ES2325673B1 - DEVICE AND METHOD FOR THE MEASUREMENT OF ELECTRICAL CONDUCTIVITY OF HIGHLY INSULATING LIQUIDS. - Google Patents
DEVICE AND METHOD FOR THE MEASUREMENT OF ELECTRICAL CONDUCTIVITY OF HIGHLY INSULATING LIQUIDS. Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
- G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
- G01N27/06—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of a liquid
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
- G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
- G01N27/06—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of a liquid
- G01N27/07—Construction of measuring vessels; Electrodes therefor
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
- G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
- G01R27/22—Measuring resistance of fluids
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
- G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
- G01R27/26—Measuring inductance or capacitance; Measuring quality factor, e.g. by using the resonance method; Measuring loss factor; Measuring dielectric constants ; Measuring impedance or related variables
- G01R27/2617—Measuring dielectric properties, e.g. constants
- G01R27/2635—Sample holders, electrodes or excitation arrangements, e.g. sensors or measuring cells
- G01R27/2641—Sample holders, electrodes or excitation arrangements, e.g. sensors or measuring cells of plate type, i.e. with the sample sandwiched in the middle
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Abstract
Dispositivo y método para la medida de la conductividad eléctrica de líquidos altamente aislantes.Device and method for measuring the electrical conductivity of highly insulating liquids.
La presente invención tiene por objeto un dispositivo y un método para medir la conductividad eléctrica de líquidos altamente aislantes. El dispositivo comprende un electrodo superior desplazable verticalmente y dividido en dos regiones aisladas eléctricamente, guiado por una estructura mecánica que asegura el paralelismo y movido por un motor que permite variar controladamente la distancia entre electrodos, y un electrodo inferior con forma de vasija que contiene la muestra de líquido. El método propuesto se caracteriza por aplicar diferencias de potencial para un espaciado fijo entre los electrodos, aplicando cada valor de la diferencia de potencial hasta alcanzar el estado estacionario en cada período y medir las corrientes eléctricas producidas en estado estacionario.The present invention aims at a device and a method to measure the electrical conductivity of highly insulating liquids. The device comprises an electrode top scrollable vertically and divided into two regions electrically insulated, guided by a mechanical structure that ensures parallelism and driven by an engine that allows you to vary controlled the distance between electrodes, and an electrode Bottom shaped vessel containing the liquid sample. He proposed method is characterized by applying differences of potential for a fixed spacing between the electrodes, applying each value of the potential difference until reaching the state stationary in each period and measure electrical currents produced in steady state.
La presente invención tiene su aplicación en la industria química para controlar la pureza de líquidos aislanteso para controlar la estabilidad de suspensiones coloidales de gran aplicación (por ejemplo, pinturas o tintas de impresión).The present invention has its application in the Chemical industry to control the purity of insulating liquids to control the stability of large colloidal suspensions application (for example, paints or printing inks).
También es necesaria en el control de la conductividad de combustibles de avión para evitar la aparición de elevados voltajes durante su flujo.It is also necessary in the control of conductivity of aircraft fuels to prevent the occurrence of high voltages during its flow.
Description
Dispositivo y método para la medida de la conductividad eléctrica de líquidos altamente aislantes.Device and method for measuring the electrical conductivity of highly insulating liquids.
La presente invención tiene por objeto un dispositivo y un método para medir la conductividad eléctrica de líquidos altamente aislantes. El dispositivo comprende un electrodo superior desplazable verticalmente y dividido en dos regiones aisladas eléctricamente, guiado por una estructura mecánica que asegura el paralelismo y movido por un motor que permite variar controladamente la distancia entre electrodos, y un electrodo inferior con forma de vasija que contiene la muestra de líquido. El método propuesto se caracteriza por aplicar diferencias de potencial para un espaciado fijo entre los electrodos, aplicando cada valor de la diferencia de potencial hasta alcanzar el estado estacionario en cada período y medir las corrientes eléctricas producidas en estado estacionario.The present invention aims at a device and a method to measure the electrical conductivity of highly insulating liquids. The device comprises an electrode top scrollable vertically and divided into two regions electrically insulated, guided by a mechanical structure that ensures parallelism and driven by an engine that allows you to vary controlled the distance between electrodes, and an electrode Bottom shaped vessel containing the liquid sample. He proposed method is characterized by applying differences of potential for a fixed spacing between the electrodes, applying each value of the potential difference until reaching the state stationary in each period and measure electrical currents produced in steady state.
