CN113866233A - High-precision online dissolved oxygen measuring instrument - Google Patents
High-precision online dissolved oxygen measuring instrument Download PDFInfo
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- CN113866233A CN113866233A CN202111280741.6A CN202111280741A CN113866233A CN 113866233 A CN113866233 A CN 113866233A CN 202111280741 A CN202111280741 A CN 202111280741A CN 113866233 A CN113866233 A CN 113866233A
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- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 title claims abstract description 283
- 229910052760 oxygen Inorganic materials 0.000 title claims abstract description 283
- 239000001301 oxygen Substances 0.000 title claims abstract description 283
- 238000005070 sampling Methods 0.000 claims abstract description 198
- 239000003990 capacitor Substances 0.000 claims description 64
- 239000007864 aqueous solution Substances 0.000 claims description 53
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- NQUNIMFHIWQQGJ-UHFFFAOYSA-N 2-nitro-5-thiocyanatobenzoic acid Chemical compound OC(=O)C1=CC(SC#N)=CC=C1[N+]([O-])=O NQUNIMFHIWQQGJ-UHFFFAOYSA-N 0.000 claims description 27
- 239000000243 solution Substances 0.000 claims description 27
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 9
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Abstract
The invention discloses a high-precision online dissolved oxygen measuring instrument which comprises a dissolved oxygen sampling circuit, a temperature compensation sampling circuit, an MCU (microprogrammed control unit) processor and a key display unit, wherein the dissolved oxygen sampling circuit, the temperature compensation sampling circuit and the key display unit are respectively and electrically connected with the MCU processor; the temperature compensation sampling circuit is divided into a constant current reference circuit, a differential amplifying circuit and a secondary amplifying circuit. On one hand, in the constant current reference circuit of the temperature compensation sampling circuit, the electric signal provided by the input end of the constant current reference circuit is shaped through the logic inverter, the waveform of the shaped electric signal has low noise, and the input signal is more stable and reliable; on the other hand, the temperature signal is amplified by the differential amplifying circuit, so that the temperature signal can be completely or partially offset, the grid current is reduced, the common-mode signal interference is inhibited, the temperature drift of the output signal is greatly reduced, and the measurement precision of the dissolved oxygen is improved.
Description
Technical Field
The invention relates to the field of online chemical analysis instruments and meters, in particular to a high-precision online dissolved oxygen measuring instrument.
Background
With the rapid development of domestic industry and agriculture, water pollution is becoming more serious, and sewage needs to be monitored and treated urgently. The oxygen content in the aqueous solution is used as an important index for evaluating the quality of the aqueous solution, and is an essential monitoring project in water quality monitoring. At present, the domestic water quality inspection comprises the detection of the oxygen content of the aqueous solution, firstly, the sampling is carried out and analyzed in a laboratory, the detection method has long detection period, consumes time and labor, most of detection instruments used for the detection adopt foreign equipment and technologies, and the foreign equipment has high price and large volume, and part of the foreign equipment can not be used even if the foreign equipment does not accord with the Chinese environmental conditions; secondly, a dissolved oxygen detector is adopted for on-line detection, the dissolved oxygen detector is generally based on current measurement of a polarographic dissolved oxygen electrode, a polarization voltage (about DC0.7V) is loaded on the dissolved oxygen electrode, the anode in the dissolved oxygen electrode outputs current at a specific temperature, the current output by the anode is in direct proportion to the oxygen partial pressure in the solution, and the oxygen content in the solution is converted according to the magnitude of the anode output current in the dissolved oxygen electrode through the relation. The dissolved oxygen detector has the advantages of low cost and good stability, but the output current of the anode in the dissolved oxygen electrode is influenced by the temperature, the atmospheric pressure, the salinity and the like of the aqueous solution, and the temperature of the aqueous solution and the atmospheric pressure and the salinity in the measuring environment need to be compensated for accurately measuring the oxygen content of the aqueous solution. However, on one hand, the existing dissolved oxygen detectors do not basically compensate for atmospheric pressure and salinity in the measurement environment; on the other hand, although the existing dissolved oxygen detectors compensate the temperature when measuring the oxygen content of the aqueous solution, most of them adopt a constant value compensation mode, that is, inputting a fixed temperature value and substituting the fixed temperature value into a formula to calculate the oxygen content of the aqueous solution, under the constant value compensation mode, the temperature of the aqueous solution is changed during the line measurement, the constant value compensation mode is not in accordance with the actual situation, and the error of the measurement result of the oxygen content of the aqueous solution is still large; although a few existing dissolved oxygen detectors adopt a dissolved oxygen electrode with a temperature sensor, the temperature of the aqueous solution is measured in real time through the temperature sensor, and the measurement of the oxygen content of the aqueous solution is compensated in real time, temperature signals transmitted by the temperature sensor in the measurement process fluctuate along with the fluctuation of the aqueous solution, the measurement result is greatly influenced by temperature drift, and the finally measured oxygen content of the aqueous solution is still inaccurate and unstable.
Disclosure of Invention
The invention aims to provide a high-precision online dissolved oxygen measuring instrument.
The technical scheme for realizing the purpose of the invention is as follows: a high-precision online dissolved oxygen measuring instrument comprises a dissolved oxygen sampling circuit, a temperature compensation sampling circuit, an MCU (microprogrammed control unit) processor and a key display unit, wherein the dissolved oxygen sampling circuit, the temperature compensation sampling circuit and the key display unit are respectively and electrically connected with the MCU processor;
the temperature compensation sampling circuit consists of a temperature sampling end, a logic inverter, an operational amplifier, a resistor and a capacitor, wherein the temperature sampling end of the temperature compensation sampling circuit comprises a temperature sampling positive end NTCA and a temperature sampling negative end NTCB, and the temperature compensation sampling circuit is divided into a constant current reference circuit, a differential amplifying circuit and a secondary amplifying circuit; wherein the content of the first and second substances,
IN the constant current reference circuit, a logic inverter U8A, a logic inverter U8B, a resistor R14 and a resistor R20 are sequentially connected IN series from an input end IN of the constant current reference circuit to the ground, a connecting end of the resistor R14 connected with a resistor R20 is connected with a non-inverting input end of an operational amplifier U9A, a resistor R26 is connected IN series from an inverting input end of the operational amplifier U9A to the ground, an output end of the operational amplifier U9A is connected with the positive temperature sampling end NTCA, and a connecting end of the resistor R26 connected with the inverting input end of the operational amplifier U9A is connected with the negative temperature sampling end NTCB;
in the differential amplifying circuit, a series resistor R29 is arranged between the positive temperature sampling end NTCA and the non-inverting input end of the operational amplifier U13A, a series resistor R30 is arranged between the non-inverting input end of the operational amplifier U13A and the ground, a series resistor R34 is arranged between the negative temperature sampling end NTCB and the inverting input end of the operational amplifier U13A, and a series resistor R37 is arranged between the inverting input end of the operational amplifier U13A and the output end of the operational amplifier U13A;
in the secondary amplifying circuit, a series resistor R33 is arranged between the non-inverting input end of an operational amplifier U13B and the output end of an operational amplifier U13A, a series resistor R41 is arranged between the inverting output end of the operational amplifier U13B and the ground, a series resistor R40 is arranged between the inverting output end of the operational amplifier U13B and the output end of an operational amplifier U13B, and the output end of the operational amplifier U13B is connected with the output end ColdT of the temperature compensation sampling circuit;
the dissolved oxygen sampling circuit is used for collecting an oxygen content signal of the aqueous solution and transmitting the collected oxygen content signal of the aqueous solution to the MCU processor; the temperature compensation sampling circuit is used for collecting a water solution temperature signal and transmitting the collected water solution temperature signal to the MCU processor; the MCU processor is used for receiving the aqueous solution oxygen content signal transmitted by the dissolved oxygen sampling circuit and the aqueous solution temperature signal transmitted by the temperature compensation sampling circuit, obtaining a final aqueous solution oxygen content signal according to the received aqueous solution oxygen content signal and the aqueous solution temperature signal, and sending the obtained final aqueous solution oxygen content signal to the key display unit for displaying.
