CN110907522A - Method for improving measurement precision of nitrogen-oxygen sensor - Google Patents
Method for improving measurement precision of nitrogen-oxygen sensor Download PDFInfo
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- CN110907522A CN110907522A CN201911218428.2A CN201911218428A CN110907522A CN 110907522 A CN110907522 A CN 110907522A CN 201911218428 A CN201911218428 A CN 201911218428A CN 110907522 A CN110907522 A CN 110907522A
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- 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
- G01N27/403—Cells and electrode assemblies
- G01N27/406—Cells and probes with solid electrolytes
- G01N27/407—Cells and probes with solid electrolytes for investigating or analysing gases
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- G—PHYSICS
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- 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
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- G01N27/406—Cells and probes with solid electrolytes
- G01N27/407—Cells and probes with solid electrolytes for investigating or analysing gases
- G01N27/4071—Cells and probes with solid electrolytes for investigating or analysing gases using sensor elements of laminated structure
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Abstract
The invention relates to a method for improving the measurement accuracy of a nitrogen-oxygen sensor, which applies pulse voltage between a reference electrode and a main electrode of a nitrogen-oxygen sensor chip, and forms peak current not lower than 10 muA in a loop when the pulse voltage is applied between the reference electrode and the main electrode. The first stage of the pulse voltage is set to be high level, and the second stage of the pulse voltage is set to be low level; the pulse falling time Tf at which the high level transits to the low level is equal to or less than the time length T2 of the low level. The measurement of the concentration of NOx by the nitrogen oxide sensor is completed in the second stage. The invention generates pulse current by directly applying voltage between the main electrode and the reference electrode, thereby pumping oxygen near the main electrode to the periphery of the reference electrode and achieving the purpose of correcting the oxygen concentration in the reference gas.
Description
Technical Field
The invention belongs to the technical field of nitrogen-oxygen sensors, and particularly relates to a method for improving the measurement accuracy of a nitrogen-oxygen sensor.
Background
The nitrogen oxide sensor measures the amount of NOx in a target gas, such as the amount of NOx in a diesel exhaust. As shown in fig. 1, the ceramic chip is a core sensing element of the nox sensor, and is composed of multiple layers of zirconia ceramic material, a reference electrode, a measuring electrode and a main electrode are printed on a zirconia ceramic material substrate, the main electrode is exposed to a target gas to be measured, the reference electrode is printed inside the ceramic chip, air around the reference electrode is referred to as reference gas, and a tail of the ceramic chip is not closed. The target gas to be detected enters the chamber 2 through the two diffusion channels, the driving voltage applied between the measuring electrode and the main electrode is fed back and adjusted based on the voltage difference between the reference electrode and the measuring electrode, and meanwhile, the concentration of the specific gas in the gas to be detected can be detected by the sensor by monitoring the current Ip 2.
As shown in fig. 4, the gas to be measured enters from the head of the ceramic chip, and the head and the tail of the ceramic chip are separated by a plurality of sealing rings, the gas to be measured may slowly pass through the sealing rings and enter the vicinity of the tail of the ceramic chip. Because the oxygen concentration in the reference gas can change under certain conditions, the potential of the electrode can be known to be related to the gas concentration around the electrode according to the Nernst principle, and the measurement accuracy of the sensor can be influenced because the change of the potential of the reference electrode of the nitrogen-oxygen sensor can influence the pressure difference between the reference electrode and the measurement electrode.
Disclosure of Invention
The invention aims to provide a method for improving the measurement accuracy of a nitrogen-oxygen sensor.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a method for improving the measurement accuracy of a nitrogen-oxygen sensor is characterized by comprising the following steps: a control voltage is applied between the reference electrode and the main electrode of the nitrogen-oxygen sensor chip.
Further, the control voltage applied between the reference electrode and the main electrode is a pulse voltage.
Further, when a pulse voltage is applied between the reference electrode and the main electrode, a peak current of not less than 10 μ A is formed in the loop.
Further, the first phase of the pulse voltage is set to be high level, and the second phase is set to be low level; the pulse falling time Tf at which the high level transits to the low level is equal to or less than the time length T2 of the low level.
Further, the measurement of the concentration of NOx by the nitrogen oxide sensor is completed in the second stage.
Further, the value of T2/Tf is greater than or equal to 2.
Further, the value of T2/Tf is more than or equal to 3.
Further, the value of T2/Tf is less than or equal to 6.
Further, the T2 is less than or equal to 10 ms.
Further, the Tf is less than or equal to 3 ms.
The invention has the beneficial effects that: the invention generates pulse current by directly applying voltage between the main electrode and the reference electrode, thereby pumping oxygen near the main electrode to the periphery of the reference electrode and achieving the purpose of correcting the oxygen concentration in the reference gas.
