Convert microsiemens/centimeter [μS/cm, uS/cm] to millisiemens/meter [mS/m] • Electrical Conductivity Converter • Electrical Engineering • Compact Calculator • Online Unit Converters (2024)

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Introduction and Definition

Electrical conductivity or specific conductance is a measure of the ability of a substance to conduct electric current or to transport an electric charge. It is the ratio of the current density to the strength of the electric field. If we consider a 1-meter cube of a conductive material, then the conductivity will be equal to the electrical conductance measured between the opposite faces of this cube.

The conductivity and conductance are related by the formula:

G = σ(A/l)

where G is the conductance, σ is the conductivity, A is the cross-sectional area of the conductor, which is perpendicular to the direction of flow of an electric current, and l is the length of the conductor. This formula can be used with any cylindrical or prismatic conductor. Note that this formula can be also used for a cuboid because it is a rectangular prism. Electrical conductivity is the reciprocal of electrical resistivity.

In the English language words, conductance and conductivity are so similar that they are often used as synonyms. Meanwhile, they have a different meaning, of course. The conductance is the extrinsic property of a given conductor or device (for example, a resistor or a galvanic bath) and the conductivity is an intrinsic property of the material from which this conductor or device was made. For example, the conductivity of copper is always the same, no matter how the object made from copper changes in terms of its shape or size, while the conductance of a copper wire depends on its length, diameter, mass, shape, and several other factors. Of course, similar objects made from materials with higher conductivity will have a higher conductance (not always).

The SI unit for electrical conductivity is siemens per meter (S/m). Note that in English, the same form of the unit of conductance "siemens" is used both for the singular and plural forms. The unit is named after the German inventor, industrialist and scientist Werner von Siemens (1816–1892). Siemens AG, the company he founded in 1847, is one of the largest engineering companies in the world producing electrical, electronic as well as transport and medical equipment.

Electrical conductivity ranges from highly resistive materials like glass (which, by the way, conducts electricity well when heated) or acrylic glass to semiconductors, which have a different conductivity under different conditions to extremely conductive materials like silver, copper, or gold. Electrical conductivity is determined by the number of charge carriers such as electrons or ions, by the speed of their movement, and by the amount of charge they carry. The conductivity of aqueous solutions, for example, electroplating baths, is between these extremes. Another example of electrolytes with moderate conductivity is our bodily fluids: blood, plasma, lymph, etc.

The conductivity of metals, semiconductors and dielectrics is discussed in detail in More about Electrical Resistance, More about Electrical Resistivity and Electrical Conductance and Conductivity TranslatorsCafe.com Unit Converter articles. In this article, we will discuss in more detail the conductivity of electrolytes and its measuring methods and equipment. We will describe several experiments using an inexpensive device for measuring conductivity.

Electrolytic Conductivity and Its Measuring

The conductivity of aqueous solutions, in which the electric current is carried by charged ions, is determined by the number of charge carriers (the concentration), the speed of their moving (the ion mobility depends on the solution temperature) and the charge they carry (valence of ions). Therefore, in most aqueous solutions, the higher concentration will lead to more ions and hence to higher conductivity. However, after reaching some maximum concentration, the conductivity may start decreasing with increasing concentration. Therefore, two different concentrations of the same salt may have the same conductivity.

The temperature also affects conductivity because at higher temperatures ions move faster, increasing the conductivity. Pure water does not conduct electricity well. The ordinary distilled water in equilibrium with carbon dioxide containing in the air and total dissolved solids of less than 10 mg/L has a conductivity of about 20 µS/cm. The conductivity of various solutions is given in the table below.

To determine the conductivity of a solution, a conductance or resistance meter (they are technically the same) is usually used and the measured value is then manually or automatically recalculated to conductivity. This is done by taking into account the physical characteristics of the measuring device or sensor. This includes the area of electrodes and the separation distance between the two electrodes. The sensors are quite simple: they comprise a pair of electrodes immersed in the electrolyte solution. The sensors for measuring conductivity are characterised by a cell constant, which is given by the ratio of the distance between electrodes D to the area normal to the current flow A:

K = D/A

This formula works well when the area of electrodes is much greater than the separation between them because in this case most of the electric current flows directly between the electrodes. Example: for 1 cubic centimeter of liquid K = D/A = 1 cm/1 cm² = 1 cm⁻¹. Note that cells with small widely-spaced electrodes have cell constants of 1.0 cm⁻¹ or more while cells with larger and closely-spaced electrodes have constants of 0.1 cm⁻¹ or less. The cell constant of various devices for measuring conductivity varies from 0.01 to 100 cm⁻¹.

To obtain the conductivity from the measured conductance, the following formula is used:

σ = K ∙ G

where

σ is the solution conductivity in S/cm,

K is the cell constant in cm⁻¹,

G is the cell conductance in siemens.

