Compared to the 2-electrode sensors, the TetraCon® 4-electrode measuring procedure offers considerable application targeted advantages, especially in the area of higher conductivities.
Conductivity as a summation parameter is a measure of the level of ion concentration of a solution. The more salts, acids or bases are dissociated, the greater the conductivity of the solution. In water or wastewater it is mainly a matter of the ions of dissolved salts, and consequently the conductivity is an index of the salt load in wastewater or, respectively, the purity of potable water. The measurement of conductivity is also widely used in industrial production, such as process control in food and pharmaceutical industries.
The measurement of conductivity is generally expressed in S/cm (or mS/cm) which is the product of the conductance of the test solution and the geometric factor of the measuring cell. The scale for aqueous solutions starts at a conductivity of 0.05 µS/cm (at 25 °C) for ultra pure water. The conductivity of natural waters, such as drinking water or surface water is typically in range of 100 – 1000 µS/cm. The upper end of the scale is reached by some acids and alkalis.
Temperature Compensation
The conductivity of a solution is critically dependent on temperature. Therefore, the conductivity readings must be referred to a common reference temperature (25°C) for comparability. The term “temperature compensation” is used in the sense of a mathematical conversion; i.e. a measured conductivity (θ) at any given temperature to the corresponding conductivity value that would be taken at the reference temperature (25°C).
The conductivity of most aqueous solutions varies more or less linearly with temperature θ. In these cases, a linear correction function to compensate for the influence of temperature can be used. For example, the correction coefficient for sewage is approx. 2%/K.
WTW monitors automatically calculate the corrected conductivity values based on the selected temperature coefficient. For the compensation of natural water a non-linear function (nLF) (i.e., built-in table for natural water properties) is available.
Analogue 4-electrode cell
Conductivity 1 µS/cm … 2 S/cm
Cell Constants K = 0.475 cm-1
Ordering Information:
301 960 TetraCon® 325 4-electrode conductivity cell with built-in temperature sensor, 4.9 ft. (1.5 m) cable and waterproof plug, cell constant K = 0.475/cm
301 970 TetraCon® 325-3 4-electrode conductivity cell with built-in temperature sensor, 9.8 ft. (3 m) cable and waterproof plug, cell constant K = 0.475/cm
301 971TetraCon® 325-6 4-electrode conductivity cell with built-in temperature sensor, 19.8 ft. (6 m) cable and waterproof plug, cell constant K = 0.475/cm
301 972 TetraCon® 325-10 4-electrode conductivity cell with built-in temperature sensor, 33 ft. (10 m) cable and waterproof plug, cell constant K = 0.475/cm
301 973 TetraCon® 325-15 4-electrode conductivity cell with built-in temperature sensor, 49.5 ft. (15 m) cable and waterproof plug, cell constant K = 0.475/cm
301 974 TetraCon® 325-20 4-electrode conductivity cell with built-in temperature sensor, 65 ft. (20 m) cable and waterproof plug, cell constant K = 0.475/cm
tetracon3250