CN114614781A - PH signal conditioning circuit - Google Patents
PH signal conditioning circuit Download PDFInfo
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- CN114614781A CN114614781A CN202011413210.5A CN202011413210A CN114614781A CN 114614781 A CN114614781 A CN 114614781A CN 202011413210 A CN202011413210 A CN 202011413210A CN 114614781 A CN114614781 A CN 114614781A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
- G01N27/28—Electrolytic cell components
- G01N27/30—Electrodes, e.g. test electrodes; Half-cells
- G01N27/302—Electrodes, e.g. test electrodes; Half-cells pH sensitive, e.g. quinhydron, antimony or hydrogen electrodes
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
- H03F3/42—Amplifiers with two or more amplifying elements having their dc paths in series with the load, the control electrode of each element being excited by at least part of the input signal, e.g. so-called totem-pole amplifiers
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
- G01N27/416—Systems
- G01N27/4166—Systems measuring a particular property of an electrolyte
- G01N27/4167—Systems measuring a particular property of an electrolyte pH
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H7/00—Multiple-port networks comprising only passive electrical elements as network components
- H03H7/01—Frequency selective two-port networks
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H7/00—Multiple-port networks comprising only passive electrical elements as network components
- H03H7/38—Impedance-matching networks
Abstract
The invention provides a pH signal conditioning circuit, wherein a pH signal is input into the pH signal conditioning circuit through a pH electrode, and the pH signal conditioning circuit comprises a cascaded pre-filter unit and a pre-impedance transformation unit, wherein the pre-filter unit is suitable for filtering noise introduced by the pH electrode, and the pre-impedance transformation unit is suitable for reducing the input impedance of the pH signal, the pre-filter unit comprises two paths of same pre-filter circuits, the input end of one path of pre-filter circuit is connected with one electrode of the pH electrode, and the input end of the other path of pre-filter circuit is connected with the other electrode of the pH electrode; the pre-impedance conversion unit comprises two paths of same pre-impedance conversion circuits, the input ends of the two paths of pre-impedance conversion circuits are respectively connected with the output ends of the two paths of pre-filter circuits, and the output ends of the two paths of pre-impedance conversion circuits are used as the output ends of the pH signal conditioning circuit. The pH signal conditioning circuit improves the stability and the accuracy consistency of the circuit.
Description
Technical Field
The invention mainly relates to the field of high-precision measurement, in particular to a low-voltage high-precision pH signal conditioning circuit.
Background
The pH measurement is widely applied to the industries of water quality monitoring, industrial control, biochemical pharmacy and the like. According to the conventional pH measurement technology, the pH measurement result is greatly influenced by the working environment of the pH measurement circuit, for example, the consistency and stability of the pH measurement result are influenced by the ambient temperature. With the increase of the requirements of green ecology and sustainable development, the measuring circuit is required to have excellent performances of low voltage and low energy consumption.
Disclosure of Invention
The invention aims to provide a low-voltage high-precision pH signal conditioning circuit.
In order to solve the technical problem, the invention provides a pH signal conditioning circuit, wherein a pH signal is input to the pH signal conditioning circuit from a pH electrode, and the pH signal conditioning circuit is characterized by comprising a cascaded pre-filter unit and a pre-impedance transformation unit, wherein the pre-filter unit is suitable for filtering noise introduced by the pH electrode, and the pre-impedance transformation unit is suitable for reducing input impedance of the pH signal, wherein the pre-filter unit comprises two paths of same pre-filter circuits, the input end of one path of pre-filter circuit is connected with one electrode of the pH electrode, and the input end of the other path of pre-filter circuit is connected with the other electrode of the pH electrode; the pre-impedance conversion unit comprises two same pre-impedance conversion circuits, the input ends of the two pre-impedance conversion circuits are respectively connected with the output ends of the two pre-filter circuits, and the output ends of the two pre-impedance conversion circuits are used as the output ends of the pH signal conditioning circuit.
In an embodiment of the present invention, the method further includes: the voltage conversion unit is suitable for converting a pH signal comprising a positive signal and a negative signal into a pH signal comprising only a positive signal, and comprises two identical voltage conversion circuits, wherein the input ends of the two voltage conversion circuits are respectively connected with the output ends of the two pre-impedance conversion circuits, and the output ends of the two voltage conversion circuits are used as the output ends of the pH signal conditioning circuit.
