A control device, calibration and control method for an oxygen concentration sensor

Abstract

The present invention discloses a control device and calibration and control method for an oxygen concentration sensor. The device is applied to the oxygen concentration sensor at an optimal working temperature at room temperature as the adjustment target value, and the heating resistor R0 of the oxygen concentration sensor at the optimal working temperature and the pump current I under the atmospheric oxygen concentration at room temperature are calibrated by adjusting the duty cycle of the PWM signal. P0 After the calibration is completed, when the oxygen concentration sensor is working normally, the duty cycle of the PWM signal is adjusted to make the heating resistance R equal to the calibrated R0, that is, the oxygen concentration sensor works at the optimal working temperature; by obtaining the pump current I in real time P , according to the calibrated I P0 Calculating the oxygen concentration can improve the measurement accuracy of the oxygen concentration sensor.

Description

Technical Field

[0001] The invention belongs to the technical field of sensors, and in particular relates to a control device and a calibration and control method for an oxygen concentration sensor. Background Art

[0002] The oxygen concentration sensor is a device used to detect the oxygen content in the air. It can be used to directly measure the oxygen content in the environment, and it can also measure the ambient humidity based on the principle that the oxygen content in the air can indirectly reflect the water vapor content. For example, an oxygen concentration sensor with a zirconia ceramic chip as the core component can be used to measure the humidity in the inner cavity of a steam-bake combination machine. Its operating temperature is between 400℃ and 600℃. The adaptively designed electronic control module controls the heating film covering the surface of the chip, and calculates the oxygen concentration value by measuring the pump current. Figure 1 As shown. Different zirconia ceramic chips have different optimal operating temperatures. Even the same type of zirconia ceramic chips have differences, which results in differences in the target temperature values ​​reached when the electronic control module controls the heating. This causes the zirconia ceramic chip to fail to work at the optimal temperature, thus affecting the accuracy of the detection. Therefore, the zirconia ceramic chip and the electronic control module need to be adapted through a set of calibration methods to eliminate this effect. Summary of the invention

[0003] In order to solve the above problems existing in the prior art, the present invention provides a control device and a calibration method for an oxygen concentration sensor.

[0004] To achieve the above object, the present invention adopts the following technical solution:

[0005] The invention provides a control device for an oxygen concentration sensor. The device comprises an oxygen concentration sensor, a controller, a power supply, an electronic switch, a filter module and a signal acquisition module. The electronic switch is connected between an input end of the filter module and a positive electrode of a power supply, and a control end thereof is connected to a PWM signal output end of the controller. The output end of the filter module is connected to H+ of the oxygen concentration sensor. The input end of the signal acquisition module is respectively connected to H+, H- and S- ends of the oxygen concentration sensor, and the output end is connected to the controller, so as to realize sampling of the voltage at the H+ end, i.e., the heating voltage, sampling and amplification of the output current at the H- end, i.e., the heating current, and sampling and amplification of the output current at the S- end, i.e., the pump current. The controller adjusts the duty cycle of the PWM signal so that a ratio R of the heating voltage to the heating current is equal to a ratio R0 of the heating voltage to the heating current at an optimal working temperature of the oxygen concentration sensor.

[0006] The present invention also provides a method for calibration using the device, comprising the following steps performed at room temperature:

[0007] Step 1, set the period and initial duty cycle of the PWM signal, output the initial PWM signal to the electronic switch, and start timing t=0;

[0008] Step 2: Get the heating voltage V H And heating current I H , and calculate the heating power P = V H ×I H ;

[0009] Step 3, gradually increase the duty cycle of the PWM signal. When P=0.5P0, stop increasing the duty cycle and wait until t=T / 2. P0 is the power at the optimal operating temperature provided in the oxygen concentration sensor manual, and T is the time required for the oxygen concentration sensor to reach equilibrium with the external temperature.

[0010] Step 4, continue to increase the duty cycle, when P = P0, dynamically adjust the duty cycle: if P>P0, reduce the duty cycle to make P = P0; otherwise, increase the duty cycle to make P = P0;

[0011] Step 5: When t = T, obtain V H ,I H , calculate and record the heating resistance R0 = V H / I H , obtain and record the pump current I P0 , I P0 Corresponding to the oxygen concentration a0 in the atmosphere at normal temperature.