Further, an input end IN of the constant current reference circuit is connected with a PWM interface of the MCU processor. The input end IN of the constant current reference circuit provides an electric signal required by the operation of the constant current reference circuit, the electric signal can be but is not limited to a PWM signal, the PWM signal can be obtained through a PWM interface of the MCU processor, the PWM signal is easy to obtain, and the obtained PWM signal is standard and easy to control, so preferably, the input end IN of the constant current reference circuit is connected to the PWM interface of the MCU processor.
Further, a resistor R23 is connected between the inverting input end of the operational amplifier U9A and the temperature sampling negative end NTCB; the capacitor C18 is connected in series between the inverting input terminal of the operational amplifier U9A and the output terminal of the operational amplifier U9A. The resistor R23 and the capacitor C18 are arranged in the circuit and play the roles of signal stabilization and protection.
Further, an operational amplifier U10A is arranged between the temperature sampling positive terminal NTCA and the resistor R29, wherein a non-inverting input terminal of the operational amplifier U10A is connected to the temperature sampling positive terminal NTCA, a resistor R31 is connected in series between an inverting input terminal of the operational amplifier U10A and an output terminal of the operational amplifier U10A, two ends of the resistor R31 are connected in parallel to a capacitor C30, and an output terminal of the operational amplifier U10A is connected to a resistor R29; an operational amplifier U10B is arranged between the temperature sampling negative end NTCB and the resistor R34, wherein the non-inverting input end of the operational amplifier U10B is connected with the temperature sampling negative end NTCB, a resistor R36 is connected between the inverting input end of the operational amplifier U10B and the output end of the operational amplifier U10B in series, two ends of the resistor R36 are connected with a capacitor C35 in parallel, and the output end of the operational amplifier U10B is connected with a resistor R34. The operational amplifier U10A and the operational amplifier U10B form a voltage follower respectively, the voltage follower is arranged, the voltage input to the rear-end differential amplification circuit is enabled to be more stable, the resistor R31 and the resistor R36 in the voltage follower play a protection role, and the capacitor C30 and the capacitor C35 play a filtering role.
Furthermore, a resistor R4 and a resistor R1 are connected in series between the resistor R14 and the non-inverting input end of the operational amplifier U9A, a capacitor C14 is also connected in series between the non-inverting input end of the operational amplifier U9A and the ground, and a capacitor C16 is connected in series between the connection end of the resistor R4 and the resistor R1 and the ground; a resistor R27 is connected in series to a connecting line between the non-inverting input end of the operational amplifier U10A and the temperature sampling positive-direction end NTCA, a capacitor C20 is connected between the non-inverting input end of the operational amplifier U10A and the ground in series, a resistor R32 is connected in series to a connecting line between the non-inverting input end of the operational amplifier U10B and the temperature sampling negative-direction end NTCB, and a capacitor C31 is connected between the non-inverting input end of the operational amplifier U10B and the ground in series; a capacitor C32 is connected in parallel with two ends of the resistor R37; a resistor R35 is connected in series on a connecting line between the output end of the operational amplifier U13B and the output end ColdT of the temperature compensation sampling circuit, and a capacitor C33 and a capacitor C34 which are connected in parallel are connected in series between the output end ColdT of the temperature compensation sampling circuit and the ground. In the constant current reference circuit, a resistor R4, a capacitor C16, a resistor R1 and a capacitor C14 form two filter circuits respectively; in the differential amplifying circuit, a resistor R27, a capacitor C20, a resistor R32 and a capacitor C31 also form two filter circuits respectively; in the two-stage amplifying circuit, the resistor R35, the capacitor C33 and the capacitor C34 also form a filter circuit. The filter circuits and the capacitor C32 can effectively reduce the noise interference in the circuit, so that the signals in the circuits are more stable and reliable.
Furthermore, the dissolved oxygen sampling circuit comprises a dissolved oxygen sampling end, an operational amplifier, a triode, a resistor and a capacitor, wherein the dissolved oxygen sampling end of the dissolved oxygen sampling circuit comprises a dissolved oxygen sampling forward end Cath and a dissolved oxygen sampling ground end Ande, and the dissolved oxygen sampling circuit is divided into a dissolved oxygen sampling reference circuit, a first-stage operational amplifier circuit and a second-stage operational amplifier circuit; wherein the content of the first and second substances,
in the dissolved oxygen sampling reference circuit, a non-inverting input terminal of an operational amplifier U15C is connected with a power supply terminal VCC1, an inverting input terminal of the operational amplifier U15C is connected with a series resistor R25 between bases of an NPN triode Q1, an output terminal of the operational amplifier U15C is connected with a series resistor R19 between bases of an NPN triode Q1, a series resistor R16 between a collector of a triode Q1 and the power supply terminal VCC2, an emitter of an NPN triode Q1 is connected with an inverting input terminal of an operational amplifier U15C, an inverting input terminal of the operational amplifier U15C is sequentially connected with a resistor R24 and a resistor R21 from ground, a connecting terminal connected with a resistor R24 and a resistor R21 is connected with a series resistor R B between the inverting input terminal of the operational amplifier U15B, a non-inverting input terminal of the operational amplifier U15B is grounded, an inverting input terminal of the operational amplifier U15B is connected with a series resistor R B between the inverting input terminal of the operational amplifier U15B;
in the first-stage operational amplifier circuit, a resistor R12 is connected between the inverting input end of an operational amplifier U15A and the positive end Cath of the dissolved oxygen sampling, and a resistor R15 is connected between the inverting input end of the operational amplifier U15A and the output end of the operational amplifier U15A;
in the two-stage operational amplifier circuit, a resistor R2 is connected in series between the inverting input terminal of the operational amplifier U15D and the output terminal of the operational amplifier U15A, a resistor R18 is connected in series between the non-inverting input terminal of the operational amplifier U15D and a power supply terminal VCC3, a resistor R13 is connected in series between the non-inverting input terminal of the operational amplifier U15D and the ground, a resistor R11 is connected in series between the inverting input terminal of the operational amplifier U15D and the output terminal of the operational amplifier U15D, and the output terminal of the operational amplifier U15D is connected with the output terminal AD _ SIn of the dissolved oxygen sampling circuit. The dissolved oxygen sampling reference circuit provides a polarization voltage (DC0.7V) for the dissolved oxygen sampling end, and simultaneously provides a reference voltage for the primary operational amplifier circuit; the first-stage operational amplifier circuit and the second-stage operational amplifier circuit amplify the collected electric signals step by step through two-stage operational amplifier so as to accord with the electric signals in the receiving range of the AD conversion built in the MCU processor.
Further, the high-precision online dissolved oxygen measuring instrument further comprises a transmitting output unit, and the transmitting output unit is electrically connected with the MCU processor. The transmitting and outputting unit receives a PWM port duty ratio waveform signal from the MCU processor, modulates and converts the PWM signal into a linear 0-20mA or 4-20mA analog signal, and outputs the linear 0-20mA or 4-20mA analog signal to external equipment to synchronously check the dissolved oxygen content value in different places; the function of the high-precision online dissolved oxygen measuring instrument is added, and the convenience and the flexibility of use are improved.
Further, the high-precision online dissolved oxygen measuring instrument further comprises a communication output circuit, and the communication output circuit is electrically connected with the MCU processor. The communication output circuit is arranged to realize real-time communication between the high-precision online dissolved oxygen measuring instrument and an external system. The communication output circuit can adopt a 485 communication circuit and comprises a 485 communication chip, a TVS protection tube and a current-limiting resistor, wherein the 485 communication chip used in the communication output circuit is powered by double power supplies, namely DC3.3V and DC5V, and the chip is internally provided with an isolation circuit, so that the design that in the traditional circuit, an optical coupler needs to be connected in a peripheral circuit for photoelectric isolation is reduced, namely, the isolation function is reserved to prevent large voltage from reversely jumping to an MCU processor, and the complexity of the peripheral circuit is reduced; two TVS protection tubes are respectively loaded at the A, B two ends of the 485 communication chip output, so that the 485 communication chip can be effectively protected from being broken down by large voltage or damaged by short circuit of the output end; the current limiting resistor is mainly used for limiting the current in the communication output circuit, so that the current in the communication output circuit is within an acceptable range, and if the current is too large, the current limiting resistor is burnt out in the first time.
