupters worked by clockwork mechanisms or (non-magnetic)

reed switch The reed switch is an Electromechanics, electromechanical switch operated by an applied magnetic field. It was invented in 1922 by professor Valentin Kovalenkov at the Peter the Great St. Petersburg Polytechnic University#Soviet era, Petrogra ...

es operated by motion of the patient's limbs. One example of such a device is found in the

Pulvermacher chain The Pulvermacher chain, or in full as it was sold the Pulvermacher hydro-electric chain, was a type of voltaic cell, voltaic battery sold in the second half of the 19th century for medical applications. Its chief market was amongst the numerous ...

.Lardner, p.289
Pulvermacher, p.2

References

Bibliography

*Bird, Goldin
"Observations on induced electric currents, with a description of a magnetic contact-breaker"
''Philosophical Magazine'', pp. 18–22, no.71, vol.12, January 1838. *Bird, Goldin
''Lectures on Electricity and Galvanism, in their physiological and therapeutical relations''
Wilson & Ogilvy, London, 1847. *Coley, N. G
"The collateral sciences in the work of Golding Bird (1814–1854)"
''Medical History'', vol.13, iss.4, pp. 363–376, October 1969. *Morus, Iwan Rhys ''Frankenstein's Children: Electricity, Exhibition, and Experiment in Early-nineteenth-century London'', Princeton University Press, 1998 . * Lardner, Dionysiusbr>''Electricity, Magnetism, and Acoustics''
London: Spottiswoode & Co. 1856. *Letheby, Henr
"A description of a new electro-magnetic machine adapted so as to give a succession of shocks in one direction"
''London Medical Gazette'', pp. 858–859, 13 November 1846. *Pulvermacher, Isaac Lewis "Improvement in voltaic batteries and apparatus for medical and other purposes", {{US patent, 9571, issued 1 February 1853. Electrical components