Bourdon tube (measurement technology)

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Front view of a manometer with double scale, outdated American pressure unit on the outside, current German pressure unit on the inside, for both negative and positive pressure
Corresponding interior view to the above picture with Bourdon tube and pointer drive

The tube spring (also Bourdon tube , Bourdon tube ) is a measuring element for measuring pressure differences. It is used in most mechanical pressure gauges. Bourdon tubes are also used in pressure switches and for temperature measurement in gas pressure thermometers and thermostats . The Bourdon tube is usually a flattened, circular, helical or helically wound metal tube; this form of the Bourdon tube is also called a Bourdon spring after its initial patent payer. Since this is the most common form of Bourdon tube, the term Bourdon tube is often used synonymously with Bourdon tube.

When pressure is applied, the spring tends to bend open. The change in path of the spring end is transmitted to a measuring mechanism via a pull rod and translated into a rotation of the pointer axis. The effect that is exploited here can most easily be illustrated by a trumpet flute.

history

The principle of pressure measurement using a Bourdon tube was discovered by chance in 1845 by a railway engineer named Rudolf Eduard Schinz when he tried to straighten deformed pipes by applying pressure. He then constructed a pressure gauge for locomotives that was based on a helically wound Bourdon tube with an elliptical cross-section. In 1848 Schinz tried to have his design patented in Prussia.

In 1848, the Parisian instrument maker Eugène Bourdon patented the measuring principle, which is still known by his name today, especially in the Anglo-Saxon and French-speaking areas. In 1859, Pat. US No. 9163, dated August 3, 1852 (ET), was successfully challenged by Lucien Vidie , the inventor of the aneroid can , and defeated with the help of his friend and patent attorney, Pierre Armand Lecomte.

Application and designs

Bourdon tube springs are used to distinguish between tension and compression springs, torsion springs and spiral springs. The tension and compression springs include u. a. the corrugated tube spring . Here, the linear expansion of a thin-walled corrugated pipe, closed on one side and pressurized on the other side, is transmitted to a measuring mechanism. Torsion or helical tube springs are straight tubes, pressed into oval or star-shaped cross-sections and twisted tubes that unwind under the action of pressure. The rotary movement is transmitted to a pointer axis. While these two versions only play a subordinate role technically, the curved spiral springs (Bourdon springs) are produced in large numbers and used in pressure gauges, gas pressure thermometers and switching devices. Bourdon springs are subdivided into circular springs (~ 0.6 ... 60 bar), helical springs (~ 60 ... 1000 bar) and coil springs (up to ~ 4000 bar) according to their type of winding. Further adaptation to different measuring ranges is made by varying the pipe wall thickness, the pipe cross-sectional geometry and the Bourdon tube material.

Bourdon tubes are mostly made of metallic materials. Since the measuring medium penetrates the Bourdon tube, the material used must be resistant to the measuring medium or a liquid-filled diaphragm seal must be used. Usually brass , Cu or CuNi alloys as well as stainless steel or unalloyed steel are used. Special Bourdon tubes made of quartz glass are used for measurements in the vacuum range up to approx. 10 −6 bar .

All types of Bourdon tube must be designed in such a way that they do not come into the area of plastic deformation during normal operation . If a pressure gauge is overloaded in this way, the pointer will no longer move to the zero point when the pressure is relieved.

literature

  • W. Wuest in Prof. Dr. P. Profos [Hrsg.]: Handbook of industrial measurement technology , Oldenbourg, 2002, ISBN 3486225928
  • H. Julien: Handbook of pressure measurement technology with spring-elastic measuring elements , Alexander Wiegand SE & Co , Klingenberg / Main, 1981, ISBN 39800364-2-1
  • H. Ahrendt, R. Gesatzke, G. Hahn, P. Herrmann, H. Julien, R. Karger, M. Kaufmann, H.-J. Krebs, J. Lucht, A. Müller, R. Müller, B. Vetter: Overpressure measuring devices according to DIN EN 837 , Beuth Verlag, 2007, ISBN 978-3-410-16626-9
  • Matthias Künzel: A contribution to optical interference precision pressure measurement with quartz Bourdon springs , Tectum Verlag, 1997, ISBN 382880022X

Individual evidence

  1. ↑ The Schinz steam manometer for locomotives. In: Polytechnisches Journal . 113, 1849, pp. 85-90.
  2. ↑ Files Patent Office Berlin, signed: Gew.Dep. M340, de November 27, 1848