Solutionless sensor calibration

Abstract

A calibration device for a conductivity sensor for an aqueous solution. The calibration device includes a first connector configured to electrically couple with sensor electrodes of the conductivity sensor. The connector is further configured to provide for application of a control 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 that causes a current between the at least two sensor electrodes to replicate a characteristic of an electrochemical calibration solution. In certain embodiments, the calibration device is configured for a pH sensor or a dissolved oxygen sensor.

Description

Technical Field

[0001] This invention generally relates to systems and methods for calibrating the following: conductivity sensors for aqueous solutions, or any electrochemical sensor technology that senses changes in potential (voltage) or loss / gain of electrons to convert them into measurements of conductivity, pH, dissolved oxygen (DO), or other applicable responses. Background Technology

[0002] In aqueous solutions, conductivity is a measure of water's ability to conduct electric current. The more ions in a solution, the higher its conductivity. Temperature also affects conductivity. As the solution temperature increases, the solubility of the material dissolved in the solution increases, and therefore the conductivity increases.

[0003] For an electric current to flow, the movement of charged particles (e.g., ions) is required. With solid NaCl or KCl crystals, there is no flow of electricity—although the solids are composed of ions, these ions are tightly held together within the crystal lattice and therefore no current flows. However, in aqueous solutions, these ions are mobile, allowing for the flow of an electric current.

[0004] Conventional manufacturing processes for aqueous conductivity sensors require the conductivity solution to be within a predetermined, permissible range of conductivity and temperature for sensor calibration. Several challenges exist related to ensuring these requirements are met during sensor calibration. For example, the conductivity of the conductivity solution can be highly variable, and in some instances, fluctuations in conductivity have been observed after inter-group updates. Furthermore, maintaining a relatively constant solution temperature during calibration without fluctuations (i.e., due to adjustments in the water bath temperature) can be difficult.

[0005] Furthermore, successful sensor calibration also depends on the accuracy of the third-party conductivity and temperature probes used for reference. Routine external calibration of these third-party probes is required to maintain specifications. However, in many instances, the third-party probes exhibit inconsistencies in temperature or conductivity readings when compared with each other.

[0006] In many conventional calibration setups, temperature loss occurs sequentially along the sensor chain, which can be difficult to control. Typically, the conductivity solution must be unused and NIST-certified. Thorough cleaning of the sensor is required after calibration, increasing the cost and manufacturing time of traditional conductivity sensors. Furthermore, the sensor body and conductivity solution require a necessary stabilization time to reach the desired temperature. This necessitates continuous operator monitoring of the sensor and solution temperatures.

[0007] Due to the aforementioned issues, in some cases, the calibration pass rate of newly manufactured conductivity sensors can be as low as 25-30% on the first calibration attempt.

[0008] Embodiments of the present invention relate to a system and method for calibrating conductivity sensors for aqueous solutions, which addresses several of the problems described above. These and other advantages of the invention, as well as additional inventive features, will become apparent from the description of the invention provided herein. Summary of the Invention

[0009] In one aspect, embodiments of the invention provide a calibration apparatus for a conductivity sensor for aqueous solutions. The calibration apparatus includes a first connector configured to electrically connect to sensor electrodes of the conductivity sensor. The connector is also configured to provide the application of a control 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 the current between the at least two sensor electrodes replicates the characteristics of an electrochemical calibration solution.

[0010] In a particular embodiment, the calibration device has a second connector that connects to a resistor and also to a conductivity monitor. In some embodiments, the first connector is configured to be electrically coupled to at least four sensor electrodes of the conductivity sensor, and the calibration device further includes a resistor network having a first resistor, a second resistor, and a third resistor, wherein each of the three resistors is coupled between two different of the four sensor electrodes. In a particular embodiment, the first resistor has a resistance value of 40.2 ohms, and the second and third resistors each have a resistance value of 221 ohms.