Further, the high-precision online dissolved oxygen measuring instrument further comprises an alarm output circuit, and the alarm output circuit is electrically connected with the MCU processor. The alarm output circuit mainly comprises a relay, a Darlington tube and a thermal pressure-sensitive protection tube, wherein the Darlington tube is used for driving the relay, when the alarm is specifically given out, the MCU processor controls the actuation and release of the relay according to an alarm value preset in a parameter, when an acquisition value exceeds a limit, an alarm event is triggered, a corresponding IO port of the MCU processor outputs a high level to the Darlington tube, the Darlington tube outputs a non-operation result and a corresponding driving electrode outputs a low level, at the moment, DC5V voltage loaded in a relay driving loop generates loop current and flows into the Darlington tube in a current filling mode, the relay driving loop is electrically actuated, and an alarm signal is generated. The high-precision online dissolved oxygen measuring instrument has the advantages that the Darlington tube has larger current filling characteristic and can drive the relay with larger power, and meanwhile, the Darlington tube supports a plurality of channels to carry out logic non-control, so that the high-precision online dissolved oxygen measuring instrument can support the design requirement of multi-channel alarm; in addition, the thermal pressure-sensitive protection tube in the alarm output circuit is used as a protection device, so that electric sparks can be absorbed quickly, and the drive circuit is protected. The model of the adopted Darlington tube of the high-precision online dissolved oxygen measuring instrument is generally ULN 2003.
Further, the online dissolved oxygen measuring instrument of high accuracy corresponds and is provided with the dissolved oxygen electrode, the dissolved oxygen electrode is including having electrode signal end and temperature compensation signal end, the dissolved oxygen electrode signal end with the dissolved oxygen sampling circuit is connected, the dissolved oxygen electrode the temperature compensation signal end with the temperature sampling circuit the temperature sampling end is connected. When the high-precision online dissolved oxygen measuring instrument measures the oxygen content of the water solution, the high-precision online dissolved oxygen measuring instrument is matched with a dissolved oxygen electrode for use, wherein the dissolved oxygen electrode usually adopts a polarographic electrode and is mainly used for sensing an oxygen content signal and a temperature signal in the solution, converting the sensed oxygen content signal and the sensed temperature signal into electric signals and transmitting the electric signals to the high-precision online dissolved oxygen measuring instrument for collection, display and the like.
When the high-precision online dissolved oxygen measuring instrument is used, the high-precision online dissolved oxygen measuring instrument is matched with a dissolved oxygen electrode for use, specifically, an electrode signal end of the dissolved oxygen electrode is connected with the dissolved oxygen sampling circuit, and a temperature compensation signal end of the dissolved oxygen electrode is connected with the temperature sampling end of the temperature compensation sampling circuit. After the dissolved oxygen electrode is inserted into the high-precision online dissolved oxygen measuring instrument, the dissolved oxygen electrode is used for sensing an oxygen content signal and a temperature signal of an aqueous solution; the dissolved oxygen sampling circuit is used for collecting an oxygen content signal of the aqueous solution sensed by the dissolved oxygen electrode and transmitting the collected oxygen content signal of the aqueous solution to the MCU processor; the temperature compensation sampling circuit is used for collecting the aqueous solution temperature signal sensed by the dissolved oxygen electrode and transmitting the collected aqueous solution temperature signal to the MCU processor; the MCU processor is used for receiving the aqueous solution oxygen content signal transmitted by the dissolved oxygen sampling circuit and the aqueous solution temperature signal transmitted by the temperature compensation sampling circuit, processing the aqueous solution oxygen content signal and the aqueous solution temperature signal according to the received aqueous solution oxygen content signal and the received aqueous solution temperature signal to obtain a final aqueous solution oxygen content signal, and meanwhile sending the final aqueous solution oxygen content signal obtained through processing to the key display unit for displaying.
In the temperature compensation sampling circuit, the constant current reference circuit provides constant current source reference for temperature sensors in dissolved oxygen electrodes connected to a temperature sampling positive end NTCA and on two ends of a temperature sampling negative end NTCB, so that resistance signals of the temperature sensors in the dissolved oxygen electrodes can be converted into voltage signals, and finally the voltage signals are gradually amplified by a differential amplifying circuit and a secondary amplifying circuit and are collected by an MCU (microprogrammed control unit) processor. On one hand, in the constant current reference circuit of the temperature compensation sampling circuit, the logic inverter U8A and the logic inverter U8B are used for shaping the electric signals provided by the input end of the constant current reference circuit, the waveform of the shaped electric signals has low noise, and the input signals are more stable and reliable, so that the constant current source reference provided for the temperature sensor in the dissolved oxygen electrode is more stable and accurate, and a reliable basis is laid for accurate sampling of temperature signals; on the other hand, the temperature signal is amplified through the differential amplifying circuit, compared with a common operational amplifying circuit, the differential amplifying circuit has the advantages that the input is differential mode input, the polarities are opposite, temperature drift generated by the fact that power-on signals at two ends of the logic inverter U8A and the logic inverter U8B are affected by the temperature can be completely or partially offset after the opposite polarities are amplified under the action of the differential amplifying circuit, grid current is reduced, common-mode signal interference is restrained, temperature drift of output signals is greatly reduced, the influence of the temperature drift in the temperature measuring process is reduced to the minimum, even the temperature drift is completely eliminated, the influence caused by the temperature drift in the temperature measuring process is effectively controlled, the temperature measuring precision is improved, and the measuring precision of dissolved oxygen is further improved.
Drawings
FIG. 1 is a functional structure diagram of a high-precision online dissolved oxygen measuring instrument according to the present invention;
FIG. 2 is a circuit diagram of a dissolved oxygen sampling circuit of the high-precision on-line dissolved oxygen measuring instrument of the present invention;
FIG. 3 is a circuit diagram of a temperature compensation sampling circuit of the high-precision online dissolved oxygen measuring instrument of the present invention;
FIG. 4 is a circuit diagram of a communication output circuit of the high-precision online dissolved oxygen measuring instrument according to the present invention;
FIG. 5 is a flow chart of the program running method in the MCU processor of the high-precision online dissolved oxygen measuring instrument.
Detailed Description
The preferred embodiments of the high-precision online dissolved oxygen measuring instrument according to the present invention will be described in detail with reference to the accompanying drawings:
as shown in fig. 1, a high-precision online dissolved oxygen measuring instrument comprises a dissolved oxygen sampling circuit 1, a temperature compensation sampling circuit 2, an MCU processor 3 and a key display unit 4, wherein the dissolved oxygen sampling circuit 1, the temperature compensation sampling circuit 2 and the key display unit 4 are respectively electrically connected to the MCU processor 3, and the dissolved oxygen sampling circuit 1 is configured to collect an oxygen content signal of an aqueous solution and transmit the collected oxygen content signal of the aqueous solution to the MCU processor 3; the temperature compensation sampling circuit 2 is used for collecting a water solution temperature signal and transmitting the collected water solution temperature signal to the MCU processor 3; the MCU processor 3 is used for receiving the aqueous solution oxygen content signal transmitted by the dissolved oxygen sampling circuit 1 and the aqueous solution temperature signal transmitted by the temperature compensation sampling circuit 2, obtaining a final aqueous solution oxygen content signal according to the received aqueous solution oxygen content signal and the aqueous solution temperature signal, and simultaneously sending the obtained final aqueous solution oxygen content signal to the key display unit 4 for display.
