Siemens (unit)

The siemens (symbol: S) is the derived unit of electric conductance, electric susceptance, and electric admittance in the International System of Units (SI). Conductance, susceptance, and admittance are the reciprocals of resistance, reactance, and impedance respectively; hence one siemens is redundantly equal to the reciprocal of one ohm, and is also referred to as the mho. The 14th General Conference on Weights and Measures approved the addition of the siemens as a derived unit in 1971.

The unit is named after Ernst Werner von Siemens. In English, the same form siemens is used both for the singular and plural.[1]

Unit systemSI derived unit
Unit ofElectric conductance
SymbolS (= Ω−1) 
Named afterErnst Werner von Siemens
In SI base units:kg−1m−2s3A2


For a conducting element, electrical resistance R and electrical conductance G are defined as

where I is the electric current through the object and V is the voltage (electrical potential difference) across the object.

The unit siemens for the conductance G is defined by

where Ω is the ohm, A is the ampere, and V is the volt.

For a device with a conductance of one siemens, the electric current through the device will increase by one ampere for every increase of one volt of electric potential difference across the device.

The conductance of a resistor with a resistance of five ohms, for example, is (5 Ω)−1, which is equal to 200 mS.


A name that is used as an alternative to the siemens is the mho /moʊ/, the reciprocal of one ohm. It is derived from spelling ohm backwards and is written as an upside-down capital Greek letter omega: , Unicode symbol U+2127 (℧). According to Maver[2] the term mho was suggested by Sir William Thomson (Lord Kelvin). The ohm officially replaced the old "siemens unit", which was a unit of resistance, at an international conference in 1881.[3]

NIST's Guide for the Use of the International System of Units (SI) refers to the mho as an "unaccepted special name for an SI unit", and indicates that it should be strictly avoided.[4]

The SI term siemens is used universally in science and often in electrical applications, while mho is still used in some electronic contexts. The inverted capital omega symbol, while not an official SI abbreviation, is less likely to be confused with a variable than the letter S when doing algebraic calculations by hand, where the usual typographical distinctions (such as italic for variables and Roman for unit names) are difficult to maintain. Likewise, it is difficult to distinguish the symbol S from the lower-case s where second is meant, potentially causing confusion.[5] So, for example, a pentode’s transconductance of 2.2 mS might alternatively be written as 2.2 or 2200 (most common in the 1930s) or 2.2 mA/V. A handwritten "S" can also be misread as the frequency space variable "s", commonly used in transfer functions.

Notes and references

  1. ^ NIST Guide to the SI, Chapter 9: Rules and Style Conventions for Spelling Unit Names, National Institute of Standards and Technology, 2008, retrieved 2017-12-22
  2. ^ Maver, William: American Telegraphy and Encyclopedia of the Telegraph: Systems, Apparatus, Operation. 1903.
  3. ^ "Siemens (Unit of Electrical Conductance)".
  4. ^ NIST Guide to the SI, Chapter 5: Units Outside the SI, National Institute of Standards and Technology, 2008, retrieved 2017-12-22
  5. ^ Eugene R. Weiner, Applications of Environmental Aquatic Chemistry: A Practical Guide, p. 109, CRC Press, 2013 ISBN 1439853320

External links


Atos is a European IT services corporation with its headquarters in Bezons, France and offices worldwide. It specialises in hi-tech transactional services, unified communications, cloud, big data and cybersecurity services. Atos operates worldwide under the brands Atos, Atos Consulting, Atos Healthcare, Atos Worldgrid, Bull, Canopy, Unify and Worldline.

Glossary of electrical and electronics engineering

Most of the terms listed in Wikipedia glossaries are already defined and explained within Wikipedia itself. However, glossaries like this one are useful for looking up, comparing and reviewing large numbers of terms together. You can help enhance this page by adding new terms or writing definitions for existing ones.

This glossary of electrical and electronics engineering pertains specifically to electrical and electronics engineering. For a broad overview of engineering, see glossary of engineering.

Index of electrical engineering articles

This is an alphabetical list of articles pertaining specifically to electrical and electronics engineering. For a thematic list, please see List of electrical engineering topics. For a broad overview of engineering, see List of engineering topics. For biographies, see List of engineers.

Index of physics articles (S)

The index of physics articles is split into multiple pages due to its size.

To navigate by individual letter use the table of contents below.

List of electrical engineers

This is a list of electrical engineers (by no means exhaustive), people who have made notable contributions to electrical engineering or computer engineering.

List of scientists whose names are used as SI units

List of scientists whose names are used as SI units is the list of those scientists whose names are assigned as the names of the international units by the International Committee for Weights and Measures. The International System of Units (abbreviated SI from French: Système international d'unités) is the most widely used system of units of measurement. There are seven base units and 22 derived units (excluding compound units). These units are used both in science and in commerce. Two of the base units and 17 of the derived units are named after scientists. By this convention, their names are immortalised. Below is the list of the scientists whose names are used as SI units. As a rule, the units are written in lowercase letters, but symbols of units derived from the name of a person begin with a capital letter.