[0011] In another embodiment of the invention, the first resistor has a resistance value ranging from 38 to 42 ohms. In a more specific 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. In some embodiments, the temperature calibration circuit includes a switching element coupled to a pair of resistors. In a particular embodiment, one of the pair of resistors has a resistance value between 200 and 300 ohms, and the second of the pair of resistors has a resistance value between 1.5 and 2.5 kiloohms. In a more specific embodiment, one of the pair of resistors has a resistance value of 226 ohms, and the second of the pair of resistors has a resistance value of 2.1 kiloohms. The calibration device may also include terminals configured for connection to an external power supply.

[0012] In another aspect, embodiments of the present 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 the current flowing between the two electrodes; and determining whether the conductivity sensor has been successfully calibrated based on whether the measured current falls within a predetermined range.

[0013] In some embodiments, 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 the plurality of electrodes of the conductivity sensor. Further embodiments of the method require simulating a 25-degree Celsius environment for the conductivity sensor being calibrated.

[0014] Specific embodiments of the method include connecting a calibration device to multiple electrodes of a conductivity sensor. The calibration device includes one or more resistors coupled to each of the multiple electrodes. Furthermore, the method requires connecting the calibration device to a temperature calibration circuit for simulating a 25-degree Celsius environment for the conductivity sensor being calibrated.

[0015] In another aspect, embodiments of the present invention provide a method for calibrating a conductivity sensor. The method includes the steps of: applying a control voltage across two electrodes of the sensor, sensing a current across the two electrodes while maintaining the sensor at a control temperature, and calculating the conductivity of the sensor based on whether the sensed current falls within a predetermined range indicating that the sensor is passing through. Embodiments of the method include the step of: applying a constant voltage from an external power source.

[0016] Specific embodiments of the invention include a calibration apparatus for a conductivity sensor of an aqueous solution, wherein the calibration apparatus applies an external control voltage across two sensor electrodes or, in an alternative embodiment, supplies a current between the two sensor electrodes, the sensor electrodes having a series of set resistors and / or capacitors to replicate the characteristics of an electrochemical calibration solution, thereby eliminating the need for direct solution contact between the sensor electrodes and the calibration process.

[0017] Other aspects, objects, and advantages of the invention will become more apparent from the following detailed description when understood in conjunction with the accompanying drawings. Attached Figure Description

[0018] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several aspects of the invention and, together with the description, serve to elucidate the principles of the invention. In the drawings:

[0019] Figure 1 This is a perspective view of a calibration device according to an embodiment of the present invention;

[0020] Figure 2 This is a schematic diagram illustrating an embodiment of the present invention. Figure 1 The resistor network used in the calibration device;

[0021] Figure 3 This is a schematic diagram illustrating the connection method of the resistor network with the first and second connectors according to an embodiment of the present invention; and

[0022] Figure 4 According to an embodiment of the present invention, in Figure 1 A schematic diagram of the temperature calibration circuit used in the calibration device; and

[0023] Figure 5 This is a schematic diagram of a calibration device used in a conductivity sensor according to an embodiment of the present invention.

[0024] Although the invention will be described in conjunction with certain preferred embodiments, it is not intended to limit the invention to these embodiments. Rather, it is intended to cover all alternatives, modifications, and equivalents included within the spirit and scope of the invention as defined in the appended claims. Detailed Implementation

[0025] In a particular embodiment, the present invention includes a conductivity sensor for aqueous solutions, wherein an external control voltage is applied across two of a plurality of sensor electrodes to facilitate a solution-free calibration process. In embodiments of the invention, the external control voltage is a constant voltage, which may be provided by an external power source. In an alternative embodiment, a current may be supplied between the two electrodes. The aforementioned sensor electrodes may have a series of defined resistors and / or capacitors to replicate the characteristics 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.

[0026] Although the embodiments of the invention described herein are related to conductivity sensors, those skilled in the art will recognize that the techniques and scope of the invention are equally applicable to the measurement of pH and / or dissolved oxygen, or to any other application involving changes in sensing potential (voltage) or loss / gain of electrons.

[0027] The relationship between current and voltage under specific nominal conductivity conditions can be roughly characterized as follows. The sensor resistance is related to the conductivity reading, as follows:

[0028] Electrical conductivity = (Ic – Im) / V;

[0029] Where Ic is the raw current from the analog-to-digital converter (ADC);

[0030] Im is the zero-level excitation current; and

[0031] V is the raw voltage from the analog-to-digital converter (ADC).