In an embodiment of the present invention, the method further includes: the rear-end filtering unit is suitable for filtering signal noise input to the rear-end filtering unit and comprises two identical rear-end filtering circuits, the input ends of the two rear-end filtering circuits are respectively connected with the output ends of the two voltage conversion circuits, and the output ends of the two rear-end filtering circuits are used as the output ends of the pH signal conditioning circuit.
In an embodiment of the present invention, the method further includes: the rear-end impedance conversion unit is suitable for reducing the input impedance of the rear-end impedance conversion unit and comprises two identical rear-end impedance conversion circuits, the input ends of the two rear-end impedance conversion circuits are respectively connected with the output ends of the two rear-end filter circuits, and the output ends of the two rear-end impedance conversion circuits are used as the output ends of the pH signal conditioning circuit.
In an embodiment of the invention, the output terminal is connected to an input terminal of an analog-to-digital conversion unit, and the analog-to-digital conversion unit is adapted to convert the pH signal into a digital signal.
In an embodiment of the present invention, the pre-filter circuit includes a first RC filter circuit, and the first RC filter circuit includes a first resistor and a first capacitor, wherein one end of the first resistor is connected to one of the pH electrodes, the other end of the first resistor is connected to one end of the first capacitor, and the other end of the first resistor serves as an output end of the pre-filter circuit; the other end of the first capacitor is connected with one input end of the pre-impedance transformation circuit, and the other end of the first capacitor is grounded.
In an embodiment of the invention, the pre-impedance transformation circuit includes a first operational amplifier, and a gain of the first operational amplifier is 1.
In an embodiment of the invention, the first operational amplifier is an operational amplifier with high input impedance.
In an embodiment of the present invention, the voltage converting circuit includes a second resistor, a third resistor, and a second capacitor, wherein one end of the second resistor is connected to the output terminal of the pre-impedance transforming circuit, the other end of the second resistor is connected to one end of the third resistor and one end of the second capacitor, and the other end of the second resistor is used as the output terminal of the voltage converting circuit; the other end of the third resistor is connected with a reference voltage; the other end of the second capacitor is grounded.
In an embodiment of the present invention, the back-end filter circuit includes a second RC filter circuit, and the second RC filter circuit includes a fourth resistor and a third capacitor, where one end of the fourth resistor is connected to one output end of the voltage conversion circuit, the other end of the fourth resistor is connected to one end of the third capacitor, and the other end of the fourth resistor is used as an output end of the back-end filter circuit; the other end of the third capacitor is grounded.
In an embodiment of the invention, the back-end impedance transformation circuit includes a second operational amplifier, and a gain of the second operational amplifier is 1.
In an embodiment of the invention, the second operational amplifier is an operational amplifier with high input impedance.
Compared with the prior art, the pH signal conditioning circuit respectively processes the pH signals measured by the two pH electrodes through at least two same pre-filter circuits and two pre-impedance transformation circuits, reduces the influence of circuit elements on the measurement performance in a pseudo-differential mode, reduces the measurement deviation caused by the external environment, and improves the stability and the precision consistency of the circuit. In addition, the pH signal conditioning circuit can reduce the requirements and the cost in the aspect of device performance selection; the circuit design modularization can select the required module and determine the parameters of the components and parts according to the requirements, and the use is flexible.
Drawings
The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the application and together with the description serve to explain the principle of the invention. In the drawings:
FIG. 1 is a schematic diagram of a pH signal conditioning circuit according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a pH signal conditioning circuit according to another embodiment of the present invention;
FIG. 3 is a schematic diagram of a pH signal conditioning circuit according to another embodiment of the present invention;
FIG. 4 is a schematic diagram of a pH signal conditioning circuit according to another embodiment of the present invention;
fig. 5 is a schematic diagram of an application scenario of a pH signal conditioning circuit according to another embodiment of the invention.
Detailed Description
In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings used in the description of the embodiments will be briefly introduced below. It is obvious that the drawings in the following description are only examples or embodiments of the application, from which the application can also be applied to other similar scenarios without inventive effort for a person skilled in the art. Unless otherwise apparent from the context, or stated otherwise, like reference numbers in the figures refer to the same structure or operation.
As used in this application and the appended claims, the terms "a," "an," "the," and/or "the" are not intended to be inclusive in the singular, but rather are intended to be inclusive in the plural unless the context clearly dictates otherwise. In general, the terms "comprises" and "comprising" merely indicate that steps and elements are included which are explicitly identified, that the steps and elements do not form an exclusive list, and that a method or apparatus may include other steps or elements.
