Interface unit for coupling a probe to a measurement system

Abstract

The present disclosure relates to an interface unit comprising: an input for receiving an input voltage from an electrochemical measurement probe; a first transistor provided with a first insulated gate terminal coupled to the input, a first source terminal coupled to a first terminal of a first resistor and a first drain terminal coupled to a first terminal of a second resistor; a first operational amplifier provided with a first non-inverting input, a first inverting input and a first output; a second transistor provided with a second source terminal coupled to a second terminal of a third resistor and a second drain terminal coupled to a first terminal of a fourth resistor; a second operational amplifier provided with a second non-inverting input, a second inverting input and a second output; the first operational amplifier being arranged to provide a variable voltage to the first source terminal of the first transistor depending on a comparison between a reference voltage and a second resistor voltage in order to control an operating point of the first transistor.

Description

Technical Field

[0001] This disclosure relates to an interface unit for coupling an output to an input of a measurement system, wherein a measurement probe transmits a voltage generated by an electrode on the output, and the measurement system is used to process the voltage signal into a measurement value relating to at least one property of the process material when the electrode is in contact with the process material.

[0002] More specifically, the interface unit and the corresponding method allow measurement probes, such as ion-sensitive measurement probes, particularly pH measurement probes, oxygen measurement probes, CO2 measurement probes, or ozone measurement probes, to be coupled to the measurement system. Background Technology

[0003] For example, the monitoring and control of industrial processes in the chemical and pharmaceutical industries, the textile industry, the food and beverage industry, the paper and cellulose processing industry, or the water and wastewater treatment fields are based on the measured values ​​of process variables determined by means of appropriate measuring probes.

[0004] According to the "Process Measurement Solutions Catalog 2005 / 06", Mettler-Toledo GmbH, CH-8902 Urdorf, Swiss, pages 8 and 9, a complete measurement system consists of a housing, a measuring probe, a cable, and a measurement converter (also called a transmitter). The measuring probe is brought into contact with the process to be measured or monitored by means of the housing, for example, by immersing and holding the probe in the process material. The measuring probe is used to measure specific characteristics of the process. The measurement signal is transmitted to the transmitter via the cable, and the transmitter communicates with the process control system, converting the measurement signal into readable data. The selection of the measuring probe depends on the characteristics of the process material to be measured.

[0005] Measurement probes are frequently exposed to high temperatures (typically above 140°C). For example, in pharmaceutical, medical, or industrial food production environments, measurement probes may come into contact with materials or products that should not be contaminated by infectious agents. Therefore, autoclave sterilization is often required. In a typical application, a measurement probe undergoes 30 to 100 autoclave cycles throughout its lifespan. Measurement probes, such as ion-sensitive probes, typically carry current through their sensing elements, which is inherent to their functional principle. The higher the temperature, the lower the resistance of the sensing element. For example, when the temperature reaches or exceeds 100°C, the glass resistance of the sensing element in a pH measurement probe drops sharply.

[0006] To amplify the voltage of the measured signal to a suitable level, the output of the sensing element of the measurement probe is typically coupled to an input stage circuit equipped with an operational amplifier. This solution is disclosed, for example, in US7,177,127B2, EP 2861975B, EP 0922 955A2, or in Ryan Edwards’ “Ion Selective Electrodes Interface – Sparky’s Widgets” (April 21, 2017), retrieved from the internet URL https: / / www.sparkyswidgets.com / portfolio-item / ion-selective-electrode-interface / . Under normal operation, the impedance of the input stage circuit is high when it is powered on. In contrast, when the input stage circuit is powered off and / or in a de-energized state, the impedance drops to a low level, typically less than 1 kOhm (kΩ). When the input stage circuitry switches to zero current (typically during high-temperature processes), the input stage is unpowered due to the low impedance of the operational amplifier, causing a rise in residual current between the sensing element and the input stage circuitry. This rapid increase in current through the sensing element can reach dangerous levels, leading to very slow signal drift and persistent damage to the sensor.

[0007] At temperatures above 100 degrees Celsius, the significant reduction in the isolation characteristics of the semiconductors used for electrostatic discharge (ESD) protection in operational amplifiers further complicates the problem. In such conditions, the ESD protection diodes in the operational amplifier may even cause a short circuit.

[0008] These issues are more critical for sensing elements equipped with active voltage sources (such as solid-state pH sensors).

[0009] A partial solution to the aforementioned current leakage problem is known from EP 1 010 249B1, which connects active sensing elements to the input stage circuitry of a measurement system. However, these types of input stages do not allow connection of probes that transmit sensing voltages varying over a wide range (typically between 0.25 and 5.5 volts) without introducing significant saturation and / or distortion problems into the output signal. Furthermore, known input stages are susceptible to variations in the manufacture of electronic components, introducing measurement errors.

