Conductivity Sensors

The measurement of specific conductivity in aqueous solutions is becoming increasingly important for the determination of impurities in water or the concentration measurement of dissolved chemicals.

What is Conductivity?

Conductivity is the measure of a solution's ability to pass or carry an electric current. The term Conductivity is derived from Ohm's Law, E=I•R; where Voltage (E) is the product of Current (I) and Resistance (R); Resistance is determined by Voltage/Current. When a voltage is connected across a conductor, a current will flow, which is dependent on the resistance of the conductor.  Conductivity is simply defined as the reciprocal of the Resistance of a solution between two electrodes.

  • Contacting Conductivity Sensors SC42/SC4A(J)

    The measurement of specific conductivity in aqueous solutions is becoming increasingly important for the determination of impurities in water.  Yokogawa has designed a full range of precision sensors and instruments to cope with these measurements, even under extreme conditions.

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  • Conductivity Sensor SC210G

    The SC210G conductivity sensor is widely used in various water and manufacturing process applications. A wide variety of mountings are available including screw-in type, flange type, flow-through type, and screw-in type with gate valve.

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  • Conductivity Sensor SC8SG

    The SC8SG conductivity sensor is widely used in applications such as liquid conductivity measurement for manufacturing processes and pure water resistivity measurement in the semiconductor, food, pharmaceutical, and power industries.

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  • Conductivity Sensor SC4AJ

    The SC4AJ conductivity sensor has a convenient, compact design and is widely used in various applications including boiler water and hydroponics conductivity measurement and pure water resistivity measurement in the semiconductor, food, pharmaceutical, and power industries.

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  • Percent Concentration Sensors ISC40

    There are numerous industrial applications where measurements and/or control of a specific chemical strength of the process is critical for optimizing the production of the end product. These specific concentrations are obtained by mixing a full strength solution with water to achieve the desired percent concentration.  

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  • Portable Conductivity Handheld Meter SC72

    Compact, lightweight, and dripproof, the SC72 is the ideal Conductivity meter for field use. Features wide-range auto-ranging, automatic temperature compensation, self-diagnostic functions, and a large, easy-to-read LCD display.

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  • High Conductivity Sensors ISC40/SC42

    The measurement of specific conductivity in aqueous solutions is becoming increasingly important for the determination of impurities in water. Yokogawa has designed a full range of precision sensors and instruments to cope with these measurements, even under extreme conditions.

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  • Product Finder

    This web tool makes it easier to find products according to the application, measurement conditions and required specifications.

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Details

The measurement of specific conductivity in aqueous solutions is becoming increasingly important for the determination of impurities in water or the concentration measurement of dissolved chemicals.

What is Conductivity?

Conductivity is the measure of a solution's ability to pass or carry an electric current. The term Conductivity is derived from Ohm's Law, E=I•R; where Voltage (E) is the product of Current (I) and Resistance (R); Resistance is determined by Voltage/Current. When a voltage is connected across a conductor, a current will flow, which is dependent on the resistance of the conductor.  Conductivity is simply defined as the reciprocal of the Resistance of a solution between two electrodes.

How do we measure Conductivity?

There are two basic sensor styles used for measuring Conductivity: Contacting and Inductive (Toroidal, Electrodeless).

When Contacting Sensors are used, the conductivity is measured by applying an alternating electrical current to the sensor electrodes (that together make up the cell constant) immersed in a solution and measuring the resulting voltage. The solution acts as the electrical conductor between the sensor electrodes.


With Inductive (also called Toroidal or Electrodeless), the sensing elements (electrode colis) of an inductive sensro do not come in direct contact with the process. These two matched (identical coils) are encapsulated in PEEK (or Teflon) protecting them from the adverse effects of the process.   


What makes a solution conductive? 

Ions present in the liquid (Na, Ca, Cl, H, OH) are what is responsible for carrying the electric current.

Conductivity is only a quantitative measurement: it responds to all ionic content and cannot distinguish particular conductive materials in the presence of others. Only ionizable materials will contribute to conductivity; materials such as sugars or oils are not conductive.

Conductivity applications cover a wide range from pure water at less than 1x10-7 S/cm to concentrated solutions with values greater than 1 S/cm. Such application examples are WIFI, demineralizer water, RO water, percent concentration, boiler blowdown and TDS.

