Thermo Scientific Russell RL060C, Руководство пользователя

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Thermo Scientific Russell RL060C Conductivity Meter User Guide
Chapter XII
Conductivity Theory
Conductance .is .a .quantity .associated .with .the .ability .of .primarily .aqueous .solutions .
to .carry .an .electrical .current, .I, .between .two .metallic .electrodes .when .a .voltage .E .is .
connected .to .them . .Though .water .itself .is .a .rather .poor .conductor .of .electricity, .the .
presence .of .ions .in .the .water .increases .its .conductance .considerably, .the .current .
being .carried .by .the .migration .of .the .dissolved .ions . .This .is .a .clear .distinction .from .the .
conduction .of .current .through .metal, .which .results .from .electron .transport . .
The .conductance .of .a .solution .is .proportional .to .and .a .good, .though .non-specific .
indicator .of .the .concentration .of .ionic .species .present, .as .well .as .their .charge .and .
mobility . .It .is .intuitive .that .higher .concentrations .of .ions .in .a .liquid .will .conduct .more .
current . .Conductance .derives .from .Ohms .law, .E .= .IR, .and .is .defined .as .the .reciprocal .
of .the .electrical .resistance .of .a .solution . .
.
C = 1 / R
. where . .C .is .conductance .(siemens) .
R .is .resistance .(ohms)
One .can .combine .Ohms .law .with .the .definition .of .conductance, .and .the .resulting .
relationship .is: .
.
C = I / E
. where . .I .is .current .(amps) .
E .is .potentials .(volts)
In .practice, .conductivity .measurements .involve .determining .the .current .through .a .
small .portion .of .solution .between .two .parallel .electrode .plates .when .an .AC .voltage .is .
applied . .Conductivity .values .are .related .to .the .conductance .(and .thus .the .resistance) .
of .a .solution .by .the .physical .dimensions .area .and .length .or .the .cell .constant .of .the .
measuring .electrode . .If .the .dimensions .of .the .electrodes .are .such .that .the .area .of .
the .parallel .plates .is .very .large, .it .is .reasonable .that .more .ions .can .reside .between .
the .plates, .and .more .current .can .be .measured . .The .physical .distance .between .the .
plates .is .also .critical, .as .it .effects .the .strength .of .the .electric .field .between .the .plates . .