[0010] This is why an improved interface unit is still needed to couple the output voltage of the sensor element of a measurement probe (e.g., a potentiometric probe such as an ion-sensitive measurement probe) to the input of a measurement system for processing the output voltage into a measurement value. The output voltage of the sensor element varies over a wide range of values, typically between 0.25 and 5.5 volts, and the current flowing through the sensing element is particularly low, typically below 1 pA—especially when temperatures reach high levels, typically starting from 100 degrees Celsius, and / or when the input stage circuitry is in a de-energized, off-state state, particularly when the sensing element is equipped with an active voltage source such as a solid-state pH sensor, while maintaining the measurement accuracy despite the combined negative impacts of high temperatures and low impedance of the input stage circuitry. Summary of the Invention

[0011] Therefore, according to a first aspect, the present invention relates to an interface unit including an input section adapted to receive an input current having an input voltage from an electrochemical measurement probe for contacting a process material.

[0012] The electrochemical measurement probe includes an electrode with a sensing element arranged to generate a sensor voltage. When the electrode is in contact with a process material, the electrode voltage is related to at least one property of the process material.

[0013] Electrochemical measurement probes are, for example, potentiometric probes. More specifically, electrochemical measurement probes can be selected from a non-exhaustive group, which includes pH measurement probes, oxygen measurement probes, CO2 measurement probes, and ozone measurement probes.

[0014] Under typical operating conditions, the impedance of the sensing element is, for example, between about 500 MOhm and about 20 GOhm, depending on the temperature.

[0015] The sensing element of the electrode may include an active layer that acts as a voltage source, so that the electrode voltage is not zero even when the electrode is not in contact with the process material.

[0016] For example, the electrode may include a solid-state pH sensor comprising an active layer that acts as a voltage source. The electrode may include an ion-sensitive pH glass substrate and multiple layers on top of said ion-sensitive pH glass substrate. These layers may include a base lithium layer, a lithium phosphorus oxynitride (LiPON) layer, and a protective layer adapted to limit the degradation of the lithium layer and provide an encapsulation structure for stabilizing the entire glass electrode and protecting it from environmental influences. Even when the glass electrode is not in contact with the process material, the potential of the glass electrode of the measuring probe is not zero (non-null).

[0017] The interface unit also includes an output section suitable for coupling to the input of an evaluation device. For example, the evaluation device functions as a measurement converter and is coupled to a processing device, such as a computer. Under typical operating conditions, the input impedance of the evaluation device is very low, for example, between approximately 100 kOhm and 10 MOhm.

[0018] The interface unit is arranged to transmit an output current with an output voltage substantially equal to the input voltage at the output section. For example, the offset voltage between the input voltage and the output voltage of the interface unit can be less than or equal to + / - 10mV. Regardless of the input voltage, the offset voltage remains substantially constant within the normal temperature range reached by the sensor coupled to the interface unit—typically from about 0°C to about 100°C.

[0019] In an advantageous embodiment, the electronic specifications of the electrical components of the interface unit are set, more specifically, the tolerances of the electronic components, such as the nominal value tolerance of resistors, are set such that the tolerance of the difference between the output voltage and the input voltage of the interface unit is at least equal to or less than + / - 0.1%. Therefore, the offset voltage between the input voltage and the output voltage of the interface unit can be less than or equal to + / - 2mV. Regardless of the input voltage, the offset voltage remains substantially constant within the normal temperature range reached by the sensor coupled to the interface unit, typically from about 0°C to about 100°C.

[0020] Advantageously, the interface unit may include a device for adjusting the output voltage by compensating for the offset voltage. Since the offset voltage remains substantially constant over the normal temperature range reached at the sensor coupled to the interface unit and is independent of the input voltage, a calibration step can be performed once and stored in the interface unit. More specifically, the interface unit can be calibrated after assembly. For this purpose, a precisely measured and stable calibration signal can be applied as the input voltage signal to the interface unit. The resulting output voltage of the interface unit is then measured; a gain value and an offset value are then calculated to compensate for the difference between the calibration signal and the output voltage, and the gain value and offset value can be stored in the interface unit, for example, in an EEPROM controller. For example, the gain and offset values ​​can be accessed on demand by measurement software to compensate for the measured values.

