Solution-free sensor calibration

Abstract

A calibration device for a conductivity sensor for aqueous solutions, the calibration device including a first connector configured to electrically couple to sensor electrodes of the conductivity sensor. The connector is further configured to provide a controlled voltage application between 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 characteristics 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] The present invention generally relates to systems and methods for calibrating conductivity sensors for aqueous solutions, or any electrochemical sensor technology that senses changes in potential (voltage) or electron loss / gain and converts them into measurements of conductivity, pH, dissolved oxygen (DO), or other applicable responses.

Background Art

[0002] The conductivity of an aqueous solution is a measure of the ability of water to conduct an electric current. The more ions present in the solution, the higher its conductivity. Temperature also affects conductivity. As the temperature of the solution increases, correspondingly, the solubility of the materials dissolved in the solution increases, resulting in an increase in conductivity.

[0003] For electricity to flow, the movement of charged particles (e.g., ions) is required. In solid NaCl or KCl crystals, no electric current flow occurs. Although this solid is composed of ions, these are held very tightly within the crystal lattice, so no current flows. However, in an aqueous solution, these ions can move, allowing for the flow of electricity.

[0004] In conventional manufacturing processes for aqueous solution conductivity sensors, in order to calibrate the sensor, the conductivity solution needs to be within a certain acceptable conductivity and temperature range. There are several problems to ensure that these requirements are met during sensor calibration. For example, the conductivity of the conductivity solution can be very variable, and in some cases, conductivity fluctuations are observed after replenishing the conductivity solution from set to set. Furthermore, it can be difficult to maintain a relatively constant solution temperature during calibration without fluctuations (i.e., due to adjustments in the water bath temperature).

[0005] Furthermore, proper sensor calibration may depend on the accuracy of reference third-party conductivity and temperature probes. Routine external calibration of third-party probes is necessary to maintain specifications. However, in many cases, when multiple third-party probes are compared to each other, they do not agree with one another in terms of temperature or conductivity readings.

[0006] In many conventional calibration devices, temperature loss occurs along the sensor chain, which can be difficult to control. Typically, the conductivity solution must be unused and NIST certified. After calibration, the sensor must be thoroughly cleaned, which increases the cost and manufacturing time of conventional conductivity sensors. Furthermore, a stabilization time is required for the sensor body and conductivity solution to reach the required temperature. This may necessitate constant monitoring of the sensor and solution temperature by the operator.

[0007] As a result of the aforementioned problems, in some cases, the calibration pass rate for newly manufactured conductivity sensors can be as low as 25-30% in the first calibration trial. [Overview of the project] [Problems that the invention aims to solve]

[0008] Embodiments of the present invention relate to a system and method for calibrating conductivity sensors for aqueous solutions, addressing many of the problems described above. The above and other advantages of the present invention, as well as further features of the present invention, will become apparent from the description of the invention provided herein. [Means for solving the problem]

[0009] In one embodiment, an embodiment of the present invention provides a calibration device for a conductivity sensor for aqueous solutions. The calibration device includes a first connector configured to be electrically coupled to the sensor electrodes of the conductivity sensor. The connector is further configured to provide the application of a controlled voltage between 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 flow between the at least two sensor electrodes reproduces the characteristics of an electrochemical calibration solution.

[0010] In a particular embodiment, the calibration device has a second connector connected to the resistor and also to a conductivity monitor. In a particular embodiment, 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 the first resistor, a second resistor, and a third resistor, where each of the three resistors is coupled between two different of the four sensor electrodes. In a particular embodiment, the resistance value of the first resistor is 40.2 ohms, and the resistance values ​​of the second and third resistors are each 221 ohms.