Drawings
FIG. 1 is a schematic diagram of the structural principle of a nitrogen-oxygen sensor.
Fig. 2 is a schematic diagram of a pulse waveform.
Fig. 3 is a schematic diagram of the residual voltage principle.
FIG. 4 is a schematic structural diagram of a probe of the nitrogen-oxygen sensor.
Detailed Description
In order to better understand the present invention, the following embodiments are further described.
The ceramic chip structure and the working principle of the nitrogen-oxygen sensor are as follows:
the ceramic chip adopts a double-chamber structure, and the structure diagram is shown in figure 1:
(1) the measured gas enters the chamber 1 through the first diffusion channel, and the diffusion coefficient adjusts the porosity and other parameters of the diffusion channel to achieve a preset value.
The first oxygen pumping unit consists of an oxygen pumping electrode and a main electrode and is used for reducing the oxygen concentration in the chamber 1 to reach a preset value.
When the zirconia ceramic chip is heated, oxygen ions can conduct on the zirconia ceramic chip, so that a driving voltage is applied between the oxygen pumping electrode and the main electrode, a current can be formed in a loop, the IP0 represents the magnitude of the current, the voltage difference between the oxygen pumping electrode and the reference electrode is enabled to be V0 and 330mV through feedback regulation, when V0 reaches a target value of 330mV, the oxygen concentration of the chamber 1 is about 1ppm, and the magnitude of the current IP0 corresponds to the oxygen concentration of the original gas.
(2) The chamber 2 is connected to the first chamber by a second diffusion channel, the diffusion coefficient of the gas from the chamber 1 to the chamber 2 also being preset.
The second oxygen pumping unit is composed of an auxiliary pumping electrode and a main electrode and is used for further reducing the oxygen concentration in the gas from the chamber 1 to reach a preset value.
The reference electrode is in contact with air (the air around the reference electrode is referred to as reference gas), a driving voltage is applied between the auxiliary pump electrode and the main electrode, and the voltage difference between the auxiliary pump electrode and the reference electrode, V1, is made equal to 450mV by feedback adjustment, and when V1 reaches a target value of 450mV, the oxygen concentration in the chamber 2 is about 0.01 ppm.
After treatment with two oxygen pumping units, the gas entering the vicinity of the measuring electrode contains substantially zero oxygen, the measuring electrode contains rhodium metal, NOx is decomposed into O2 and N2 at the measuring electrode, and O2 generated by NOx decomposition can be pumped out to the air by applying a voltage of 400mV between the reference electrode and the measuring electrode, at which time the magnitude of current IP2 corresponds to the concentration of NOx in the original gas.
Examples
As shown in FIGS. 2 and 3, a method for improving the measurement accuracy of a nitrogen oxygen sensor applies a control voltage between a reference electrode and a main electrode of a nitrogen oxygen sensor chip. The control voltage applied between the reference electrode and the main electrode is a pulse voltage, and the oxygen gas on the main electrode side is pumped to the vicinity of the reference electrode, and the waveform of the pulse voltage is as shown in fig. 2, and the pulse period is T, the high level time Ton and the low level time Toff.
When a control voltage Vp3 is applied between the reference electrode and the main electrode, a current Ip3 is formed in the loop, in this embodiment the peak current Ip3max flowing from the main electrode into the reference electrode should not be lower than 10 μ a, note that both the peak current Ip3max and the average current flowing into the reference electrode increase as the control voltage increases. Meanwhile, the higher the average current flowing into the reference electrode, the more effectively the decrease in the oxygen concentration in the reference gas can be compensated. It is noted that the decrease in the oxygen concentration around the reference electrode can be sufficiently compensated by the peak current Ip3max being not less than 10 μ a.
The first phase of the pulse sets the pulse voltage to a high level (T1 in fig. 2) at which the potential difference between the reference electrode and the main electrode is large, and the second phase sets the pulse voltage to a low level (T2 in fig. 2), and when the transition from the first phase to the second phase starts to fall, the potential difference between the reference electrode and the main electrode starts to fall, the pulse fall time is Tf, and the pulse fall time satisfies the following inequality (1).
Tf≤T2 (1)
As shown in fig. 2, Tf is the time during which the potential difference between the reference electrode and the main electrode is decreased between the first stage and the second stage, T2 is the length of time during the second stage, and the nitrogen oxide sensor measures the concentration of NOx at the completion of the second stage. The control voltage applied between the reference electrode and the main electrode also affects the potential of the reference electrode, but the control voltage has smaller influence on the potential of the reference electrode in the second stage than in the first stage, so that the gas concentration is detected in the second stage, and the influence of the control voltage on the measurement accuracy can be effectively reduced.