[0021] The interface unit includes a first transistor having a first insulated gate terminal coupled to an input section, a first source terminal coupled to a first terminal of a first resistor, and a first drain terminal coupled to a first terminal of a second resistor. A second terminal of the second resistor is coupled to a point that maintains a constant voltage at a constant value; the first transistor is arranged to generate a second resistor voltage in the second resistor according to the input voltage.

[0022] The interface unit includes a first operational amplifier with a first non-inverting input coupled to a point in the circuit that maintains a reference voltage at a constant value. The first operational amplifier also has a first inverting input coupled to a first drain terminal of a first transistor. The first operational amplifier further has a first output coupled to a second terminal of a first resistor.

[0023] The interface unit also includes a second transistor, which has a second source terminal coupled to the second terminal of the third resistor and a second drain terminal coupled to the first terminal of the fourth resistor. The first terminal of the third resistor is coupled to the second terminal of the first resistor. The second terminal of the fourth resistor is coupled to a point that maintains a constant voltage.

[0024] The interface unit also includes a second operational amplifier, which has a second non-inverting input coupled to the second drain terminal of the second transistor. The second operational amplifier also has a second inverting input coupled to the first inverting input of the first operational amplifier. The second operational amplifier further has a second output coupled to the second insulated gate terminal of the second transistor and the output of the interface unit.

[0025] The first operational amplifier is arranged to provide a variable voltage to the first source terminal of the first transistor based on a comparison between a reference voltage and a second resistor voltage, so as to control the operating point of the first transistor.

[0026] The interface unit acts as an impedance buffer to send weak input signals received from the high-impedance input section to the low-impedance output section.

[0027] According to the present invention, the evaluation device is not fed directly by the electrode voltage itself, as is typically the case in conventional input stage circuits, nor by an amplified voltage obtained directly from the pre-amplified electrode voltage. Instead, it is fed by a decoupling voltage transmitted through the interface unit. Furthermore, the electrode voltage is fed into the input section through the insulated gate of a first transistor, thereby providing a high insulation barrier. The interface unit provides an effective current barrier, preventing any effective load from flowing through the input section, typically less than 1 pA. Therefore, due to the decoupling effect of the interface unit, the sensor element of the electrode is no longer charged. Even at high temperatures, such as during autoclaving, the effect of residual current on the sensor element of the electrode EL remains exceptionally low. It provides an effective solution to significantly limit the negative impact of residual current on the electrode, especially when the measurement probe switches to zero current, which is typically done during high-temperature processes.

[0028] By using transistors with insulated gates, the interface unit according to the invention allows coupling to an output signal processing unit having a conventional input stage circuit including an operational amplifier.

[0029] Furthermore, because the effect of residual current on the sensor element of the electrode EL is greatly reduced by the action of the transistor with an insulated gate, the interface unit according to the invention allows the use of electrodes including an active layer that acts as a voltage source, even in environments where the temperature reaches or exceeds 100 degrees Celsius. For electrodes with sensor elements containing a base lithium layer, it allows for a significant reduction in elemental lithium consumption and an increase in probe lifetime. This is advantageous for, for example, solid-state pH sensors.

[0030] The first operational amplifier is arranged to control the operating point, also known as the Q-point or bias point, of the first transistor such that the first transistor operates without saturation, distortion, or other nonlinear interference over a wide range of input voltage values ​​(typically between 0.25 and 5.5 volts). The first operational amplifier maintains a nearly constant operating point over the wide range of input voltage values. Furthermore, because the gate of the first transistor is not linearly controlled relative to the current flowing between the source and drain of the first operational amplifier, maintaining a fixed operating point allows for control over the input voltage V. IN The nonlinear performance is reduced over a wide range to increase the accuracy of the first operational amplifier's performance. In summary, the interface unit introduces an output voltage that is related to the input voltage V. IN The error was significantly reduced.

[0031] In contrast, in known solutions that apply a steady-state DC voltage or constant current to bias the source of a transistor, the input voltage can vary only within a more limited range of values ​​compared to the present invention, due to saturation and / or distortion problems caused by the fixed characteristics of the bias current.

[0032] Furthermore, by coupling the inverting input of the second operational amplifier to the inverting input of the first operational amplifier, the interface unit is arranged to compensate for differences between electronic components, such as those caused by manufacturing tolerances, by adjusting the output voltage of the second operational amplifier accordingly.

[0033] Advantageously, the first resistor can have a resistance substantially the same as that of the third resistor; and the second resistor can have a resistance substantially the same as that of the third and fourth resistors. The first transistor and the second transistor can also be of the same type.