La presente invención tiene su aplicación en la industria química para controlar la pureza de líquidos aislantes o para controlar la estabilidad de suspensiones coloidales de gran aplicación (por ejemplo, pinturas o tintas de impresión). También es necesaria en el control de la conductividad de combustibles de avión para evitar la aparición de elevados voltajes durante su flujo.The present invention has its application in the chemical industry to control the purity of insulating liquids or to control the stability of large colloidal suspensions application (for example, paints or printing inks). Too it is necessary in the control of the conductivity of fuels of plane to avoid the appearance of high voltages during its flow.
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Se define la conductividad eléctrica como la constante de proporcionalidad entre el campo eléctrico y la densidad de corriente eléctrica. El medio que satisface tal proporcionalidad se denomina óhmico. Los medios considerados normalmente conductores de la electricidad, tales como los metales o las disoluciones electrolíticas, transportan corrientes relativamente elevadas ante campos eléctricos relativamente pequeños. Tal corriente eléctrica es causada por el arrastre que el campo eléctrico realiza sobre los portadores de carga presente en el volumen, electrones en el caso de los metales o iones en el de las disoluciones electrolíticas. Estos líquidos suelen presentar un comportamiento claramente óhmico y, como consecuencia de la facilidad con la que conducen la corriente, el campo eléctrico en su interior tiene un valor normalmente pequeño. En el caso de los dieléctricos líquidos los portadores de carga en el volumen son relativamente escasos y el campo eléctrico en su seno puede alcanzar valores elevados. Los portadores de carga en líquidos aislantes son resultado de la ionización de impurezas o de las propias moléculas del líquido siendo su concentración resultado de un equilibrio químico. Estos portadores producen una conducción óhmica siempre que el campo eléctrico aplicado no sea tan intenso que altere el equilibrio químico (véase [1] para una revisión de la conducción en dieléctricos líquidos). Por otra parte, los elevados campos eléctrico que pueden soportar estos líquidos dan lugar a fenómenos adicionales, tales como la inyección de carga en los electrodos o la generación de movimientos en el fluido (flujos electrohidrodinámicos). Adicionalmente deben tenerse en cuenta la presencia de capas de iones en las proximidades de los electrodos (polarización de los electrodos). Estas capas se dan también en el caso de líquidos conductores, pero su extensión hacia el seno del líquido es mucho mayor en el caso de los dieléctricos.The electrical conductivity is defined as the proportionality constant between the electric field and the electric current density. The medium that satisfies such proportionality is called ohmic . Means normally considered conductors of electricity, such as metals or electrolyte solutions, carry relatively high currents to relatively small electric fields. Such electric current is caused by the drag that the electric field makes on the charge carriers present in the volume, electrons in the case of metals or ions in that of electrolytic solutions. These liquids usually have a clearly ohmic behavior and, as a result of the ease with which they conduct the current, the electric field inside has a normally small value. In the case of liquid dielectrics, the charge carriers in the volume are relatively scarce and the electric field within it can reach high values. The charge carriers in insulating liquids are the result of the ionization of impurities or of the molecules of the liquid itself, its concentration being the result of a chemical equilibrium. These carriers produce an ohmic conduction as long as the applied electric field is not so intense that it alters the chemical equilibrium (see [1] for a review of the conduction in liquid dielectrics). On the other hand, the high electric fields that these liquids can withstand give rise to additional phenomena, such as the injection of charge in the electrodes or the generation of movements in the fluid (electrohydrodynamic flows). Additionally, the presence of ion layers in the vicinity of the electrodes (polarization of the electrodes) must be taken into account. These layers also occur in the case of conductive liquids, but their extension into the liquid is much greater in the case of dielectrics.
