Conductivity&salinity

Overview

Conductivity is the ability of an object to conduct electrical current. The measuring principle of the conductivity meter is to place two parallel plates into the solution to be measured, add a certain potential (usually a sine wave voltage) to both ends of the plates, and then measure the electric potential flowing between the plates. current. According to Ohm’s law, conductivity (G) – the reciprocal of resistance (R), is determined by the conductor itself. The basic unit of conductivity is the Siemens (S), originally known as the ohm. Because the geometry of the conductivity cell affects the conductivity value, standard measurements are expressed in unit conductivity S/cm to compensate for differences caused by various electrode sizes. Unit conductivity (C) is simply the product of the measured conductivity (G) and the conductivity cell constant (L/A). Here L is the length of the liquid column between the two plates, and A is the area of ​​the plate.

The conductivity of water has a certain relationship with the amount of inorganic acids, alkalis, and salts it contains. When their concentration is low, the conductivity increases with increasing concentration. Therefore, this indicator is often used to estimate the total concentration of ions or salt content in water. Different types of water have different conductivities. The conductivity of fresh distilled water is 0.2-2μS/cm, but after being left for a period of time, it increases to 2-4μS/cm due to the absorption of CO2; The conductivity of ultrapure water is less than 0.10/μS/cm; the conductivity of natural water is mostly between 50-500μS/cm, and the conductivity of mineralized water can reach 500-1000μS/cm; the conductivity of industrial wastewater containing acids, alkali and salts Often exceeds 10 000 μS/cm; the conductivity of seawater is about 30 000 μS/cm.

The electrode constant is often measured using a standard methyl chloride solution of known conductivity. The conductivity (25°C) of methyl chloride solutions with different concentrations is listed in the table below. The conductivity of the solution is related to factors such as its temperature, polarization phenomenon on the electrode, and electrode distribution capacitance. Compensation or elimination measures are generally adopted on the instrument. Water samples should be measured as soon as possible after collection. If they contain coarse suspended

substances, oil and grease, which interfere with the measurement, they should be filtered or extracted to remove them.

Ultra-high conductivity in water will lead to poor water quality, and high impurity content will destroy the reverse osmosis membrane and pose a threat to human health. For example, high levels of sulfate may cause diarrhea, abdominal pain and other symptoms; high levels of fluoride may cause dental lesions.
Measures to deal with high conductivity of boiler water. If water containing hardness enters the boiler without treatment, after a period of operation, some solid sediments will be firmly attached to the heating surface on the water side of the boiler. This phenomenon is called scaling. Solid deposits adhering to heating surfaces are called scale. Under certain conditions, solid sediments will also precipitate in the pot water and form a loose suspension, which is called water slag. The water slag can be removed with the sewage discharge, but if the sewage discharge is not timely, some of the water slag will also settle on the heating surface or parts where the water flow is sluggish and turn into scale (often called “secondary scale”).

Application

Surface water monitoring, lakes, aquaculture, medicine, rural sewage monitoring, industrial sewage discharge, swimming pool, etc.

Details