How does the conductivity meter work

- Mar 16, 2018-

Conductivity is a digital representation of the ability of a solution to conduct current. The conductivity of water has a certain relationship with the amount of inorganic acids, alkalis and salts it contains. When their concentrations are low, the conductivity increases with the increase of concentration. Therefore, this indicator is often used to estimate the total amount of ions in water. Concentration or salt content.

Water quality hardness unit conversion

Hardness unit ppm German hardness French hardness British hardness

1ppm = 1.000ppm 0.0560 0.1 0.0702

1 German hardness = 17.847ppm 1 1.7847 1.2521

1 French hardness = 10.000ppm 0.5603 1 0.7015

1 UK Hardness = 14.286 ppm 0.7987 1.4285 1

Conductivity and water hardness

The conductivity of the aqueous solution is directly proportional to the dissolved solids concentration, and the higher the solids concentration, the higher the conductivity. The relationship between conductivity and dissolved solids concentration is approximately expressed as: 1.4 μS/cm=1 ppm or 2 μS/cm=1 ppm (per million units of CaCO3). The total hardness value of water can be obtained indirectly by using a conductivity meter or total dissolved solids meter. As described above, in order to facilitate the conversion, the conductivity is 1μs/cm = 0.5ppm.

But need to pay attention:

(1) Indirect measurement of water hardness by electrical conductivity, theoretical error of about 20-30 ppm

(2) The conductivity of the solution determines the motion of the molecule and the temperature affects the motion of the molecule. To compare the measurement results, the test temperature is generally set at 20°C or 25°C.

(3) The use of reagent testing can obtain more accurate water hardness values.

Soft and hard water

Water is soft water or hard water. Water that does not contain or contains a small amount of calcium and magnesium ions is called soft water, and vice versa is called hard water. The hardness component of water, if it is caused by sodium bicarbonate or magnesium bicarbonate, is temporary hard water (boiling temporary hard water, decomposed sodium bicarbonate, precipitated by insoluble carbonate formed, and water changed from hard water to soft water) If it is caused by sulphate or chloride containing calcium, magnesium, it is a permanent hard water. According to the general hardness of water, the total hardness of 0-30ppm is called soft water, the total hardness of more than 60ppm is called hard water, high-quality drinking water does not exceed 25ppm, and the total high-quality soft water hardness is below 10ppm. In natural water, the uncontaminated rain and snow far away from the city belong to soft water; springs, streams, rivers and reservoirs are mostly temporary hard water, and part of the groundwater is of high hardness.

About the water quality hardness conversion common unit conversion:

1 mmol/L (1/2Ca2+, 1/2Mg2+)=50 ppm (Calculated by CaC03)

1 mmol/L (1/2Ca2+, 1/2Mg2+) = 2.92 grain/gallon (grain/gallon)

Lgrain/gallon = 17.1ppm (Calculated by CaC03)

1m3=264gallon (US)=22O ganon(UK) (Ingallon)

Lkg=2.2pounds (pound sterling)


TDS (total dissolved solids) is used to measure the total content of all ions in water, usually expressed in ppm.

In pure water who manufactures, conductivity can also be used to indirectly represent TDS.

The conductivity of the solution is equal to the sum of the conductivity of the various ions in the solution.

The empirical formula is: Half the conductivity in microsiemens is approximately equal to TDS (ppm)

Sometimes TDS is also represented by other salts, such as CaCO3 (the coefficient is 0.66)

The conversion factor for TDS and conductivity can be adjusted between 0.4 and 1.0 to correspond to different types of electrolyte solutions.


Conductivity is the ability of a substance to carry current, as opposed to the resistance, in Siemens/cm.

Water hardness

The hardness of water refers to the concentration of calcium and magnesium ions in water. The hardness unit is ppm, and 1 ppm represents calcium carbonate content in water at 1 mg/L (mg/L).

The conductance (G) is the reciprocal of the resistance (R). Therefore, when two electrodes (usually platinum electrodes or platinum black electrodes) are inserted into the solution, the resistance R between the two electrodes can be measured. According to Ohm's law, when the temperature is constant, this resistance value is proportional to the electrode distance L (cm) and is inversely proportional to the cross-sectional area A (cm2) of the electrode, that is, R = ρ×(L/A); where ρ is the resistivity and is long 1cm, the resistance of the conductor with a cross-sectional area of 1cm2 depends on the nature of the material.

According to the above equation, the conductance (G) of the conductor can be expressed as follows: G = 1/R = (1/ρ) × (A/L) = K × (1/J) ; where K = 1/ρ For conductivity, J = L/A is called the electrode constant; conductivity of the electrolyte solution refers to the conductance of a 1 cm3 solution between two parallel electrodes spaced 1 cm apart. From the above equation, when the electrode constant (J) is known and the solution resistance (R) or conductance (G) is measured, the conductivity can be determined.

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