[0012] The present invention also provides a method for controlling by using the device, comprising the following steps after calibration by using the calibration method:

[0013] Get V in real time H ,I H , calculate the heating resistance R = V H / I H ;

[0014] If R>R0, reduce the duty cycle of the PWM signal to make R=R0; otherwise, increase the duty cycle to make R=R0.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] The control device of the oxygen concentration sensor proposed in the present invention is applied to the oxygen concentration sensor at the optimal working temperature at room temperature. The electric power P0 applied to the oxygen concentration sensor at the optimal working temperature is used as the adjustment target value. The heating resistor R0 of the oxygen concentration sensor at the optimal working temperature and the pump current I under the atmospheric oxygen concentration a0 (21%) at room temperature are calibrated by adjusting the duty cycle of the PWM signal. P0After calibration, when the oxygen concentration sensor works normally, the duty cycle of the PWM signal is adjusted to make the heating resistance R equal to the calibrated R0, that is, the oxygen concentration sensor works at the optimal working temperature; the pump current I P , according to the calibrated I P0 Calculate the oxygen concentration a=a0×I P / I P0 , which can improve the measurement accuracy of the oxygen concentration sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a working principle diagram of an oxygen concentration sensor with a zirconium oxide ceramic chip as the core component;

[0018] Figure 2 This is a block diagram of a control device for an oxygen concentration sensor according to an embodiment of the present invention;

[0019] Figure 3 It is a circuit schematic diagram of the connection between the oxygen concentration sensor, the filter module and the electronic switch, and U1 is the oxygen concentration sensor.

[0020] Figure 2 Among them, 1-oxygen concentration sensor, 2-controller, 3-filter module, 4-electronic switch, 5-power supply, 6-signal acquisition module. DETAILED DESCRIPTION

[0021] The present invention will be further described in detail below in conjunction with the accompanying drawings.

[0022] The present invention provides a control device for an oxygen concentration sensor 1, such as Figure 2 As shown, it includes an oxygen concentration sensor 1, a controller 2, a power supply 5, an electronic switch 4, a filter module 3 and a signal acquisition module 6; the electronic switch 4 is connected between the input end of the filter module 3 and the positive electrode of the power supply 5, and its control end is connected to the PWM signal output end of the controller 2; the output end of the filter module 3 is connected to the H+ of the oxygen concentration sensor 1; the input end of the signal acquisition module 6 is respectively connected to the H+, H-, and S- ends of the oxygen concentration sensor 1, and the output end is connected to the controller 2, for realizing sampling of the H+ end voltage, i.e., the heating voltage, sampling and amplification of the H- end output current, i.e., the heating current, and sampling and amplification of the S- end output current, i.e., the pump current; the controller 2 adjusts the duty cycle of the PWM signal so that the ratio R of the heating voltage to the heating current is equal to the ratio R0 of the heating voltage to the heating current at the optimal operating temperature of the oxygen concentration sensor 1.

[0023] In this embodiment, the device is mainly composed of an oxygen concentration sensor 1, a controller 2, a power supply 5, an electronic switch 4, a filter module 3 and a signal acquisition module 6. The connection relationship between the modules is as follows: Figure 2Each module is introduced below.

[0024] The oxygen concentration sensor 1 is the controlled object in this embodiment. It uses a zirconium oxide ceramic chip as a core component. The working principle diagram is as follows: Figure 1 There are 4 pins in total, namely H+, H-, S+, S-. During normal operation, 7±0.5V DC heating voltage is added between H+ and H-, and 0.8±0.1V DC pump voltage is added between S+ and S-. Pump current I P The size is proportional to the oxygen concentration. By measuring I P Calculate the oxygen concentration.