The relative arrangement of the components and steps, the numerical expressions, and numerical values set forth in these embodiments do not limit the scope of the present application unless specifically stated otherwise. Meanwhile, it should be understood that the sizes of the respective portions shown in the drawings are not drawn in an actual proportional relationship for the convenience of description. Techniques, methods, and apparatus known to those of ordinary skill in the relevant art may not be discussed in detail but are intended to be part of the specification where appropriate. In all examples shown and discussed herein, any particular value should be construed as merely illustrative, and not limiting. Thus, other examples of the exemplary embodiments may have different values. It should be noted that: like reference numbers and letters refer to like items in the following figures, and thus, once an item is defined in one figure, further discussion thereof is not required in subsequent figures.
In the description of the present application, it is to be understood that the orientation or positional relationship indicated by the directional terms such as "front, rear, upper, lower, left, right", "lateral, vertical, horizontal" and "top, bottom", etc., are generally based on the orientation or positional relationship shown in the drawings, and are used for convenience of description and simplicity of description only, and in the case of not making a reverse description, these directional terms do not indicate and imply that the device or element being referred to must have a particular orientation or be constructed and operated in a particular orientation, and therefore, should not be considered as limiting the scope of the present application; the terms "inner and outer" refer to the inner and outer relative to the profile of the respective component itself.
It will be understood that when an element is referred to as being "on," "connected to," "coupled to" or "contacting" another element, it can be directly on, connected or coupled to, or contacting the other element or intervening elements may be present. In contrast, when an element is referred to as being "directly on," "directly connected to," "directly coupled to" or "directly contacting" another element, there are no intervening elements present. Similarly, when a first component is said to be "in electrical contact" or "electrically coupled" to a second component, there is an electrical path between the first component and the second component that allows current to flow. The electrical path may include capacitors, coupled inductors, and/or other components that allow current to flow even without direct contact between the conductive components.
It should be noted that the terms "first", "second", and the like are used to define the components, and are only used for convenience of distinguishing the corresponding components, and the terms have no special meanings unless otherwise stated, and therefore, the scope of protection of the present application is not to be construed as being limited. Further, although the terms used in the present application are selected from publicly known and used terms, some of the terms mentioned in the specification of the present application may be selected by the applicant at his or her discretion, the detailed meanings of which are described in relevant parts of the description herein. Further, it is required that the present application is understood not only by the actual terms used but also by the meaning of each term lying within.
Fig. 1 is a schematic structural diagram of a pH signal conditioning circuit according to an embodiment of the present invention. Referring to fig. 1, a pH signal is input to a pH signal conditioning circuit 100 from pH electrodes 101 and 102, and the pH signal conditioning circuit 100 of this embodiment includes a pre-filtering unit 110 and a pre-impedance transformation unit 120 which are cascaded. The pre-filtering unit 110 is adapted to filter out noise introduced by the pH electrodes 101, 102, and the pre-impedance transformation unit 120 is adapted to reduce the input impedance of the pH signal.
The pre-filter unit 110 includes two identical pre-filter circuits 111 and 112, wherein an input terminal of one of the pre-filter circuits is connected to one of the pH electrodes, and an input terminal of the other of the pre-filter circuits is connected to the other of the pH electrodes.
In the embodiment shown in fig. 1, one electrode 101 of the pH electrodes is connected to an input of a pre-filter circuit 111 and the other electrode 102 of the pH electrodes is connected to an input of a pre-filter circuit 112.
As shown in fig. 1, the pre-impedance transformation unit 120 according to the embodiment of the present invention includes two identical pre-impedance transformation circuits 121 and 122, input ends of the two pre-impedance transformation circuits 121 and 122 are respectively connected to output ends of the two pre-filter circuits 111 and 112, and output ends 121 and 122 of the two pre-impedance transformation circuits are used as output ends 103 and 104 of the pH signal conditioning circuit.
The pH signal conditioning circuit is used for being connected with a pH electrode with two electrodes. Each pH electrode is connected with a pre-filter circuit, and a pH signal measured from the pH electrode is input into a pre-impedance conversion unit after being filtered by the pre-filter circuit, so that the input impedance of the filtered pH signal is reduced. The signals output by the outputs 103, 104 are thus pH signals after filtering and impedance reduction.
