Classifications

• • 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
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
  • G01D21/00—Measuring or testing not otherwise provided for
  • G01D21/02—Measuring two or more variables by means not covered by a single other subclass
• • 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
  • G01N27/045—Circuits
  • G01N27/046—Circuits provided with temperature compensation
• • 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
  • G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
  • G01N27/416—Systems
  • G01N27/4163—Systems checking the operation of, or calibrating, the measuring apparatus
• • 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
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R35/00—Testing or calibrating of apparatus covered by the other groups of this subclass
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R35/00—Testing or calibrating of apparatus covered by the other groups of this subclass
  • G01R35/005—Calibrating; Standards or reference devices, e.g. voltage or resistance standards, "golden" references

Definitions

• the present invention generally relates to a system and method for the calibration of conductivity sensors for aqueous solutions, or any electrochemical sensor technology that sense a change in potential (voltage) or loss/gain of electrons to translate to the measurement of conductivity, pH, dissolved oxygen (DO), or other applicable responses.
• Conductivity in aqueous solutions, is a measure of the ability of water to conduct an electric current. The more ions there are in the solution, the higher its conductivity.
• Temperature also impacts the conductivity. As the temperature of the solution increases, there is a corresponding increase in the solubility of the material being dissolved in the solution, and a resulting increase in the conductivity.
• successfully calibrating the sensor may be dependent on the accuracy of third-party conductivity and temperature probes for reference. Routine external calibration of third-party probes is required to maintain specification. However in many instances, third party probes do not agree with one another for temperature or conductivity readings when compared to each other.
• the calibration pass rate for newly manufactured conductivity sensors can be as low as 25-30% on first attempt at calibration.
• Embodiments of the present invention relate to a system and method for calibration conductivity sensors for aqueous solutions that address many of the problems described above.
• embodiments of the invention provide a calibration device for a conductivity sensor for aqueous solutions.
• the calibration device includes a first connector configured to electrically couple with the sensor electrodes of the conductivity sensor.
• the connector is further configured to provide for the application of a controlled voltage across at least two of the sensor electrodes.
• a first resistor is connected between the at least two sensor electrodes and coupled to the first connector. The resistor has a value such that a current flow between the at least two sensor electrodes replicates the properties of an electrochemical calibration solution.
• the calibration device has a second connector connected to the resistor, and also connected to a conductivity monitor.
• the first connector is configured to electrically couple with at least four sensor electrodes of the conductivity sensor, and the calibration device further includes a resistor network with the first resistor, a second resistor, and a third resistor, wherein each of the three resistors is coupled between a different two of the four sensor electrodes.
• the first resistor has a resistance value of 40.2 ohms
• the second and third resistors each have a resistance value of 221 ohms.
• the first resistor has a resistance value that ranges from 38 to 42 ohms. In a more particular embodiment, the first resistor has a resistance value of 40.2 ohms.
• the calibration device may further include a temperature calibration circuit configured to simulate a 25-degree-Celsius environment for the conductivity sensor being calibrated.
• the temperature calibration circuit includes a switching element coupled to a pair of resistors. In particular embodiments, one of the pair of resistors has a resistance value of between 200 and 300 ohms, and a second of the pair of resistors has a resistance value of between 1.5 and 2.5 kilo-ohms.
• one of the pair of resistors has a resistance value of 226 ohms, and a second of the pair of resistors has a resistance value of 2.1 kilo-ohms.
• the calibration device may further include a terminal configured for connection to an external power source.
• embodiments of the invention provide a method for calibrating a conductivity sensor for aqueous solutions.
• the method includes the steps of applying a voltage across two electrodes of the conductivity sensor to replicate the properties of an electrochemical calibration solution, measuring an electrical current flowing between the two electrodes, and determining whether the conductivity sensor is successfully calibrated based on whether the measured current falls within a predetermined range.
• the method further includes connecting a resistor between the two electrodes.
• the method may also include providing a resistor network that connects at least one resistor to each of a plurality of electrodes of the conductivity sensor. Further embodiments of the method call for simulating a 25-degree-Celsius environment for the conductivity sensor being calibrated.
• a particular embodiment of the method includes connecting a calibration device to a plurality of electrodes of the conductivity sensor.
• the calibration device includes one or more resistors coupled to each of the plurality of electrodes.
• the method may call for connecting a calibration device with a temperature calibration circuit for simulating a 25-degree- Celsius environment for the conductivity sensor being calibrated.
• embodiments of the invention provide a method for calibrating a conductivity sensor.