[0025] The controller 2 is mainly used to realize certain data processing and control functions. For example, by performing A / D conversion and necessary data processing on the signal input by the signal acquisition module 6, the heating voltage, heating current, pump current and oxygen concentration are calculated; for another example, a PWM signal with adjustable duty cycle is output to the electronic switch 4, and the ratio of the heating voltage to the heating current (the input resistance at the H+~H- terminal, also called the heating resistance) R of the oxygen concentration sensor 1 is changed by changing the duty cycle, so that the ratio of the heating voltage to the heating current R0 when the oxygen concentration sensor 1 works at the optimal working temperature is always kept constant. The value of R0 is measured in advance by calibration, and a specific calibration method will be given later. When the temperature remains unchanged, the size of the heating resistance R generally remains unchanged, and the heating resistance generally increases as the temperature rises. Therefore, it can be considered that there is a fixed relationship between the heating resistance R and the temperature. The heating resistance R always keeps the heating resistance R0 unchanged at the optimal working temperature, so that the oxygen concentration sensor 1 can always work at the optimal working temperature, thereby improving the measurement accuracy of the oxygen concentration.

[0026] The power supply 5, the electronic switch 4 and the filter module 3 provide a heating voltage for the oxygen concentration sensor 1 under the control of the PWM signal output by the controller 2. The power supply 5 generally adopts a +12V battery voltage. The PWM signal is added to the control end of the electronic switch 4 to control the on and off of the electronic switch 4 (on during the PWM high level period and off during the low level period), so that the electronic switch 4 outputs a PWM pulse voltage with an amplitude of 12V, and outputs a heating voltage proportional to the duty cycle after charging and discharging the filter module 3.

[0027] The signal acquisition module 6 is mainly used to realize the sampling and amplification processing of the heating voltage, heating current and pump current. It includes three acquisition channels: the input end of one channel is connected to the H+ end of the oxygen concentration sensor 1, which is used to realize the heating voltage V H+The input ends of the other two channels are connected to H- and S- respectively, which are used to sample the heating current and the pump current. Since the current sampling is realized by measuring the voltage on the sampling resistor, and the value of the sampling resistor is generally very small, the voltage on it is also very small, therefore, it is generally necessary to amplify the current sampling signal (voltage) before inputting it into the controller 2.

[0028] As an optional embodiment, the filtering module 3 is mainly composed of two capacitors C1 and C2 connected in parallel between the H+ terminal and the ground.

[0029] This embodiment provides a technical solution for the filter module 3. Figure 3 As shown, the filter module 3 is composed of two capacitors C1 and C2 connected in parallel. C2 is an electrolytic capacitor with a larger capacitance value, which is used to achieve low-frequency filtering and convert the input PWM pulse signal into a DC signal; C1 has a smaller capacitance value and is used to filter out high-frequency clutter interference.

[0030] As an optional embodiment, the electronic switch 4 is mainly composed of a P-type MOS tube Q1 and an N-type MOS tube Q2; the source of Q1 is connected to the positive electrode of the power supply 5, the drain is connected to the H+ terminal, the gate is connected to the drain of Q2 and one end of a resistor R1, and the other end of R1 is connected to the positive electrode of the power supply 5; the source of Q2 is grounded, the gate is connected to one end of resistors R2 and R3, the other end of R3 is grounded, and the other end of R2 is connected to the PWM signal output end of the controller 2.

[0031] This embodiment provides a technical solution for the electronic switch 4. The electronic switch 4 of this embodiment is constructed by separate components, mainly consisting of a P-type MOS transistor Q1 and an N-type MOS transistor Q2. The specific connection relationship is as follows: Figure 3 When PWM is high, Q2 and Q1 are turned on, and the +12V power supply charges the capacitor (C1, C2). The larger the duty cycle, the higher the charging voltage. When PWM is low, Q2 and Q1 are turned off, and the capacitor discharges through the heating resistor (the input resistor at the H+~H- terminals).

[0032] As an optional embodiment, the signal acquisition module 6 includes: a resistor series voltage divider circuit connected between the H+ terminal and the ground; a resistor R4 connected between the H- terminal and the ground, and a first operational amplifier connected to the H- terminal; a resistor R5 connected between the S- terminal and the ground, and a second operational amplifier connected to the S- terminal; the output ends of the resistor series voltage divider circuit, the first operational amplifier, and the second operational amplifier are respectively connected to the controller 2.