According to the pH signal conditioning circuit, the pH electrodes 101 and 102 are respectively connected with the same two circuits which respectively comprise the cascaded pre-filter circuit and the pre-impedance conversion circuit, and the pH signal conditioning circuit forms a pseudo-differential effect, so that after the pH signal measured by the pH electrode is processed by the pseudo-differential of the two circuits, the noises in the two circuits are mutually offset, and the influence of the environment and time on the pH measurement is reduced.
In some embodiments, the pre-filter circuit may be an RC filter circuit, an LC filter circuit, or an active filter, and the specific parameters of the electronic components are selected according to actual conditions.
In a preferred embodiment, the pre-filter circuit comprises a first RC filter circuit, the first RC filter circuit comprises a first resistor R1 and a first capacitor C1, wherein one end of the first resistor R1 is connected with one pH electrode, the other end of the first resistor R1 is connected with one end of the first capacitor C1, and the other end of the first resistor R1 is used as an output end of the pre-filter circuit; the other end of the first capacitor C1 is connected to an input end of a pre-impedance transformation circuit, and the other end of the first capacitor C1 is also grounded.
Referring to fig. 1, taking a pre-filter circuit 111 as an example, the pre-filter circuit 111 includes a first RC filter circuit composed of a first resistor R11 and a first capacitor C11. One end of the first resistor R11 is connected to the pH electrode 101, the other end of the first resistor R11 is connected to one end of the first capacitor C11, and the other end of the first capacitor C11 is grounded and is also connected to the input end of the subsequent pre-impedance transformation circuit 121.
The structure of the pre-filter circuit 112 and the pre-filter circuit 111, the parameters of the electronic components, and the like are the same, wherein the first resistor R12 is the same as the first resistor R11, and the first capacitor C12 is the same as the first capacitor C11.
In other embodiments, the first resistors R11, R12 may be replaced by inductors or magnetic beads. The resistance element is adopted by the first resistor, so that the electromagnetic compatibility interference rejection capability of the pH signal conditioning circuit can be enhanced.
In some embodiments, the pre-impedance transformation circuit comprises an amplification circuit.
In a preferred embodiment, the pre-impedance transformation circuit includes a first operational amplifier U1, the gain of the first operational amplifier U1 being 1.
In the preferred embodiment, the first operational amplifier U1 is a high input impedance type of operational amplifier.
Referring to fig. 1, taking a pre-impedance transformation circuit 121 as an example, the pre-impedance transformation circuit 121 includes a first operational amplifier U11, and the gain of the first operational amplifier U11 is 1. The output terminal of the pre-filter circuit 111 is connected to the positive input terminal (+) of the first operational amplifier U11. Similarly, the pre-impedance transformation circuit 122 includes a first operational amplifier U12 with a gain of 1. The output of the pre-filter circuit 112 is connected to the positive input (+) of the first operational amplifier U12.
The first operational amplifier U11 is the same as the first operational amplifier U12, indicating that its output bias voltage is the same and the bias current is the same. The variations and drifts of the bias voltage and bias current over time and environment are approximate. Therefore, the two pre-impedance conversion circuits form a pseudo-differential effect, circuit noise and signal noise can be mutually offset, and the influence of time and environment on pH measurement is reduced.
In some embodiments, the pH signal conditioning circuit of the present invention further includes a voltage conversion unit adapted to convert a pH signal including a positive signal and a negative signal into a pH signal including only a positive signal, the voltage conversion unit includes two identical voltage conversion circuits, input ends of the two voltage conversion circuits are respectively connected to output ends of the two pre-impedance transformation circuits, and output ends of the two voltage conversion circuits are used as output ends of the pH signal conditioning circuit.
Fig. 2 is a schematic structural diagram of a pH signal conditioning circuit according to another embodiment of the present invention. This embodiment differs from the embodiment shown in fig. 1 in that a voltage converting unit is added. Referring to fig. 2, the pH signal conditioning circuit 200 includes a voltage converting unit 130 in addition to the pre-filtering unit 110 and the pre-impedance transforming unit 120. The voltage converting unit 130 includes two identical voltage converting circuits 131 and 132. Taking the voltage converting circuit 131 as an example, the input terminal of the voltage converting circuit 131 is connected to the output terminal of the pre-impedance transforming circuit 121, and the output terminal of the voltage converting circuit 131 is used as the output terminal 103 of the pH signal conditioning circuit 200.
