Conductivity Meter – ConductiSense

Conductivity is the measurement of the ionic species in a solution. It is defined as the conductance in a given volume. Conductance is the ability of the solution to conduct electric current.

Conductance is the ability of a solution to conduct electric current, while conductivity is the conductance in a given volume (usually measured in μΩ/cm or μS/cm).

Temperature has an effect on your conductivity measurement but all Pi Conductivity Sensors have a built-in temperature sensor and provide automatic temperature compensation.

No, all substances possess some conductive properties. Generally organic compounds (such as benzene, alcohols, and petroleum products) have very low conductivities, while metals have very high conductivities. Measuring the conductivity of highly flammable liquids is very risky.

The cell constant, K, is equal to the area (a) normal to the current flow in centimetres squared divided by the distance in centimetres between the electrodes (d). For solutions with low conductivities the electrodes can be placed closer together or made larger so that the cell constant is less than one. This has the effect of raising the conductance so as to produce a value more easily measured by the electronics. The opposite also applies, in high conductivity solutions, the electrodes are placed farther apart or made smaller. Different cell constants are used as range multipliers. The standard K value is 1 with a K value of 0.1 being used for low conductivity water and a K value of 10 for higher conductivity water.

Dissolved solids in a solution (TDS) contribute to the conductivity of that solution. Most people are happy to use a standard multiplier to convert conductivity to TDS (typically 0.65). This multiplier works for a NaCI solutions. Different solutions will have different multipliers.

Making your own standard will yield the most accurate results. This is done by making a mixture of salts in relative proportions that simulate the solution to be tested, then dissolving the mixture into distilled water. This should be done according to the following formula: 1 mg salt mixture/litre of distilled water = 1 ppm TDS, or in other words, X ppm TDS = X mg of salts + one litre of distilled water.

Remember that “X mg of salts” is the number of milligrams of a mixture of salt whose proportions simulate your test solution. An appropriate value for “X” is determined by the following rule:
Choose a ppm value for a calibrated solution as close as possible to the expected ppm values of the test solutions. If the ppm content of the test solution is expected to vary a great deal, it is best to choose a ppm value for the calibrated solution in the upper ¹/₃ of the TDS conductivity range.

There is no difference. Micromhos (µ℧/cm) is more common in the U.S., while microsiemens (μS/cm) is more common in Europe.

Clean electrodes with mild liquid detergent and/or dilute nitric acid (0.1 M) by dipping the sensor into solution and agitating for 2 to 3 minutes. Dilute HCl (hydrochloric acid) or H₂SO₄ (sulfuric acid) may also be used.

Rinse it in tap water when you are finished using it. You can store your electrode either wet or dry. If it is stored dry you will need to recondition the electrode before use.

Place the probe in a standard solution or tap water and have power running to the probe. Let the probe soak for 30 minutes to 1 hour unless otherwise specified.

The probe is the same for conductivity and salinity, but in a salinity meter a correction factor is applied to the reading. The correction factor takes the conductivity reading and converts it to ppm of a specific salt. The salt varies from manufacturer to manufacturer of standardised solutions. Some use NaCl while others use CaCO₃.

Usually the Pi electronics can accommodate other sensors. Please contact Pi for help.

Calibrate using a standard solution in the range of the samples you are testing. Place the probe in standard solution, condition, rinse the probe in second sample of standard solution, use a third sample of standard solution to calibrate, and then adjust on the analyser until the specified value is displayed. Recalibrate when you change ranges, or if readings seem to be incorrect.

The three types of conductivity sensor supplied by Pi are ‘Toroidal’, ‘Graphite’ and ‘Stainless Steel’. The toroidal sensor covers the higher ranges from 0 µS/cm to 2,000,000 µS/cm or more often expressed as 0 mS/cm to 2000 mS/cm.

The graphite sensor covers the range from 0-5000 µS/cm, although higher ranges are available by special request. Within that range we use different range constants (K- factor) to make the sensor more suitable for different applications. If you are measuring in the range 0-100 µS/cm then you will need a K- factor of 0.1. If you are measuring in the range 0-1000 µS/cm then a K-factor of 1.

The stainless steel sensor covers the range from 0-50,000 µS/cm. As with the graphite sensors, within that range we use different range constants (K- factor) to make the sensor more suitable for different applications. The stainless steel sensors utilise the same technology as the graphite sensors but are better suited to high temperature, high pressure environments.