The high-precision online dissolved oxygen measuring instrument is correspondingly provided with a dissolved oxygen electrode 10, the dissolved oxygen electrode 10 comprises an electrode signal end 101 and a temperature compensation signal end 102, the electrode signal end 101 of the dissolved oxygen electrode 10 is connected with the dissolved oxygen sampling circuit 1, and the temperature compensation signal end 102 of the dissolved oxygen electrode 10 is connected with the temperature compensation sampling circuit 2. The dissolved oxygen electrode 10 is provided with a temperature sensor therein, and the temperature compensation signal terminal 102 is two terminals of the temperature sensor in the dissolved oxygen electrode 10. Since the structure having the temperature sensor in the dissolved oxygen electrode 10 is prior art, it will not be described in detail in this application.
The high-precision online dissolved oxygen measuring instrument is used together with a dissolved oxygen electrode 10 when measuring the oxygen content of an aqueous solution, wherein the dissolved oxygen electrode 10 generally adopts a polarographic electrode and is mainly used for sensing an oxygen content signal and a temperature signal in the solution, converting the sensed oxygen content signal and the sensed temperature signal into electric signals, and transmitting the electric signals to the high-precision online dissolved oxygen measuring instrument for collection, display and the like.
As shown in fig. 2, the dissolved oxygen sampling circuit 1 of the high-precision online dissolved oxygen measuring instrument comprises a dissolved oxygen sampling end, an operational amplifier, a triode, a resistor and a capacitor, wherein the dissolved oxygen sampling end of the dissolved oxygen sampling circuit 1 comprises a dissolved oxygen sampling forward end Cath and a dissolved oxygen sampling ground end Anode, the dissolved oxygen sampling ground end Anode is grounded, and the dissolved oxygen sampling circuit 1 is divided into a dissolved oxygen sampling reference circuit 11, a primary operational amplifier circuit 12 and a secondary operational amplifier circuit 13; wherein the content of the first and second substances,
in the dissolved oxygen sampling reference circuit 11, a non-inverting input terminal of an operational amplifier U15C is connected to a power supply terminal VCC1, an inverting input terminal of the operational amplifier U15C is connected to a series resistor R25 between bases of an NPN triode Q1, an output terminal of the operational amplifier U15C is connected to a series resistor R19 between bases of an NPN triode Q1, a series resistor R16 between a collector of the triode Q1 and the power supply terminal VCC2, an emitter of the NPN triode Q1 is connected to an inverting input terminal of an operational amplifier U15C, an inverting input terminal of the operational amplifier U15C is connected to ground in series with a resistor R24 and a resistor R21 in sequence, a connection terminal where the resistor R24 and the resistor R21 are connected to an inverting input terminal of the operational amplifier U15B, a non-inverting input terminal of the operational amplifier U15B is grounded, an inverting input terminal of the operational amplifier U15B is connected to an output terminal of the operational amplifier U15B in series resistor R B, and an inverting input terminal of the operational amplifier U15B are connected to a series resistor B;
in the first-stage operational amplifier circuit 12, a resistor R12 is connected in series between the inverting input terminal of the operational amplifier U15A and the positive terminal Cath of the dissolved oxygen sample, and a resistor R15 is connected in series between the inverting input terminal of the operational amplifier U15A and the output terminal of the operational amplifier U15A;
in the two-stage operational amplifier circuit 13, a series resistor R2 is connected between the inverting input terminal of the operational amplifier U15D and the output terminal of the operational amplifier U15A, a series resistor R18 is connected between the non-inverting input terminal of the operational amplifier U15D and the power supply terminal VCC3, a series resistor R13 is connected between the non-inverting input terminal of the operational amplifier U15D and the ground, a series resistor R11 is connected between the inverting input terminal of the operational amplifier U15D and the output terminal of the operational amplifier U15D, and the output terminal of the operational amplifier U15D is connected to the output terminal AD _ SIn of the dissolved oxygen sampling circuit.
In the dissolved oxygen sampling reference circuit 11 of the dissolved oxygen sampling circuit 1, an operational amplifier U15C and an NPN triode Q1 form an operational amplifier circuit, the operational amplifier U15C mainly provides driving voltage for a back-end circuit, and the operational amplifier U15C has small output current, and the NPN triode Q1 which is matched with the operational amplifier U15C has a current expansion function and is used for increasing current on a circuit so as to meet the driving requirement of the back-end circuit. In the dissolved oxygen sampling circuit 1, an operational amplifier U15B, a resistor R3 and a resistor R7 form an inverse operational amplifier circuit, which amplifies and adjusts an electric signal of the circuit to output a stable and reliable voltage (DC0.7V), and then provides a reference voltage for the primary operational amplifier circuit 12, and provides a polarization voltage of DC0.7V for the dissolved oxygen electrode 10 after being connected and matched with the dissolved oxygen electrode 10 when in use.
The invention relates to a high-precision online dissolved oxygen measuring instrument.A reference voltage of a primary operational amplifier circuit 12 is provided by a dissolved oxygen sampling reference circuit 11; the reference voltage of the secondary operational amplifier circuit 13 is provided by a voltage dividing circuit of the resistor R18 and the resistor 13.
The high-precision online dissolved oxygen measuring instrument is used for connecting a dissolved oxygen electrode 10, wherein the electrode signal end 101 of the dissolved oxygen electrode 10 is connected with the dissolved oxygen sampling end of the dissolved oxygen sampling circuit 1, and specifically, the electrode signal end 101 of the dissolved oxygen electrode 10 is connected to a dissolved oxygen sampling positive end Cath and a dissolved oxygen sampling ground end Anode; after connection, the dissolved oxygen electrode 10 obtains a polarization voltage of DC0.7V supplied from the dissolved oxygen sampling reference circuit 11, oxygen in the solution diffuses through the membrane in the dissolved oxygen electrode 10, electrons are released from the cathode of the dissolved oxygen electrode 10, and electrons are received by the anode of the dissolved oxygen electrode 10, so that a current is generated, and the current value is usually small and is of the order of nA. The dissolved oxygen electrode 10 generates current which is input into the dissolved oxygen sampling circuit 1 and sequentially passes through a first-stage operational amplifier circuit 12 and a second-stage operational amplifier circuit 13 in the dissolved oxygen sampling circuit 1, wherein the first-stage operational amplifier circuit 12 converts the input current signal into a direct-current voltage signal and then amplifies the direct-current voltage signal; the second-stage operational amplifier circuit 13 performs a second amplification on the voltage signal at the output terminal of the first-stage operational amplifier circuit 12, so that the final sampling signal can be received within the range that can be received by the AD conversion in the MCU processor 3.
The invention relates to a high-precision online dissolved oxygen measuring instrument, which inputs an electric signal generated by a dissolved oxygen electrode 10 in a dissolved oxygen sampling circuit 1, outputs and transmits the electric signal to an MCU (microprogrammed control unit) processor 3 after being amplified step by a first-stage operational amplifier circuit 12 and a second-stage operational amplifier circuit 13, and converts the electric signal into a digital quantity signal which can be identified by the MCU processor 3 by an AD (analog-to-digital) converter in the MCU processor 3 so as to finish sampling of an oxygen content signal in a solution.
In the high-precision online dissolved oxygen measuring instrument, under an ideal state, a current signal generated by the dissolved oxygen electrode 10 linearly changes along with the oxygen content in the solution; in actual measurement, the output current of the dissolved oxygen electrode 10 is greatly influenced by the temperature of the solution, the temperature of the solution is increased, and the output current of the dissolved oxygen electrode 10 is correspondingly increased. In order to improve the accuracy of the measurement of the oxygen content in the solution, the collected oxygen content signal of the solution needs to be subjected to nonlinear compensation, wherein the temperature compensation sampling circuit 2 is mainly used for collecting the temperature signal of the electrode film temperature sensor in the electrode.
