How to measure conductivity of water

How to measure conductivity of water (conductometry)

Insight to conductivity measurement (conductivity to resistivity) 

This How to measure conductivity of water PDF offers insight to conductivity measurement (conductivity to resistivity) using a conductometry meter. Below are excerpts from whitepaper...

Figure No. 1 Traditional two-plate conductivity probe.

Conductivity measurement meter operation and use. The electrical conductivity of water based solutions (and its opposite, conductivity to resistivity) indicate its electrical current carrying ability. High conductivity occurs when many charged atoms and ions are in the water. This typically means the presence of dissolved metals, salts, acidic or alkali chemicals. Conductivity measurement probes are used to measure the total level of charged particles present. This article explains how conductivity measurement probes work and their application in boiler water treatment and management.

The more charged particles that are present, the easier it is for the electricity to flow. The amount of electricity that flows is a direct reflection of the amount of chemicals present in the water. Conductivity measurement, measures the Total Dissolved Solids (TDS) present and can be used as an indication of contamination. Some charged particles contribute more than others. Organic compounds, like fuels, oils, alcohols, sugars, do not behave in the same way and conductivity cannot be used as a measure of contamination.

Conductivity measurement:

To pass electric current through water a conductivity meter has two probes a small distance apart. A known amount of electricity is put down one probe and the amount that gets through to the other probe is measured. The greater the electric current, the greater the number of charged particles present in the water. Figure No. 1 shows how the earliest conductivity probes were designed. To make the probes more sensitive when fewer charged particles were present the distance between the plates was reduced.

The size of the plates/probes and their distance apart establishes a cell constant for the probe. The meter’s sensitivity can be selected by choosing the probe’s cell constant. Low conduction solutions require big probe surface areas close together while highly conducting solutions use smaller surfaces further apart. Click to learn more about how to measure conductivity of water.

Conductometry probes:

The sensor end of the probe is mounted in the water stream and the read-out is displayed locally or in a control room. Conductivity meters are regularly installed in boiler water purification plants to prove the treatment is removing the dissolved salts and metals that would otherwise go into the boiler and scale-up the heat transferring metal surfaces.

Conductivity meters are also used to measure the TDS build-up inside boilers and to automatically open and close a control valve to blow down the boiler contents and lower the TDS. The probe senses the contamination increasing as water is boiled away into steam. Once the conductivity is above a set limit the automated blow down valve opens and discharges the high TDS water. The probe also monitors the falling TDS levels in the boiler and shuts the blow down valve when the lower set point is reached. Click to learn more about how to measure conductivity of water.

References: Process Control Operative Certificate in Chemical Plant Skills, Holmesglen Collage of TAFE.
Aquarius Technical Bulletin #2, Aquarius Technologies P/L

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