Conductivity Meter Working Principle Co

 Conductivity Meter Working Principle Co

Conductivity meter is a tool to measure the value of the electrical conductivity (specific / electric conductivity) of a solution or liquid. The value of the electrical conductivity of a liquid is a reference to the number of ions and the concentration of solids (Total Dissolved Solid / TDS) dissolved in it. Measurement of the number of ions in a liquid becomes important in some cases. One example is to monitor the quality of boiler water (read the following article). This is related to the effect of the concentration of mineral ions on the occurrence of corrosion in the boiler pipe (galvanic corrosion).

The concentration of ions in a solution is directly proportional to their electrical conductivity. The more dissolved mineral ions, the greater the ability of the solution to conduct electricity. This chemical property is used as the working principle of the conductivity meter.

A conductivity meter system consists of two electrodes, which are connected to a voltage source and an ampere meter. The electrodes are arranged so that there is a certain distance between them (usually 1 cm). At the time of measurement, these two electrodes are immersed in the sample solution and given a certain amount of voltage. The value of the electric current that is read by the ampere meter, is used further to calculate the value of the electrical conductivity of the solution.

You are certainly familiar with the following basic electric circuit formula:

V = R x I

…..(1)

Where V is the circuit voltage (volts), I is the circuit electric current (amperes), and R is the circuit electrical resistance (Ω).

The electrical resistance (R) is directly proportional to the distance between the two electrodes (l) of the conductivity meter, and inversely proportional to the electrode area (A; in the figure above S).

R = ( l/A ) x

…..(2)

Where is the specific electrical resistance (Ω.m) of the solution.

If equations (1) and (2) are combined, the following equation will be obtained:

V/I = ( l/A ) x

And because the value ( l/A ) is constant for each conductivity meter, it can be replaced by a constant (C):

V/I = C x

…..(3)

Conductivity meter actually does not measure the value of electrical conductivity, but measures specific electrical conductivity (specific conductivity). Specific electrical conductivity is the value of electrical conductivity for each one unit length. This specific electrical conductivity is symbolized by (Kappa), which is the reciprocal of the specific electrical resistance (ρ):

    = /

Where the specific electrical conductivity uses units of S/m (Siemens per meter). And if the above equation is inserted into equation (3), then we will get the general equation for calculating the specific electrical conductivity value:

    = C x I / V

…..(3)

The working principle of the conductivity meter uses equation (3) above. Where the electric voltage (V) is determined by the system, the electric current (I) is the measured parameter, and the constant (C) was obtained previously from the conductivity meter calibration process using a solution of known specific conductivity value.