[0032] As used herein, the "zero-level excitation current" refers to the small current flowing in the primary winding of a transformer when a normal voltage is applied to the primary winding terminals with the secondary winding terminals open. This current is called the transformer excitation current and flows continuously throughout the transformer's operation. The excitation current is necessary to maintain the magnetic field within the transformer core and is largely independent of the load on the secondary winding.

[0033] In a specific example of routine calibration of a conductivity sensor, single-point calibration can be performed using a 12.88 millisiemens (mS) conductivity solution produced in-production. In this example, when the voltage is 33,872 ± 1,069 volts and the current is 394,871 ± 53,662 mA, the conductivity reading is 12,880 microsiemens (μS) or 12.88 millisiemens (mS). The current level sensed and measured by the conductivity monitor when the voltage is applied should be within the range of 394,871 ± 53,662 mA to indicate a successfully calibrated sensor.

[0034] • The voltage is controlled to a reference of 12880μS (from the table).

[0035] • Nominal conductivity: 12880 μS.

[0036]

[0037]

[0038] IC-IM = 436.271A

[0039] A higher-than-expected current value indicates a potential problem with the calibration equipment or conductivity sensor, requiring further investigation.

[0040] Referring to this invention, the conductivity calibration process is designed as an alternative to calibration using a solution with a known conductivity of 12.88 millisiemens (mS) at 25 degrees Celsius. However, as indicated above, a version of this process can also be used as an alternative to conventional calibration processes for pH or DO sensors. To achieve this in terms of conductivity, the claimed system is used to simulate the characteristics of a solution with a known conductivity. The claimed system and method allow for a more controlled and repeatable calibration setup process (at ambient room temperature), which is significantly different from existing calibration setup processes that require the use of a fluid with a known conductivity of 12.88 mS in a temperature-controlled chamber at 25 degrees Celsius.

[0041] Figure 1 This is a three-dimensional view of the calibration device 100. (Example) Figure 1 As shown, the calibration device 100 does not include a housing; however, it is envisioned that commercial embodiments of the device 100 will be housed within a housing. Figure 1 An embodiment of the calibration device 100 shown includes a circuit board 102 configured for connection to a conductivity sensor on one side of the circuit board 102 and a conductivity monitor (not shown) connected to a second side of the circuit board 102 opposite to the first side. However, it is contemplated that alternative embodiments of the invention may also allow the sensor and monitor to be connected to the same side of the circuit board 102. In alternative embodiments of the invention, the circuit board 102 is also configured for connection to a pH sensor, a DO sensor, etc.

[0042] The calibration device 100 achieves this by fully utilizing two sub-circuits: a passive sub-circuit for conductivity and an active sub-circuit for temperature compensation. The passive conductivity sub-circuit includes a resistive network equivalent to a conductivity of 12.88 mS, which will be described in more detail below. During the calibration process, the resistive network is connected to the electrode signal lines of the conductivity sensor. This produces a conductivity feedback response equivalent to 12.88 mS returned to the conductivity monitor.

[0043] In a particular embodiment, a conductivity sensor is connected to circuit board 102 at a first connector 104, while a conductivity monitor is connected to circuit board 102 at a second connector 106. Although the conductivity monitor is not shown, those skilled in the art will recognize that it is used to detect the current flowing between the electrodes of the sensor through its connection to the second connector 106, thereby allowing for the determination of successful calibration of the conductivity sensor. The conductivity sensor also controls the voltage applied to the electrodes of the conductivity sensor, as well as the operation of the temperature calibration circuitry described below.

[0044] exist Figure 1 In the first connector 104 and the second connector 106, a cap 108 is used to protect the connector terminals when not in use. The calibration device 100 includes a resistor network having three resistors connected between the conductivity monitor and the conductivity sensor: R1 110, R3 112, and R5 114. In a particular embodiment of the invention, R1 has a resistance of 221 ohms, R3 has a resistance of 40.2 ohms, and R5 has a resistance of 221 ohms.