[0011] In another embodiment of the present invention, the resistance of the first resistor is 38 to 42 ohms. In a more specific embodiment, the resistance of the first resistor is 40.2 ohms. The calibration device may further include a temperature calibration circuit configured to simulate a 25°C environment for the conductivity sensor to be calibrated. In some embodiments, the temperature calibration circuit includes a switching element coupled to a pair of resistors. In a specific embodiment, one of the pair of resistors has a resistance of 200 to 300 ohms, and the second of the pair of resistors has a resistance of 1.5 to 2.5 kilohms. In a more specific embodiment, one of the pair of resistors has a resistance of 226 ohms, and the second of the pair of resistors has a resistance of 2.1 kilohms. The calibration device may further include terminals configured for connection to an external power supply.

[0012] In another embodiment, 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 between two electrodes of the conductivity sensor to reproduce the characteristics of an electrochemical calibration solution; measuring a current flowing between the two electrodes; and determining whether the conductivity sensor is well calibrated based on whether the measured current is within a predetermined range.

[0013] In some embodiments, the method further includes the step of connecting a resistor between two electrodes. The method may also include the step of providing a resistor network to which at least one resistor is connected to each of the multiple electrodes of the conductivity sensor. Furthermore, embodiments of the method require the step of simulating a 25°C environment for the conductivity sensor to be calibrated.

[0014] A particular embodiment of the above method includes the step of 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 further require the step of connecting the calibration device to a temperature calibration circuit for simulating a 25°C environment for the conductivity sensor to be calibrated.

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

[0016] A particular embodiment of the present invention includes a calibration device for a conductivity sensor for aqueous solutions, the calibration device applying a controlled external voltage between two sensor electrodes, or, in an alternative embodiment, supplying current between two sensor electrodes having a series of resistors and / or capacitors to reproduce the characteristics of an electrochemical calibration solution, thereby eliminating the need for direct contact between the solution and the sensor electrodes during the calibration process.

[0017] Other aspects, purposes, and advantages of the present invention will become further apparent from the following "Modes for Carrying Out the Invention" when interpreted in conjunction with the accompanying drawings.

[0018] The accompanying drawings incorporated herein and forming part thereof illustrate several aspects of the present invention and serve to illustrate the principles of the present invention in conjunction with this description. [Brief explanation of the drawing]

[0019] [Figure 1] Figure 1 is a perspective view of a calibration device according to one embodiment of the present invention. [Figure 2] Figure 2 is a schematic diagram showing a resistor network used in the calibration device of Figure 1 according to one embodiment of the present invention. [Figure 3] Figure 3 is a schematic diagram showing how a resistor network is coupled to the first and second connectors according to one embodiment of the present invention. [Figure 4] Figure 4 is a schematic diagram of a temperature calibration circuit used in the calibration device shown in Figure 1, according to one embodiment of the present invention. [Figure 5] Figure 5 is a schematic diagram of a calibration device used in a conductivity sensor according to one embodiment of the present invention. [Modes for carrying out the invention]

[0020] The present invention will be described with respect to specific preferred embodiments, but the intention is not to limit the present invention to these embodiments. Rather, it is intended to embrace all alternatives, modifications, and equivalents that fall within the spirit and scope of the present invention as defined by the appended claims.

[0021] In certain embodiments, the present invention includes a conductivity sensor for an aqueous solution that aids in a calibration process without using a solution by applying a controlled external voltage between two of a plurality of sensor electrodes. In embodiments of the present invention, the controlled external voltage is a constant voltage, which can be provided by an external power source. In alternative embodiments, a current may be supplied between these two electrodes. The above-described sensor electrodes may have a series of resistors and / or capacitors for reproducing 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.

[0022] The embodiments of the present invention described herein relate to conductivity sensors, but those skilled in the art will recognize that the techniques and scope of the present invention can be equally applied to any other applications involving the measurement of pH and / or dissolved oxygen, or the sensing of changes in potential (voltage) or electron loss / gain.

[0023] The relationship between current and voltage at a specific nominal conductivity can generally be characterized in the manner shown below. The sensor resistance is related to the conductivity reading as follows: Conductivity = (Ic - Im) / V; where Ic is the raw current from an Analog to Digital Converter (ADC); Im is the zero-level excitation current; V is the raw voltage from an Analog to Digital Converter (ADC).

