Conductivity is the ability of any material to pass an electric current. It is typically measured in aqueous solutions, and in this context, it can be defined as the ability of a solution to conduct an electric current between two electrodes. It is used as a measure of the number of ions dissolved in a solution.

Factors to consider

Conductivity can be measured in lab processes or in the field. Choosing the right conductivity electrode is important to ensure that the right product is being used to give the most accurate readings.

The following features require consideration:

• Measuring range/cell constant
• 2-pole or 4-pole
• Temperature compensation
• Meter or instrument being used (this will determine the connector)
• Material compatibility (plate material and shaft material)
• Physical requirements

All Sentek conductivity sensors have an analogue signal and can be used with most meters on the market.

Measuring Range

Conductivity electrodes are given cell constants, which is a ratio between the surface area of the plates of the sensor and the distance between them. The range is dependent upon the cell constant, and can be found on the specification for each sensor. As a general rule, if the measuring range is low (e.g. 0-500µS), then a low cell constant is desirable (e.g. K=0.1). Some sensors come with a predefined cell constant printed on the label, while others rely on customer calibration.

2-pole or 4-pole

• 2-pole sensors tend to be more economical and compatible with a vast range of instruments.
• The limitations are that 2 pole sensors have a maximum measuring range and can be subject to the effects of polarisation.
• 4-pole cells are less prone to error from polarisation, therefore have increased accuracy over a wider range (0.1 microSiemens to 1,000 millisiemens).

Temperature Compensation

Since conductivity is affected by temperature, the majority of conductivity electrodes have built-in temperature sensors; PT100, PT1000, 10KΩ and 30KΩ for example. The type of temperature sensor will depend upon the instrument or meter that is being used. If you are unsure, please get in touch with our team by telling us the make and model of your meter and we will be able to assist you.

Meter or Instrument

Sentek conductivity probes can be used with most meters that are on the market. The instrument that is used will determine the type of connector required – 7-pin-din, 8-pin-din, BNC, bananas, are examples of connectors that may be required to ensure compatibility with your instrument. Sensors can also be provided with clean finished ends, which allows customers to attach their own plug or hardwire into instruments. If this is the case, we are able to provide wiring diagrams on request.

Plate Material

Plate materials vary depending on the application. Carbon is used for samples that will cause the electrode to become dirty easily, as carbon can be easily cleaned with a small brush. Carbon is also a more robust option, and is often used for industrial applications. Platinum plates provide good levels of accuracy and reproducibility; however, the plates are more difficult to clean. Scratches on platinum plates can cause errors in measurement, however they can be replated if necessary. We offer a range of plate materials to suit a variety of applications, including Platinum, Graphite/Carbon and Stainless Steel.

Shaft Material

Glass is generally used for benchtop or laboratory measurements, or samples that may damage an epoxy body. Glass electrodes in general are able to withstand higher temperatures and are compatible with solvents. Epoxy is a more robust sensor, and is advisable for field measurements. Our industrial sensors are Ryton which are able to withstand high temperatures for prolonged periods of time, and have good chemical resistance.

Physical Requirements

Sensors are available in a wide range of shapes and sizes, from flat surface, to industrial , we are able to customise shape, diameter, length to suit any application. If you have a low volume of sample, we have micro designs that allow a small immersion depth, or flow cell conductivity electrodes. We can also customise cable length.

Temperature and Pressure Considerations

Some applications have demands for electrodes that are rated to certain temperatures or pressures. Higher temperature and pressure rated sensors are often fitted with threads to ensure they are fixed in place, and are built to ensure that the sealants and materials can withstand the conditions outlined in the product specification. We can offer a range of thread types to suit your needs, including PG13.5 or ¾” NPT. Please enquire for further information or custom requests.

Application Advice

Measuring conductivity is a vital part of monitoring and quality processes – it can provide useful information about the chemical concentration of a sample. It is often necessary to know if a certain threshold of ions has been reached, or if a water source has been contaminated, particularly in industrial and environmental applications.

The applications commonly used include;

High purity water: Purified water is used in many applications, such as laboratories, cosmetics, pharmaceuticals and the food industry and is monitored by conductivity measurement.

Environmental: Significant changes (usually increases) in conductivity may indicate that a discharge or some other source of disturbance has decreased the relative condition or health of the water body and its associated plant and animal life.

Agricultural: The measurement of soil conductivity is widely used in agriculture. It correlates with various soil properties, such as soil texture and water holding capacity. It can also be used for ‘precision fertilisation management’.

Industrial: Conductivity measurement is used to determine the effectiveness of water treatment processes in preventing corrosion in plant equipment and in leak detection. When cleaning in place is used in process equipment it is important to know that the appropriate amounts of cleaning solutions are used and that those solutions have been removed completely before the next processing run. Conductivity measurement can help confirm these processes. Conductivity measurement is used in chemical processing and food and beverage manufacturing. Conductivity is used to determine the effectiveness of desalination.

Pharmaceutical: The quality of highly-purified water is crucial to the pharmaceutical industry and conductivity measurement is the most widely accepted quality control method.

Conductivity Electrodes from Sentek

Here at Sentek we make a range of conductivity probes for use in the laboratory or in the field.

To find out more about our range of electrodes and for more technical insight, visit us online or contact us by phone to speak to a member of the team.