[0033] This embodiment provides a technical solution for the signal acquisition module 6. The signal acquisition module 6 is composed of three circuit parts, which respectively realize the sampling of the H+ terminal voltage, i.e., the heating voltage, the H- terminal current, i.e., the heating current, and the S- terminal current, i.e., the pump current and amplification. The first circuit part is a resistor series voltage divider circuit, which realizes the sampling of the heating voltage. Since the heating voltage is generally about 7V, which is greater than the maximum operating voltage of the controller 2, it is necessary to use a voltage divider circuit to reduce the voltage before outputting it to the controller 2. The second and third circuit parts are current sampling and amplification circuits, both of which use resistor current sampling, that is, the measured current is calculated by measuring the voltage on the sampling resistor, such as Figure 3 Since the voltage on R4 and R5 is generally very small, it needs to be amplified to a certain amplitude before being output to the controller 2, so the second and third circuits also include an amplifier connected to the output end of the sampling resistors R4 and R5, namely the first operational amplifier and the second operational amplifier.

[0034] The present invention provides a method for calibration using the device, comprising the following steps performed at room temperature:

[0035] S101, setting the period and initial duty cycle of the PWM signal, outputting the initial PWM signal to the electronic switch 4, and starting timing t=0;

[0036] S102, obtain heating voltage V H And heating current I H , and calculate the heating power P = V H ×I H ;

[0037] S103, gradually increase the duty cycle of the PWM signal, and when P=0.5P0, stop increasing the duty cycle and wait until t=T / 2, where P0 is the power at the optimal operating temperature provided in the manual of the oxygen concentration sensor 1, and T is the time required for the oxygen concentration sensor 1 to reach equilibrium with the external temperature;

[0038] S104, continue to increase the duty cycle, when P = P0, dynamically adjust the duty cycle: if P>P0, reduce the duty cycle to make P = P0; otherwise, increase the duty cycle to make P = P0;

[0039] S105. When t=T, obtain V H ,I H , calculate and record the heating resistance R0 = V H / I H , obtain and record the pump current I P0 , I P0 Corresponding to the oxygen concentration a0 in the atmosphere at normal temperature.

[0040] This embodiment provides a technical solution for calibrating the oxygen concentration sensor 1 using the device. The oxygen concentration sensor 1 with a zirconia ceramic chip as the core component has two important parameters, namely the optimal operating temperature and its corresponding heating voltage (also called the rated heating voltage). Due to the differences between different oxygen concentration sensors 1, when the same heating voltage is applied to two oxygen concentration sensors 1 of the same type at room temperature, their operating temperatures are often different after the temperature stabilizes, and the difference is even quite large. Considering that at a fixed ambient temperature, a fixed heating voltage is applied to the oxygen concentration sensor 1, and after a long time, the temperature field of the oxygen concentration sensor 1 reaches equilibrium with that of the surrounding air, and the temperature no longer changes, in this embodiment, during the calibration process, the electric power applied when the oxygen concentration sensor 1 is at the optimal operating temperature is used as the adjustment target value, the heating voltage is used as the adjustment amount, and the electric power is used as the feedback amount for adjustment. Finally, the heating resistance R0 at the optimal operating temperature and the pump current I at the normal temperature oxygen concentration a0 (21%) are measured. P0 . Since there is a fixed relationship between the heating resistance and the working temperature, the chip can always work at the optimal working temperature as long as the heating resistance is always equal to R0 during normal operation. The specific calibration method is shown in S101 to S105, where T is generally 3 minutes. The calibration process of this embodiment takes 3 minutes, which can ensure that the temperature field of the chip and the outside atmosphere is balanced.

[0041] An embodiment of the present invention provides a method for controlling by using the device, comprising the following steps after calibration by using the calibration method:

[0042] Get V in real time H ,I H , calculate the heating resistance R = V H / I H ;

[0043] If R>R0, reduce it so that R=R0; otherwise, increase the duty cycle so that R=R0.

[0044] This embodiment provides a technical solution for controlling the oxygen concentration sensor 1 during normal operation after the oxygen concentration sensor 1 has been calibrated. The specific control method is: by adjusting the duty cycle of the PWM signal, the heating resistor R is equal to R0.