[0024] As used herein, “zero level of excitation current” refers to the small current that flows through the primary winding of a transformer when a normal voltage is applied to the primary winding terminals while the terminals of the secondary winding are open. This current is called the transformer excitation current and is always present while the transformer is operating. The excitation current is necessary to maintain the magnetic field inside the transformer core and is largely independent of the load on the secondary winding.

[0025] In a specific example of conventional calibration of conductivity sensors, a single-point calibration may be performed using a solution with a conductivity of 12.88 millisiemens (mS). In this example, when the voltage is 33,872 ± 1,069 volts and the current is 394,871 ± 53,662 milliamperes, the conductivity is read as 12,880 microsiemens (μS) or 12.88 millisiemens (mS). For a well-calibrated sensor to be indicated, the current level sensed and measured by the conductivity monitor when a voltage is applied must be within the range of 394,871 ± 53,662 milliamperes. • The voltage is controlled to 12880 μS (from the table). The conductivity is nominally 12880 μS.

[0026]

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[0027] An unexpectedly high current value may indicate a problem with the calibration equipment or conductivity sensor, requiring further inspection.

[0028] With respect to the present invention, the conductivity calibration process was designed as an alternative to calibration using a solution having a known conductivity of 12.88 millisiemens (mS) at 25°C. However, as described above, modifications of this process can be used as an alternative to conventional calibration processes for pH sensors or DO sensors. To achieve this for conductivity, the claimed system operates to simulate the properties of a solution of known conductivity. The claimed system and method enable a more controlled and repeatable calibration process (at ambient room temperature), in contrast to the processes of existing calibration devices that require the use of a known 12.88 mS solution in a temperature-controlled chamber at 25°C.

[0029] Figure 1 is a perspective view of the calibration device 100. As shown in Figure 1, the calibration device 100 does not include a housing, but commercially available embodiments of the device 100 are expected to be housed within a housing. The embodiment of the calibration device 100 shown in Figure 1 includes a circuit board 102, which is configured to be connected to a conductivity sensor on a first side of the circuit board 102 and to a conductivity monitor (not shown) on a second side of the circuit board 102 opposite to the first side. However, in alternative embodiments of the present invention, it is conceivable that the sensor and monitor could be connected to the same side of the circuit board 102. In alternative embodiments of the present invention, the circuit board 102 is configured to be connected to a pH sensor, a DO sensor, etc.

[0030] The calibration device 100 achieves the above objectives by utilizing two subcircuits. One passive subcircuit is for conductivity, and one active subcircuit is for temperature compensation. The passive conductivity subcircuit consists of a resistance network corresponding to a conductivity of 12.88 mS, which will be described in more detail below. During the calibration process, the resistance network is connected to the electrode signal line of the conductivity sensor. This generates a conductivity feedback response corresponding to 12.88 mS, which is returned to the conductivity monitor.

[0031] In a particular embodiment, the conductivity sensor is connected to the circuit board 102 via a first connector 104, and the conductivity monitor is connected to the circuit board 102 via a second connector 106. Although the conductivity monitor is not shown, those skilled in the art will recognize that it is used to enable determination of good calibration of the conductivity sensor by detecting the current flowing between the electrodes of the sensor via its connection to the second connector 106. The conductivity sensor also controls the voltage applied to the conductivity sensor electrodes to initiate the operation of the temperature calibration circuit described below.

[0032] In Figure 1, the first connector 104 and the second connector 106 are covered with caps 108 to protect the connector terminals when not in use. The calibration device 100 includes a resistor network having three resistors: R1 110, R3 112, and R5 114 connected between the conductivity monitor and the conductivity sensor. In one specific embodiment of the present invention, the resistance of R1 is 221 ohms, the resistance of R3 is 40.2 ohms, and the resistance of R5 is 221 ohms.