Los aparatos que miden resistencia eléctrica en sólidos no son adecuados para la medida en líquidos. La inmensa mayoría de los dispositivos propuestos para la medida de conductividades de líquidos están diseñados para líquidos de relativamente alta conductividad, especialmente agua o disoluciones acuosas. Para evitar la corrosión de los electrodos suelen funcionar con corriente alterna y para minimizar el efecto de la polarización de los electrodos suelen contar con sistemas de cuatro electrodos, dos excitadores y dos de medida (casos representativos son las patentes [2], [3] y [4]). En el caso de líquidos muy aislantes el uso de corriente alterna, aunque posible, no es ventajoso puesto que la corriente capacitiva supera en mucho a la corriente de conducción que se desea medir, en factores de 10^{6} a 10^{7} para una frecuencia de 50 Hz.The devices that measure electrical resistance in solids are not suitable for measurement in liquids. The immense most of the devices proposed for measuring liquid conductivities are designed for liquids of relatively high conductivity, especially water or solutions aqueous. To prevent corrosion of electrodes usually operate with alternating current and to minimize the effect of electrode polarization usually have four systems electrodes, two exciters and two measuring (representative cases they are patents [2], [3] and [4]). In the case of liquids very insulators the use of alternating current, although possible, is not advantageous since the capacitive current far exceeds the conduction current to be measured, in factors of 10 6 at 10 7 for a frequency of 50 Hz.
Existen también aparatos específicamente diseñados para medir la conductividad de líquidos dieléctricos entre los que cabe destacar el de Hilaire et al [5]. Las patentes de Scozzari [6] y Beijk [7] se basan en métodos similares, aunque no se afirme en ellas que sean específicas para líquidos dieléctricos. Estos dispositivos aplican un señal periódica cuadrada o trapezoidal y analizan la corriente transitoria producida tomando medidas bien en determinados instantes considerados determinantes según algún modelo teórico ([5] y [7]) o bien tomando la intensidad de corriente en varios instantes y ajustándola a una expresión teórica [6].There are also devices specifically designed to measure the conductivity of dielectric liquids, among which Hilaire et al [5]. The patents of Scozzari [6] and Beijk [7] are based on similar methods, although they are not claimed to be specific for dielectric liquids. These devices apply a square or trapezoidal periodic signal and analyze the transient current produced by taking measurements at certain moments considered determinants according to some theoretical model ([5] and [7]) or by taking the current intensity in several moments and adjusting it to a theoretical expression [6].
El dispositivo y método propuestos en la presente solicitud de patente son adecuados para la medida de conductividades de líquidos aislantes gracias a las pequeñas diferencias de potencial aplicadas que impiden la aparición de los fenómenos enumerados anteriormente. Realiza medidas en estado estacionario a potenciales lo suficientemente pequeños como para no alterar el equilibrio termodinámico del líquido de modo que no requiere hipótesis para seleccionar un momento u otro de un transitorio. Además, al no realizar hipótesis, permite medidas significativas en regímenes óhmicos o no óhmicos. Para ello, sigue un protocolo que incluye la variación de la distancia entre electrodos, recurso no explotado en invenciones previas.The device and method proposed in the This patent application are suitable for the measurement of conductivities of insulating liquids thanks to the small potential differences applied that prevent the appearance of phenomena listed above. Make measurements in state stationary to potentials small enough not to alter the thermodynamic balance of the liquid so that no requires hypothesis to select a moment or another of a transient. In addition, by not making hypotheses, it allows measurements significant in ohmic or non-ohmic regimes. To do this, follow a protocol that includes the variation of the distance between electrodes, resource not exploited in previous inventions.