• the method includes the steps of applying a controlled voltage across two electrodes of the sensor, sensing a current across the two electrodes while maintaining the sensor at a controlled temperature, and calculating the conductivity of the sensor, based on whether the sensed current falls within a predetermined range indicating a pass of the sensor.
• Embodiments of this method include the step of applying a constant voltage from an external power source.
• Particular embodiments of the invention include a calibration device, for a conductivity sensor for aqueous solutions, that applies external controlled voltage across two sensor electrodes or, in an alternate embodiment, supplies current between two sensor electrodes, which have a set series of resistors and/or capacitors to replicate the properties of an electrochemical calibration solution, thereby eliminating the need for direct solution contact with the sensor electrodes during the calibration process.
• FIG. 1 is a perspective view of the calibration device in accordance with an embodiment of the invention
• FIG. 2 is a schematic diagram showing a resistor network used in the calibration device of FIG. 1, in accordance with an embodiment of the invention
• FIG. 3 is a schematic diagram showing how the resistor network is coupled to first and second connectors, in accordance with an embodiment of the invention.
• FIG. 4 is a schematic diagram of the temperature calibration circuit used in the calibration device of FIG. 1, in accordance with an embodiment of the invention.
• FIG. 5 is a schematic illustration of the calibration device as used in a conductivity sensor in accordance with an embodiment of the invention.
• the present invention includes a conductivity sensor for aqueous solutions, in which an external controlled voltage is applied across two of a plurality of sensor electrodes to facilitate a solutionless calibration process.
• the external controlled voltage is a constant voltage, which may be provided by an external power source.
• a current may be supplied between these two electrodes.
• the aforementioned sensor electrodes may have a set series of resistors and/or capacitors to replicate the properties of an electrochemical calibration solution, thereby eliminating the need for direct contact between the sensor electrodes and the electrochemical calibration solution during the calibration process.
• V is the raw voltage from Analog to Digital Converter (ADC).
• ADC Analog to Digital Converter
• zero level of excitation current refers to the small amount of current that flows in the primary winding of a transformer when a normal voltage is applied to the primary winding terminals when the terminals of the secondary windings are open-circuited.
• This current is called a transformer excitation current and flows all of the time during the operation of the transformer.
• the excitation current is required to sustain a magnetic field inside the core of the transformer, and is largely independent of the load on the secondary windings.
• a one- point calibration may be performed using a 12.88-millisiemen (mS) conductivity solution in production.
• mS 12.88-millisiemen
• the conductivity is read as 12,880 microsiemens ( ⁇ S) or 12.88 millisiemens (mS).
• Current levels, sensed and measured by the conductivity monitor, should be within the range of 394,871 ⁇ 53,662 milliamperes when the voltage is applied to indicate a successfully calibrated sensor.
• a higher-than-expected current value is an indication that there may be problems with the calibration equipment or conductivity sensor that require additional inspection.
• the conductivity calibration process was designed as a substitute for calibration using a solution with a known conductivity of 12.88 millisiemens (mS) at 25 degrees Celsius.
• mS millisiemens
• versions of this process could be used as a substitute for conventional calibration processes for pH sensors or DO sensors.
• the claimed system acts to simulate the properties of the solution of known conductivity.
• the claimed system and method allow for a more controlled and repeatable calibration setup process (in ambient room temperature) as oppose to the existing calibration setup process which requires the use of a known 12.88 mS fluid in a temperature-controlled chamber at 25 degrees Celsius.
• FIG. 1 is a perspective view of the calibration device 100.
• the calibration device 100 does not include a housing, though it is envisioned that commercial embodiments of the device 100 will be disposed within a housing.
• the embodiment of the calibration device 100 shown in FIG. 1 includes a circuit board 102 that configured for connection to the conductivity sensor on one side of the circuit board 102, and to the conductivity monitor (not shown) on a second side of the circuit board 102 opposite the first side.
• the circuit board 102 is configured for connection to a pH sensor, DO sensor, etc.
• the calibration device 100 achieves this goal by leveraging two sub-circuits.
• the passive conductivity sub-circuit consists of a resistance network, which will be described in more detail below, equivalent to a conductivity of 12.88 mS.
• the resistance network is connected to the conductivity sensor’s electrode signal lines. This creates a conductivity feedback response equivalent to 12.88 mS back to the conductivity monitor.
• the conductivity sensor is connected to the circuit board 102 at a first connector 104, while the conductivity monitor is connected to the circuit board 102 at a second connector 106.
• the conductivity monitor is not shown, those of ordinary skill in the art will recognize that the conductivity monitor is used to detect, through its connection to the second connector 106, the current flowing between the electrodes of the sensor thus allowing for a determination as to the successful calibration of the conductivity sensor.
• the conductivity sensor also controls the voltage applied to the conductivity sensor electrodes, and initiates operation of a temperature calibration circuit to be described below.