[0033] Figures 2 and 3 are schematic diagrams of a circuit configuration used in a calibration device 100 according to one embodiment of the present invention. Figures 2 and 3 show the resistor network described above, having three resistors R1 110, R3 112, and R5 114. As shown in Figure 3, the three resistors R1 110, R3 112, and R5 114 are coupled to a first connector 104 connected to a conductivity sensor and also to a second connector 106 connected to a conductivity monitor.

[0034] The resistor network arranged as shown in Figures 2 and 3 helps to form the claimed conductivity calibration system and method, which in this embodiment simulates 12.88 mS liquid using these specific resistors arranged across the excitation (EX+ / -) and sensing (SN+ / -) EX+, SN+, SN-, and EX- signal lines. In a particular embodiment, each of these four signal lines is connected to the sensor electrode 120 of the conductivity sensor 118 (see Figure 5). Figures 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- and SN-. Resistor R3 112, with an exemplary value of 40.2 ohms, is connected between SNS- and SNS+. A resistor R5 114 with an exemplary value of 221 ohms is connected between SNS+ and EX-.

[0035] Since conductivity is temperature-dependent, one of the requirements for good calibration of conductivity sensors relates to the temperature stability of the sensor body. Ideally, conductivity sensors should be stored for a long period of time at 25°C inside a temperature-controlled system, and the temperature of all conductivity sensors should be observed to be stable (e.g., a thermal camera should show temperature uniformity).

[0036] Figure 4 is a schematic diagram of a temperature calibration circuit 140 used in a calibration device 100 according to one embodiment of the present invention. The temperature calibration circuit 140 simulates a 25°C environment by applying a temperature resistor network to a serial data (SDA) signal line 142 during calibration. In one particular embodiment of the present invention, the resistor network includes two resistors: R17 144 and R19 146. In one specific embodiment, the resistance of R17 144 is 226 ohms and the resistance of R19 146 is 2.1 kilohms. A switch component U3 148 shown in Figure 4 is triggered by a conductivity monitor (see pins 15 and 10 of U3) during calibration to apply the temperature calibration circuit 140. The temperature calibration circuit 140 targets 25°C in order to effectively "trick" the sensor to believe that it is at 25°C during calibration.

[0037] In a specific embodiment, during the calibration process, the active sub-circuit, namely the temperature calibration circuit 140, is the temperature calibration circuit of the conductivity sensor under test. to This applies a firmware-controlled voltage bias. This is the temperature calibration circuit for the conductivity sensor during testing. to The system responds with a voltage corresponding to 25°C, which is most commonly associated with ambient room temperature. In a particular embodiment, the voltage bias signal is delivered via a second connector 106, and the voltage is controlled by firmware within the conductivity monitor. This allows for precise timing settings for applying temperature compensation during sensor calibration and removing the temperature compensation before writing the calibration offset value to the conductivity sensor's non-volatile memory.

[0038] In the tests, the temperature calibration method described above using the temperature calibration circuit 140 proved effective, as units calibrated using this method were found to have a standard deviation percentage equivalent to or better than that of conductivity sensors calibrated using conventional methods. After calibration, each conductivity sensor is given a unique calibration factor (CF) and temperature offset (TO) value applied to the read output (conductivity reading). The operator then observes the expected CF and TO values ​​as indicators to classify the conductivity sensor as pass or fail after calibration. Failed sensors are typically separated and inspected, and their final disposal is determined.

[0039] Figure 5 is a schematic diagram of a calibration device 100 used in a conductivity sensor 118 according to one embodiment of the present invention. A schematic diagram of the calibration device 100 is shown, where the calibration device 100 is connected to four electrodes 120 of the conductivity sensor 118. Alternative embodiments of the calibration device 100 may have fewer than four or five or more electrodes 120. In the embodiment of Figure 5, the calibration device 100 is powered by an external power supply 152. electric Power is supplied, but an alternative embodiment of the calibration device 100 is, for example, a battery. electric It is assumed that power will be supplied.

