An electrometer is an electrical instrument for measuring electric charge or electrical potential difference. There are many different types, ranging from historical hand-made instruments to high-precision electronic devices. Modern electrometers based on vacuum tube or solid state technology can be used to measure extremely small currents down to 1 femtoampere. A simpler but related instrument, the electroscope, works on similar principles but indicates only the relative magnitudes of voltages or charges. Lightning strikes during a night-time thunderstorm. ... Electric charge is a fundamental conserved property of some subatomic particles, which determines their electromagnetic interactions. ... Potential difference is a quantity in physics related to the amount of energy that would be required to move an object from one place to another against various types of force. ... Femto is an SI prefix (symbol f) in the SI system of units denoting a factor of 10−15 or 0. ...

Simple charge indicating device

Gold-leaf electroscope

The gold-leaf electroscope was one of the first instruments to indicate electric charge. It is still used for science demonstrations but has been superseded in most applications by electronic measuring instruments. The instrument consists of two thin leaves of foil suspended from an electrode. When the electrode is charged by induction or by contact, the leaves acquire similar electric charges and repel each other due to the Coulomb force. Their separation is a direct indication of the net charge stored on them. The leaves may be enclosed in a glass envelope to protect them from draughts, and the envelope may be evacuated to minimize charge leakage. A further cause of charge leakage is ionizing radiation, so to prevent this, the electrometer must be surrounded by lead shielding. Image File history File links Download high resolution version (811x1077, 59 KB) Electrometer (electroscope) Drawn by User:Stw using Inkscape and GIMP. Available as SVG upon request. ... Image File history File links Download high resolution version (811x1077, 59 KB) Electrometer (electroscope) Drawn by User:Stw using Inkscape and GIMP. Available as SVG upon request. ... An electrode is a conductor used to make contact with a nonmetallic part of a circuit (e. ... Electrostatic induction is a method by which an electrically charged object can be used to create an electrical charge in a second object, without contact between the two objects. ... In physics, Coulombs law is an inverse-square law indicating the magnitude and direction of electrical force that one stationary, electrically charged substance of small volume (ideally, a point source) exerts on another. ... Look up Vacuum in Wiktionary, the free dictionary. ... Ionizing radiation is either particle radiation or electromagnetic radiation in which an individual particle/photon carries enough energy to ionize an atom or molecule by completely removing an electron from its orbit. ... General Name, Symbol, Number lead, Pb, 82 Chemical series poor metals Group, Period, Block 14, 6, p Appearance bluish white Atomic mass 207. ...

It should be noted that this type of electroscope purely acts as an indicator and not a measuring device. The Braun electroscope replaced the gold-leaf electroscope for more accurate measurements.

Another way to construct an electrometer is to suspend two aluminum or copper foil pieces on wire (tantalum or platinum is best), or (far less expensively) nylon monofilament. The most common radiation measurement device, and widely used in the nuclear industry, the Quartz Fibre Electrometer (or QFE) personal dosimeter, is actually a ruggedized, calibrated electroscope. This uses the leakage effect mentioned above to detect ionising radiation. General Name, Symbol, Number tantalum, Ta, 73 Chemical series transition metals Group, Period, Block 5, 6, d Appearance gray blue Atomic mass 180. ... General Name, Symbol, Number platinum, Pt, 78 Chemical series transition metals Group, Period, Block 10, 6, d Appearance grayish white Atomic mass 195. ... Monofilament lines have been around for years and are commonly used as fishing lines. ... Cross section diagram of dosimeter released by the Federal Civil Defense Authority A dosimeter is any device used to measure an individuals exposure to a hazardous environment, particularly when the hazard is cumulative over long intervals of time, or ones lifetime. ...

Capacitance electroscopes

Although appearing to sound similar to the simple electroscope described above, this type of instrument is usually calibrated to enable quantitative measurements. A capacitance electroscope is a type of electroscope in which a dielectric material is sandwiched between the leaves of the electroscope. As a result, the charge accumulated on the leaves is increased. A special type of capacitance electroscope, in which the leaves were comprised of different metals, was commonly used to measure the Volta effect [1] A capacitance electroscope is a type of electroscope in which a dielectric material is sandwiched between the leaves of the electroscope. ... A dielectric, or electrical insulator, is a substance that is highly resistant to the flow of electric current and has a relative permittivity greater than unity. ... The Volta effect is an obsolete name for the weak potential developed by the contact of different metals. ...