[0045] As an optional embodiment, the method further comprises a step of measuring the oxygen concentration: obtaining the pump current I in real time P , calculate the oxygen concentration a=a0×I P / I P0 .

[0046] This embodiment provides a method for measuring oxygen concentration. P , according to the formula a=a0×IP / I P0 Calculate the oxygen concentration a.

[0047] The above only illustrates several specific embodiments of the present invention, but it cannot be regarded as the protection scope of the present invention. Any equivalent changes or modifications or proportional enlargement or reduction made according to the design spirit of the present invention should be considered to fall within the protection scope of the present invention.

Claims

1. A control device for an oxygen concentration sensor, characterized in that: The device comprises an oxygen concentration sensor, a controller, a power supply, an electronic switch, a filter module and a signal acquisition module; the electronic switch is connected between the input end of the filter module and the positive electrode of the power supply, and the control end thereof is connected to the PWM signal output end of the controller; the output end of the filter module is connected to the H+ of the oxygen concentration sensor; the input end of the signal acquisition module is respectively connected to the H+, H- and S- ends of the oxygen concentration sensor, and the output end is connected to the controller, for sampling the H+ end voltage, i.e., the heating voltage, sampling and amplifying the H- end output current, i.e., the heating current, and sampling and amplifying the S- end output current, i.e., the pump current; the controller adjusts the duty cycle of the PWM signal so that the ratio R of the heating voltage to the heating current is equal to the ratio R0 of the heating voltage to the heating current at the optimal working temperature of the oxygen concentration sensor; The electronic switch is composed of a P-type MOS tube Q1 and an N-type MOS tube Q2; the source of Q1 is connected to the positive electrode of the power supply, the drain is connected to the H+ terminal, the gate is connected to the drain of Q2 and one end of a resistor R1, and the other end of R1 is connected to the positive electrode of the power supply; the source of Q2 is grounded, the gate is connected to one end of resistors R2 and R3, the other end of R3 is grounded, and the other end of R2 is connected to the PWM signal output end of the controller; The filtering module consists of two capacitors C1 and C2 connected in parallel between the H+ terminal and the ground; The signal acquisition module includes: a resistor series voltage divider circuit connected between the H+ terminal and the ground; a resistor R4 connected between the H- terminal and the ground, and a first operational amplifier connected to the H- terminal; a resistor R5 connected between the S- terminal and the ground, and a second operational amplifier connected to the S- terminal; the output ends of the resistor series voltage divider circuit, the first operational amplifier, and the second operational amplifier are respectively connected to the controller.

2. A method for calibration using the device of claim 1, characterized in that: The process comprises the following steps performed at room temperature: Step 1, set the period and initial duty cycle of the PWM signal, output the initial PWM signal to the electronic switch, and start timing t=0; Step 2: Get the heating voltage V H And heating current I H , and calculate the heating power P=V H ×I H ; Step 3, gradually increase the duty cycle of the PWM signal. When P=0.5P0, stop increasing the duty cycle and wait until t=T / 2, where P0 is the power of the oxygen concentration sensor at the optimal operating temperature, and T is the time required for the oxygen concentration sensor to reach equilibrium with the external temperature; Step 4, continue to increase the duty cycle, when P=P0, dynamically adjust the duty cycle: if P>P0, reduce the duty cycle to make P=P0; Otherwise, increase the duty cycle to make P=P0; Step 5, when t=T, obtain V H ,I H , calculate and record the heating resistance R0=V H / I H , obtain and record the pump current I P0 , I P0 Corresponding to the oxygen concentration a0 in the atmosphere at normal temperature; It also includes the oxygen concentration measurement step: real-time acquisition of pump current I P , calculate the oxygen concentration a=a0×I P / I P0 .

3. A method for controlling using the device of claim 1, characterized in that: The method comprises the following steps after the calibration is performed by the calibration method according to claim 2: Get V in real time H ,I H , calculate the heating resistance R=V H / I H ; If R>R0, reduce the duty cycle of the PWM signal to make R=R0; otherwise, increase the duty cycle to make R=R0.

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