[0034] Specifically, the first and third resistors can use the same type of electronic components. The first and second transistors can use the same type of electronic components. The first and second operational amplifiers can use the same type of electronic components. The interface unit then presents a balanced and symmetrical design, providing a favorable solution for reducing the cumulative impact of environmental parameter variations (e.g., temperature variations, variations in manufacturing tolerances of electronic components, and variations in electronic noise) on the interface unit. Compared to asymmetrical circuit designs, this significantly reduces the cumulative impact of environmental parameter variations on the interface unit.

[0035] Advantageously, the first and second operational amplifiers can be embedded in a single package of a single electronic component, as can the first and second transistors. These features allow for further reduction of the impact of variations in environmental parameters, manufacturing tolerances of electronic components, and electronic noise. Furthermore, the footprint of the interface unit can be further reduced, while production costs can be lowered.

[0036] More specifically, the first transistor and / or the second transistor can be selected from the following list of transistor types:

[0037] • Insulated-gate field-effect transistor (IGFET), where the gate has no electrostatic discharge protection element; or

[0038] Metal-oxide-semiconductor field-effect transistors (MOSFETs) provide a particularly effective insulating barrier on the gate and are suitable for environments where temperatures can vary greatly and exceed 100 degrees Celsius because an oxide layer is used between the gate and channel of the MOSFET to prevent current flow over a wide temperature range; or

[0039] • Metal-Insulator-Semiconductor Field-Effect Transistor (MISFET); or

[0040] • Insulated Gate Bipolar Transistor (IGBT).

[0041] The signal processing unit may include an operational amplifier with electrostatic discharge (ESD) protection and configured to receive decoupling voltages. Therefore, a conventional input stage circuit with standard ESD protection can be used, followed by a proven and reliable signal processing unit, without requiring any costly redesign and / or custom solutions.

[0042] According to a second aspect, the present invention also relates to a measurement system, comprising:

[0043] • Based on the interface unit of the first aspect; and

[0044] • An electrochemical measurement probe for contact with process materials, comprising an electrode having a sensing element arranged to generate a sensor voltage, the electrode voltage being related to at least one property of the process material when the electrode is in contact with the process material; the electrochemical measurement probe is adapted to transmit the sensor voltage to an input section of an interface unit.

[0045] • An evaluation device having an input section adapted to be coupled to the output section of an interface unit for receiving the output voltage for converting the output voltage into a measurement value.

[0046] The sensing element of the electrode may include an active layer that acts as a voltage source, so that the electrode voltage is not zero even when the electrode is not in contact with the process material.

[0047] The measurement probe can be selected from: pH measurement probe, oxygen measurement probe, CO2 measurement probe and ozone measurement probe.

[0048] The sensing element of the electrode may include a lithium phosphorus oxynitride layer. Attached Figure Description

[0049] The details of the disclosed methods and apparatus will become apparent from the description of the embodiments illustrated in the accompanying drawings with schematic and simplified representations, wherein:

[0050] Figure 1 The main structure of a system for measuring at least one property of a material 6 in a process by means of a measuring probe 1 is shown;

[0051] Figure 2 An electrochemical measurement probe 1 is schematically shown, which is immersed in the process material 6 and coupled to the evaluation device 3;

[0052] Figure 3 A schematic circuit diagram representing interface unit 4;

[0053] Figure 4 A timing diagram showing the various voltages measured in the circuit of interface unit 4, such as input voltage signals;

[0054] Figure 5 The error graph is shown, where the offset voltage diff.mV between the input and output voltages of the interface unit and the associated measurement error are represented over time (the horizontal axis represents time in milliseconds). Detailed Implementation

[0055] Figure 1A measurement system with a container 8 is shown, the container 8 including a holding dish 81 containing process material 6. The properties of the process material 6 are measured by at least one electrochemical measurement probe 1, which is connected to an interface unit 4 via a signal transmission device 2. The interface unit 4 is also coupled to an evaluation device 3, which, among other functions, acts as a measurement converter and is coupled to a processing device 500, such as a computer. The electrochemical measurement probe is, for example, a potentiometric probe. More specifically, the electrochemical measurement probe may be selected from a non-exhaustive group, which includes: pH measurement probes, oxygen measurement probes, CO2 measurement probes, and ozone measurement probes.

[0056] Figure 2 The schematic diagram illustrates the main design structure of an electrochemical measurement probe (e.g., a pH measurement probe) comprising a glass electrode 16, a reference electrode 15, and an auxiliary electrode 18 in a single-bar measurement chain structure. However, the present invention is not limited to pH measurement probes and can be applied to any type of electrochemical measurement probe, such as an oxygen measurement probe, a CO2 measurement probe, or an ozone measurement probe.