• the calibration device 100 includes a resistor network with three resistors: R1 110, R3 112, and R5 114 that are connected between the conductivity monitor and the conductivity sensor.
• R1 is 221 ohms
• R3 is 40.2 ohms
• R5 is 221 ohms.
• FIGS. 2 and 3 are schematic diagrams of the circuitry used in the calibration device 100, in accordance with an embodiment of the invention.
• FIGS. 2 and 3 show the aforementioned resistor network with three resistors R1 110, R3 112, and R5 114.
• the three resistors R1 110, R3 112, and R5 114 are coupled to the first connector 104, which is connected to the conductivity sensor, and also coupled to the second connector 106, which is connected to the conductivity monitor.
• the resistor network arranged as shown in FIGS. 2 and 3, helps form the claimed conductivity calibration system and method which, in this embodiment, simulates a 12.88 mS fluid with those specific resistors placed across the excitation (EX +/-) and sensing (SN +/-) EX+,SN+,SN-, & EX- signal lines.
• each of these four signal lines is connected to a sensor electrode 120 of the conductivity sensor 118 (see FIG. 5).
• FIGS. 2 and 3 show how the three resistors R1 110, R3 112, and R5 114 are implemented across the signal lines.
• Resistor R1 110 with an exemplary value of 221 ohms is connected between EX- & SNS- .
• Resistor R3 112 with an exemplary value of 40.2 ohms is connected between SNS- & SNS+.
• Resistor R5 114, with an exemplary value of 221 ohms is connected between SNS+ & EX-.
• FIG. 4 is a schematic diagram of the temperature calibration circuit 140 used in the calibration device 100, in accordance with an embodiment of the invention.
• the temperature calibration circuit 140 simulates a 25-degree-Celsius environment by applying a temperature resistor network to the serial data line (SDA) signal line 142 during calibration.
• the resistor network includes two resistors: R17 144, and R19 146.
• R17 144 has a resistance value of 226 ohms
• R19 146 has a resistance value of 2.1 kilo-ohms.
• a switch component U3 148 shown in FIG. 4, is triggered by the conductivity monitor (see U3 pins 15 & 10) during calibration to apply the temperature calibration circuit 140.
• the temperature calibration circuit 140 targets 25 degrees Celsius to effectively “trick” the sensor to believe it is at 25 degrees Celsius during calibration.
• the active sub-circuit, or temperature calibration circuit 140 applies a firmware controlled voltage bias to the temperature calibration circuit 140 of the conductivity sensor under test.
• the voltage bias signal is delivered via the second connector 106, the voltage being controlled by firmware within the conductivity monitor. This allows for precision timing for applying temperature compensation during sensor calibration and for removing temperature compensation before writing calibration offset values to the conductivity sensor’s non-volatile memory.
• the temperature calibration method described above using the temperature calibration circuit 140 proved effective as units calibrated using this method were found to have an equal or better standard deviation percentage than conventionally-calibrated conductivity sensors.
• each of the conductivity sensors is given a unique Calibration Factor (CF) and Temperature Offset (TO) value that are applied to the reading output (conductivity reading).
• CF Calibration Factor
• TO Temperature Offset
• the operator observes the expected CF and TO values as indications of whether to categorize the conductivity sensor as PASS or FAIL after the calibration. Those that fail are typically separated and inspected for defects to determine their final disposition.
• FIG. 5 is a schematic illustration of the calibration device 100 as used in a conductivity sensor 118 in accordance with an embodiment of the invention.
• a schematic representation of the calibration device 100 is illustrated in which the calibration device 100 connects to four electrodes 120 of the conductivity sensor 118. Alternate embodiments of the calibration device 100 may have fewer or greater than four electrodes 120.
• the calibration device 100 is supplied with power from an external power source 152, though it is envisioned that alternate embodiments of the calibration device 100 are battery- powered, for example.
• the connector portion of the calibration device 100 is configured to apply a controlled voltage to at least two of the four electrodes 120 of the conductivity sensor 118.
• This connector portion may also provide the additional function of straightening the four sensor electrodes 120. This may be a useful function as electrode spacing (i.e., diameter, height, and distance) is important in conductivity sensors 118. If the electrodes 120 are too close, current will arc between the electrodes 120 and cause errors in readings. If the electrodes 120 a spaced too far apart, the current will not be able to carry as effectively between electrodes 120 and will cause errors in readings.
• the solutionless calibration device 100 replicates the current carried by a conductivity solution - thus eliminating the need for an actual solution when calibrating the conductivity sensors 118.
• the current can then be measured by the conductivity monitor to determine whether the sensor 118 falls within a predetermined range of acceptable values.
• the claimed calibration device 100 provides certain other advantages with respect to the manufacture and calibration of conductivity sensors 118 for aqueous solutions. As explained above, in alternate embodiments of the invention, these advantages may also be realized with respect to the manufacture and calibration of pH sensors or DO sensors. Specifically, the claimed system and method reduces the cost of calibration, improves the lead time to customers, increases yield, and reduces the risk of contaminating the product from calibration process. Further, the calibration device 100 improves the accuracy and tolerance of sensor specifications through more consistent calibration.