[0045] Figure 2 and Figure 3 This is a schematic diagram of a circuit used in a calibration device 100 according to an embodiment of the present invention. Figure 2 and Figure 3 The resistor network described above, consisting of three resistors R1 110, R3 112, and R5 114, is shown. Figure 3 As shown, three resistors R1 110, R3 112 and R5 114 are connected to a first connector 104 and also to a second connector 106. The first connector is connected to a conductivity sensor and the second connector is connected to a conductivity monitor.

[0046] according to Figure 2 and Figure 3 The resistor network arranged as shown helps to form the claimed conductivity calibration system and method, which in this embodiment utilizes these specific resistors placed across the excitation (EX+ / -) and sensing (SN+ / -) EX+, SN+, SN-, and EX- signal lines to simulate a fluid of 12.88 mS. In a particular embodiment, each of these four signal lines is connected to the sensor electrode 120 of the conductivity sensor 118 (see [link to relevant documentation]). Figure 5 ). Figure 2 and Figure 3 This diagram illustrates how three resistors, R1 110, R3 112, and R5 114, are connected across the signal lines. Resistor R1 110 (with an example value of 221 ohms) is connected between EX- and SNS-. Resistor R3 112 (with an example value of 40.2 ohms) is connected between SNS- and SNS+. Resistor R5 114 (with an example value of 221 ohms) is connected between SNS+ and EX-.

[0047] Since conductivity is temperature-dependent, one of the requirements for successfully calibrating a conductivity sensor is related to the temperature stability of the sensor body. Ideally, the conductivity sensors will be stored at 25 degrees Celsius for an extended period of time within a temperature control system, where each conductivity sensor is observed to be temperature stable (e.g., when a thermal camera displays temperature uniformity).

[0048] Figure 4 This is a schematic diagram of a temperature calibration circuit 140 used in a calibration apparatus 100 according to an embodiment of the present invention. During calibration, the temperature calibration circuit 140 simulates a 25-degree Celsius environment by applying a network of temperature resistors to a serial data line (SDA) signal line 142. In a particular embodiment of the invention, the resistor network includes two resistors: R17 144 and R19 146. In a particular embodiment, R17 144 has a resistance value of 226 ohms, and R19 146 has a resistance value of 2.1 kΩ. Figure 4The switch unit U3 148 shown is triggered during calibration by a conductivity monitor (see pins 15 and 10 of U3) to apply temperature calibration circuit 140. Temperature calibration circuit 140 targets 25 degrees Celsius to effectively "trick" the sensor into believing it is at 25 degrees Celsius during calibration.

[0049] In a particular embodiment, during the calibration process, an 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. This forces the temperature calibration circuit 140 of the conductivity sensor under test to respond with a voltage equivalent to 25 degrees Celsius, most commonly associated with ambient room temperature. In a particular embodiment, the voltage bias signal is delivered via a second connector 106, the voltage being controlled by firmware within the conductivity monitor. This allows for precise timing of applying temperature compensation during sensor calibration, as well as precise timing of removing the temperature compensation before writing the calibration offset value to the non-volatile memory of the conductivity sensor.

[0050] In testing, the temperature calibration method described above using the temperature calibration circuit 140 proved effective because units calibrated using this method were found to have the same or better percentage of standard deviation as conventionally calibrated conductivity sensors. After calibration, each of the conductivity sensors is given a unique calibration coefficient (CF) and temperature offset (TO) value, which are applied to the reading output (conductivity reading). The operator then observes the expected CF and TO values ​​as an indication of whether the conductivity sensor should be classified as "pass" or "fail" after calibration. Those that fail are typically distinguished and inspected for defects to determine their final disposal.

[0051] Figure 5 This is a schematic diagram of a calibration device 100 used in a conductivity sensor 118 according to an embodiment of the present invention. The schematic representation of the calibration device 100 is illustrated, wherein the calibration device 100 is connected to four electrodes 120 of the conductivity sensor 118. Alternative embodiments of the calibration device 100 may also have fewer or more than four electrodes 120. Figure 5 In one embodiment, power from an external power source 152 is supplied to the calibration device 100; however, alternative embodiments of the calibration device 100 are contemplated, for example, battery-powered.