[0057] In the measuring probe 1, a glass electrode with a conductive lead element 16 and a reference electrode with a reference lead element 15 are constructed and combined in one unit. Within a first chamber within the inner tube 11 and within a thin-walled glass hemisphere or glass membrane 111 adjacent to the tube, the conductive lead element 16 is immersed in a solution with a defined pH value, specifically in an inner buffer 14, thereby establishing a conductive connection between the conductive lead element 16 and the interior of the glass membrane 111. Within the outer tube 12, the reference lead element 15 is immersed in an electrolyte, specifically in an outer buffer 13, thereby allowing charge exchange with the measuring material 6 through a porous insulating wall or diaphragm 121.

[0058] The potentials at conductor lead element 16, reference lead element 15, and / or auxiliary electrode 18 are intended to be measured and then further processed by evaluation device 3 and processing device 500.

[0059] A temperature measurement sensor 17 is arranged in the internal buffer space, which provides the possibility of automatically compensating for temperature effects and recording temperature cycles.

[0060] The measurement probe 1 typically includes an active layer that acts as a voltage source. For example, the measurement probe 1 may be a solid-state pH sensor, and the glass electrode 16 of the measurement probe 1 typically includes an ion-sensitive pH glass substrate and multiple layers above the ion-sensitive pH glass substrate. These layers may include a base lithium layer, a lithium phosphorus oxynitride (typically abbreviated as LiPON) layer, and a protective layer adapted to limit the degradation of the lithium layer and provide an encapsulation structure for stabilizing the entire glass electrode and protecting it from environmental influences. Even when the conductor lead element 16 is not immersed in the holding dish 81 containing the process material 6, the potential of the glass electrode 16 of the measurement probe 1 is not zero (non-null). This performance is particularly due to the electrical properties of the base lithium layer and the lithium phosphorus oxynitride layer.

[0061] Figure 3 A circuit diagram of interface unit 4 in an advantageous embodiment is shown. For an exemplary input voltage signal, Figure 4 A timing diagram showing the various voltages measured in the circuitry of interface unit 4 (referenced below). Interface unit 4 includes components adapted to receive input voltage V. IN The input section 110 is typically adapted to be coupled to the output section of the measurement probe 1, which includes at least one electrode EL, such as a glass electrode, and a reference electrode, to receive the sensor voltage V. SENSOR Depending on the type of measuring probe 1 used, for example, in the case of using a solid-state pH sensor, the sensor voltage V can be observed only when the measuring probe 1 is immersed in the process material 6. SENSOR Or continuously observe the sensor voltage V SENSOR The electrode EL itself forms a voltage source SQ. When the glass electrode 16 of the measuring probe 1 is coupled to the input section 110, the input impedance Z observed at the input section 110, depending on the application, is as follows: at the sensor's typical operating temperature, typically from approximately 0°C to approximately 100°C. in It is particularly high, and typically exceeds 2 GΩ. For example, when the sensor temperature is around 25°C, the input impedance Z observed at input section 110 is... in It is typically around 2.5 GΩ. However, due to the electrode resistance R... E The electrode resistance R depends on the temperature observed at measuring probe 1, so it is higher than 100 degrees Celsius. E It can become very small, typically below 50 MOhm. When the measurement probe 1 includes an active layer, the sensor voltage V of the signal source SQ... SENSOR The voltage is not zero; even when the conductor lead element 16 is not immersed in the holding dish 81, for example, when the glass electrode is not in contact with the process material 6, the voltage observed at the glass electrode 16 is approximately -3V.

[0062] Alternatively, the input unit 110 is typically electrically coupled to a test or calibration device that transmits test signals. The interface unit 4 includes an output unit 120, which is particularly suitable for electrical coupling to the input unit of the evaluation device 2. The interface unit 4 is configured to transmit an output voltage V on the output unit 120. OUT When the input of the evaluation device 2 is coupled to the output 120, the output impedance Z observed at the output 120 is... OUT It is particularly low, and usually below 100 Ohms.

[0063] Interface unit 4 is arranged such that the input voltage V observed at input section 110 is... IN The output voltage V is mirrored into the output unit 120, meaning that over time, the output voltage V... OUT Basically, it remains equal to the input voltage V. IN Typically, such as Figure 5 As shown, for an input voltage varying from 0.25V to 5.5V, the difference between the input voltage and the output voltage is between 0.1mV and -0.4mV.