[1] M. Hilaire, C. Marteau, R. Tobazeon, IEEE Trans. Electr. Insul. (73), 779-787, 1988.[1] M. Hilaire , C. Marteau , R. Tobazeon , IEEE Trans. Electr. Insul . ( 73 ), 779-787, 1988 .
[2] Goldsmith Herbert, Self alarming four double electrodes conductivity cell, US4365200, 1982.[2] Goldsmith Herbert, Self alarming four double electrodes conductivity cell , US4365200, 1982 .
[3] Alex D. Colvin, James W. Butler, Instrument for on-line measurement of the absolute electrical conductivity of a liquid, US4751466, 1988.[3] Alex D. Colvin , James W. Butler , Instrument for on-line measurement of the absolute electrical conductivity of a liquid , US4751466, 1988 .
[4] Norbert Kordas, Integrable conductivity measuring device, US5543717, 1996.[4] Norbert Kordas , Integrable conductivity measuring device , US5543717, 1996 .
[5] M. Hilaire, C. Marteau, R. Tobazeon, Procédé et dispositif de mesure de résistivité, notamment pour liquides diélectrìques de résistivité très élevée, FR2581196, 1985.[5] M. Hilaire , C. Marteau , R. Tobazeon , Procédé et mecanif de mesure de résistivité, notamment pour liquides diélectrìques de résistivité très élevée, FR2581196, 1985 .
[6] A. Scozzari, Method and device for liquid conductivity measurement, WO2007010320, 2007.[6] A. Scozzari , Method and device for liquid conductivity measurement , WO2007010320, 2007 .
[7] J. M. Beijk, Method and device for measuring the conductivity of a liquid, with which the influence of polarisation is counteracted, EP0288099, 1988.[7] JM Beijk , Method and device for measuring the conductivity of a liquid, with which the influence of polarization is counteracted , EP0288099, 1988 .
Figura 1.- Esquema de la celda de medida.Figure 1.- Diagram of the measuring cell.
- 1)one)
- electrodo superior de medida,upper measuring electrode,
- 2)2)
- electrodo inferior en forma de vasija,vessel-shaped lower electrode,
- 3)3)
- electrodo de guarda,guard electrode,
- 4)4)
- estructura externa,external structure,
- 5)5)
- bloque deslizante,sliding block,
- 6) y 7)6) and 7)
- bloques de material dieléctrico,blocks of dielectric material,
- 8) 8)
- motor paso a paso,stepper motor,
- 9) 9)
- conexión de medida,measurement connection,
- 10) 10)
- conexión para el electrodo inferior,connection for the lower electrode,
- 11)eleven)
- micrómetro digital,digital micrometer,
- 12)12)
- ejes fijos a la estructura externa.fixed axes to the external structure.
Figura 2.- Esquema del montaje que se compone de la celda de medida, amperímetro, motor y controladora, generador de funciones y un ordenador de control.Figure 2.- Assembly diagram that consists of The measuring cell, ammeter, motor and controller, generator functions and a control computer.
La presente invención tiene por objeto un dispositivo y un método para medir la conductividad eléctrica de líquidos altamente aislantes. El dispositivo comprende dos electrodos planos paralelos de separación controlable.The present invention aims at a device and a method to measure the electrical conductivity of highly insulating liquids. The device comprises two parallel flat electrodes with controllable separation.