In addition, the potential of the reference electrode does not change abruptly due to the influence of the capacitive component of the reference electrode, so that during the second phase T2, there may be a residual control voltage on the reference electrode, which may affect the driving voltage between the main electrode and the measuring electrode, and thus the residual voltage may affect the measuring accuracy of the sensor, and the lower the residual voltage, the higher the measuring accuracy. In addition, the inequality (1) is satisfied (i.e., T2/Tf is not less than 1), and the time T2 is set relatively long, which can effectively reduce the residual voltage in the second stage, thereby improving the accuracy in the second-stage measurement. Note that the value of T2/Tf should not be less than 2 or less than 3, nor should the value of T2/Tf be greater than 6.
The time T2 in the control voltage waveform is 10ms or less, note that the longer the time T2, the less the average current flowing into the reference electrode, and once the average current flowing into the reference electrode is too low, the compensation for oxygen in the reference gas is insufficient. When T2 is not greater than 10ms, the reduction in oxygen in the reference gas can be sufficiently compensated.
In fig. 2, the voltage Vref is the potential difference between the reference electrode and the main electrode, the fall time Tf in the curve of the voltage Vref is not more than 3ms, and the shorter the fall time Tf is, the faster the residual control voltage falls, and the smaller the influence on the measurement electrode is. When the time Tf is equal to or less than 3ms, the time T2 is relatively small, and the residual control voltage can be effectively lowered, thereby ensuring the measurement accuracy of the sensor.
Equation (2) calculates that the lower the voltage Dvref10, the smaller the voltage Dvref10, the smaller the residual voltage on the reference electrode, and the higher the accuracy of the measurement can be ensured when Dvref10 is 55mV or less.
Dvref10＝(Vref2-Vref1)*0.1+Vref1-Vref0 (2)
Wherein Vref0 is the voltage difference between the reference electrode and the main electrode when the control voltage is 0; vref1 is the minimum value of the voltage difference between the reference electrode and the main electrode when the control voltage is varied back and forth between a high level and a low level; vref2 is the maximum value of the voltage difference between the reference electrode and the main electrode when the control voltage is varied back and forth between a high level and a low level.
The above description is only an application example of the present invention, and certainly, the present invention should not be limited by this application, and therefore, the present invention is still within the protection scope of the present invention by equivalent changes made in the claims of the present invention.
Claims (10)
1. A method for improving the measurement accuracy of a nitrogen-oxygen sensor is characterized by comprising the following steps: a control voltage is applied between the reference electrode and the main electrode of the nitrogen-oxygen sensor chip.
2. The method for improving the measurement accuracy of the nitrogen-oxygen sensor according to claim 1, wherein: the control voltage applied between the reference electrode and the main electrode is a pulse voltage.
3. The method for improving the measurement accuracy of the nitrogen-oxygen sensor as claimed in claim 2, wherein: when a pulse voltage is applied between the reference electrode and the main electrode, a peak current of not less than 10 μ A is formed in the loop.
4. The method for improving the measurement accuracy of the nitrogen-oxygen sensor as claimed in claim 2, wherein: the first stage of the pulse voltage is set to be high level, and the second stage of the pulse voltage is set to be low level; the pulse falling time Tf at which the high level transits to the low level is equal to or less than the time length T2 of the low level.
5. The method for improving the measurement accuracy of the nitrogen-oxygen sensor according to claim 4, wherein: the measurement of the concentration of NOx by the nitrogen oxide sensor is completed in the second stage.
6. The method for improving the measurement accuracy of the nitrogen-oxygen sensor according to claim 4, wherein: wherein the value of T2/Tf is greater than or equal to 2.
7. The method for improving the measurement accuracy of the nitrogen-oxygen sensor according to claim 4, wherein: wherein the value of T2/Tf is greater than or equal to 3.
8. The method for improving the measurement accuracy of the nitrogen oxygen sensor according to claim 6 or 7, wherein: wherein the value of T2/Tf is less than or equal to 6.
9. The method for improving the measurement accuracy of the nitrogen-oxygen sensor according to claim 4, wherein: the T2 is less than or equal to 10 ms.
10. The method for improving the measurement accuracy of the nitrogen-oxygen sensor according to claim 4, wherein: tf is less than or equal to 3 ms.
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| CN201911218428.2A CN110907522A (en) | 2019-12-03 | 2019-12-03 | Method for improving measurement precision of nitrogen-oxygen sensor |
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| CN201911218428.2A CN110907522A (en) | 2019-12-03 | 2019-12-03 | Method for improving measurement precision of nitrogen-oxygen sensor |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN113250798A (en) * | 2021-05-14 | 2021-08-13 | 高鑫环保科技(苏州)有限公司 | Nitrogen-oxygen sensor |
| CN114965578A (en) * | 2022-06-08 | 2022-08-30 | 北京智感度衡科技有限公司 | Nitrogen-oxygen sensor probe, calibration circuit, calibration method and system |
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