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What Are Conductance Sensors And How Do They Work?

What Are Conductance Sensors And How Do They Work?

November 13 , 2023 0

I.What Is A Conductance Sensor?

Conductivity sensor technology is a very important engineering technology research field, used to measure the conductivity of liquids, is widely used in human production and life, become electric power, chemical, environmental protection, food, semiconductor industry, Marine research and development and other industrial production and technology development of an indispensable detection and monitoring device. The conductivity sensor mainly measures and detects industrial production water, human living water, seawater characteristics, and electrolyte properties in batteries.

A conductivity sensor is a sensor used to measure electrical conductivity, also known as a conductivity sensor or conductivity sensor. Conductivity refers to the ability of a material or liquid to conduct an electric current, and it is related to the concentration of ions in it and the ability of the electrolyte. Conductivity sensors measure the conductivity in an electrolyte to assess its solute concentration or purity.
A conductivity sensor usually consists of two electrodes, which are placed in an electrolyte or liquid. A small voltage (usually a few millivolts to a few hundred millivolts) is applied between the two electrodes, and the current flowing through the electrodes is measured. The size of the current is proportional to the concentration of ions in the electrolyte, so the conductivity of the electrolyte can be inferred from the measured current.

II.The Working Principle OF The Conductivity Sensor

The working principle of the conductivity sensor is based on the conduction of electric current and Ohm's law. They use two electrodes (usually parallel metal electrodes) to measure the conductivity in an electrolyte or liquid. The following is a detailed description of the working principle of the conductivity sensor:

Construction: The conductivity sensor usually consists of two electrodes, which are placed in an electrolyte or liquid. These electrodes are usually made of materials with good conductivity, such as metals.

Voltage application: A small voltage is applied between the two electrodes of a conductance sensor in an electrolyte or liquid. This voltage is usually DC and usually ranges from a few millivolts to a few hundred millivolts.

Measuring current: After applying a voltage, the ions in the electrolyte (such as cations and anions) move according to the electric field strength. Because the electrolyte has a certain conductivity, the current will pass through the electrolyte and flow through the electrode.

Current measurement: A current measuring device (such as an ammeter or amplifier) is used to measure the current passing through an electrolyte. The magnitude of the current is proportional to the ion concentration and conductivity in the electrolyte.

Conductivity calculation: By measuring the current value and applying the voltage, the conductivity of the electrolyte can be calculated according to Ohm's law. Ohm's law is expressed as I = σ × E, where I is the current, σ is the conductivity of the electrolyte, and E is the electric field strength.

The results show that the measured conductivity value can be converted into the desired units (such as Siemens/meter or millisiemens/centimeter) and displayed on the corresponding instrument or display.

It is important to note that the measurement results of the conductivity sensor may be affected by temperature. The conductivity of an electrolyte usually changes with temperature, so when using a conductivity sensor, temperature correction is usually required to obtain accurate conductivity measurements.

III.How Many Types OF Capacitive Sensors Are There

Conductivity sensors can be divided into electrode conductivity sensors, inductance conductivity sensors and ultrasonic conductivity sensors according to the different measurement principles and methods.
Electrode type conductivity sensor according to the principle of electrolytic conductivity using the resistance measurement method to measure the conductivity, the conductivity measurement electrode in the measurement process is a complex electrochemical system, inductance type conductivity sensor based on the principle of electromagnetic induction to achieve the measurement of liquid conductivity, ultrasonic conductivity sensor according to the ultrasonic wave changes in the liquid to measure the conductivity. The first two types of sensors are the most widely used.

IV.Compare And Contrast Different Types OF Conductance Sensors In Detail

4.1 Technology status and characteristics of two-electrode conductivity sensor

Two-electrode conductivity sensor conductivity cell "consists of a pair of electrodes, a constant voltage is applied to the electrode, the change in the resistance of the liquid in the conductivity cell leads to a change in the current of the measuring electrode, and conforms to Ohm's law, with conductivity instead of resistivity, with conductivity instead of resistance in the metal, that is, conductivity and conductance to represent the conductivity of the liquid. Thus the measurement of liquid conductivity is realized.
At present, the measurement range of the two-electrode conductivity sensor 9 is 0~20000uS/cm, and the electrode constant is different with different ranges: the electrode constant is 0.01 /cm, and the measurement range is 0~20uS /cm; The electrode constant is 0.1 /cm, and the measuring range is 0.1-200uscm. The electrode constant is 1.0 /cm, and the measurement range is 10-20 000uS/cm.
The electrode of the specific electrode type conductivity sensor is composed of a pair of flat electrodes, and the electrode constant is determined by the area and distance of the electrodes. The electrode structure is simple, the production process is simple, but the electrode has a power line edge effect and the electrode is opposite the area, the electrode distance is difficult to determine the problem, the electrode constant can not be calculated by the size measurement, need to be calibrated by the standard, the most commonly used standard solution is 0.0100 mol /l potassium chloride standard solution. According to the principle of conductivity cell, the plate electrode is improved, and the cylindrical electrode, the point electrode, the line electrode and the composite electrode are developed.
Electrode type conductivity sensor has the following characteristics: 1) simple structure, convenient manufacturing, 2) follow-up processing circuit is simple, easy to achieve :3) high measurement accuracy :4) easy to use.