[0040] As shown in Figure 5, 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 can be a useful function because the spacing between the electrodes (i.e., diameter, height, and distance) is important in the conductivity sensor 118. If the electrodes 120 are too close together, the current will arc between the electrodes 120, resulting in errors in the readings. If the electrodes 120 are too far apart, the current will not flow effectively between the electrodes 120, resulting in errors in the readings.

[0041] In the tests, this conductivity calibration method proved effective. Conductivity sensors 118 calibrated by the solution-free method described herein reported conductivity values ​​that were in general agreement with sensors calibrated by conventional methods. Overall, the tests confirmed that conductivity sensors 118 perform comparably to or better than conductivity sensors calibrated by conventional methods.

[0042] Therefore, as described above, by applying a controlled external voltage to at least two of the multiple sensor electrodes 120 of the conductivity sensor 118 (which has a series of resistors), the solution-free calibration device 100 replicates the current carried by a conductivity solution, thereby eliminating the need for an actual solution when calibrating the conductivity sensor 118. The current can then be measured with a conductivity monitor to determine whether the sensor 118 is within a predetermined range of acceptable values.

[0043] Furthermore, it can be confirmed that the claimed calibration device 100 provides other specific advantages relating to the manufacture and calibration of conductivity sensors 118 for aqueous solutions. As described above, in alternative embodiments of the present invention, these advantages can also be realized relating to the manufacture and calibration of pH sensors or DO sensors. Specifically, the claimed system and method reduce calibration costs, improve lead times to customers, increase yield, and reduce the risk of product contamination by the calibration process. In addition, the calibration device 100 improves the accuracy and tolerances of sensor specifications through more consistent calibration.

[0044] All references herein, including publications, patent applications, and patents, are incorporated herein by reference in the same way as if they were included herein, when each reference is indicated to be incorporated individually and specifically by reference.

[0045] In the context describing the present invention (particularly in the context of the following claims), the use of the terms “a, an,” “the,” and similar indicators shall be construed as encompassing both singular and plural unless otherwise specifically indicated herein or expressly refuted by the context. The terms “comprising,” “having,” “including,” and “containing” shall be construed as non-restrictive terms (i.e., “including, but not limited to”) unless otherwise specifically indicated herein. The enumeration of value ranges herein is intended merely as a simplified way of referring individually to each of the individual values ​​within that range unless otherwise specifically indicated herein, and each individual value is incorporated herein as if it were individually described herein. All methods described herein may be carried out in any preferred order unless otherwise specifically indicated herein or expressly refuted by the context. Any examples or illustrative phrases provided herein (e.g., "such as") are intended solely to further illustrate the invention and, unless otherwise claimed, do not limit the scope of the invention. Nothing in this specification should be construed as indicating that any element not covered by the claims is essential for the practice of the invention.

[0046] Preferred embodiments of the Invention, including the best mode known to the inventors with respect to the implementation of the Invention, are described herein. Modifications of these preferred embodiments may be apparent to those skilled in the art by reading the above description. The inventors expect that those skilled in the art will appropriately adopt these modifications, and they intend that the Invention may be implemented in ways other than those specifically described herein. Accordingly, the Invention includes all modifications and equivalents of the subject matter enumerated in the claims appended herein, as permitted by applicable law. Furthermore, unless otherwise specifically indicated herein or expressly rejected by the context, any combination of the above elements in all possible variations is encompassed in the Invention.

Claims

1. A calibration device for a conductivity sensor for aqueous solutions, wherein the calibration device is A first connector configured to be electrically coupled to the sensor electrodes of the conductivity sensor, the first connector further configured to provide a voltage between at least two of the sensor electrodes; A first resistor connected between the at least two sensor electrodes and coupled to the first connector, the first resistor having a value such that when the voltage is applied between the at least two sensor electrodes, the current flow between the at least two sensor electrodes reproduces the characteristics of the electrochemical calibration solution; and A temperature calibration circuit that applies a voltage bias to another temperature calibration circuit of the conductivity sensor to be calibrated via a second connector connected to the first resistor and also connected to a conductivity monitor, wherein the temperature calibration circuit of the conductivity sensor responds with a voltage corresponding to a room temperature of 25°C. A calibration device equipped with [a specific feature / feature].