El electrodo superior es desplazable verticalmente y está dividido en dos regiones aisladas eléctricamente: una región central y otra periférica que hace de electrodo de guarda. Está guiado por una estructura mecánica que asegura el paralelismo y movido por un motor que permite variar controladamente la distancia entre electrodos. El electrodo superior está unido a un sistema de deslizamiento vertical, que permita el desplazamiento manteniendo el paralelismo entre electrodos. Cuanto más estricta sea la tolerancia mecánica de este desplazamiento menor será la incertidumbre de las medidas. El electrodo de guarda puede ir unido directamente al sistema de deslizamiento, mientras que el electrodo central debe ir unido por medio de un bloque de material dieléctrico que lo aísle eléctricamente.The upper electrode is movable vertically and is divided into two isolated regions electrically: a central and peripheral region that makes guard electrode It is guided by a mechanical structure that ensures parallelism and driven by an engine that allows you to vary The distance between electrodes is controlled. Electrode upper is attached to a vertical sliding system, which allow displacement maintaining the parallelism between electrodes The stricter the mechanical tolerance of this Minor displacement will be the uncertainty of the measures. He Guard electrode can be attached directly to the system sliding, while the central electrode must be joined by middle of a block of dielectric material that insulates it electrically
El electrodo inferior tiene forma de vasija con el objeto de contener la muestra de líquido.The lower electrode is shaped like a vessel with in order to contain the liquid sample.
El sistema de deslizamiento se desplaza controladamente por medio de un motor unido a una estructura externa de la que forma parte y que contiene también a los electrodos, sirviendo tanto de soporte mecánico del dispositivo como de blindaje electromagnético, por lo que debe conectarse a masa. El electrodo inferior reposa sobre esta estructura a través de un bloque de material aislante.The sliding system moves controlled by means of a motor attached to a structure external part of which it is part and which also contains the electrodes, serving as both mechanical support of the device and of electromagnetic shielding, so it must be grounded. He lower electrode rests on this structure through a block of insulating material.
Por seguridad y simplicidad en el diseño, el potencial eléctrico se aplica al electrodo inferior mientras que el superior se coloca a masa.For safety and simplicity in design, the electrical potential is applied to the lower electrode while the Upper is placed in bulk.
El área de los electrodos debe ser lo suficientemente grande como para proporcionar valores medibles de la intensidad de corriente con potenciales aplicados necesarios para obtener condiciones de conductividad óhmica en dieléctricos líquidos (del orden de 10^{-12}\Omega^{Q-1}m^{-1}).The area of the electrodes should be large enough to provide measurable current intensity values with applied potentials necessary to obtain ohmic conductivity conditions in liquid dielectrics (of the order of 10 - 12} \ Omega - Q-1 m -1).
El sistema de deslizamiento y el electrodo superior deben permitir el acceso del líquido al electrodo inferior y permitir la limpieza de los electrodos, puesto que pequeñas cantidades de contaminantes falsean totalmente la medida de la conductividad. Los electrodos y las piezas eléctricas de soporte deben ser químicamente compatibles con las muestras a medir, principalmente líquidos orgánicos. Por tanto, deben evitarse tanto materiales porosos que pudiesen contaminarse como plásticos solubles en hidrocarburos.The sliding system and the electrode upper should allow liquid access to the lower electrode and allow cleaning of the electrodes, since small quantities of pollutants totally distort the extent of conductivity. Electrodes and electrical support parts they must be chemically compatible with the samples to be measured, mainly organic liquids. Therefore, both should be avoided porous materials that could be contaminated as plastics soluble in hydrocarbons.
El líquido sólo entra en contacto con el material del que están hechos los electrodos, lo que evita la contaminación.The liquid only comes into contact with the material from which the electrodes are made, which prevents pollution.
El electrodo superior recibe un potencial dado por el protocolo de medida mientras que el electrodo inferior está conectado eléctricamente a masa.The upper electrode receives a given potential by the measurement protocol while the lower electrode is electrically grounded.
El electrodo superior se une al mecanismo de guiado mecánico mediante un bloque dieléctrico que asegura el aislamiento eléctrico del electrodo de medida de cualquier otra parte conductora de electricidad del dispositivo.The upper electrode joins the mechanism of mechanical guidance through a dielectric block that ensures the electrical insulation of the measuring electrode of any other Conductive part of the device's electricity.