[0052] like Figure 5As indicated, the connector portion of the calibration device 100 is configured to apply a control 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 is a useful feature because the electrode spacing (i.e., diameter, height, and distance) is important in the conductivity sensor 118. If the electrodes 120 are too close together, current will arc between the electrodes 120, leading to reading errors. If the electrodes 120 are too far apart, current will not be effectively carried between the electrodes 120, also resulting in reading errors.

[0053] In testing, the conductivity calibration method proved effective. The conductivity sensor 118, calibrated according to the solution-free method described herein, reported conductivity values ​​substantially consistent with conventionally calibrated sensors. Overall, the tests confirmed that the performance of the conductivity sensor 118 is as good as or better than that of conventionally calibrated conductivity sensors.

[0054] Therefore, as described above, by applying an external control voltage (using a set resistor) to at least two of the plurality of sensor electrodes 120 of the conductivity sensor 118, the solution-free calibration device 100 replicates the current carried by the conductivity solution—thus eliminating the need for a real solution when calibrating the conductivity sensor 118. The current can then be measured by a conductivity monitor to determine whether the sensor 118 falls within a predetermined range of acceptable values.

[0055] Furthermore, the claimed calibration apparatus 100 offers several additional advantages in the manufacture and calibration of the conductivity sensor 118 for aqueous solutions. As described above, these advantages can also be achieved in the manufacture and calibration of pH or DO sensors in alternative embodiments of the invention. Specifically, the claimed system and method reduce calibration costs, improve delivery cycles to customers, increase production volume, and reduce the risk of product contamination during the calibration process. Moreover, the calibration apparatus 100 improves the accuracy and tolerance of sensor specifications through more consistent calibration.

[0056] All references cited in this article, including publications, patent applications and patents, are hereby incorporated by reference as if each reference were individually and specifically indicated to be incorporated by reference and to elaborate in full in this article.

[0057] In the context of describing this invention (particularly in the context of the appended claims), the terms “a,” “this,” “the,” and similar pronouns shall be interpreted as including both the singular and plural, unless otherwise indicated herein or the context clearly contradicts. Unless otherwise stated, the terms “comprising,” “having,” “including,” and “including” shall be interpreted as open-ended terms (i.e., meaning “including but not limited to”). Unless otherwise indicated herein, the description of ranges of values ​​herein is intended only as a shorthand method of individually referring to each individual value falling within that range, and each individual value is incorporated into this specification as if it were described individually herein. All methods described herein may be practiced in any suitable order, unless otherwise indicated herein or the context clearly contradicts. The use of any and all examples or exemplary language (e.g., “for example”) provided herein is intended only to better illustrate the invention and does not constitute a limitation on the scope of the invention, unless otherwise required. No language in the specification should be construed as indicating any unclaimed element as necessary for the practice of the invention.

[0058] Preferred embodiments of the invention have been described herein, including the best mode known to the inventors for carrying out the invention. Variations of these preferred embodiments will become apparent to those skilled in the art upon reading the above description. The inventors expect those skilled in the art to adopt such variations as appropriate, and the inventors also intend that the invention be practiced in ways other than those specifically described herein. Accordingly, the invention includes all modifications and equivalents of the subject matter recited in the appended claims as permitted by applicable law. Furthermore, the invention also covers any combination of the foregoing elements in all possible variations thereof, unless otherwise indicated herein or otherwise obviously contradicted by the context.

Claims

1. A calibration apparatus for a conductivity sensor in aqueous solutions, the calibration apparatus being used for a solution-free calibration process, the calibration apparatus comprising: A first connector, configured to be electrically connected to the sensor electrodes of the conductivity sensor, is further configured to provide the application of a control voltage across at least two of the sensor electrodes. A first resistor, connected between the at least two sensor electrodes and coupled to a first connector, has a value such that the current between the at least two sensor electrodes replicates the characteristics of an electrochemical calibration solution. A second connector is connected to the resistor and also to the conductivity monitor; as well as A temperature calibration circuit configured to simulate a 25-degree Celsius environment for the conductivity sensor being calibrated; A voltage bias signal delivered via the second connector can be applied to the temperature calibration circuit of the conductivity sensor under test, the voltage being controlled by firmware within the conductivity monitor.