As shown in fig. 3, the temperature compensation sampling circuit 2 of the high-precision online dissolved oxygen measuring instrument comprises a temperature sampling end, a logic inverter, an operational amplifier, a resistor and a capacitor, wherein the temperature sampling end of the temperature compensation sampling circuit 2 comprises a temperature sampling positive end NTCA and a temperature sampling negative end NTCB, and the temperature compensation sampling circuit 2 is divided into a constant current reference circuit 21, a differential amplifying circuit 22 and a secondary amplifying circuit 23; wherein the content of the first and second substances,
IN the constant current reference circuit 21, an input end IN of the constant current reference circuit 21 is connected with a PWM interface of the MCU processor 3, a logic inverter U8A, a logic inverter U8B, a resistor R14 and a resistor R20 are sequentially connected IN series between an input end IN of the constant current reference circuit 21 and the ground, a resistor R4 and a resistor R1 are sequentially connected IN series between a connecting end of a resistor R14 and a resistor R20 and a non-inverting input end of an operational amplifier U9A, a capacitor C14 is further connected IN series between the non-inverting input end of the operational amplifier U9A and the ground, a capacitor C16 is connected IN series between a connecting end of the resistor R4 and the resistor R1 and the ground, a resistor R23 and a resistor R26 are sequentially connected IN series between an inverting input end of the operational amplifier U9A and the ground, a capacitor C18 is connected IN series between an inverting input end of the operational amplifier U9A and an output end of the operational amplifier U9A, an output end of the operational amplifier U9A is connected with the positive temperature sampling end NTCA, and an NTCB connected end of the resistor R23 and the resistor R26 is connected with the negative temperature sampling end NTCB;
in the differential amplifier circuit 22, a resistor R27 is connected in series between the temperature sampling positive terminal NTCA and the non-inverting input terminal of the operational amplifier U10A, a capacitor C20 is connected in series between the non-inverting input terminal of the operational amplifier U10A and the ground, a resistor R31 is connected in series between the inverting input terminal of the operational amplifier U10A and the output terminal of the operational amplifier U10A, a capacitor C30 is connected in parallel between the two terminals of the resistor R31, a resistor R29 is connected between the output terminal of the operational amplifier U10A and the non-inverting input terminal of the operational amplifier U13A, and a resistor R30 is connected in series between the non-inverting input terminal of the operational amplifier U13A and the ground; a resistor R32 is connected between the temperature sampling negative end NTCB and the non-inverting input end of the operational amplifier U10B in series, a capacitor C31 is connected between the non-inverting input end of the operational amplifier U10B and the ground in series, a resistor R36 is connected between the inverting input end of the operational amplifier U10B and the output end of the operational amplifier U10B in series, a capacitor C35 is connected between two ends of the resistor R36 in parallel, a resistor R34 is connected between the output end of the operational amplifier U10B and the inverting input end of the operational amplifier U13A in series, a resistor R37 is connected between the inverting input end of the operational amplifier U13A and the output end of the operational amplifier U13A in series, and a capacitor C32 is connected between two ends of the resistor 37 in parallel;
in the second-stage amplifying circuit 23, a series resistor R33 is connected between the non-inverting input terminal of the operational amplifier U13B and the output terminal of the operational amplifier U13A, a series resistor R41 is connected between the inverting output terminal of the operational amplifier U13B and the ground, a series resistor R40 is connected between the inverting output terminal of the operational amplifier U13B and the output terminal of the operational amplifier U13B, a resistor R35 is connected in series on a connection line between the output terminal of the operational amplifier U13B and the output terminal ColdT of the temperature compensation sampling circuit 2, and a parallel capacitor C33 and a parallel capacitor C34 are connected in series between the output terminal of the temperature compensation sampling circuit 2 and the ground.
IN the high-precision online dissolved oxygen measuring instrument, IN the constant current reference circuit 21 of the temperature compensation sampling circuit 2, an electric signal provided by an input end IN of the constant current reference circuit 21 passes through a logic inverter U8A and a logic inverter U8B, and is shaped by the logic inverter U8A and a logic inverter U8B; the shaped input signal is stably input to an operational amplifier U9A through voltage division of a resistor R14 and a resistor R20, so that the voltage loaded on the resistor R26 is constant, and the current flowing through the resistor R26 is constant; because the current flowing from the temperature sampling positive terminal NTCA to the temperature sampling negative terminal NTCB and the current flowing through the resistor R26 are on the same line, the constant current reference circuit 21 can provide a constant current source reference for the differential amplifier circuit 22, so that the temperature sensors in the dissolved oxygen electrode 10 connected to the temperature sampling positive terminal NTCA to the two ends of the temperature sampling negative terminal NTCB obtain voltage signals.
The high-precision online dissolved oxygen measuring instrument is connected with a dissolved oxygen electrode 10 when in use, wherein the temperature compensation signal end 102 of the dissolved oxygen electrode 10 is connected with the temperature sampling end of the temperature compensation sampling circuit 2, and specifically, the temperature compensation signal end 102 of the dissolved oxygen electrode 10 is connected to a temperature sampling positive end NTCA and a temperature sampling negative end NTCB. After connection, the differential amplification circuit 22 obtains a constant current source provided by the constant current reference circuit 21, resistance signals of the temperature sensor in the dissolved oxygen electrode 10, which are connected to the input side of the differential amplification circuit 22 by two ends of a temperature sampling positive end NTCA and a temperature sampling negative end NTCB, are converted into voltage signals, and the voltage signals converted from the resistance signals of the temperature sensor in the dissolved oxygen electrode 10 and the temperature signals induced by the dissolved oxygen electrode 10 change linearly; the voltages at the two ends of the temperature sampling positive end NTCA and the temperature sampling negative end NTCB are input into a differential amplification circuit 22 which is mainly formed by an operational amplifier U13A, a resistor R29, a resistor R30, a resistor R34 and a resistor R37, and signals input at the temperature sampling positive end NTCA and the temperature sampling negative end NTCB are subjected to differential one-stage amplification through the differential amplification circuit 22; then, the differential signals are input into a secondary amplifying circuit 23, and the secondary amplifying circuit 23 directly couples and amplifies the differential signals of the primary amplifying circuit, so that the final output signals of the temperature compensation sampling circuit 2 are within the range capable of being received by the AD conversion in the MCU processor 3.
According to the high-precision online dissolved oxygen measuring instrument, after receiving the electric signal collected by the temperature compensation sampling circuit 2, the MCU processor 3 converts the electric signal into a recognizable digital quantity signal to finish sampling of a maximum solution temperature signal, and carries out nonlinear compensation on an oxygen content signal in a solution according to the collected solution temperature signal. Specifically, after the temperature signal is acquired, the MCU processor 3 calculates the electrode constants at different temperatures according to the oxygen solubility of the known solution at different temperatures to form a temperature and electrode constant comparison table, and uses a table lookup method to obtain the corresponding electrode constants for the calculation and conversion of the oxygen content of the solution to realize the temperature compensation during the measurement of the oxygen content of the solution.
The invention relates to a high-precision online dissolved oxygen measuring instrument, in particular to an MCU processor 3The electrode constant comparison table in the internal is usually corresponding to one electrode constant at intervals of 0.2 ℃ or 0.5 ℃, and when the temperature compensation is carried out on the measurement of the oxygen content of the solution, the compensation precision is low. In order to improve the temperature compensation precision when measuring the oxygen content of the solution, the internal program of the MCU processor 3 can adopt a linear interpolation algorithm to perform linear compensation on discrete sampling points of the temperature signal. Specifically, the MCU processor 3 reads two sets of interpolation data corresponding to the temperature interpolation points from the electrode constant comparison table, reads the measurement values within the two sets of interpolation data, and substitutes the two sets of interpolation data into a formula for conversion, wherein the formula is as follows: y = y0+(y1-y0)/(x1-x0)*(x-x0) Where x is an interpolated point on the abscissa, y is the ordinate interpolated point measurement, x0、y0、x1、y1Two sets of interpolation point data known in the coordinate system, respectively.
According to the high-precision online dissolved oxygen measuring instrument, after the MCU processor 3 collects the temperature signals, the electrode constant which is more accurate and corresponds to the collected temperature signals can be obtained through the interpolation algorithm, and the temperature compensation precision for measuring the oxygen content in the solution is higher. Wherein, the corresponding electrode constants can be calculated at every temperature of 0.1 ℃ by the above conversion.