The cell constant is usually not calculated, but measured for a particular measuring device or setup using a solution of known conductivity. This measured value is entered into the meter, which automatically calculates the conductivity from measured conductance or resistance. Because the conductivity depends on the solution temperature, devices for measuring conductivity often contain a temperature sensor that allows measuring the temperature and providing the automatic temperature compensation (ATC) to the standard temperature of 25°C.

The simplest method of measuring the conductance is applying a voltage to two flat electrodes immersed in the solution and measuring the resulting current. This is called a potentiometric method. According to Ohm’s law, the conductance G is the ratio of current I to voltage V:

G = I/V

However, things are not as simple as they seem. There are many difficulties. When DC voltage is used, ions can accumulate near the electrode surfaces and chemical reactions can occur at the surfaces. This will lead to increasing polarization resistance on the electrode surfaces, which, in turn, may lead to erroneous results. If we try to measure the resistance of, for example, sodium chloride solution using a multimeter, we will clearly see that the reading on the display is increasing rather quickly. To mitigate this problem, often four electrodes are used instead of two.

Electrode polarization can be prevented or reduced by applying an alternating current and adjusting the measuring frequency. Low frequencies are used to measure low conductivity, where the polarization resistance is comparatively small. Higher frequencies are used to measure high conductivity values. Frequency is usually automatically adjusted taking into account the measured conductivity of a solution. Modern digital 2-electrode conductivity meters usually use complex alternating current waveforms and temperature compensation. They are calibrated at the factory and often recalibration is required in the field because of the cell constant changes with time. It can be changed due to contamination or the physical-chemical modification of electrodes.

In a traditional 2-electrode conductivity meter, an alternating voltage is applied between the two electrodes, and the resulting current is measured. This meter, though simple, has one disadvantage — it measures not only the solution resistance but also the resistance caused by the polarization of the electrodes. To minimize the effect of polarization, 4-electrode cells, as well as platinized cells covered with platinum black, are often used.

Total Dissolved Solids (TDS)

Devices for measuring electrical conductivity are often used to measure total dissolved solids (TDS). It is a measure of the total weight of all organic and inorganic substances contained in a liquid in various forms: ionized, molecular (dissolved), colloidal and suspended (not dissolved). Dissolved solids refer to any inorganic salts, mostly calcium, potassium, magnesium, sodium, chlorides, bicarbonates and sulfates, and some organic matter dissolved in water. The solid substances contained in a liquid, which is considered for TDS, must be either dissolved or in the form of very small particles that will remain the solution after filtration through a filter with very small pores (2 micrometers or less). Substances that are permanently suspended in a solution, but cannot pass through a filter are called total suspended solids or TSS. Total dissolved solids are usually measured in water to determine its quality.

There are two main methods of measuring total dissolved solids: gravimetric analysis, which is the most accurate method, and conductivity measurement. The first method is the most accurate, but it is time-consuming because all water must be evaporated, to dryness, usually at 180°C under strict laboratory conditions and then the mass of residues is measured.

The second method is not as accurate as the gravimetric analysis. However, the conductivity method is the most convenient, useful, widespread, and fastest method because it is a simple measurement of conductivity and temperature, which can be done in seconds using a low-cost device. This method can be used because the electrical conductivity of water is directly related to the concentration of ionized substances dissolved in water. It is especially useful for quality control purposes like control of drinking water or estimation of the total number of ions in a solution.

The conductivity measurements are temperature dependent, that is, if the temperature increases, the conductivity also increases because the ions in a solution are moving faster. To obtain temperature-independent measurements, the concept of reference temperature was introduced. It allows a comparison of conductivity results obtained at different temperatures. Thus, the conductivity meter can measure the actual conductivity and the temperature and then use a temperature correction function to automatically convert the measured value to the reference temperature of 20 or 25°С. If very high accuracy is necessary, the sample can be put into a thermostat, and then the meter will be calibrated at exactly the same temperature that is used for measurement.

Most modern conductivity meters contain a built-in temperature sensor that can be used for temperature correction as well as for temperature measurement. The most sophisticated meters can measure and display conductivity, resistivity, salinity, TDS, and concentration. However, all of them measure only conductivity and temperature and then calculate the necessary physical value and make temperature compensation.

Experiment: Measuring TDS and Conductivity

We will conduct several experiments using an inexpensive TDS meter TDS-3. The price on eBay with delivery at the time of writing this article for a no-name device is less than US$3.00. The same device with a brand name probably made at the same factory will cost 10 times more. But that’s for those who like to pay just for the brand name. The meter is temperature calibrated and can measure not only TDS but also a temperature using the temperature sensor, which is installed near the electrodes. It should be noted that the two actual physical values that this device measures are the resistance of the solution between the two electrodes and the temperature of the solution.