El dispositivo y métodos propuestos en la presente solicitud, son adecuados para la medida de conductividades de líquidos aislantes gracias a su sensibilidad y a las pequeñas diferencias de potencial aplicadas. Realiza medidas en estado estacionario a potenciales lo suficientemente pequeños como para no alterar el equilibrio termodinámico del líquido de modo que no requiere hipótesis para seleccionar un momento u otro de un transitorio. Realiza un protocolo de variación de la distancia entre electrodos, recurso no explotado en invenciones previas, el cual permite determinar si existe un régimen óhmico. En caso de que exista, encuentra el valor de la conductividad por ajuste de la resistencia de la celda frente al espaciado entre electrodos.The device and methods proposed in the present application, are suitable for conductivity measurement of insulating liquids thanks to its sensitivity and small potential differences applied. Make measurements in state stationary to potentials small enough not to alter the thermodynamic balance of the liquid so that no requires hypothesis to select a moment or another of a transient. Make a distance variation protocol between electrodes, resource not exploited in previous inventions, the which allows to determine if there is an ohmic regime. If exist, find the value of the conductivity by adjusting the resistance of the cell against spacing between electrodes.
El método propuesto es capaz de distinguir la conductividad óhmica de otros procesos que pueden darse en el seno del líquido ó en la interfaz líquido-electrodo. La conductividad eléctrica es un parámetro básico cuyo control es esencial en multitud de procesos.The proposed method is able to distinguish the Ohmic conductivity of other processes that may occur within of the liquid or at the liquid-electrode interface. The electrical conductivity is a basic parameter whose control is Essential in a multitude of processes.
El protocolo de medida debe aplicar varios valores de la diferencia de potencial. Estos valores deben ser como máximo del orden de varios voltios, para no alterar el equilibrio termodinámico del líquido. Además, la aplicación de cada uno de los valores de la diferencia de potencial debe prolongarse lo suficiente para superar el transitorio alcanzando un estado estacionario. La duración del transitorio depende de la conductividad del líquido. El ajuste de la intensidad de corriente frente al potencial aplicado proporciona un valor de la resistencia. El conjunto de valores de potencial debe repetirse para varios valores del espaciado. El ajuste de los valores de la resistencia para distintos espaciados frente a la distancia entre electrodos proporciona un valor de la conductividad en el caso en que la resistencia se comporte linealmente con la distancia.The measurement protocol must apply several values of the potential difference. These values should be like maximum of the order of several volts, so as not to disturb the balance Thermodynamic of the liquid. In addition, the application of each of the values of the potential difference should be prolonged sufficiently to overcome the transitory reaching a steady state. The Transient duration depends on the conductivity of the liquid. The adjustment of the current intensity versus the potential applied provides a resistance value. The set of potential values should be repeated for several values of the spacing. Adjusting resistance values for different spaced against the distance between electrodes provides a conductivity value in the case where the resistance behaves linearly with distance.
El método se caracteriza por aplicar diferencias de potencial para un espaciado fijo entre los electrodos, aplicando cada valor de la diferencia de potencial hasta alcanzar el estado estacionario en cada período y medir las corrientes eléctricas producidas en estado estacionario. El valor de los potenciales aplicados, del orden de varios voltios, es lo suficientemente pequeño para no alterar el equilibrio termodinámico del líquido. Mediante ajuste a este conjunto de medidas se obtiene un valor de la resistencia para un valor del espaciado. Realizando medidas a diferentes espaciados entre electrodos, se obtienen un conjunto de valores de la resistencia para distintos espaciados. Del ajuste lineal de los valores de la resistencia frente al espaciado se extrae el valor de la conductividad eléctrica del líquido. En caso contrario, si el ajuste no es aplicable, el líquido no se encuentra en régimen óhmico y no tiene sentido hablar de la conductividad.The method is characterized by applying differences of potential for a fixed spacing between the electrodes, applying each value of the potential difference until reaching the state stationary in each period and measure electrical currents produced in steady state. The value of the potentials applied, of the order of several volts, is sufficiently Small so as not to disturb the thermodynamic balance of the liquid. By adjusting to this set of measures a value of the resistance for a spacing value. Making measurements to different spaced between electrodes, a set of resistance values for different spacing. Of adjustment linear values of resistance to spacing are extracts the value of the electrical conductivity of the liquid. In case Otherwise, if the setting is not applicable, the liquid is not found in ohmic regime and it makes no sense to talk about conductivity.