4.2 Current status and characteristics of four-electrode conductivity sensor technology

The four-electrode conductance cell is composed of 2 current electrodes and 2 voltage electrodes, the voltage electrode and the current electrode are coaxial, the measured liquid passes through the gap between the 2 current electrodes, an AC signal is applied at both ends of the current electrode and the electric field is established in the liquid medium, and the 2 voltage electrodes are induced to generate voltage, so that the voltage at both ends of the 2 voltage electrodes remains constant. The current between the two current electrodes has a linear relationship with the liquid conductivity
In order to meet the needs of Marine research and development, Li Jianguo of China National Oceanographic Technology Center has carried out research and development of open four-electrode conductivity sensors, and successfully developed a four-electrode conductivity sensor for the measurement of seawater conductivity %, and its performance indicators have reached the international advanced level: the measurement range is 0~ 65 ms /cm; The measurement accuracy is 0.007mS/cm.
At present, the mature four-electrode conductivity sensor has a measuring range of 0-2s /cm, and different electrode constants have different measuring ranges
The four-electrode conductivity sensor has the following characteristics :1) The current electrode is separated from the voltage electrode, and the constant current source % is used to supply power on the current electrode, which effectively avoids the influence of polarization impedance; 2) High sensitivity, strong anti-pollution ability; 3) The four-electrode conductance cell has ultrastructure, large diversion space and short distance, which is suitable for long-term field measurement.

4.3 The Application OF Electrode Conductivity Sensor

Electrode type conductivity sensor is widely used in production, life and military fields: 1) human drinking water quality monitoring; 2) Industrial water quality monitoring Q, 3) Monitoring of battery electrolyte density :4) Monitoring of water quality in electrolytic oxygen and hydrogen production devices :5) Marine survey, Marine resource survey, Marine environment monitoring

4.4 Electrode Type Conductivity Sensor Key Technology

1) Elimination of electrode polarization effect only
In order to reduce the measurement deviation caused by electrode polarization, methods such as increasing the frequency of the power supply, coating the electrode plate with platinum black, and increasing the plate area are usually adopted.
2) Elimination of capacitance effect %
In order to eliminate the capacitance effect and improve the measurement sensitivity, two methods are usually adopted: one is to increase the liquid resistance, which is not easy to achieve; the other is to increase the frequency and reduce the capacitive reactance. However, the improvement of frequency will be subject to certain limitations, generally using low frequency when high resistance, low resistance using high frequency.
3) Design and manufacture of multi-electrode conductance cell
The multi-electrode conductance cell requires each pair of electrodes to maintain strict symmetry, and the distance relative to other electrodes is fixed, which puts forward high requirements for the machining of the electrode base. The electrode base is mostly made of high-performance ceramic materials, and the electrode material is mostly made of high-performance metal materials, and the expansion coefficient of the two is quite different, which makes the sintering and packaging of the electrode difficult. Usually, transition materials with intermediate temperature coefficient are used for sintering and encapsulation, but the effect is not very ideal.

4.5 Future Development Trend OF Electrode Type Conductivity Sensing

1) Multi-electrode and microelectrode have become one of the development directions of electrode conductivity sensors. Due to the existence of electrode polarization, the measurement range and measurement accuracy of the two-electrode conductivity sensor are greatly limited, and the multi-electrode system conductivity sensor has made breakthroughs in the measurement range and measurement accuracy. After years of research and development, at present, the conductivity sensor with four-electrode structure has been successfully developed and successfully commercialized. China National Marine Technology Center has carried out research and development of seven-electrode conductivity sensor, and has made some achievements in electrode structure design, sintering, packaging and so on
2) The conductivity sensor is combined with single-chip microcomputer technology and microsystem technology. The conductivity sensor is combined with single-chip microcomputer technology and microsystem technology to realize the automation of conductance measurement and improve the adaptability and measurement accuracy of conductance measurement
3) Optimize the form of the excitation signal to make the measurement data more accurate and faster.
4) In the case that the increase of the number of electrodes is limited, the excitation sequence is optimized to obtain as many independent measurement data as possible for the same conductivity distribution.

4.6 Electrode Material Development

Because the conductive electrode of the conductivity sensor has certain particularity, there are certain requirements for the materials used to make the electrode: good conductivity; Because the chemical or electrochemical reaction between the electrode and the measured medium will corrode the electrode surface, the electrode is required to have stable chemical characteristics
Commonly used electrode materials are platinum, stainless steel, copper, silver and so on. Platinum is an excellent electrode material, but the price is high, in practical applications, generally use stainless steel and metal copper as electrode materials
With the development and progress of materials science, some new materials are used to process conductivity sensor electrodes, such as conductive ceramics, alloys, etc., and have achieved good results.