Guide to Understanding Conductivity

Knowing what materials have the ability to conduct electricity can be very valuable. Distinct measures of conductivity can indicate various useful things such as water purity or ionic strength of a solution. Check out PE Facts to learn more about how conductivity is measured!

Many jobs in the industry deal with conductivity daily. Whether you work in semi-conductor manufacturing, industrial plating operations, or in a laboratory, conductivity is an essential part of your job. In order to perform your daily activities safely and more efficiently, you must understand the basic principles of conductivity.

Conductivity is the measurement of the ability to conduct electricity. Most materials can transfer electrical currents naturally; however, some do more easily than others. It is important to understand which materials are conductive and which are not. Metal is an example of a highly conductive material, while plastic and glass are non-conductive. This means that metals can easily carry electricity while plastic and glass cannot carry it at all. An electronic charge can be transferred to aqueous solutions, however, they are not as highly conductive as metal.

Conductivity indicates different things in many industries. Here are some examples of jobs that depend on specific conductivity measurements:

  • Semiconductor Manufacturing: The purity of the water which cleans the semiconductors is monitored for conductivity. The operators are alerted when the conductivity is high because it indicates that the water needs to be changed.
  • Boiler Blow down: The purity of the water coming out of the boiler is monitored for conductivity. High conductivity suggests a dirty boiler.
  • Laboratory Analysis: Researchers need pure water to ensure their experiments are valid, so they check their lab water for conductivity. Low conductivity tells them the water is pure.
  • Industrial Cleaning, Sterilizing, and Plating Operations: These activities use conductivity to obtain ionic strength readings for the solutions. Depending on the strength of the residue or solution, you may recycle or replenish them. The conductivity can also indicate the effectiveness of a solution.

How is Conductivity Measured?

Conductivity is measured by the number of charged carriers present, how much charge each one is carrying, and how fast they are moving. The way the charge is carried is different for various materials. Metals transfer the electric current through electrons. However, aqueous solutions used charged ions to carry the current. The number of charged ions present determines how easy to current will flow; the more ions present, the faster.

Conductivity is measured in siemens and ohms. The more siemens contained in a liquid, the greater its conductivity.

Here is the conductivity for some typical liquids:

Deionized (distilled) water

0.055 uS/cm

Boiler water

1.0 uS/cm

Drinking water

100.00 uS/cm

Ocean water

53 mS/cm

10% NaOH

355 mS/cm

10% H2S04

432 mS/cm

Key: 1/uS=0.0001 mS 1mS=1000 /uS

Types of Measurement Tools

The easiest way to measure conductivity is to use a 2-electrode cell. This involves applying voltage to two flat plates immersed in the solution and measuring the resulting current. A 3-electrode cell could also be used, but there is a risk that it could weaken the ions near the plates, causing polarization. Other things that could take away from the conductivity measurement are deposits developing on the electrode, or the use of DC voltage causing a higher resistance.

The 4-electode cell contains two drive electrodes (current electrodes) and two sense electrodes (voltage electrodes). This significantly reduces the polarization caused by the 3-electrode cell. An alternating voltage is applied, therefore, the alternating current measured determines the conductivity. The voltage measured at the sense electrodes controls the amplitude of the alternating voltage. Since the sense electrodes are located in a low current area of the cell, and the voltage is measured using high impedance circuit, it is a more precise illustration of the force of the electric field within the cell. If this field strength is held constant, we can assume that the conductivity is equal to the current that flows at the drive electrodes, and that the errors within the sample are insignificant. Most conductivity testers today use the 4-electrode cell.

Commonly Asked Questions

Q. How should my conductivity cell be stored?
A. When you are finished, rinse it off with tap water. The electrode can be stored either wet or dry. However, if it is stored dry, you will need to recondition it before you use it again.

Q. How do I condition the probe?
A. You should submerge the probe in a standard solution tap water and have power running to it. Leave it to soak for 30 minutes to an hour unless otherwise specified.

Q. How and when should I calibrate the probe?
A. You can calibrate the probe using a standard solution in a range of the samples you are going to be testing. Place the probe in the standard solution to condition it, then rinse the probe in a second sample of standard solution. Use a third sample of standard solution to calibrate it, and then adjust the cell constant until the specified value is displayed. You must recalibrate if you change ranges, or if your readings seem to be inaccurate.

Please Note: The information contained in this publication is intended for general information purposes only. This publication is not a substitute for review of the applicable government regulations and standards, and should not be construed as legal advice or opinion. Readers with specific questions should refer to the cited regulation or consult with an attorney.