Modern electrometers

In modern parlance, an electrometer is a highly sensitive electronic voltmeter whose input impedance is so high that the current flowing into it can be considered, for practical purposes, to be zero. They are of use in nuclear physics as they are able to amplify the tiny 'photo' currents created by radiation. The most common use for modern electrometers is probably the measurement of radiation with ionization chambers. Two digital voltmeters A voltmeter is a measuring instrument for measuring the voltage between two points in an electric circuit. ... The input impedance or sometimes loading impedance of a circuit or electronic device is the impedance actually experienced by a signal which is connected to its input. ... Nuclear physics is the branch of physics concerned with the nucleus of the atom. ...

Vibrating reed electrometers

Vibrating reed electrometers used a variable capacitor formed between a moving electrode (in the form of a vibrating reed) and a fixed input electrode. As the distance between the two electrodes varied, the capacitance also varied and electric charge was forced in and out of the capacitor. The ac signal produced by the flow of this charge was amplified and used as an analogue for the dc voltage applied to the capacitor. The input resistance of the electrometer was determined solely by the leakage resistance of the capacitor (although its ac input impedance was clearly less than infinity). A reed is a thin strip of material which vibrates to make music. ... A capacitor is a device that stores energy in the electric field created between a pair of conductors on which electric charges of equal magnitude, but opposite sign, have been placed. ... City lights viewed in a motion blurred exposure. ... Direct current (DC or continuous current) is the continuous flow of electricity through a conductor such as a wire from high to low potential. ... In electrical engineering, Impedance is a measure of opposition to a sinusoidal electric current. ...

For convenience of use, the vibrating reed assembly was often attached by a cable to the rest of the electrometer. This allowed for a relatively small unit to be located near the charge to be measured while the much larger reed-driver and amplifier unit could be located wherever it was convenient for the operator.

Valve electrometers

Valve type electrometers use an unbiased vacuum tube with a very high gain (mutual conductance) and input resistance. The input current is allowed to flow into the high impedance grid, and the voltage so generated is vastly amplified in the anode (plate) circuit. The best examples of these valves can detect currents as low as a few femtoamperes (10^-15 amperes). This type of valve can be ruined by handling with ungloved hands as the salts left on the glass envelope can provide leakage paths for these tiny currents. In electronics, gain is usually taken as the mean ratio of the signal output of a system to the signal input of the system. ... Transconductance, also known as mutual conductance, is a property of certain electronic components. ... Diagram of a zinc anode in a Daniells cell. ... Plate has several meanings: A plate electrode in a vacuum tube. ...

Solid-state electrometers

The most modern electrometers consist of a solid-state amplifier circuit using FETs, connections for external measurement devices, and also possibly a display, data-logging connections, and/or a high-voltage supply. The amplifier magnifies small currents so that they are more easily measured. The external connections are usually of a co-axial or tri-axial design, and allow attachment of diodes or ionization chambers for radiation measurement. The display or data-logging connections allow the user to see the data or record it for later analysis. The high-voltage supply is an integral power supply which is used to supply a voltage to the ionization chamber or diode. Solid state may refer to: In computing: Solid state devices are data storage device components that uses memory chips, such as SDRAMs, to store data. ... For the British rock band of the same name, see Amplifier (band) An amplifier can be considered to be any device that uses a small amount of energy to control a source of a larger amount of energy, although the term today usually refers to an electronic amplifier. ... FET can mean: FET, field effect transistor FET, a Mazda piston engine This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ... Types of diodes In electronics, a diode is a component that restricts the direction of movement of charge carriers. ... An ionization chamber is a device used for two major purposes: detecting particles in air (as in a smoke detector), and for detection or measurement of ionizing radiation. ... Radiation in physics is a process of emission of energy or particles. ...

Solid-state electrometers are often multipurpose devices that can measure voltage, charge, resistance and current. They measure voltage by means of "voltage balancing", in which the input voltage is compared with an internal reference voltage source using an electronic circuit with a very high input impedance (of the order of 10¹⁴ ohms). A similar circuit modified to act as a current-to-voltage converter enables the instrument to measure tiny currents of the order of one femtoampere. Combined with an internal voltage source, the current-measuring mode can be adapted to measure very high resistances, of the order of 10¹⁷ ohms. Finally, by calculation from the known capacitance of the electrometer's input terminal, the instrument can measure very small electric charges, down to a small fraction of a picocoulomb, on the terminal. [2] Electrical resistance is a measure of the degree to which an electrical component opposes the passage of current. ... // Definition Capacitance is a measure of the amount of electric charge stored (or separated) for a given electric potential. ... Electric charge is a fundamental conserved property of some subatomic particles, which determines their electromagnetic interactions. ...

