Specifications
Conductivity/TDS | About Conductivity/TDS Measurement
The Principle of Conductivity Measurement
The principle by which instruments measure conductivity is simple – two
plates are placed in the sample, a potential is applied across the plates
(normally a sine wave voltage), and the current is measured. Conductivity
(G), the inverse of Resistivity (R) is determined from the voltage and
current values according to Ohm’s law.
G = I/R = I (amps) / E (volts)
Since the charge on ions in solution facilitates the conductance of
electrical current, the conductivity of a solution is proportional to its
ion concentration. In some situations, however, conductivity may
not correlate directly to concentration. The graphs below illustrate
the relationship between conductivity and ion concentration for two
common solutions. Notice that the graph is linear for sodium chloride
solution, but not for highly concentrated sulfuric acid. Ionic interactions
can alter the linear relationship between conductivity and concentration
in some highly concentrated solutions.
About Conductivity Measurement
Introduction to Conductivity, TDS and Salinity
Electrical Conductivity (EC) meters measure the capacity of ions in an
aqueous solution to carry electrical current. As the ranges in aqueous
solutions are usually small, the basic units of measurements are
milliSiemens/cm (mS/cm) and microSiemens/cm (µS/cm).
Conductivity is used widely to determine the level of impurities in water
supplies for domestic consumption as well as industrial use. Industries
that employ this method include the chemical, semi-conductor, power
generation, hospitals, textile, iron and steel, food and beverage, mining,
electroplating, pulp and paper, petroleum and marine industries.
Specic applications include chemical streams, demineraliser output,
reverse osmosis, stream boilers, condensate return, waste streams,
boiler blowdown, cooling towers, desalinisation, laboratory analysis, fruit
peeling and salinity level detection in oceanography.
Eutech oers a wide range of conductivity meters for these various
applications. Models include the ECTestr™ series, EcoScan CON 6,
CyberScan handheld CON 11 and CON 110, CyberScan waterproof
CON 400 and CON 410 and CyberScan bench meters CON 510,
CON 1500, CON 6000 as well as the handheld multi-parameters
PC 10, PC 300, PC 510 and colour touchscreen research-grade
bench series PC 6000, PC 6500 and PCD 6500.
The total TDS is a mass estimate and is dependent on the mix of chemical
species as well as the concentration while conductivity is only dependent
on the concentration of chemical species. Some applications require
the measurement of Total Dissolved Solids (TDS) in mg/L, parts per
million (ppm) or parts per thousand (ppt). The TDS concentration can
be obtained by multiplying the conductivity value with a factor which
is empirically determined.
Eutech oers meters that allow the direct reading of TDS values.
These include the TDSTestr™ series, EcoScan TDS 6, CyberScan standard
handheld CON 11, CON 110 and waterproof handheld CON 410. Bench
meters for advanced level laboratory research are the CyberScan
CON 510, CON 1500 and colour touchscreen research-grade CON 6000.
Salinity measurements are common in industries like agriculture,
aquaculture, hydroponics, food, pools and spas where it is necessary to
monitor the salt level constantly. The values are usually read in parts per
thousand (ppt) or % (1 ppt = 1 gram per litre).
The Eutech salinity pocket testers SaltTestr™ series are specially
developed to provide direct readings in these applications.
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Solution Conductivity
Absolute pure water 0.055 µS/cm
Power plant boiler water 1.0 µS/cm
Good city water 50 µS/cm
Ocean water 53 mS/cm
Distilled water 0.5 µS/cm
Deionised water 0.1 - 10 µS/cm
Demineralised water 0 - 80 µS/cm
Drinking water 0.5 - 1 mS/cm
Wastewater 0.9 - 9 mS/cm
Seawater 53 mS/cm
10 % NaOH 355 mS/cm
10 % H
2
SO
4
432 mS/cm
31 % HNO
3
865 mS/cm