The pH signal typically measured by the pH electrode is a voltage signal that includes both positive signals greater than 0V and negative signals less than 0V. For example, the voltage peak of the pH signal is between ± 2V. The voltage conversion circuit may adjust the pH signal to include only positive signals. The positive signal is suitable as an input to an analog-to-digital conversion unit for facilitating analog-to-digital conversion of the signal.
In a preferred embodiment, the voltage conversion circuit comprises a second resistor R2, a third resistor R3 and a second capacitor C2, wherein one end of the second resistor R2 is connected to the output end of the pre-impedance transformation circuit, the other end of the second resistor R2 is connected to one end of the third resistor R3 and one end of the second capacitor C2, and the other end of the second resistor R2 is used as the output end of the voltage conversion circuit; the other end of the third resistor R3 is connected with a reference voltage Vref; the other terminal of the second capacitor C2 is connected to ground.
Referring to fig. 2, the voltage converting circuit 131 is taken as an example, and includes a second resistor R21, a third resistor R31, and a second capacitor C21. One end of the second resistor R21 is connected to the output end of the pre-impedance transformation circuit 121, the other end of the second resistor R21 is connected to one end of the third resistor R31 and one end of the second capacitor C21, and the other end of the second resistor R21 is used as the output end of the voltage conversion circuit; the other end of the third resistor R31 is connected with a reference voltage Vref; the other terminal of the second capacitor C21 is connected to ground.
The voltage converting circuit 132 includes a second resistor R22, a third resistor R32, and a second capacitor C22, which are the same as the voltage converting circuit 131. The second resistor R21 is the same as the second resistor R22, the third resistor R31 is the same as the third resistor R32, and the second capacitor C21 is the same as the second capacitor C22.
In the embodiment shown in fig. 2, the output terminal of the voltage conversion circuit 131 serves as the output terminal 103 of the pH signal conditioning circuit, and the output terminal of the voltage conversion circuit 132 serves as the output terminal 104 of the pH signal conditioning circuit.
In some embodiments, the pH signal conditioning circuit of the present invention further includes a back-end filtering unit adapted to filter signal noise input to the back-end filtering unit, where the back-end filtering unit includes two identical back-end filtering circuits, input ends of the two back-end filtering circuits are respectively connected to output ends of the two voltage converting circuits, and output ends of the two back-end filtering circuits are used as output ends of the pH signal conditioning circuit.
Fig. 3 is a schematic structural diagram of a pH signal conditioning circuit according to another embodiment of the present invention. This embodiment differs from the embodiment shown in fig. 2 in that a back-end filtering unit is added. Referring to fig. 3, the pH signal conditioning circuit 300 includes a back-end filtering unit 140 in addition to the pre-filtering unit 110, the pre-impedance transforming unit 120, and the voltage converting unit 130. The back-end filtering unit 140 includes two identical back- end filtering circuits 141 and 142. For example, the back-end filter circuit 141 has an input end connected to the output end of the voltage conversion unit 131, and an output end of the back-end filter circuit 141 is used as the output end 103 of the pH signal conditioning circuit 300.
In some embodiments, the back-end filter circuit may be an RC filter circuit, an LC filter circuit, or an active filter, and the specific parameters of the electronic components are selected according to actual situations.
In a preferred embodiment, the back-end filter circuit comprises a second RC filter circuit, the second RC filter circuit comprises a fourth resistor R4 and a third capacitor C3, wherein one end of the fourth resistor R4 is connected to an output end of one voltage conversion circuit, the other end of the fourth resistor R4 is connected to one end of the third capacitor C3, and the other end of the fourth resistor R4 serves as an output end of the back-end filter circuit; the other terminal of the third capacitor C3 is connected to ground.
Referring to fig. 3, taking a back-end filter circuit 141 as an example, the back-end filter circuit 141 includes a second RC filter circuit composed of a fourth resistor R41 and a third capacitor C31. One end of the fourth resistor R41 is connected to the output end of the voltage converting circuit 131, the other end of the fourth resistor R41 is connected to one end of the third capacitor C31, and the other end of the fourth resistor R41 is used as the output end of the back-end filter circuit 141, which is the output end 103 of the pH signal conditioning circuit 300; the other end of the third capacitor C31 is connected to ground.
The back-end filter circuit 141 and the back-end filter circuit 142 have the same structure, the same parameters of electronic components, and the like, wherein the fourth resistor R41 is the same as the fourth resistor R42, and the third capacitor C31 is the same as the third capacitor C32.
