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form of potentiometer is a uniform high-resistance wire attached to an insulating support, marked with a linear measuring scale. In use, an adjustable regulated voltage source E, of greater magnitude than the potential to be measured, is connected across the wire so as to pass a steady current through it.
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Between the end of the wire and any point along it will be a potential proportional to the length of wire to that point. By comparing the potential at points along the wire with an unknown potential, the magnitude of the unknown potential can be determined. The instrument used for comparison must be
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The principle of a potentiometer is that the potential dropped across a segment of a wire of uniform cross-section carrying a constant current is directly proportional to its length. The potentiometer is a simple device used to measure the electrical potentials (or compare the e.m.f of a cell). One
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To make a potentiometric determination of an analyte in a solution, the potential of the cell is measured. This measurement must be corrected for the reference and junction potentials. It can also be used in standardisation methods. The concentration of the analyte can then be calculated from the
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The galvanometer does not need to be calibrated, as its only function is to read zero or not zero. When measuring an unknown voltage and the galvanometer reads zero, no current is drawn from the unknown voltage and so the reading is independent of the source's internal resistance, as if by a
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Because the resistance wire can be made very uniform in cross-section and resistivity, and the position of the wiper can be measured easily, this method can be used to measure unknown DC voltages greater than or less than a calibration voltage produced by a standard cell without drawing any
552:. Potentiometers for use with thermocouples also measure the temperature at which the thermocouple wires are connected, so that cold-junction compensation may be applied to correct the apparent measured EMF to the standard cold-junction temperature of 0 degrees C.
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portion of the resistance wire when the galvanometer gives a zero reading for an unknown voltage, the distance AX is measured or read from a pre-printed scale next to the resistance wire. The unknown voltage can then be calculated:
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A metre bridge is a simple type of potentiometer which may be used in school science laboratories to demonstrate the principle of resistance measurement by potentiometric means. A resistance wire is laid along the length of a
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This is a form of the constant resistance potentiometer described above but designed to minimize the effects of contact resistance and thermal emf. This equipment is satisfactorily used down to readings of 1000 nV or so.
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by a slider. When the galvanometer reads zero, the ratio between the lengths of wire to the left and right of the slider is equal to the ratio between the values of a known and an unknown resistor in a parallel circuit.
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of the resistance wire. The wiper is moved until no current flows into or out of the source of unknown voltage, as indicated by the galvanometer in series with the unknown voltage. The voltage across the selected
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The constant resistance potentiometer is a variation of the basic idea in which a variable current is fed through a fixed resistor. These are used primarily for measurements in the millivolt and microvolt range.
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section of wire is then equal to the unknown voltage. The final step is to calculate the unknown voltage from the fraction of the length of the resistance wire that was connected to the unknown voltage.
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sensitive, but need not be particularly well-calibrated or accurate so long as its deflection from zero position can be easily detected.
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Another development of the standard types was the 'thermocouple potentiometer' especially adapted for temperature measurement with
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An unknown DC voltage, in series with the galvanometer, is then connected to the sliding wiper, across a variable-length section R
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resistance wire is AB, where A is the (-) end and B is the (+) end, and the movable wiper is at point X at a distance AX on the R
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In this arrangement, a fraction of a known voltage from a resistive slide wire is compared with an unknown voltage by means of a
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is the resistance of the entire resistance wire. The arrow head represents the moving
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or 'potential difference' by comparison of an unknown voltage with a known reference
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307:{\displaystyle {R_{2} \over R_{1}}={{\mbox{cell voltage}} \over V_{\mathrm {S} }}}
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This article is about the measuring instrument. For the electrical component, see
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Electrical calibration equipment including various measurement potentiometers
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Measurement potentiometers are divided into four main classes listed below.
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If the potentiometer is attached to a constant voltage DC supply such as a
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Dial potentiometer, with built-in galvanometer and reference voltage source
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A potentiometer being calibrated and then measuring an unknown voltage.
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This null balance measuring method is still important in electrical
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and standards work and is also used in other areas of electronics.
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around 1841 and became a standard laboratory measuring technique.
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wire that corresponds to the voltage of a standard cell so that
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516:{\displaystyle V_{U}=(Calibration\ Cell\ Voltage){AX \over AB}}
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Dept of
Physics. Thermodynamics: Thermocouple Potentiometer.
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for use as a voltage divider. The potentiometer is first
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by positioning the wiper (arrow) at the spot on the R
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is used whose emf is known (e.g. 1.0183 volts for a
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76:"Potentiometer" measuring instrument
682:"Ian Hickson's Metre Bridge Experiment"
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339:is equal to the standard cell voltage.
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223:In this circuit, the ends of a uniform
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705:Pictures of measuring potentiometers
65:adding citations to reliable sources
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526:Constant resistance potentiometer
760:Adsorptive stripping voltammetry
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593:Potentiometer (voltage divider)
143:is an instrument for measuring
52:needs additional citations for
1012:Faraday's laws of electrolysis
896:Hanging mercury drop electrode
800:Differential pulse voltammetry
780:Cathodic stripping voltammetry
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201:Constant current potentiometer
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835:Rotated electrode voltammetry
231:are connected to a regulated
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770:Anodic stripping voltammetry
157:Johann Christian Poggendorff
951:Standard hydrogen electrode
941:Saturated calomel electrode
331:is then adjusted until the
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876:Dropping mercury electrode
616:Thomas B. Greenslade, Jr.
544:Thermocouple potentiometer
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946:Silver chloride electrode
746:Electroanalytical methods
820:Normal pulse voltammetry
815:Linear sweep voltammetry
372:from the standard cell.
926:Rotating disk electrode
901:Ion selective electrode
535:Microvolt potentiometer
987:Butler–Volmer equation
840:Squarewave voltammetry
810:Hydrodynamic technique
765:Amperometric titration
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386:If the length of the R
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180:Principle of operation
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1002:Debye–Hückel equation
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620:. Physics.kenyon.edu
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956:Ultramicroelectrode
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871:Auxiliary electrode
684:. Academia.hixie.ch
618:"The Potentiometer"
906:Mercury coulometer
795:Cyclic voltammetry
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825:Polarography
686:. Retrieved
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622:. Retrieved
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653:Archived
587:See also
362:infinite
235:supply V
659:Scenta.
370:current
149:voltage
145:voltage
101:scholar
975:Theory
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