The conductivity of a liquid can be measured using the conductive or toroidal measuring principles. This video shows what it is about and how these measuring principles work. www.products.endress.com/conductivity
I am an English teacher and I teach English for chemistry to advanced VET students. Could you please upload this tanscript of the video? It would be extremely useful for foreing students doing chemistry. Thank you. Many liquids are essential in our daily life. They may include water, beverages, dairy products, chemicals (acids and bases) or pharmaceutical products. The quality of those liquids is determined by their chemical and physical properties. To assess those properties, various principles of measurement are used. One of those principles is the measurement of electrical conductivity. Let’s start with a closer look on why liquids are conductive. The electrical conductivity of a liquid arises from the dissociation of soluble salts, acids and bases, to form positively charged cations and negatively charged anions. These ions contribute to the charge transport in the electrical field, and thus to the current flow, just like electrons in a metal. In 1869, German physician Friedrich Kohlrausch developed the first conductometre for electrical conductivity by using an alternating current to measure electrolytic resistivity for the first time. The physical unit of electrical conductivity is S•m-1. To determine the value, the so-called conductive and inductive measuring principles can be used. In case of the conductive measuring principle, two electrodes are positioned opposite from each other. An AC voltage is applied to the electrodes, which generates a current in the medium. The cations move to the negatively charged electrode, while the anions move to the positively charged electrode. The more free-charged carriers the liquid contains, the higher the electrical conductivity and the current flow. A 10% acid, for example, is a very good conductor because it contains many ions that transport the charge. In contrast to this, pure and ultrapure water are bad conductors because they contain only few ions. If, however, the ion concentration becomes too high, the Coulomb force increases. This electrostatic force leads to a mutual repulsion of the ions and thus a reduction of the current. The effect is called polarization and occurs with highly concentrated media. The electric resistance (or its reciprocal value, the conductance) is calculated from the measured current according to the Ohm’s Law. To derive the specific conductivity from the conductance, the so-called cell constant must be determined. It is based on the geometry of the electrode arrangement and reflects the distance of the electrodes in relation to its surface. It varies depending on the electrode design and influences their suitability for different areas of application. Conductivity is also dependent on the medium temperature. Therefore, the temperature is measured in parallel and the conductivity values are referred to a reference temperature of 25° Celsius by the transmitter. Conductivity sensors have a simple design and are highly sensitive, which makes them suitable for a wide range of applications, from ultrapure water to drinking water and more. The inductive measuring principle uses the inductive conductivity sensor. It contains an electromagnetic transmission and reception coil in a protective plastic coating. An alternating magnetic field is generated in the transmission coil, which induces an electric voltage in a liquid. This causes the positively and negatively charged ions of the liquid to move and generate an alternating current. This current again induces an alternating magnetic field, and thus a current to flow in the reception coil. The intensity of the current depends on the number of free ions in the medium. It is evaluated by the transmitter and the conductivity is calculated. The advantage of inductive conductivity measurement is the galvanic isolation from the medium. Polarization effect cannot occur and the measuring principle is insensitive to soiling. The conductive and inductive conductivity measurement by Endress and Hausser enables precise control of water treatment and cleaning and rinsing processes, for example in the food, life sciences and chemical industries. For further information on liquid analysis and the latest conductivity sensor generation, featuring Memosense technology, visit the Endress and Hausser RU-vid channel or www.endress.com.
Amazing video. Fast, concise and elucidate the basis of conductivity measurement. As all physical and chemical principles that EH brings to us. Thanks.
I belive there are two different concepts here. The instrument measures conductivity of the same amount of liquid. This volume depends of the electrode geometry. Conductivity is the reverse of resistivity, not resistence.
Pedro Federici if I have a bigger volume the resistance decreases and conductivity increases ? as more electrolytes more pathways are to electrons run ¿right?
+Estuar Gonzalez, the electrodes have small dimensions compared to the vessels. They measure the conductivity through the resistance (of the material) at their boundaries and this measuring depends on the electrode geometry. This relationship (resistance versus conductivity) is precalculated by the manufacturer considering the that geometry. Of course the resistance of all amount of material, change if the volume changes. But, conductivity is a material (liquid on this case) characteristics, not a body (all amount) characteristics. Lat's use a solid example. If you take an one meter copper wire its resistance will be lower than a two meter wire (same cross section). But the copper resistivity (and conductivity) is still the same.