In the high-precision online dissolved oxygen measuring instrument, in the temperature compensation sampling circuit 2, a constant current reference circuit 21 provides constant current source reference for temperature sensors in the dissolved oxygen electrode 10 connected to two ends of a temperature sampling positive end NTCA and a temperature sampling negative end NTCB, so that a resistance signal of the temperature sensor in the dissolved oxygen electrode 10 can be converted into a voltage signal, and finally, the voltage signal is gradually amplified by a differential amplifying circuit 22 and a secondary amplifying circuit 23 and then is acquired by an MCU (microprogrammed control unit) processor 3. On one hand, in the constant current reference circuit 21 of the temperature compensation sampling circuit 2, the logic inverter U8A and the logic inverter U8B are used for shaping the electric signals provided by the input end of the constant current reference circuit 21, the waveform of the shaped electric signals has low noise, and the input signals are more stable and reliable, so that the constant current source reference provided for the temperature sensor in the dissolved oxygen electrode 10 is more stable and accurate, and a reliable basis is laid for accurate sampling of the temperature signals; on the other hand, the differential amplifying circuit 22 amplifies the temperature signal, compared with a common operational amplifying circuit, the differential amplifying circuit 22 has differential mode input and opposite polarity, the temperature drift generated by the temperature influence of the power-on signals at the two ends of the logic inverter U8A and the logic inverter U8B can be completely or partially offset after the opposite polarity is amplified under the action of the differential amplifying circuit 22, so that the grid current is reduced, the common-mode signal interference is inhibited, the temperature drift of the output signal is greatly reduced, the influence of the temperature drift in the temperature measuring process is reduced to the minimum, even the temperature drift is completely eliminated, the influence caused by the temperature drift in the temperature measuring process is effectively controlled, the temperature measuring precision is improved, and the measuring precision of the dissolved oxygen is further improved.
In the high-precision online dissolved oxygen measuring instrument, the combination of the constant-current reference circuit 21 and the differential amplification circuit 22 in the temperature compensation sampling circuit 2 provides a wider measuring range and higher measuring precision for measuring temperature signals, so that the temperature compensation in the dissolved oxygen measuring process is more accurate.
In the high-precision online dissolved oxygen measuring instrument, temperature signals are collected through the temperature compensation sampling circuit 2, nonlinear compensation is carried out on the measurement of dissolved oxygen, and when the temperature compensation sampling is closed, a fixed temperature set value in the MCU processor 3 is used for fixed temperature compensation; in addition, the internal parameters of the MCU processor 3 can be set through a manual interface, the atmospheric pressure and salinity of a measuring point are set, and the mode adopting parameter compensation is corrected.
In the high-precision online dissolved oxygen measuring instrument, in the temperature compensation sampling circuit 2, the input end of the constant current reference circuit 21 provides an electric signal required by the operation of the constant current reference circuit 21, the electric signal can be but is not limited to a PWM signal, since the PWM signal can be obtained through the PWM interface of the MCU processor 3, the PWM signal is easy to obtain, and the obtained PWM signal is standard and easy to control, the input end of the constant current reference circuit 21 is preferably connected with the PWM interface of the MCU processor 3.
In the high-precision online dissolved oxygen measuring instrument, the resistor R23 and the capacitor C18 in the constant current reference circuit 21 are arranged to play a role in stabilizing and protecting signals.
In the high-precision online dissolved oxygen measuring instrument, in the differential amplifying circuit 22, the operational amplifier U10A and the operational amplifier U10B respectively form a voltage follower, the arrangement of the voltage follower ensures that the voltage input to the rear-end differential amplifying circuit is more stable, a resistor R31 and a resistor R36 in the voltage follower play a role in protection, and a capacitor C30 and a capacitor C35 play a role in filtering.
According to the high-precision online dissolved oxygen measuring instrument, a resistor R14 and the in-phase input end of an operational amplifier U9A are connected in series with a resistor R4 and a resistor R1, the in-phase input end of the operational amplifier U9A and the ground are also connected in series with a capacitor C14, and the connecting end of the resistor R4 and the resistor R1, which are connected, is connected in series with a capacitor C16; a resistor R27 is connected in series to a connecting line between the non-inverting input end of the operational amplifier U10A and the temperature sampling positive-direction end NTCA, a capacitor C20 is connected between the non-inverting input end of the operational amplifier U10A and the ground in series, a resistor R32 is connected in series to a connecting line between the non-inverting input end of the operational amplifier U10B and the temperature sampling negative-direction end NTCB, and a capacitor C31 is connected between the non-inverting input end of the operational amplifier U10B and the ground in series; a capacitor C32 is connected in parallel with two ends of the resistor 37; a resistor R35 is connected in series on a connecting line between the output end of the operational amplifier U13B and the output end of the temperature compensation sampling circuit 2, and a capacitor C33 and a capacitor C34 which are connected in parallel are connected in series between the output end of the temperature compensation sampling circuit 2 and the ground. In the constant current reference circuit 21, a resistor R4, a capacitor C16, a resistor R1 and a capacitor C14 form two filter circuits respectively; in the differential amplifier circuit 22, the resistor R27 and the capacitor C20, the resistor R32 and the capacitor C31 also form two filter circuits, respectively; in the second-stage amplifying circuit 23, the resistor R35, the capacitor C33, and the capacitor C34 also form a filter circuit. The filter circuits and the capacitor C32 can effectively reduce the noise interference in the circuit, so that the signals in the circuits are more stable and reliable.
In the high-precision online dissolved oxygen measuring instrument, a plurality of capacitors are also arranged in the dissolved oxygen sampling circuit 1 and are used for signal filtering of a circuit or protection of the circuit.
The high-precision online dissolved oxygen measuring instrument further comprises a transmitting output unit 5, and the transmitting output unit 5 is electrically connected with the MCU processor 3. The transmitting and outputting unit 5 receives the PWM port duty ratio waveform signal from the MCU processor 3, modulates and converts the PWM signal into a linear 0-20mA or 4-20mA analog signal, and outputs the linear 0-20mA or 4-20mA analog signal to external equipment to synchronously check the dissolved oxygen content value in different places; the online dissolved oxygen measuring instrument realizes linear remote transmission of collected signals, increases the functions of the high-precision online dissolved oxygen measuring instrument, and improves the convenience and flexibility of use.
The high-precision online dissolved oxygen measuring instrument further comprises a communication output circuit 6, and the communication output circuit 6 is electrically connected with the MCU processor 3. The communication output circuit 6 is arranged to realize real-time communication between the high-precision online dissolved oxygen measuring instrument and an external system. The communication output circuit 6 can adopt a 485 communication circuit, as shown in fig. 4, the communication output circuit comprises a 485 communication chip, a TVS protection tube and a current-limiting resistor, wherein the 485 communication chip used in the communication output circuit 6 is powered by double power supplies, namely DC3.3V and DC5V, the chip is internally provided with an isolation circuit, the design that the peripheral circuit in the traditional circuit needs to be connected with an optical coupler for photoelectric isolation is reduced, namely, the isolation function is reserved to prevent large voltage from jumping to the MCU processor, and the complexity of the peripheral circuit is reduced; two TVS protection tubes are respectively loaded at the A, B two ends of the 485 communication chip output, so that the 485 communication chip can be effectively protected from being broken down by large voltage or damaged by short circuit of the output end; the current limiting resistor is mainly used for limiting the current in the communication output circuit 6, so that the current in the communication output circuit 6 is within an acceptable range, and if the current is too large, the current limiting resistor is burnt out in the first time. The 485 conversion chip can adopt but not limited to the 485 conversion chip with the model number of ISO3082 DWR.
The high-precision online dissolved oxygen measuring instrument further comprises an alarm output circuit 7, and the alarm output circuit 7 is electrically connected with the MCU processor 3. The alarm output circuit 7 mainly comprises a relay, a Darlington tube and a thermal pressure-sensitive protection tube, the alarm output circuit 7 receives a control signal of the MCU processor 3 corresponding to an IO port, the control signal is connected to the Darlington tube in the alarm output circuit, the Darlington tube has a logic non-operation function, when the MCU processor 3 provides a high level for an input end of the Darlington tube, the output end of the Darlington tube outputs a low level, one end of a driving electrode of the relay is connected with the high level, and the other end of the driving electrode of the relay is connected with the output end of the Darlington tube; and conversely, the relay is released, and the external equipment loses power and stops working.