In other embodiments, the fourth resistors R41, R42 may be replaced by inductors or magnetic beads. The resistance element is adopted by the fourth resistor, so that the electromagnetic compatibility and interference rejection capability of the pH signal conditioning circuit can be enhanced.
In some embodiments, the pH signal conditioning circuit of the present invention further includes a back-end impedance transformation unit adapted to reduce an input impedance of the back-end impedance transformation unit, where the back-end impedance transformation unit includes two identical back-end impedance transformation circuits, input ends of the two back-end impedance transformation circuits are respectively connected to output ends of the two back-end filter circuits, and output ends of the two back-end impedance transformation circuits are used as output ends of the pH signal conditioning circuit.
Fig. 4 is a schematic structural diagram of a pH signal conditioning circuit according to another embodiment of the present invention. This embodiment differs from the embodiment shown in fig. 3 in that a back-end impedance transformation unit is added. Referring to fig. 4, the pH signal conditioning circuit 400 includes a back-end impedance transforming unit 150 in addition to the pre-filtering unit 110, the pre-impedance transforming unit 120, the voltage converting unit 130, and the back-end filtering unit 140. The back-end impedance transformation unit 150 includes two identical back-end impedance transformation circuits 151 and 152. Taking the back-end impedance transformation circuit 151 as an example, the input end of the back-end impedance transformation circuit 151 is connected to the output end of the back-end filter circuit 141, and the output end of the back-end impedance transformation circuit 151 is used as the output end 103 of the pH signal conditioning circuit 400.
In some embodiments, the back-end impedance transformation circuit comprises an amplification circuit.
In a preferred embodiment, the back-end impedance transformation circuit includes a second operational amplifier U2, the gain of the second operational amplifier U2 being 1.
In the preferred embodiment, the second operational amplifier U2 is a high input impedance type of operational amplifier.
Referring to fig. 4, taking a back-end impedance transformation circuit 151 as an example, the back-end impedance transformation circuit 151 includes a second operational amplifier U21, and the gain of the second operational amplifier U21 is 1. The output terminal of the back-end filter circuit 141 is connected to the positive input terminal (+) of the second operational amplifier U21. Similarly, the back-end impedance transformation circuit 152 includes a second operational amplifier U22 with a gain of 1. The output terminal of the back-end filter circuit 142 is connected to the positive input terminal (+) of the second operational amplifier U22.
The second operational amplifier U21 is the same as the second operational amplifier U22, indicating that the output bias voltage is the same and the bias current is the same. The variations and drifts of the bias voltage and bias current over time and environment are approximate. Therefore, the two pre-impedance conversion circuits form a pseudo-differential effect, circuit noise and signal noise can be mutually offset, and the influence of time and environment on pH measurement is reduced.
In some embodiments, the output of the pH signal conditioning circuit of the present invention is connected to the input of an analog-to-digital conversion unit adapted to convert the pH signal to a digital signal.
Fig. 5 is a schematic diagram of an application scenario of a pH signal conditioning circuit according to another embodiment of the invention. This embodiment differs from the embodiment shown in fig. 4 in that an analog-to-digital conversion unit is added. Referring to fig. 5, the output ends 103 and 104 of the pH signal conditioning circuit are connected to an analog-to-digital conversion unit 510, so that the pH signal conditioned by the pH signal conditioning circuit is input to the analog-to-digital conversion unit 510, and the analog-to-digital conversion unit 510 performs an analog-to-digital conversion process on the received pH signal, and converts the analog signal into a digital signal. The digital signal may be used for subsequent further calculations or displays.
In some embodiments, if the analog-to-digital conversion unit 510 includes two input terminals to which the differential signal can be directly accessed, the output terminals 103 and 104 are respectively connected; if the analog-to-digital conversion unit 510 includes an input end and cannot directly access the differential signal, the differential signal output by the output ends 103 and 104 of the pH signal conditioning circuit is processed, and the two paths of signals are converted into single-ended signals and input to the input end of the analog-to-digital conversion unit 510. Therefore, the pH signal conditioning circuit can be flexibly connected with various analog-to-digital conversion units.
In some embodiments, by selecting appropriate second and third resistors R2 and R3, the performance of the voltage converting unit 130 can be ensured to be optimal. Referring to fig. 5, taking the voltage conversion circuit 131 as an example, the optimal values of the second resistor R21 and the third resistor R31 may be determined according to the following formulas.
