Large dynamic range current conversion circuit for hydrogen flame ion measurement

Abstract

The utility model is applicable to the field of ionization measurement, and provides a large dynamic range current conversion circuit for hydrogen flame ionization measurement, which comprises a logarithmic amplification circuit connected with an ionization chamber, the input end of the logarithmic amplification circuit is also connected with a logarithmic amplification bias generation circuit, and the logarithmic amplification bias generation circuit is connected with a reference voltage source. The output end of the logarithmic amplification circuit is sequentially connected with a square root amplification circuit, a high-precision ADC and a microprocessor, the reference voltage source is further connected to the square root amplification circuit, and the microprocessor is further connected to the square root amplification circuit through a DAC biasing circuit. According to the circuit structure, the temperature influence can be eliminated, the microprocessor provides bias voltage through the square root amplification circuit, system noise of the microprocessor is introduced into a loop of the square root amplification circuit, the system noise and the noise can be mutually counteracted in post-stage measurement of the microprocessor, and the measurement accuracy is ensured.

Description

Technical Field

[0001] The utility model belongs to the technical field of ionization measurement, and particularly relates to a large dynamic range current conversion circuit for hydrogen flame ion measurement. Background Art

[0002] Ionization chambers are usually used to measure the intensity of (ionizing radiation / flames or others)) ionization. The magnitude of the current generated by the ionization chamber is usually proportional to the intensity of ionization. The current intensity generated by ionization is usually between 1 pA and 100 nA. Therefore, the dynamic range requirements for the corresponding ionization chamber current conversion circuit are very high, and the sensitivity requirements are also very high. Moreover, due to the very low current lower limit, the generated signal is easily affected by external factors such as electromagnetic interference.

[0003] The traditional ionization chamber ionization signal processing circuit has the following problems:

[0004] First, the existing processing circuit uses multi-stage amplification. However, multi-stage amplification is prone to introduce more noise, and the noise of the previous stage is easily amplified by the subsequent stage, resulting in a limited measurement lower limit.

[0005] Second, in the multi-stage amplification circuit, the temperature compensation is insufficient, and it is very easy to significantly generate temperature drift, resulting in a positive correlation between the measured value and the temperature.

[0006] Third, the existing processing circuit uses a manual form such as an adjustable resistor for biasing. As time goes by, the adjustable resistor is prone to instability. Summary of the Utility Model

[0007] In view of the above problems, the purpose of the present utility model is to provide a large dynamic range current conversion circuit for hydrogen flame ion measurement, aiming to solve the technical problems such as multi-stage amplification, obvious temperature drift, and manual biasing conditions in the existing ionization chamber ionization signal processing circuit.

[0008] The present utility model adopts the following technical solutions:

[0009] The large dynamic range current conversion circuit for hydrogen flame ion measurement includes a logarithmic amplification circuit connected to an ionization chamber. The input end of the logarithmic amplification circuit is also connected to a logarithmic amplification bias generation circuit. A reference voltage source is connected to the logarithmic amplification bias generation circuit. The output end of the logarithmic amplification circuit is sequentially connected to a square root amplification circuit, a high-precision ADC, and a microprocessor. The reference voltage source is also connected to the square root amplification circuit. The microprocessor is also connected to the square root amplification circuit through a DAC bias circuit.

[0010] Further, the logarithmic amplification bias generation circuit includes an integrated operational amplifier AU4A and a triode AU1D. The positive electrode of the integrated operational amplifier AU4A is grounded, and the negative electrode is connected to the reference voltage source through resistors AR19 and AR17. The output terminal of the integrated operational amplifier AU4A serves as the output terminal of the logarithmic amplification bias generation circuit through resistor AR15, denoted as test point 2. The base of the triode AU1D is grounded, the collector is connected to the negative electrode of the integrated operational amplifier AU4A, and the emitter is connected to test point 2.