The high-precision online dissolved oxygen measuring instrument has the advantages that the Darlington tube has larger current filling characteristic and can drive the relay with larger power, and meanwhile, the Darlington tube supports up to 7 channels for logic non-control, so that the high-precision online dissolved oxygen measuring instrument can support the design requirement of multi-channel alarm; in addition, the thermal pressure-sensitive protection tube in the alarm output circuit 7 is used as a protection device, so that electric sparks can be absorbed quickly, and the drive circuit is protected. The model of the adopted Darlington tube of the high-precision online dissolved oxygen measuring instrument is generally ULN 2003.
In the high-precision online dissolved oxygen measuring instrument, the MCU processor 3 usually adopts a 32-bit high-speed processor with an ARM core, the processor integrates a plurality of interfaces such as PWM (pulse width modulation), interrupt, I2C bus, SPI (serial peripheral interface) bus, UART (universal asynchronous receiver/transmitter) interface and the like, and the processor is used as the brain of a product, controls each external circuit through the abundant interfaces, and performs formula conversion according to a program recorded in the processor to obtain the oxygen content of the monitored aqueous solution.
In the high-precision online dissolved oxygen measuring instrument, the key display unit 4 usually comprises a plurality of keys and an LCD screen. The key display unit 4 is used for receiving signals of the MCU processor 3 for display, such as dissolved oxygen measurement signals, temperature measurement signals and the like; human-computer interaction is completed through keys, and various parameters in the product are set.
In the high-precision online dissolved oxygen measuring instrument, each circuit can be arranged on one PCB or can be separately arranged on a plurality of PCBs, and if the key display unit 4 independently forms the key display panel 20; the dissolved oxygen sampling circuit 1, the temperature compensation sampling circuit 2, the MCU processor 3 and the communication output circuit 6 can be arranged on the same PCB as a main board 30; the transmitting and conveying unit 5 can be independently arranged on a PCB (printed circuit board), and can also be arranged on the main board 30 together with the temperature compensation sampling circuit 2, the MCU processor 3 and the communication output circuit 6; in addition, the high-precision online dissolved oxygen measuring instrument of the present invention is also generally provided with a power supply board 40 for supplying power to each circuit, wherein the alarm output circuit 7 can be arranged on the power supply board 40.
The invention discloses a high-precision online dissolved oxygen measuring instrument, and also provides a program running method in an MCU processor 3, as shown in FIG. 5, comprising the following steps:
s1, after the high-precision online dissolved oxygen measuring instrument is electrified and reset, initializing operation is carried out, wherein the initializing operation comprises system initialization, peripheral initialization and watchdog starting;
s2, collecting and calculating the dissolved oxygen; wherein, the dissolved oxygen collection and calculation comprises the following steps:
s2.1, starting AD conversion in the MCU processor 11;
s2.2, collecting a dissolved oxygen signal input by the dissolved oxygen sampling circuit 1;
s2.3, collecting a temperature compensation signal input by the temperature compensation sampling circuit 2;
s2.4, linear interpolation algorithm is adopted to carry out linear correction on discrete sampling points of the temperature compensation signals;
s2.5, calculating the dissolved oxygen:
s2.6, carrying out data verification;
s2.7, closing the AD conversion in the MCU processor 11;
s3, event management; wherein the event management comprises the following steps:
s3.1, reading and maintaining parameters;
s3.2, output processing of the transmitting and conveying unit 5;
s3.3, performing overrun alarm processing on the alarm output circuit 7;
s3.4, refreshing the display of the key display unit 4;
s4, feeding dogs;
s5, processing the key operation of the key display unit 4;
s6, the communication signal inputted from the communication output circuit 6 is processed.
It will be apparent to those skilled in the art that various modifications, additions, substitutions, and the like can be made without departing from the spirit of the invention and these are therefore considered to be within the scope of the invention.
Claims (10)
1. The utility model provides an online dissolved oxygen measuring instrument of high accuracy which characterized in that: the system comprises a dissolved oxygen sampling circuit, a temperature compensation sampling circuit, an MCU (microprogrammed control unit) processor and a key display unit, wherein the dissolved oxygen sampling circuit, the temperature compensation sampling circuit and the key display unit are respectively and electrically connected with the MCU processor;
the temperature compensation sampling circuit consists of a temperature sampling end, a logic inverter, an operational amplifier, a resistor and a capacitor, wherein the temperature sampling end of the temperature compensation sampling circuit comprises a temperature sampling positive end NTCA and a temperature sampling negative end NTCB, and the temperature compensation sampling circuit is divided into a constant current reference circuit, a differential amplifying circuit and a secondary amplifying circuit; wherein the content of the first and second substances,
IN the constant current reference circuit, a logic inverter U8A, a logic inverter U8B, a resistor R14 and a resistor R20 are sequentially connected IN series from an input end IN of the constant current reference circuit to the ground, a connecting end of the resistor R14 connected with a resistor R20 is connected with a non-inverting input end of an operational amplifier U9A, a resistor R26 is connected IN series from an inverting input end of the operational amplifier U9A to the ground, an output end of the operational amplifier U9A is connected with the positive temperature sampling end NTCA, and a connecting end of the resistor R26 connected with the inverting input end of the operational amplifier U9A is connected with the negative temperature sampling end NTCB;
in the differential amplifying circuit, a series resistor R29 is arranged between the positive temperature sampling end NTCA and the non-inverting input end of the operational amplifier U13A, a series resistor R30 is arranged between the non-inverting input end of the operational amplifier U13A and the ground, a series resistor R34 is arranged between the negative temperature sampling end NTCB and the inverting input end of the operational amplifier U13A, and a series resistor R37 is arranged between the inverting input end of the operational amplifier U13A and the output end of the operational amplifier U13A;
in the secondary amplifying circuit, a series resistor R33 is arranged between the non-inverting input end of an operational amplifier U13B and the output end of an operational amplifier U13A, a series resistor R41 is arranged between the inverting output end of the operational amplifier U13B and the ground, a series resistor R40 is arranged between the inverting output end of the operational amplifier U13B and the output end of an operational amplifier U13B, and the output end of the operational amplifier U13B is connected with the output end ColdT of the temperature compensation sampling circuit;
the dissolved oxygen sampling circuit is used for collecting an oxygen content signal of the aqueous solution and transmitting the collected oxygen content signal of the aqueous solution to the MCU processor; the temperature compensation sampling circuit is used for collecting a water solution temperature signal and transmitting the collected water solution temperature signal to the MCU processor; the MCU processor is used for receiving the aqueous solution oxygen content signal transmitted by the dissolved oxygen sampling circuit and the aqueous solution temperature signal transmitted by the temperature compensation sampling circuit, obtaining a final aqueous solution oxygen content signal according to the received aqueous solution oxygen content signal and the aqueous solution temperature signal, and sending the obtained final aqueous solution oxygen content signal to the key display unit for displaying.
2. The high-precision online dissolved oxygen measuring instrument according to claim 1, characterized in that: and the input end IN of the constant current reference circuit is connected with the PWM interface of the MCU processor.
3. The high-precision online dissolved oxygen measuring instrument according to claim 1, characterized in that: a resistor R23 is connected between the inverting input end of the operational amplifier U9A and the temperature sampling negative end NTCB; the capacitor C18 is connected in series between the inverting input terminal of the operational amplifier U9A and the output terminal of the operational amplifier U9A.
4. The high-precision online dissolved oxygen measuring instrument according to claim 1, characterized in that: an operational amplifier U10A is arranged between the temperature sampling positive end NTCA and the resistor R29, wherein the non-inverting input end of the operational amplifier U10A is connected with the temperature sampling positive end NTCA, a resistor R31 is connected in series between the inverting input end of the operational amplifier U10A and the output end of the operational amplifier U10A, two ends of a resistor R31 are connected with a capacitor C30 in parallel, and the output end of the operational amplifier U10A is connected with a resistor R29; an operational amplifier U10B is arranged between the temperature sampling negative end NTCB and the resistor R34, wherein the non-inverting input end of the operational amplifier U10B is connected with the temperature sampling negative end NTCB, a resistor R36 is connected between the inverting input end of the operational amplifier U10B and the output end of the operational amplifier U10B in series, two ends of the resistor R36 are connected with a capacitor C35 in parallel, and the output end of the operational amplifier U10B is connected with a resistor R34.