Wherein Vadcd is the minimum input value of the analog-to-digital conversion unit 510, and is generally 0; vi is the output voltage of the pre-filter circuit 111, and Vi is also the input voltage of the pre-impedance transformation circuit 121; omega1,ω2The weight value is less than 1. Omega1The value is between 0 and 0.2, and in order to prevent the circuit output from deviating downwards beyond the minimum value of the range that the analog-to-digital conversion unit 510 can input due to the parameter tolerance of the circuit when the minimum input of the voltage conversion circuit is input, it is recommended that a typical value be set to be between 0.05 and 0.2. Omega2The value is between 0.8 and 1, in order to preventWhen the maximum input of the voltage conversion circuit is reached, the circuit output deviates upwards beyond the maximum value of the range that the analog-to-digital conversion unit 510 can input due to the parameter tolerances of the circuit, suggesting a typical value set between 0.8 and 0.95. Omega1And ω2The specific value of (c) depends on the parameter tolerance of the voltage conversion circuit and the parameters of the analog-to-digital conversion unit 510.
The pH signal conditioning circuit has the following beneficial effects:
firstly, the method comprises the following steps: the pH signals measured by the pH electrode are respectively processed by at least two same pre-filter circuits and two pre-impedance transformation circuits, and the influence of circuit elements on the measurement performance is reduced by a pseudo-differential mode.
Secondly, the method comprises the following steps: the requirements and the cost can be reduced in the aspect of device performance selection. For example, the first operational amplifier U1 and the second operational amplifier U2 may select devices with high input impedance, without requiring devices that satisfy both high input impedance and low output bias voltage.
Thirdly, the method comprises the following steps: the method has good filtering performance, reduces the measurement deviation caused by the external environment, and improves the stability and the precision consistency of the circuit.
Fourthly: the circuit design modularization can select the required module and determine the parameters of the components and parts according to the requirements, and the use is flexible.
This application uses specific language to describe embodiments of the application. Reference to "one embodiment," "an embodiment," and/or "some embodiments" means a feature, structure, or characteristic described in connection with at least one embodiment of the application. Therefore, it is emphasized and should be appreciated that two or more references to "an embodiment" or "one embodiment" or "an alternative embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, some features, structures, or characteristics of one or more embodiments of the present application may be combined as appropriate.
Similarly, it should be noted that in the preceding description of embodiments of the application, various features are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure aiding in the understanding of one or more of the embodiments. This method of disclosure, however, is not intended to require more features than are expressly recited in the claims. Indeed, the embodiments may be characterized as having less than all of the features of a single embodiment disclosed above.
Numerals describing the number of components, attributes, etc. are used in some embodiments, it being understood that such numerals used in the description of the embodiments are modified in some instances by the use of the modifier "about", "approximately" or "substantially". Unless otherwise indicated, "about", "approximately" or "substantially" indicates that the number allows a variation of ± 20%. Accordingly, in some embodiments, the numerical parameters used in the specification and claims are approximations that may vary depending upon the desired properties of the individual embodiments. In some embodiments, the numerical parameter should take into account the specified significant digits and employ a general digit preserving approach. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the range are approximations, in the specific examples, such numerical values are set forth as precisely as possible within the scope of the application.
Although the present application has been described with reference to the present specific embodiments, it will be recognized by those skilled in the art that the foregoing embodiments are merely illustrative of the present application and that various changes and substitutions of equivalents may be made without departing from the spirit of the application, and therefore, it is intended that all changes and modifications to the above-described embodiments that come within the spirit of the application fall within the scope of the claims of the application.
Claims (12)
1. A pH signal conditioning circuit, wherein the pH signal is input into the pH signal conditioning circuit from a pH electrode, the pH signal conditioning circuit is characterized by comprising a pre-filtering unit and a pre-impedance transformation unit which are cascaded, the pre-filtering unit is suitable for filtering noise introduced by the pH electrode, the pre-impedance transformation unit is suitable for reducing the input impedance of the pH signal, wherein,
the pre-filter unit comprises two paths of same pre-filter circuits, wherein the input end of one path of pre-filter circuit is connected with one electrode of the pH electrodes, and the input end of the other path of pre-filter circuit is connected with the other electrode of the pH electrodes;
the pre-impedance conversion unit comprises two same pre-impedance conversion circuits, the input ends of the two pre-impedance conversion circuits are respectively connected with the output ends of the two pre-filter circuits, and the output ends of the two pre-impedance conversion circuits are used as the output ends of the pH signal conditioning circuit.
