Siphon recorder
Encyclopedia
The syphon or siphon recorder is an item of telecommunications equipment invented by William Thomson, 1st Baron Kelvin
William Thomson, 1st Baron Kelvin
William Thomson, 1st Baron Kelvin OM, GCVO, PC, PRS, PRSE, was a mathematical physicist and engineer. At the University of Glasgow he did important work in the mathematical analysis of electricity and formulation of the first and second laws of thermodynamics, and did much to unify the emerging...

 in 1858. It was used to automatically record the receipt of a telegraph message, as a wiggling ink line on a roll of paper tape. Little skill was required to record the message, but a trained telegrapher was still required to read and understand it.

In many ways, it anticipated the modern inkjet printer
Inkjet printer
An inkjet printer is a type of computer printer that creates a digital image by propelling droplets of ink onto paper. Inkjet printers are the most commonly used type of printer and range from small inexpensive consumer models to very large professional machines that can cost up to thousands of...

 though it seldom operated reliably.

Principles

The principle of the telegraph
Telegraphy
Telegraphy is the long-distance transmission of messages via some form of signalling technology. Telegraphy requires messages to be converted to a code which is known to both sender and receiver...

 siphon recorder is exactly the inverse of the mirror galvanometer
Mirror galvanometer
thumb|right|200px|A mirror galvanometerA mirror galvanometer is a mechanical meter that senses electric current, except that instead of moving a needle, it moves a mirror. The mirror reflects a beam of light, which projects onto a meter, and acts as a long, weightless, massless pointer...

. In the latter we have a small magnet suspended in the centre of a large coil of wire—the wire enclosing the magnet, which is free to rotate round its own axis. In the former we have a small coil suspended between the poles of a large magnet—the magnet enclosing the coil, which is also free to rotate round its own axis. When a current passes through this coil, so suspended in the highly magnetic space between the poles of the magnet, the coil itself experiences a mechanical force, causing it to take up a particular position, which varies with the nature of the current, and the siphon which is attached to it faithfully figures its motion on the running paper. The point of the siphon does not touch the paper, to avoid impeding the motion of the coil.

Kelvin's electrostatic syphon

The siphon and an ink reservoir are together supported by an ebonite
Ebonite
Ebonite is a brand name for very hard rubber first obtained by Charles Goodyear by vulcanizing rubber for prolonged periods. It is about 30% to 40% sulfur. Its name comes from its intended use as an artificial substitute for ebony wood...

 bracket, separate from the rest of the instrument, and insulated from it. This separation permits the ink to be electrified to a high potential while the body of the instrument, including the paper and metal writing tablet, are grounded, and at low potential. The tendency of a charged body is to move from a place of higher to a place of lower potential, and consequently the ink tends to flow downwards to the writing tablet. The only avenue of escape for it is by the fine glass siphon, and through this it rushes accordingly and discharges itself upon the paper. The natural repulsion between its like-electrified particles causes the shower to issue in spray. As the paper moves over the pulleys a delicate hair line is marked, straight when the syphon is stationary, but curved when the siphon is pulled from side to side by the oscillations of the signal coil.

Power to pull the roll of paper tape through the syphon recorder was usually supplied by one Froment's mouse mill motor
Mouse mill motor
Froment's "mouse mill" motor was an early form of electric motor, also known as the Revolving Armature Engine. It is similar to the contemporary switched reluctance motor and stepper motor, although there is no continuous magnetic circuit between opposed poles.As the mouse mill motor was simple to...

s. These also drove an electrostatic machine to generate the electricity to power the syphon.

Muirhead's vibrating recorder

A simpler mechanism was developed by Alexander Muirhead
Alexander Muirhead
Alexander Muirhead, FRS, born in East Saltoun, East Lothian, Scotland was an electrical engineer specialising in wireless telegraphy.-Biography:...

. This used a vibrating pen to avoid the same problem of the ink sticking to the paper. The recording pen was suspended on a thin wire, vibrated by an electromagnet and break contact, similar to that of an electric bell
Electric bell
An electric bell is a mechanical bell that functions by means of an electromagnet. When an electric current is applied, it produces a repetitive buzzing or clanging sound...

.
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