[0064] Interface unit 4 also functions as an impedance buffer to send weak input signals received from the high-impedance input section to the low-impedance output section. Interface unit 4 also provides a current barrier to prevent any effective load from flowing through input section 110, typically less than 0.2 pA. Therefore, due to interface unit 4, the sensor element of electrode EL is no longer charged. This is why the effect of residual current on the sensor element of electrode EL remains exceptionally low even at high temperatures, such as during autoclaving. It provides an effective solution to significantly limit the negative impact of residual current on electrode EL, especially when measurement probe 1 typically switches to zero current during high-temperature processes.

[0065] Interface unit 4 is also provided with decoupling circuit 200 and potential mirror circuit 300.

[0066] The decoupling circuit 200 includes a first transistor 210, a first operational amplifier 220, a first resistor 230 representing resistance R1, and a second resistor 240 representing resistance R2. The first transistor 210 has an insulated gate terminal coupled to the input section 110.

[0067] The potential mirror circuit 300 includes a second transistor 310, a second operational amplifier 320, a third resistor 330 representing resistor R1, and a fourth resistor 340 representing resistor R4. The output section 120 is coupled to the output section of the second operational amplifier 320 and the insulated gate terminal of the second transistor 310.

[0068] The first transistor 210 also includes a source terminal coupled to a first terminal of the first resistor 230 and a drain terminal coupled to a first terminal of the second resistor 240. The second terminal of the second resistor 240 is coupled to a point in the circuit where a voltage V is applied. C It is kept at a substantially constant value, typically -5.25V.

[0069] The first operational amplifier 220 has a non-inverting input V+, which is coupled to a reference voltage V in the circuit. ref The voltage is maintained at a constant value, typically -5V. The first operational amplifier 220 also has an inverting input V-, which is coupled to the drain terminal of the first transistor 210, the first terminal of the second resistor 240, and the inverting input V- of the second operational amplifier 320.

[0070] The output of operational amplifier 220 is coupled to the second terminal of first resistor 230 and the first terminal of third resistor 330.

[0071] The first operational amplifier 220 is arranged according to the reference voltage V received on its non-inverting input V+. ref The voltage V received on its inverting input V- R2 The comparison between the two provides a variable voltage to the source terminal of the first transistor 210. The first operational amplifier 220 is arranged to control the operating point (also called the Q-point or bias point) of the first transistor 210 such that the first transistor 210 responds to the input voltage V. IN It operates without saturation, distortion, or other nonlinear interference over a wide range of values ​​(typically between 0.25 and 5.5 volts). By performing as described above, the first operational amplifier 220 operates at an input voltage V... IN It maintains a nearly identical operating point over a wide range of values. Furthermore, since the gate current flowing between the source and drain of the first operational amplifier 220 is not linearly controlled, reducing the input voltage V... IN The nonlinear behavior over a wide range of values, while maintaining a substantially fixed operating point, allows for increased accuracy in the performance of the first operational amplifier 220. In summary, as for example... Figure 5 As shown, the interface unit outputs voltage V OUT Relative to input voltage V IN The introduced error is significantly reduced.

[0072] In contrast, in known solutions that apply a steady-state DC voltage or constant current to bias the source of a transistor, the input voltage can vary only within a more limited range of values ​​compared to the present invention, due to saturation and / or distortion problems caused by the fixed characteristics of the bias current.

[0073] The second transistor 310 has an insulated gate terminal coupled to the output of the second operational amplifier 320, a source terminal coupled to the second terminal of the third resistor 330, and a drain terminal coupled to the first terminal of the fourth resistor 340. The second terminal of the fourth resistor 340 is coupled to the circuit's sustaining voltage V. C point.

[0074] The second operational amplifier 320 has a non-inverting input V+ coupled to the drain terminal of the second transistor 310 and the first terminal of the fourth resistor 340. The second operational amplifier 320 also has an inverting input V-, which is coupled to the inverting input V- of the first operational amplifier 220, the first terminal of the second resistor 240, and the drain terminal of the first transistor 210.

[0075] The potential mirror circuit 300 and the decoupling circuit 200 share a balanced symmetrical design in the following sense:

[0076] The resistance R1 of the first resistor 230 and the resistance R3 of the third resistor 330 are basically the same; and,

[0077] The resistance R2 of the second resistor 240 and the resistance R4 of the fourth resistor are essentially the same; and,

[0078] The first transistor 210 and the second transistor 310 have essentially the same characteristics and performance, and / or belong to the same type.

[0079] Specifically, the first resistor 230 and the third resistor R3 can use the same type of electronic components. The first transistor 210 and the second transistor 310 can use the same type of electronic components. The first operational amplifier 220 and the second operational amplifier 320 can use the same type of electronic components. Since the potential mirror circuit 300 and the decoupling circuit 200 share a balanced symmetrical design, the cumulative effect of changes in environmental parameters (e.g., temperature changes, variations in manufacturing tolerances of electronic components, and variations in electrical noise) on the interface unit 4 can be greatly reduced compared to asymmetrically designed circuits.