This TDS meter will help you find out the total dissolved solids in any application such as monitoring the quality of drinking water or testing salt levels in freshwater aquariums and ponds or testing water filtration and purification system to know when to change filters and membranes. The meter is calibrated using a 342 ppm solution of sodium chloride NaCl. Its range is 0–9990 ppm or mg/L. PPM is parts per million. It is a dimensionless quantity. For example, a mass concentration of 5 mg/kg = 5 mg in 1,000,000 mg = 5 parts per million. Just as a percent means out of a hundred, the parts per million unit means out of a million. Therefore, PPM is a way of measuring the concentration of very dilute solutions.

The meter actually measures the conductance between the two electrodes (which is reciprocal of resistance), then recalculates the result into electrical conductivity (often abbreviated as EC) using the formula above and the known cell constant K, then makes another recalculation, multiplying the conductance by the conversion factor of 500. The result of these calculations is displayed in the form of TDS in ppm. We will discuss these calculations below.

This TDS meter cannot be used to test the water with a high concentration of salts. Examples of substances with a high concentration of salts are some food products and seawater. The maximum concentration of NaCl the device can measure is 9990 ppm or about 10 g/L. That is only the normal concentration of salt in many food products. This meter will also not be able to check the salinity of seawater, which is approximately 35 grams per liter or 35,000 ppm, which is much higher than this device can measure. If you try to measure the TDS of such concentrated electrolyte, the meter will show Err.

TDS-3 measures conductivity and uses the 500 (NaCl) scale for calibration. That means 1.0 mS/cm x 500 = 500 ppm. There are many different scales in many industries. For example, three scales are usually used in hydroponics: the 500, 640, and 700 scales. The difference between them is in their use. The 700 scale is based on measuring the potassium chloride KCl concentration in a solution:

1.0 mS/cm x 700 makes 700 ppm

The 640 scale uses a conversion factor of 640 to convert from mS/cm to ppm:

1.0 mS/cm x 640 makes 640 ppm

For our experiment, we will first measure the total dissolved solids in distilled water. The meter shows 0 ppm and the multimeter shows 1.21 MΩ.

Let us prepare a 1000 ppm solution of NaCl and measure its ppm with a TDS-3 meter. To prepare 100 mL of the solution, we will need 100 mg of sodium chloride and up to 100 mL of distilled water. To make a solution, we will put the sodium chloride into the measuring cylinder, add some distilled water and stir it until all sodium chloride is dissolved. Then add distilled water to the 100 mL mark and mix well again.

As you can see in the picture, TDS-3 measures 955 ppm. The conductivity of this solution should be 1000 ppm / 500 = 2 mS/cm (NaCl or 500 scale).

To determine the conductance experimentally, we prepared two electrodes made from the same material, with the size and distance between them exactly as in TDS-3. Then we measured the resistance between the electrodes. The measured resistance was 2.5 kΩ.

Now, when we know the resistance and ppm, we can approximately calculate the cell constant of TDS-3 using the formula above:

K = σ/G = 2 mS/cm x 2.5 kΩ = 5 cm⁻¹

This value of 5 cm⁻¹ is close to the calculated value of the cell constant of TDS-3 with the following electrode dimensions:

• D = 0.5 cm is the distance between the electrodes
• W = 0.14 cm is the electrode width
• L = 1.1 cm is the length of the electrode

Cell constant of TDS-3 cell is K = D/A = 0.5/0.14x1.1 = 3.25 cm⁻¹. This is slightly less than the value of 5 cm⁻¹. Note that the formula for calculating the cell constant can give only approximate value.

This article was written by Anatoly Zolotkov

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Electrical Engineering

Electrical engineering is a field of engineering that deals with the study and application of electricity, electronics, and electromagnetism. It covers subtopics like power, electronics, control systems, signal processing and telecommunications.

Electrical Conductivity Converter

Electrical conductivity or specific conductance is the reciprocal of resistivity. It is a property of any conductive material. It measures a material’s ability to conduct an electric current.

The SI unit for electrical conductivity is siemens per meter (S/m) and the CGSE unit is a reciprocal second (s⁻¹).

Using the Electrical Conductivity Converter Converter

This online unit converter allows quick and accurate conversion between many units of measure, from one system to another. The Unit Conversion page provides a solution for engineers, translators, and for anyone whose activities require working with quantities measured in different units.

You can use this online converter to convert between several hundred units (including metric, British and American) in 76 categories, or several thousand pairs including acceleration, area, electrical, energy, force, length, light, mass, mass flow, density, specific volume, power, pressure, stress, temperature, time, torque, velocity, viscosity, volume and capacity, volume flow, and more.
Note: Integers (numbers without a decimal period or exponent notation) are considered accurate up to 15 digits and the maximum number of digits after the decimal point is 10.

In this calculator, E notation is used to represent numbers that are too small or too large. E notation is an alternative format of the scientific notation a · 10^x. For example: 1,103,000 = 1.103 · 10⁶ = 1.103E+6. Here E (from exponent) represents “· 10^”, that is “times ten raised to the power of”. E-notation is commonly used in calculators and by scientists, mathematicians and engineers.

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