2. The calibration apparatus according to claim 1, wherein, The first connector is configured to be electrically connected to at least four sensor electrodes of the conductivity sensor, and the calibration device further includes a resistor network having a first resistor, a second resistor, and a third resistor, wherein each of the three resistors is connected between two different of the four sensor electrodes.

3. The calibration apparatus according to claim 2, wherein, The first resistor has a resistance of 40.2 ohms, and the second and third resistors each have a resistance of 221 ohms.

4. The calibration apparatus according to claim 1, wherein, The first resistor has a resistance value ranging from 38 to 42 ohms.

5. The calibration apparatus according to claim 4, wherein, The first resistor has a resistance of 40.2 ohms.

6. The calibration apparatus according to claim 1, wherein, The temperature calibration circuit includes a switching element connected to a pair of resistors.

7. The calibration apparatus according to claim 6, wherein, One of the resistors in the pair has a resistance value between 200 and 300 ohms, and the second resistor in the pair has a resistance value between 1.5 and 2.5 kiloohms.

8. The calibration apparatus according to claim 6, wherein, One of the resistors in the pair has a resistance of 226 ohms, and the second resistor in the pair has a resistance of 2.1 kiloohms.

9. The calibration apparatus of claim 1 further includes a terminal configured for connection to an external power source.

10. The calibration apparatus according to claim 6, wherein, The switching element is configured to be triggered by a conductivity monitor.

11. The calibration apparatus according to claim 10, wherein, The temperature calibration circuit is configured to simulate a 25-degree Celsius environment during calibration by applying a network of temperature resistors, including the pair of resistors, to a serial data line connected to the conductivity monitor.

12. A method for calibrating a conductivity sensor for aqueous solutions, comprising the following steps: The calibration device according to any one of claims 1 to 11 is connected to at least two sensor electrodes of the conductivity sensor, thereby connecting the first resistor between the at least two sensor electrodes; A voltage is applied across the two electrodes of the conductivity sensor to replicate the properties of the electrochemical calibration solution; Measure the current flowing between the two electrodes; as well as Whether the conductivity sensor has been successfully calibrated is determined based on whether the measured current falls within a predetermined range.

13. The method according to claim 12, wherein, Applying a voltage across the two electrodes of the conductivity sensor to replicate the properties of an electrochemical calibration solution involves connecting a resistor between the two electrodes.

14. The method of claim 12, further comprising providing a resistor network that connects at least one resistor to each of the plurality of electrodes of the conductivity sensor.

15. The method of claim 12, further comprising simulating a 25-degree Celsius environment for the calibrated conductivity sensor.

16. The method according to claim 12, wherein, Applying a voltage across the two electrodes of a conductivity sensor to replicate the properties of an electrochemical calibration solution involves connecting a calibration device to multiple electrodes of the conductivity sensor, the calibration device including one or more resistors coupled to each of the multiple electrodes.

17. The method according to claim 12, wherein, Connecting the calibration device to multiple electrodes of the conductivity sensor includes connecting the calibration device to a temperature calibration circuit that simulates a 25-degree Celsius environment for the conductivity sensor being calibrated.

18. A method for calibrating a conductivity sensor, comprising the following steps: The calibration device according to any one of claims 1 to 11 is connected to at least two sensor electrodes of the conductivity sensor, thereby connecting the first resistor between the at least two sensor electrodes; a. Apply a control voltage across the two electrodes of the sensor; b. Sensing the current across the two electrodes while maintaining the sensor at a controlled temperature; as well as c. Calculate the conductivity of the sensor based on whether the sensed current falls within a predetermined range indicating that the sensor has passed through.

19. The method according to claim 18, wherein, Applying a control voltage includes applying a constant voltage from an external power source.

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