Mohs or MoHS can refer to:

Friedrich Mohs, a 19th-century German geologist who developed:

Mohs scale of mineral hardness, a scale used in materials science to describe hardness

Frederic E. Mohs, an American doctor who developed:

Mohs surgery, a microscopically controlled surgery highly effective for common types of skin cancer

Erik Mohs, a German professional racing cyclist

Mohs Automobile, an automobile built by the American Mohs Seaplane Corporation

Moanalua High School, a public, co-educational college preparatory high school in Hawaiʻi

The Melancholy of Haruhi Suzumiya, a 2006 anime sci-fi television series

Mount Olive High School, a U.S. public high school in Flanders, New Jersey


The ohm (symbol: Ω) is the SI derived unit of electrical resistance, named after German physicist Georg Simon Ohm. Although several empirically derived standard units for expressing electrical resistance were developed in connection with early telegraphy practice, the British Association for the Advancement of Science proposed a unit derived from existing units of mass, length and time and of a convenient size for practical work as early as 1861. The definition of the ohm was revised several times. Today, the definition of the ohm is expressed from the quantum Hall effect.

Olkiluoto Nuclear Power Plant

The Olkiluoto Nuclear Power Plant (Finnish: Olkiluodon ydinvoimalaitos) is on Olkiluoto Island, which is on the shore of the Gulf of Bothnia in the municipality of Eurajoki in western Finland. It is one of Finland's two nuclear power plants, the other being the two-unit VVER Loviisa Nuclear Power Plant. The plant is owned and operated by Teollisuuden Voima (TVO), a subsidiary of Pohjolan Voima.

The Olkiluoto plant consists of two Boiling Water Reactors (BWRs) producing 880 MW and 890 MW of electricity.

A third reactor, Unit 3, is expected to be online in January 2020.Unit 3 is an EPR reactor and is under construction since 2005.

The start of commercial operation was originally planned for May 2009 but the project is delayed and the latest estimate (as of November 2018) for start of regular production is January 2020.

In December 2012, the French multi-national building contractor, Areva, estimated that the full cost of building the reactor will be about €8.5 billion, or almost three times the delivery price of €3 billion.A decision-in-principle for a fourth reactor to be built at the site was granted by the Finnish parliament in July 2010, but in June 2015 TVO decided that it will not apply for a construction license for Olkiluoto 4.


Siemens AG (Aktiengesellschaft) (German pronunciation: [ˈziːməns] or [-mɛns]) is a German conglomerate company headquartered in Berlin and Munich and the largest industrial manufacturing company in Europe with branch offices abroad.

The principal divisions of the company are Industry, Energy, Healthcare (Siemens Healthineers), and Infrastructure & Cities, which represent the main activities of the company. The company is a prominent maker of medical diagnostics equipment and its medical health-care division, which generates about 12 percent of the company's total sales, is its second-most profitable unit, after the industrial automation division. The company is a component of the Euro Stoxx 50 stock market index. Siemens and its subsidiaries employ approximately 379,000 people worldwide and reported global revenue of around €83 billion in 2018 according to its earnings release.

Siemens (disambiguation)

Siemens is a German engineering and technology conglomerate founded by Werner von Siemens

Siemens may also refer to

Siemens mercury unit

The Siemens mercury unit is an obsolete unit of electrical resistance. It was defined by Werner von Siemens in 1860 as the resistance of a mercury column with a length of one metre and uniform cross-section of 1 mm2 held at a temperature of zero degrees Celsius. It is equivalent to approximately 0.953 ohm.

Glass tube cross sections are typically irregularly conical rather than perfect cylinders, which presented a problem in constructing precise measuring devices. One could make many tubes and test them for conical regularity, discarding the least regular ones; their regularity can be measured by inserting a small drop of mercury into one end of the tube, then measuring its length while sucking it along. The cross-sectional area at each end can then be measured by filling the tube with pure mercury at a fixed temperature, weighing it, and comparing that weight to the relative lengths of the mercury drop at each end. The tube can then be used for measurement by applying a formula obtained from these measurements that corrects for its conical shape.In 1971, the 14th General Conference on Weights and Measures formally adopted the name siemens as the unit of electric conductivity, equal to the inverse of the ohm for resistance. The Siemens mercury unit was superseded in 1881 by the ohm.

Väo Power Plant

The Väo Power Plant (also known as Tallinn Power Plant) is a biomass and peat-fired combined heat and power plant in Tallinn, Estonia. It's located in the eastern end of Tallinn in Väo, in a depleted part of Väo limestone quarry. The plant supplies heat to Lasnamäe and the central districts of Tallinn.

Construction started in 2007 and the power plant was commissioned in 2009. Originally, the project was started by Estonian businessman Urmas Sõõrumaa and was sold then to an affiliate of Dalkia. Since 2011 majority stake is owned by Estonian businessman Kristjan Rahu company Utilitas.The power plant has capacity of 25 MW of electrical power and 49 MW of heat. It is fired by wood chips and peat. It has he a 70-metre (230 ft) high flue gas stack, supplied by Finnish company Noviter. The main contractor was KMG Inseneriehitus, turbine was provided by Siemens, fuel handling system provided by BMH Technology Oy, boiler was provided by Noviter and Metso.In 2014, construction of the Väo 2 power plant started. Väo 2 will have capacity of 21.4 MW of electrical power and 76.5 MW of heat. Like Väo 1, it will be fired by wood chips and peat. The main contractor is Axis Technologies. The turbine is supplied by MAN SE. The plant is expected to be commissioned in October 2016.

Base units
Derived units
with special names
Other accepted units
See also

This page is based on a Wikipedia article written by authors (here).
Text is available under the CC BY-SA 3.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.