Landscapes

• General Physics & Mathematics (AREA)
• Physics & Mathematics (AREA)
• Chemical & Material Sciences (AREA)
• Health & Medical Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Analytical Chemistry (AREA)
• Biochemistry (AREA)
• General Health & Medical Sciences (AREA)
• Immunology (AREA)
• Pathology (AREA)
• Molecular Biology (AREA)
• Investigating Or Analyzing Materials By The Use Of Electric Means (AREA)
• Measurement Of Resistance Or Impedance (AREA)

Priority Applications (7)

Applications Claiming Priority (2)

Related Child Applications (1)

Publications (1)

Family

ID=76959078

Family Applications (1)

Country Status (8)

Citations (5)

Family Cites Families (13)

• 2021
  • 2021-06-22 JP JP2022575766A patent/JP7836771B2/ja active Active
  • 2021-06-22 CN CN202180041735.7A patent/CN116018514A/zh active Pending
  • 2021-06-22 KR KR1020227043378A patent/KR20230025397A/ko active Pending
  • 2021-06-22 EP EP21742968.7A patent/EP4168787A1/en active Pending
  • 2021-06-22 MX MX2022016349A patent/MX2022016349A/es unknown
  • 2021-06-22 WO PCT/US2021/038346 patent/WO2021262630A1/en not_active Ceased
  • 2021-06-22 CA CA3181073A patent/CA3181073A1/en active Pending
• 2022
  • 2022-12-14 US US18/066,147 patent/US12298333B2/en active Active

Patent Citations (5)

Also Published As

Similar Documents

Legal Events