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

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

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 passive two-terminal electrical component that stores energy in a magnetic field when electric current flows through it. An inductor typically consists of an insulated wire wound into a c ...

(coil of wire) to produce increased voltages either by a back emf effect or through

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

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 electrical transformer used to produce high-voltage pulses from a low-voltage direct current (DC) supply. p.98 To ...

, 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 tubes, around the turn of the 20th century. Its largest use was the contact breaker or "points" in the distributor of the ignition system of gasoline engines, which served to periodically interrupt the current to the ignition coil 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 ...

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 Charles Page (June 2, 1860 – December 27, 1926) was a businessman and important philanthropist in the early history of Tulsa, Oklahoma. After his father died when Page was an 11-year-old boy in Wisconsin, he left school early to try to help sup ...

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

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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 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 Reed or Reeds may refer to: Science, technology, biology, and medicine * Reed bird (disambiguation) * Reed pen, writing implement in use since ancient times * Reed (plant), one of several tall, grass-like wetland plants of the order Poales * Re ...

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 battery sold in the second half of the 19th century for medical applications. Its chief market was amongst the numerous quack practi ...

.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