5. The high-precision online dissolved oxygen measuring instrument according to claim 4, characterized in that: a resistor R4 and a resistor R1 are connected in series between the resistor R14 and the non-inverting input end of the operational amplifier U9A, a capacitor C14 is also connected in series between the non-inverting input end of the operational amplifier U9A and the ground, and a capacitor C16 is connected in series between the connection end of the resistor R4 and the resistor R1 and the ground; a resistor R27 is connected in series to a connecting line between the non-inverting input end of the operational amplifier U10A and the temperature sampling positive-direction end NTCA, a capacitor C20 is connected between the non-inverting input end of the operational amplifier U10A and the ground in series, a resistor R32 is connected in series to a connecting line between the non-inverting input end of the operational amplifier U10B and the temperature sampling negative-direction end NTCB, and a capacitor C31 is connected between the non-inverting input end of the operational amplifier U10B and the ground in series; a capacitor C32 is connected in parallel with two ends of the resistor R37; a resistor R35 is connected in series on a connecting line between the output end of the operational amplifier U13B and the output end ColdT of the temperature compensation sampling circuit, and a capacitor C33 and a capacitor C34 which are connected in parallel are connected in series between the output end ColdT of the temperature compensation sampling circuit and the ground.
6. The high-precision online dissolved oxygen measuring instrument according to claim 1, characterized in that: the dissolved oxygen sampling circuit comprises a dissolved oxygen sampling end, an operational amplifier, a triode, a resistor and a capacitor, wherein the dissolved oxygen sampling end of the dissolved oxygen sampling circuit comprises a dissolved oxygen sampling forward end Cath and a dissolved oxygen sampling ground end Andode, and the dissolved oxygen sampling circuit is divided into a dissolved oxygen sampling reference circuit, a first-stage operational amplifier circuit and a second-stage operational amplifier circuit; wherein the content of the first and second substances,
in the dissolved oxygen sampling reference circuit, a non-inverting input terminal of an operational amplifier U15C is connected with a power supply terminal VCC1, an inverting input terminal of the operational amplifier U15C is connected with a series resistor R25 between bases of an NPN triode Q1, an output terminal of the operational amplifier U15C is connected with a series resistor R19 between bases of an NPN triode Q1, a series resistor R16 between a collector of a triode Q1 and the power supply terminal VCC2, an emitter of an NPN triode Q1 is connected with an inverting input terminal of an operational amplifier U15C, an inverting input terminal of the operational amplifier U15C is sequentially connected with a resistor R24 and a resistor R21 from ground, a connecting terminal connected with a resistor R24 and a resistor R21 is connected with a series resistor R B between the inverting input terminal of the operational amplifier U15B, a non-inverting input terminal of the operational amplifier U15B is grounded, an inverting input terminal of the operational amplifier U15B is connected with a series resistor R B between the inverting input terminal of the operational amplifier U15B;
in the first-stage operational amplifier circuit, a resistor R12 is connected between the inverting input end of an operational amplifier U15A and the positive end Cath of the dissolved oxygen sampling, and a resistor R15 is connected between the inverting input end of the operational amplifier U15A and the output end of the operational amplifier U15A;
in the two-stage operational amplifier circuit, a resistor R2 is connected in series between the inverting input terminal of the operational amplifier U15D and the output terminal of the operational amplifier U15A, a resistor R18 is connected in series between the non-inverting input terminal of the operational amplifier U15D and a power supply terminal VCC3, a resistor R13 is connected in series between the non-inverting input terminal of the operational amplifier U15D and the ground, a resistor R11 is connected in series between the inverting input terminal of the operational amplifier U15D and the output terminal of the operational amplifier U15D, and the output terminal of the operational amplifier U15D is connected with the output terminal AD _ SIn of the dissolved oxygen sampling circuit.
7. The high-precision online dissolved oxygen measuring instrument according to claim 1, characterized in that: the high-precision online dissolved oxygen measuring instrument further comprises a transmitting output unit, and the transmitting output unit is electrically connected with the MCU processor.
8. The high-precision online dissolved oxygen measuring instrument according to claim 1, characterized in that: the high-precision online dissolved oxygen measuring instrument further comprises a communication output circuit, and the communication output circuit is electrically connected with the MCU processor.
9. The high-precision online dissolved oxygen measuring instrument according to claim 1, characterized in that: the high-precision online dissolved oxygen measuring instrument further comprises an alarm output circuit, and the alarm output circuit is electrically connected with the MCU processor.
10. The high-precision online dissolved oxygen measuring instrument according to claim 1, characterized in that: the high-precision online dissolved oxygen measuring instrument is correspondingly provided with a dissolved oxygen electrode, the dissolved oxygen electrode comprises an electrode signal end and a temperature compensation signal end, the dissolved oxygen electrode comprises the electrode signal end and a dissolved oxygen sampling circuit, the dissolved oxygen electrode comprises a temperature compensation signal end and a temperature compensation sampling circuit, and the temperature sampling end is connected with the temperature compensation sampling circuit.
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Citations (8)
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| US4921582A (en) * | 1987-09-04 | 1990-05-01 | Wang Henry Y | Dissolved oxygen measuring method |
| EP0366831A1 (en) * | 1988-11-04 | 1990-05-09 | Horiba, Ltd. | Temperature compensating circuit |
| KR20100086784A (en) * | 2009-01-23 | 2010-08-02 | 하태안 | Control apparatus of dissolved oxygen & temperature in fish farm |
| KR101526217B1 (en) * | 2014-12-01 | 2015-06-05 | 길주형 | On-Line Smart DO Analyzer |
| CN208672507U (en) * | 2017-11-30 | 2019-03-29 | 苏州禹山传感科技有限公司 | A kind of temperature compensation system of optical dissolved oxygen Demarcate Gas |
| CN112649485A (en) * | 2021-01-08 | 2021-04-13 | 金陵科技学院 | Dissolved oxygen electrode calibration and dissolved oxygen calculation method and electronic equipment |
| CN113030211A (en) * | 2021-03-10 | 2021-06-25 | 广东海洋大学 | Polarographic dissolved oxygen meter and dissolved oxygen measurement compensation method |
| CN216208769U (en) * | 2021-11-01 | 2022-04-05 | 福建顺昌虹润精密仪器有限公司 | High-precision online dissolved oxygen measuring instrument |
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2021
- 2021-11-01 CN CN202111280741.6A patent/CN113866233A/en active Pending
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4921582A (en) * | 1987-09-04 | 1990-05-01 | Wang Henry Y | Dissolved oxygen measuring method |
| EP0366831A1 (en) * | 1988-11-04 | 1990-05-09 | Horiba, Ltd. | Temperature compensating circuit |
| KR20100086784A (en) * | 2009-01-23 | 2010-08-02 | 하태안 | Control apparatus of dissolved oxygen & temperature in fish farm |
| KR101526217B1 (en) * | 2014-12-01 | 2015-06-05 | 길주형 | On-Line Smart DO Analyzer |
| CN208672507U (en) * | 2017-11-30 | 2019-03-29 | 苏州禹山传感科技有限公司 | A kind of temperature compensation system of optical dissolved oxygen Demarcate Gas |
| CN112649485A (en) * | 2021-01-08 | 2021-04-13 | 金陵科技学院 | Dissolved oxygen electrode calibration and dissolved oxygen calculation method and electronic equipment |
| CN113030211A (en) * | 2021-03-10 | 2021-06-25 | 广东海洋大学 | Polarographic dissolved oxygen meter and dissolved oxygen measurement compensation method |
| CN216208769U (en) * | 2021-11-01 | 2022-04-05 | 福建顺昌虹润精密仪器有限公司 | High-precision online dissolved oxygen measuring instrument |
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