[0080] In one embodiment, the first transistor 210 and / or the second transistor 310 are metal-oxide-semiconductor field-effect transistors configured to adjust their conductivity σ according to their gate terminals. DEC .

[0081] In one embodiment, the first transistor 210 and / or the second transistor 310 are insulated-gate field-effect transistors (IGFETs). The first transistor 210 and / or the second transistor 310 have no electrostatic discharge protection elements at their gates. Therefore, the interface unit can be implemented using various types of transistors, thus providing greater flexibility in the manufacturing process in terms of allowing for the search for secondary supply sources and optimizing costs.

[0082] In another embodiment, the first transistor 210 and / or the second transistor 310 are metal-insulator-semiconductor field-effect transistors (MISFETs).

[0083] In another embodiment, the first transistor 210 and / or the second transistor 310 are insulated gate bipolar transistors (IGBTs).

[0084] Since the first transistor 210 and / or the second transistor 310 can be specifically selected from the aforementioned options, a variety of different types of transistors can be used to implement the interface unit, thereby providing greater flexibility in the manufacturing process in terms of allowing for the search for a second source of supply and / or optimizing costs.

[0085] In an advantageous embodiment, the first operational amplifier 220 and the second operational amplifier 320 are embedded in a package of a single electronic component, and / or the first transistor 210 and the second transistor 310 are embedded in a package of a single electronic component. These features allow for further improvement in mitigating the effects of environmental parameter variations, manufacturing tolerances of electronic components, and electrical noise. Furthermore, the footprint of the interface unit can be further reduced, while production costs can be lowered.

[0086] The first transistor 210 is arranged such that it responds to the input voltage V received at the insulated gate terminal. IN A decoupling voltage V is generated in the second resistor 240. R2 More specifically, the decoupling voltage V in the second resistor 240 R2 The current flowing through the source to the gate of the first transistor 210 into the second resistor 240 is proportional to the current flowing through the first resistor 230 into the second resistor 240. By coupling the first transistor 210 to the input section 110 through an insulated gate terminal, current leakage through the input section 110 is greatly reduced. Therefore, the first transistor 210 acts as an insulating barrier between the input section 110 and the rest of the interface unit, especially the output section 120, thereby preventing load on the input section 110.

[0087] Because the inverting gate V- of the second operational amplifier 320 is coupled to the first terminal of the second resistor 240, and the second terminal of the second resistor 240 is maintained at voltage V... C Therefore, the output voltage V transmitted from the output terminal of the second operational amplifier 320OUT According to voltage V C The gate of the second transistor 310 is controlled. Therefore, the second transistor 310 behaves similarly to the first transistor 210. The second transistor 310 is arranged to replicate the behavior of the first transistor 210, thereby ensuring symmetrical operation of the interface unit 4.

[0088] The second transistor 310 is arranged such that, based on the output voltage V received at the insulated gate terminal and transmitted from the output terminal of the second operational amplifier 320, it... OUT A voltage V is generated in the fourth resistor 340. R4 Furthermore, the output section 120 is also coupled to the insulated gate terminal of the second operational amplifier 320. More specifically, the voltage V in the fourth resistor 240... R4 The current flowing through the source to the gate of the second transistor 310 and into the fourth resistor 340 in the third resistor 330 is proportional to the current flowing through the third resistor 330. Therefore, by coupling the output terminal of the second operational amplifier 320 to the output section 120, the interface unit 4 can reliably generate the output voltage V. OUT .