El control de la conductividad en líquidos aislantes es esencial en multitud de aplicaciones, bien para aumentarla o para disminuirla. Así, los combustibles de avión deben tener una conductividad mínima para impedir la aparición de elevados voltajes durante su flujo y son supervisados y normalizados. Por otra parte, se utilizan líquidos dieléctricos como aislantes en electrotecnia, especialmente el aceite de transformador que se utiliza como dieléctrico y refrigerante.The conductivity control in liquids insulators is essential in many applications, well for increase it or to decrease it. Thus, airplane fuels must have a minimum conductivity to prevent the appearance of high voltages during their flow and are monitored and normalized. By On the other hand, dielectric liquids are used as insulators in electrical engineering, especially the transformer oil that Used as a dielectric and refrigerant.
La conductividad es, además, una medida de gran sensibilidad de la pureza de líquidos aislantes, puesto que varía incluso órdenes de magnitud por la presencia de impurezas ionizadas. Es también clave en la estabilidad de suspensiones coloidales de gran aplicación, tales como pinturas o tintas de impresión.Conductivity is also a measure of great purity sensitivity of insulating liquids, since it varies even orders of magnitude for the presence of impurities ionized It is also key in the stability of suspensions colloidal of great application, such as paints or inks of Print.
La conductividad eléctrica de líquidos aislantes es un parámetro fundamental cuya monitorización es esencial en multitud de actividades. Por tanto, la presente invención tiene su aplicación en la industria química para controlar la pureza de líquidos aislantes o para controlar la estabilidad de suspensiones coloidales de gran aplicación (por ejemplo, pinturas o tintas de impresión). También es necesario controlar la conductividad de combustibles de avión para evitar la aparición de elevados voltajes durante su flujo.The electrical conductivity of insulating liquids it is a fundamental parameter whose monitoring is essential in multitude of activities Therefore, the present invention has its application in the chemical industry to control the purity of insulating liquids or to control the stability of suspensions colloidal of great application (for example, paints or inks of Print). It is also necessary to control the conductivity of airplane fuels to avoid the appearance of high voltages during its flow.
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Se ha realizado en laboratorio un prototipo. Este prototipo ha sido realizado en acero inoxidable y como elementos aislantes se han usado piezas de teflón.A prototype has been made in the laboratory. This prototype has been made in stainless steel and as insulating elements Teflon pieces have been used.
El radio de los electrodos ha sido elegido para obtener intensidades de corriente del orden del pico amperio para espaciados entre electrodos del orden del milímetro y conductividades típicas de líquidos dieléctricos. Se ha elegido un radio de 3 cm. para el electrodo interno. El diámetro del electrodo de guarda ha sido optimizado mediante simulación numérica.The radius of the electrodes has been chosen to obtain current intensities of the order of the peak ampere for spaced between electrodes of the order of the millimeter and Typical conductivities of dielectric liquids. You have chosen a 3 cm radius for the internal electrode. Electrode diameter Guard has been optimized by numerical simulation.
El mecanismo de desplazamiento se desliza a lo largo de tres ejes de precisión embutidos en la carcasa externa. Tres rodamientos lineales de precisión engranan el sistema deslizante con los ejes.The sliding mechanism slides to length of three precision shafts embedded in the external housing. Three precision linear bearings gear the system Sliding with the axes.
