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Four-terminal sensing

 

 
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Four-terminal sensing (4T sensing) or 4-point probes method is an electrical impedance
Electrical impedance

Electrical impedance, or simply impedance, describes a measure of opposition to a sinusoidal alternating current . Electrical impedance extends the concept of Electrical resistance to AC circuits, describing not only the relative amplitudes of the voltage and Electric current, but also the relative Phase ....
 measuring technique that uses separate pairs of current
Electric current

Electric current is the flow of electric charge. The electric charge may be either electrons or ions.The International System of Units unit of electric current intensity is the ampere....
-carrying and voltage
Voltage

Electrical tension is the potential difference between two points of an electrical or electronic circuit, expressed in volts. It is the measurement of the potential for an electric field to cause an electric current in an electrical conductor....
-sensing electrodes to make more accurate measurements than traditional two-terminal (2T) sensing. 4T sensing is used in some ohmmeter
Ohmmeter

An ohmmeter is an electricity measuring instrument that measures electrical resistance, the opposition to an electric current. Micro-ohmmeters make low resistance measurements....
s and impedance analyzers, and in precision wiring configurations for strain gauge
Strain gauge

A strain gauge is a device used to measure the Strain of an object. Invented by Edward E. Simmons and Arthur C. Ruge in 1938, the most common type of strain gauge consists of an Electrical insulation flexible backing which supports a metallic foil pattern....
s and resistance thermometer
Resistance thermometer

Resistance thermometers, also called resistance temperature detectors , are temperature sensors that exploit the predictable change in electrical resistance of some materials with changing temperature....
s.






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4wirebetter
Four-terminal sensing (4T sensing) or 4-point probes method is an electrical impedance
Electrical impedance

Electrical impedance, or simply impedance, describes a measure of opposition to a sinusoidal alternating current . Electrical impedance extends the concept of Electrical resistance to AC circuits, describing not only the relative amplitudes of the voltage and Electric current, but also the relative Phase ....
 measuring technique that uses separate pairs of current
Electric current

Electric current is the flow of electric charge. The electric charge may be either electrons or ions.The International System of Units unit of electric current intensity is the ampere....
-carrying and voltage
Voltage

Electrical tension is the potential difference between two points of an electrical or electronic circuit, expressed in volts. It is the measurement of the potential for an electric field to cause an electric current in an electrical conductor....
-sensing electrodes to make more accurate measurements than traditional two-terminal (2T) sensing. 4T sensing is used in some ohmmeter
Ohmmeter

An ohmmeter is an electricity measuring instrument that measures electrical resistance, the opposition to an electric current. Micro-ohmmeters make low resistance measurements....
s and impedance analyzers, and in precision wiring configurations for strain gauge
Strain gauge

A strain gauge is a device used to measure the Strain of an object. Invented by Edward E. Simmons and Arthur C. Ruge in 1938, the most common type of strain gauge consists of an Electrical insulation flexible backing which supports a metallic foil pattern....
s and resistance thermometer
Resistance thermometer

Resistance thermometers, also called resistance temperature detectors , are temperature sensors that exploit the predictable change in electrical resistance of some materials with changing temperature....
s. 4-point probes are also used to measure sheet resistance
Sheet resistance

The sheet resistance is a measure of Electrical resistance of thin films that have a uniform thickness. It is commonly used to characterize materials made by semiconductor doping, metal deposition, resistive paste printing, and Insulated glazing....
 of thin film
Thin film

Thin films are thin material Layer s ranging from fractions of a nanometre to several micrometres in thickness. Electronics semiconductor devices and optical coatings are the main applications benefiting from thin film construction....
s. 4T sensing is also known as Kelvin sensing, after William Thomson, Lord Kelvin
William Thomson, 1st Baron Kelvin

William Thomson, 1st Baron Kelvin , Order of Merit , Royal Victorian Order, Privy Council of the United Kingdom, Presidents of the Royal Society, Royal Society of Edinburgh, was an Ireland-born United Kingdom of Great Britain and Ireland Mathematical physics and engineer....
, who invented the Kelvin bridge
Kelvin bridge

A Kelvin bridge is a measuring instrument invented by William Thomson, 1st Baron Kelvin. It is used to measure an unknown electrical resistance below 1 Ohm....
 in 1861 to measure very low resistances.

2T versus 4T

The key difference between 4T and 2T sensing is that the separation of current and voltage electrodes in 4T allows the ohmmeter/impedance analyzer to eliminate the impedance contribution of the wiring and contact resistances, given that the voltage electrodes have high enough output impedance
Output impedance

Any linear electric or electronic circuit or device which generates a voltage may be represented as an ideal voltage source in series with an Electrical impedance....
.

Links

  • for a 4-point probe, from UC Berkeley
  • using 4-point probes