[0089] List of reference numerals

[0090] 1 Electrochemical Measurement Probe

[0091] 2 signal leads

[0092] 3 Evaluation device

[0093] 4 Interface Unit

[0094] 6. Measuring materials

[0095] 8 containers

[0096] 81. Holding dish

[0097] 500 processing unit

[0098] 11 Inner tube

[0099] 12 outer tubes

[0100] 13 External buffer

[0101] 14 Internal buffer

[0102] 15 Reference Electrode

[0103] 16 Glass Electrode

[0104] 17 Temperature Measurement Sensor

[0105] 18 Auxiliary Electrodes

[0106] 111 Thin-walled glass hemisphere or glass film

[0107] 121 Diaphragm

[0108] 19 signal lines

[0109] 110 Interface Unit Input Section

[0110] 120 Interface Unit Output Section

[0111] 200 decoupling circuit

[0112] 210 First Transistor

[0113] 220 First Operational Amplifier

[0114] 230 First Resistor

[0115] 240 Second Resistor

[0116] 300 Potential Mirror Circuit

[0117] 310 Second Transistor

[0118] 320 Second Operational Amplifier

[0119] 330 Third Resistor

[0120] 340 Fourth Resistor

Claims

1. An interface unit (4) comprising an input section (110) adapted to receive an input voltage (V) from an electrochemical measurement probe (1) for contacting a process material (6). IN The input current of the electrochemical measurement probe (1) includes an electrode (EL), the electrode (EL) being provided with a sensing element, the sensing element being arranged to generate a sensor voltage (V). SENSOR When the electrode is in contact with the process material, the electrode voltage is related to at least one characteristic of the process material; the interface unit (4) further includes an output (120) adapted to be coupled to the input of the evaluation device (3); the interface unit is arranged to transmit voltages on the output (120) that are related to the input voltage (V). IN The output voltages (V) are basically equal. OUT The output current of ) is characterized in that, Interface unit (4) includes: The first transistor (210) has a first insulated gate terminal coupled to the input section (110), a first source terminal coupled to the first terminal of the first resistor (230), and a first drain terminal coupled to the first terminal of the second resistor (240); the second terminal of the second resistor is coupled to a constant voltage (V) C The point where the input voltage (V) remains constant; the first transistor is arranged to be able to adjust according to the input voltage (V) IN The second resistor generates a second resistor voltage (V) in the second resistor. R2 ), The first operational amplifier (220) includes: a first non-inverting input section coupled to a circuit with a reference voltage (V) ref The first inverting input is coupled to the first drain terminal of the first transistor (210); and the first output is coupled to the second terminal of the first resistor (230). The second transistor (310) has a second source terminal coupled to the second terminal of the third resistor (330) and a second drain terminal coupled to the first terminal of the fourth resistor (340); the first terminal of the third resistor (330) is coupled to the second terminal of the first resistor (230); the second terminal of the fourth resistor (340) is coupled to a voltage that maintains a constant voltage (V). C ) point; The second operational amplifier (320) includes: a second non-inverting input coupled to the second drain terminal of the second transistor (310); a second inverting input coupled to the first inverting input of the first operational amplifier (220); and a second output coupled to the second insulated gate terminal of the second transistor (310) and the output of the interface unit (4) (120). The first operational amplifier (220) is arranged such that it can operate according to a reference voltage (V). ref ) and the voltage of the second resistor (V) R2 The comparison between the two transistors provides a variable voltage to the first source terminal of the first transistor (210) in order to control the operating point of the first transistor (210).

2. The interface unit according to claim 1, wherein, The first resistor (230) has a resistance that is substantially the same as that of the third resistor (330); wherein the second resistor (240) has a resistance that is substantially the same as that of the fourth resistor (340).

3. The interface unit according to claim 1 or 2, wherein, The first transistor (210) and the second transistor (310) are of the same type.

4. The interface unit according to claim 1 or 2, wherein, The first operational amplifier (220) and the second operational amplifier (320) are embedded in a package of a single electronic component.

5. The interface unit according to claim 1 or 2, wherein, The first transistor (210) and the second transistor (310) are embedded in a package of a single electronic component.

6. The interface unit according to claim 1 or 2, wherein, The first transistor (210) and / or the second transistor (310) are insulated-gate field-effect transistors, or metal-oxide-semiconductor field-effect transistors, or metal-insulator-semiconductor field-effect transistors, or insulated-gate bipolar transistors.

7. A measurement system, comprising: Interface unit (4) according to any one of claims 1 to 6; as well as, An electrochemical measurement probe (1) for contact with process material (6) includes an electrode (EL) having a sensing element arranged to generate a sensor voltage (V). SENSOR When the electrode is in contact with the process material, the electrode voltage is related to at least one property of the process material; the electrochemical measurement probe is adapted to measure the sensor voltage (V) SENSOR ) is transmitted to the input section (110) of the interface unit. Evaluation device (3), which has an input section suitable for coupling to the output section (120) of interface unit, for receiving output voltage (V) OUT ( ), used to convert the output voltage into a measured value.

8. The measurement system according to claim 7, wherein, The sensing element of the electrode includes an active layer that acts as a voltage source, so that the electrode voltage is not zero even when the electrode is not in contact with the process material.

9. The measurement system according to any one of claims 7 to 8, wherein, The measurement probe is selected from the group consisting of: pH measurement probe, oxygen measurement probe, CO2 measurement probe and ozone measurement probe.

10. The measurement system according to any one of claims 7 to 8, wherein, The sensing element of the electrode includes a lithium phosphorus oxynitride layer.

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