El sistema deslizante es movido gracias a un motor paso a paso fijo a la tapa superior de la estructura externa. La distancia entre placas es monitorizada por un micrómetro digital de precisión fijo a la tapa de la carcasa externa cuyo palpador toca al sistema deslizante.The sliding system is moved thanks to a stepper motor fixed to the top cover of the external structure. The distance between plates is monitored by a digital micrometer precision fixed to the outer housing cover whose probe Touch the sliding system.
El sistema deslizante se compone de una plataforma a la cual van unidos los rodamientos lineales y en la que se encuentran las conexiones eléctricas y la pieza de unión con el motor. El electrodo de guarda va unido directamente a esta plataforma con tornillos mientras que el electrodo de medida va anclado a la plataforma por medio de un bloque de teflón.The sliding system consists of a platform to which the linear bearings are attached and in the that are the electrical connections and the connecting piece with the motor. The guard electrode is attached directly to this platform with screws while the measuring electrode goes anchored to the platform by means of a Teflon block.
El sistema es controlado por un ordenador equipado con una tarjeta GPIB. La intensidad de corriente es medida mediante un electrómetro de precisión y la diferencia de potencial es impuesta mediante un generador de onda arbitraria. El motor es controlado mediante la salida digital de una tarjeta de adquisición de datos.The system is controlled by a computer Equipped with a GPIB card. The current intensity is measured. using a precision electrometer and the potential difference It is imposed by an arbitrary wave generator. The engine is controlled by the digital output of an acquisition card of data.
El protocolo de medida es gobernado por una rutina informática que aplica un potencial escalonado con potenciales positivos y negativos. La serie de potenciales se aplica para distintas distancias entre los electrodos, obteniendo características intensidad de corriente-diferencia de potencial para varias distancias entre electrodos. De cada una de estas características se extrae un valor de la resistencia. Los valores de resistencia resultantes de varias series se ajustan frente a la distancia. Si el ajuste lineal resulta preciso se extrae de él la conductividad óhmica del líquido. En caso contrario, el líquido no se encuentra en régimen óhmico y no tiene sentido hablar de la conductividad, pudiéndose proporcionar solamente una cota superior.The measurement protocol is governed by a computer routine that applies a phased potential with positive and negative potentials. The series of potentials applies for different distances between the electrodes, obtaining current intensity-difference characteristics of potential for several distances between electrodes. Of each one from these characteristics a resistance value is extracted. The resistance values resulting from various series are adjusted in front of the distance. If the linear adjustment is accurate, it is removed from it the ohmic conductivity of the liquid. Otherwise, the liquid is not in ohmic regime and it makes no sense to speak of conductivity, being able to provide only one dimension higher.
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|---|---|---|---|
| ES200800749A ES2325673B1 (en) | 2008-03-10 | 2008-03-10 | DEVICE AND METHOD FOR THE MEASUREMENT OF ELECTRICAL CONDUCTIVITY OF HIGHLY INSULATING LIQUIDS. |
| PCT/ES2009/000132 WO2009112613A1 (en) | 2008-03-10 | 2009-03-10 | Device and method for measuring the electroconductivity of highly insulating liquids |
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| ES200800749A ES2325673B1 (en) | 2008-03-10 | 2008-03-10 | DEVICE AND METHOD FOR THE MEASUREMENT OF ELECTRICAL CONDUCTIVITY OF HIGHLY INSULATING LIQUIDS. |
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| GB982290A (en) * | 1960-03-16 | 1965-02-03 | Wayne Kerr Lab Ltd | Improvements in or relating to apparatus for measuring the electrical conductivity of liquids |
| JP3047141B2 (en) * | 1992-05-07 | 2000-05-29 | セイコーインスツルメンツ株式会社 | Parallel plate dielectric constant measuring device |
| US5874832A (en) * | 1996-12-20 | 1999-02-23 | Raytheon Company | Precise high resolution non-contact method to measure dielectric homogeneity |
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