In general, the measurement of conductivity is a rapid and inexpensive way of determining the ionic strength of a solution. Conductivity is used to measure the purity of water or the concentration of ionized chemicals in water. It is a nonspecific technique, unable to distinguish between different types of ions, giving instead a reading that is proportional to the combined effect of all the ions present.

The accuracy of the measurement is strongly influenced by temperature variations, polarization effects at the surface of the contacting electrodes, cable capacitances, etc.

Yokogawa has designed a full range of precision sensors and instruments to cope with these measurements, even under extreme conditions.

How do I select the right sensor? 

When selecting a conductivity sensor for an application we need to consider the following:

  • What is the measurement range? (This dictates which cell constant will be required).
  • What is the process temperature? (We have standardized on Pt1000)
  • What is the chemical makeup of the process? (This determines what material of construction we offer to ensure chemical compatibility).

What is a cell constant, and why do we need to be concerned about it?

The cell constant is mathematical value for a "multiplying factor" that is used to determine the measuring range of the sensor. This mathematical value is determined by the geometric design of the cell. It is calculated by dividing the distance (length) between the two measuring plates by the area of the plates (area of the plates is determined by the area of the outside-the area of the inside = area between the electrodes).

The raw conductivity value is then multiplied by the cell constant which is why we see the unit µS (microsiemen)/cm.

Yokogawa offers four cell constants: 0.01, 0.1, 1.0, and 10.0, which provide accurate of the entire Measurement range of 0-2,000,000 µS. These values are known as the nominal cell constant, whereas the printed cell constant on the sensor can vary slightly (you will see 0.0198 instead of 0.02) is the specific cell constant for that sensor. 

One of the problems that occur when an incorrect cell constant is used is Polarization

correct_cc_selected

The first example shows a solution with the correct cell constant where the ions are free to travel from one plate to the other.

wrong_cc_used

The second example shows the same cell constant being used in a highly conductive solution.  When the voltage alternates (switches polarity), the ions cannot freely move to the other plate because the ion density is too high.  This results in fewer ions contacting the correct plate which will result in a false low reading.


However for the ISC40 Inductive Sensor there is only one cell factor (constant). It covers the entire conductivity measruement range 0-2,000 S/cm. But on only the low end (below 50µS) does teh accuracy of the sensor suffer.

Resources

Overview:

To defray energy costs, many industrial plants have their own boilers to generate steam in order to produce a portion of their energy needs. In addition to generating power, the steam may also be used directly in plant processes or indirectly via heat exchangers or steam jacketed vessels.

Overview:

In the past, the boiler feed tank systems in sugar factories had to be checked several times a day to make sure there were no sugar solution leaks. This was a very laborious process and, as continuous monitoring was not possible, monitoring results were not reliable. When a leak occurred, recovery operations were very costly and time-consuming. (AN10D01K01-02E)

Industries:
Overview:

Caustic soda and hydrochloric acid, produced in electrolyzer plants, are fundamental materials used in varieties of industries; chemicals, pharmaceuticals, petrol-chemicals, pulp and papers, etc. Profit is the result of the effective production with minimized running / maintenance cost. Proper control of the process brings you stabilized quality of products with the vast operational profit.

Industries:
Overview:

Control of sodium chloride (NaCl) concentration at a salt dissolver where solid salt is dissolved in water, is highly important because of the electrolysis efficiency. A conventional way of measuring the concentration of supersaturated NaCl solution had been performed by using non-contact type sensors (e.g., γ-ray density meter) since NaCl, impurities, and precipitates are in the solution.

Overview:

In a semiconductor plant, a variety of chemicals are used in various manufacturing processes. The chemicals used for specific purposes are produced by diluting raw liquid with demineralized water using in diluting equipment, and the control of the concentration at this point is performed by conductivity measurement. 

Overview:

In the manufacturing process of Pharmaceutical, Chemical and Food & Beverage industries, the cleaning and sterilization of tanks and piping are done with various cleaning solutions, fresh or hot water and steam after manufacturing products. Clean-In-Place (CIP) is the system designed for automatic cleaning and disinfecting.

Overview:

Reverse osmosis (RO) is a separation process that uses pressure to force a solution through a membrane that retains the solute on one side and allows the pure solvent to pass to the other side. More formally, it is the process of forcing a solvent from a region of high solute concentration through a membrane to a region of low solute concentration by applying a pressure in excess of the osmotic pressure.

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