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

3. The calibration device according to claim 2, wherein the resistance value of the first resistor is 40.2 ohms, and the resistance values ​​of the second and third resistors are each 221 ohms.

4. The calibration device according to claim 1, wherein the resistance value of the first resistor is 40.2 ohms.

5. The calibration device according to claim 1, wherein the temperature calibration circuit includes a pair of resistors connected in series and a switching element coupled to the pair of resistors, one end of one of the resistors of the pair is coupled to a common terminal of the switching element, and the other end of one of the resistors of the pair is coupled to the other common terminal of the switching element.

6. The calibration device according to claim 5, wherein one of the pair of resistors has a resistance of 226 ohms, and the second resistor of the pair has a resistance of 2.1 kiloohms.

7. The calibration device according to claim 1, wherein power is supplied from an external power source located outside the calibration device.

8. A method for calibrating a conductivity sensor for aqueous solutions: The step of connecting a resistor between the two electrodes of the conductivity sensor, The reproduction step involves applying a voltage between the two electrodes of the conductivity sensor to reproduce the characteristics of an electrochemical calibration solution, the reproduction step comprising connecting a calibration device having a temperature calibration circuit to the conductivity sensor and applying a voltage bias to another temperature calibration circuit of the conductivity sensor via a connector connected to the resistor and also connected to a conductivity monitor, the voltage bias causing the other temperature calibration circuit of the conductivity sensor to respond with a voltage corresponding to room temperature of 25°C; A step of measuring the current flowing between the two electrodes; and A step to determine whether the conductivity sensor is properly calibrated based on whether the measured current is within a predetermined range. Methods that include...

9. The method according to claim 8, further comprising the step of providing a resistor network to which at least one resistor is connected to each of a plurality of electrodes of the conductivity sensor, wherein the resistor network comprises a plurality of resistors.

10. The method according to claim 8, wherein the step of applying a voltage between two electrodes of the conductivity sensor to reproduce the properties of an electrochemical calibration solution includes connecting a calibration device to a plurality of electrodes of the conductivity sensor, the calibration device including one or more resistors coupled to each of the plurality of electrodes.

11. A method for calibrating a conductivity sensor: a. A step of reproducing the characteristics of an electrochemical calibration solution by connecting a resistor between the two electrodes of the conductivity sensor and further applying a voltage between the two electrodes of the conductivity sensor, wherein the step of reproducing the characteristics of an electrochemical calibration solution by applying a voltage comprises connecting a calibration device having a temperature calibration circuit to the conductivity sensor, applying a voltage bias to another temperature calibration circuit of the conductivity sensor being calibrated via a connector connected to the resistor and also connected to a conductivity monitor, and causing the other temperature calibration circuit of the conductivity sensor to respond to the voltage bias with a voltage corresponding to room temperature of 25°C; b. A step of sensing the current between the two electrodes; and c. A step of determining whether the conductivity sensor is well calibrated based on whether the sensed current is within a predetermined range indicating that the conductivity sensor is acceptable; Methods that include...

12. The method according to claim 11, wherein the step of applying the voltage includes the step of supplying power from an external power source located outside the calibration device.

13. The calibration device according to claim 1, wherein the temperature calibration circuit and the first resistor are arranged on the same circuit board.

14. The calibration device according to claim 2, wherein the temperature calibration circuit and the resistor network are arranged on the same circuit board.

15. The calibration device according to claim 1, wherein the temperature calibration circuit includes a network of two or more resistors connected in series, and a switch component coupled to the network of resistors, wherein one end of one of the resistors is coupled to a common terminal of the switch component, and the other end of one of the resistors is coupled to another common terminal of the switch component.

16. The calibration device according to claim 15, wherein the switch component is configured to be triggered by a conductivity monitor connected to a second connector of the calibration device.

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