I was not aware of the inductive method of conductivity measurement. I am interested in the topology of the sensor. The video shows two toroidal coils, one assumed to be the driver coil the other the sensor coil. The question is how the magnetic field couples to the solution under test, if it is confined to the toroidal core?
For this kind of questions we recommend to contact our Sales Center near to you: www.endress.com/en/contact Our colleagues will be glad to support you. Thank you in advance!
Endress+Hauser thank you, but I think I have now worked out how the probes works for my self. If I am correct, the coils act as two independent torroidal transformers with a common single turn of solution coupling the two transformers together. Current in the driving transformer couples to the solution under test, via the loop of solution that passes through the hole in the first toroidal transformer. Because of the way the transformers are sealed together, the loop of solution, carrying the induced current, also passes through the second transformer in the same fashion as the first, effective linking the two transformers together by a single loop of conductive solution. The strength of the coupling current loop is proportional to the conductivity of the solution. Hence the EMF generated by the second sense transformer is proportional to the current induced in the loop of solution passing through it. One question remains, in foul water, how do you stop the hole from blocking, as any reduction in the dimensions of the hole will reduce the conductivity of the current loop and degrade the accuracy of the measurement.
This is Mohammad S. Bhuyan, a graduate student from OSU, Columbus, OH. I am having difficulty to measure electrical conductivity of liquid paint . I need a tool to measure electrical conductivity of resin based paint. Any help or advice is greatly appreciated.
Hi Mohammad. In talking to one of our Analytical experts here at Endress+Hauser, this was the feedback he gave: "Measuring the electrical conductivity of paint will depend on the dissolved ions present in the paint solution. That will be dependent on what the paint is made of. Oil based vs water based paints will have different conductivity / resistivity values. Additionally, the paint will tend to coat the surface area of the electrodes used in the measurement sensor, changing the cell constant and thereby affecting the reading. More information will have to be obtained in order to specify which sensor is best for your particular application." Please feel free to contact us 888-ENDRESS (363-7377) and you can be connected with a local engineer that can discuss the application with you further. Thanks!
due to coulomb force or coloumns force(didn't get) ,the electrostatic force increases and with it increase repulsion occurs,,so the current comes less.....did I got it...if I had any mistake in understanding,,,can u tell it again....by the way..video was awesome
could you please add CC english is not my first language so i found it hard to keep up with the lesson I m sure I m not the only one so I hope this could be considered as a suggestion thank you
For this kind of questions we recommend to contact our Sales Center near to you: www.endress.com/en/contact Our colleagues will be glad to support you. Please understand that we can't answer such specific questions in the comment stack of an video. Thank you in advance!
+Estuar Gonzalez no, this is not equal. For calculating the conductivity you not only need the distance between the elctrodes but also the surface area of the electrodes.
+ Estuar Gonzalez: To optain conductivity K (Kappa) of a solution, besides conductance the geometry of the sensor must be known. K=G*d/A (d=electrode distance/ A=electrode surface) d/A is a proper physical unit of the conductivity measurement cell and is called cell constand k.
+Endress+Hauser ohhh thanks!! then that: m exp -1 represents the separation among the electrodes? ; if I use higher amounts of solution the conductivity increases? that is to say each electrolyte molecule is a resistor, if I increase the number of resistor the resistance decreases ! ¿right?
+Estuar Gonzalez: The amount of liquid has no influence on the conductivity. It is the concentration of the liquid that influences the conductivity e.g. a higher salt concentration will lead to a higher conductivity. So it does not matter if I have 1 liter or 2 liter of liquid but it does matter if I put 1 spoon of salt in 1 liter of water or 2 spoons of salt in 1 liter of water. If you now want to calculate the conductivity k, then you need to know the electrode surface A (in cm²), the distance between the electrodes d (in cm) and the Conductance G (in µS). The Conductance is the inverse of the Resistance, so G= 1/R=I/U with I being the current and U the voltage. k=G*d/A. You cannot just use the separation/distance of the electrode.