2. The pH signal conditioning circuit of claim 1, further comprising: the voltage conversion unit is suitable for converting a pH signal comprising a positive signal and a negative signal into a pH signal comprising only a positive signal, and comprises two identical voltage conversion circuits, wherein the input ends of the two voltage conversion circuits are respectively connected with the output ends of the two pre-impedance conversion circuits, and the output ends of the two voltage conversion circuits are used as the output ends of the pH signal conditioning circuit.
3. The pH signal conditioning circuit of claim 2, further comprising: the rear-end filtering unit is suitable for filtering signal noise input to the rear-end filtering unit and comprises two identical rear-end filtering circuits, the input ends of the two rear-end filtering circuits are respectively connected with the output ends of the two voltage conversion circuits, and the output ends of the two rear-end filtering circuits are used as the output ends of the pH signal conditioning circuit.
4. The pH signal conditioning circuit of claim 3, further comprising: the rear-end impedance conversion unit is suitable for reducing the input impedance of the rear-end impedance conversion unit and comprises two identical rear-end impedance conversion circuits, the input ends of the two rear-end impedance conversion circuits are respectively connected with the output ends of the two rear-end filter circuits, and the output ends of the two rear-end impedance conversion circuits are used as the output ends of the pH signal conditioning circuit.
5. The pH signal conditioning circuit of any one of claims 1 to 4, wherein the output is connected to an input of an analog-to-digital conversion unit adapted to convert the pH signal to a digital signal.
6. The pH signal conditioning circuit of claim 1, wherein the pre-filter circuit comprises a first RC filter circuit comprising a first resistor and a first capacitor, wherein one end of the first resistor is connected to one of the pH electrodes, the other end of the first resistor is connected to one end of the first capacitor, and the other end of the first resistor serves as an output of the pre-filter circuit; the other end of the first capacitor is connected with one input end of the pre-impedance transformation circuit, and the other end of the first capacitor is grounded.
7. The pH signal conditioning circuit of claim 1, wherein the pre-impedance transformation circuit comprises a first operational amplifier having a gain of 1.
8. The pH signal conditioning circuit of claim 7, wherein the first operational amplifier is a high input impedance operational amplifier.
9. The pH signal conditioning circuit according to claim 2, wherein the voltage conversion circuit comprises a second resistor, a third resistor and a second capacitor, wherein one end of the second resistor is connected to the output end of the pre-impedance transformation circuit, the other end of the second resistor is connected to one end of the third resistor and one end of the second capacitor, and the other end of the second resistor is used as the output end of the voltage conversion circuit; the other end of the third resistor is connected with a reference voltage; the other end of the second capacitor is grounded.
10. The pH signal conditioning circuit of claim 3, wherein the back end filter circuit comprises a second RC filter circuit comprising a fourth resistor and a third capacitor, wherein one end of the fourth resistor is connected to one output terminal of the voltage conversion circuit, the other end of the fourth resistor is connected to one end of the third capacitor, and the other end of the fourth resistor is used as the output terminal of the back end filter circuit; the other end of the third capacitor is grounded.
11. The pH signal conditioning circuit of claim 4, wherein the back-end impedance transformation circuit comprises a second operational amplifier having a gain of 1.
12. The pH signal conditioning circuit of claim 11, wherein the second operational amplifier is a high input impedance operational amplifier.
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202011413210.5A CN114614781A (en) | 2020-12-04 | 2020-12-04 | PH signal conditioning circuit |
| PCT/CN2021/135315 WO2022117070A1 (en) | 2020-12-04 | 2021-12-03 | Ph signal conditioning circuit |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202011413210.5A CN114614781A (en) | 2020-12-04 | 2020-12-04 | PH signal conditioning circuit |
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| CN114614781A true CN114614781A (en) | 2022-06-10 |
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| JPS5892854A (en) * | 1981-11-11 | 1983-06-02 | Horiba Ltd | Ion concentration analyser |
| CN101135662B (en) * | 2006-08-30 | 2010-11-10 | 梅特勒-托利多仪器（上海）有限公司 | Electric potential analyse electric pole measuring method and apparatus |
| US9851337B2 (en) * | 2013-12-06 | 2017-12-26 | The University Of Akron | Universal water condition monitoring device |
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