Experiments with an electroscope

1. Touch the terminal with a charged conductor. Electrons flow into or out of the electroscope until its potential equals that of the conductor. The net surplus or deficit of electrons on the leaves causes them to repel each other. The charge that transfers, and therefore the deflection, are functions of the original potential difference between the conductor and the uncharged electroscope.
2. Place an isolated, charged conductor in contact with the terminal. The proportion of the conductor's charge that ends up on the terminal depends on their relative capacitances. This charge remains on the electroscope when you take the conductor away. The electroscope indicates this charge.
3. Bring a charged insulator near to the terminal but don't allow any charge to transfer between them. In this case, the deflection indicates the net charge on the electrons that have been temporarily pushed towards or away from the leaves. This charge is related to the charge density on the part of the insulator near to the terminal, and the relative shapes and positions of the two. What the electroscope is measuring in this case is quite vague, because there is no sharp boundary between the electron-rich and electron-depleted regions of the electroscope.
4. Place a charged insulator on or near the terminal, ground the terminal and then withdraw the insulator. This leaves the electroscope with a net charge. The electrons redistribute themselves over the terminal and the leaves, causing the leaves to repel each other. The deflection is monotonically related to the net charge left behind on the electroscope, in a similar way to the previous case.

Patents

The USPTO uses the class schedule of class 324 of Electricity: measuring and testing, subclass 109 of electrostatic attraction or piezoelectric. Other applicable subclasses included 458, electrostatic fields using modulation-type electrometer, and 158.1, miscelleanous. Class 399 of electrophotography has a subclass 48, having detection of photoconductor potential, and subclass 73, electrometer detail which includes means or where a method is provided for measuring a potential or charge level. The electrometer may also be called an electrostatic voltmeter. This is used to connote a measuring instrument (eg., a voltmeter) for measuring the voltage between two points in an electrostatic circuit. The United States Patent and Trademark Office (PTO or USPTO) is an agency in the United States Department of Commerce that provides patent and trademark protection to inventors and businesses for their inventions and corporate and product identification. ... Two digital voltmeters A voltmeter is a measuring instrument for measuring the voltage between two points in an electric circuit. ... Electrostatics is the branch of physics that deals with the force exerted by a static (i. ...

• U.S. Patent 3997839, Electrometer. Gerard Dreyfus, 1976.
• U.S. Patent 1815606, Electroscope. R. Barton, 1931.
• U.S. Patent 1783297, Indicating means for high frequency oscillations. A. Meissner, 1930.
• U.S. Patent 1764294, High voltage voltmeter. F. D. Fielder, 1930.
• U.S. Patent 1726866, Electrostatic voltage meter. H. Starke, 1929.
• U.S. Patent 1716700, Electroscope. Richard D. Kleeman, 1929.
• U.S. Patent 1679524, Measuring instrument. C. G. Hershey, 1928.
• U.S. Patent 1610784, Transformer. T. Isono, 1926.
• U.S. Patent 1601042, Electroscope and charge device therefore. F. Rosa, 1926.
• U.S. Patent 1551374, Electrostatic voltmeter. W. P. Davey, 1925.
• U.S. Patent 1517249, Electric relay. B. Rosenbaum, 1924.
• U.S. Patent 1446748, Electroscopic apparatus. F. A Johnsen, 1923.
• U.S. Patent 1417114, Electrometer. F. R. Sommer, 1922
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• U.S. Patent 0771968, Electrostatic instrument. F. H. Sowman, 1904.
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• U.S. Patent 0516341, Safety device for electrostatic measuring instruments. W. E. Ayrton and T. Mather, 1894.
• U.S. Patent 0514581, Electrical measuring instrument. E. G. Willyoung, 1894.
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• U.S. Patent 0500236, Static voltmeter. A. E. Kennelly, 1893.

Elihu Thomson (March 29, 1853 - March 13, 1937) was an engineer who was instrumental in the founding of major electrical companies in the United States, Britain and France. ... William Edward Ayrton (14 September 1847 - 8 November 1908) was a British physicist. ... Arthur Edwin Kennelly (December 17, 1861 - June 18, 1939), was an American engineer in electricity. ...

See also

• Electron
• Radiation

Properties The electron is a lightweight fundamental subatomic particle that carries a negative electric charge. ... Radiation in physics is a process of emission of energy or particles. ...

External links

• Build this FET electrometer - A very simple circuit - 2 components
• Simple FET electrometer - A simple bridged circuit
• An op-amp electrometer
• Early electrometers
• Charging an Electroscope by Induction Using a Negatively-Charged Balloon from Multimedia Physics Studios