[0011] Further, the logarithmic amplification circuit includes an integrated operational amplifier AU2 and a triode AU1A. Test point 2 is connected to the positive electrode of the integrated operational amplifier AU2 and the base of the triode AU1A. The output terminal of the ionization chamber is denoted as test point 0. Test point 0 is connected to the negative electrode of the integrated operational amplifier AU2 and the collector of the triode AU1A through resistors AR8 and AR9. The output terminal of the integrated operational amplifier AU2 serves as the output terminal of the logarithmic amplification circuit through a limiting protection circuit, denoted as test point 1. The emitter of the triode AU1A is connected to test point 1.

[0012] Further, an RC filter circuit is also connected to test point 1.

[0013] Further, the limiting protection circuit includes resistors AR2 and AR7 connected in series. The node between resistors AR2 and AR7 is connected to the ground through a voltage stabilizing diode TD1. The RC filter circuit includes a resistor AR12 connected in series to the ground and a capacitor AC20.

[0014] Further, the square root amplification circuit includes an integrated operational amplifier AU8B, an integrated operational amplifier AU4B, and triodes AU1B and AU1C. After passing through a voltage follower, the reference voltage source is divided by resistors DR6 and DR7 and connected to the positive electrode of the integrated operational amplifier AU8B. The bias voltage provided by the DAC bias circuit of the microprocessor is connected to the negative electrode of the integrated operational amplifier AU8B through resistors DR11 and DR8. The integrated operational amplifier AU8B is connected with a feedback resistor DR9. The output terminal of the integrated operational amplifier AU8B is divided by resistors DR5 and DR10 and then connected to the positive electrode of the integrated operational amplifier AU4B. The integrated operational amplifier AU8B is connected with a feedback resistor AR3. Test point 1 is connected to the negative electrode of the integrated operational amplifier AU4B after being amplified by the square root formed by triodes AU1B and AU1C.

[0015] The beneficial effects of the present utility model are as follows: By designing a bias generation circuit for the logarithmic amplifier circuit, the present utility model provides a bias voltage for the logarithmic amplifier circuit under the influence of the same temperature, so that the temperature influences cancel each other out. In addition, a square root amplifier circuit is adopted. Compared with other amplifier circuits, the square root operation can perform lossless amplification without bringing side effects. Moreover, the microprocessor provides a bias voltage for the square root amplifier circuit through the DAC bias circuit. The square root amplifier circuit is in the positive direction, and at the same time, the system noise of the microprocessor is introduced into the loop of the square root amplifier circuit. In the post-stage measurement of the microprocessor, the system noise can cancel out this noise, ensuring the measurement accuracy. Description of the Drawings

[0016] Figure 1 is the schematic diagram of the large dynamic range current conversion circuit for hydrogen flame ion measurement provided by the embodiment of the present utility model;

[0017] Figure 2 is the circuit diagram of the logarithmic amplifier bias generation circuit and the logarithmic amplifier circuit;

[0018] Figure 3 is the circuit diagram of the square root amplifier circuit. Specific Embodiments

[0019] In order to make the objectives, technical solutions and advantages of the present utility model clearer, the present utility model will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present utility model and are not used to limit the present utility model.

[0020] In order to illustrate the technical solutions described in the present utility model, the following will be described through specific embodiments.

[0021] As Figure 1 shown, the large dynamic range current conversion circuit for hydrogen flame ion measurement provided by this embodiment includes a logarithmic amplifier circuit connected to the ionization chamber. The input end of the logarithmic amplifier circuit is also connected to a logarithmic amplifier bias generation circuit. A reference voltage source is connected to the logarithmic amplifier bias generation circuit. The output end of the logarithmic amplifier circuit is sequentially connected to a square root amplifier circuit, a high-precision ADC, and a microprocessor. The reference voltage source is also connected to the square root amplifier circuit. The microprocessor is also connected to the square root amplifier circuit through a DAC bias circuit.

[0022] As Figure 2As shown in the figure, the upper part is a logarithmic amplification bias generation circuit, including an integrated operational amplifier AU4A and a triode AU1D. The positive electrode of the integrated operational amplifier AU4A is grounded, and the negative electrode is connected to the reference voltage source through resistors AR19 and AR17. The output terminal of the integrated operational amplifier AU4A is used as the output terminal of the logarithmic amplification bias generation circuit through resistor AR15, denoted as test point 2. The base of the triode AU1D is grounded, the collector is connected to the negative electrode of the integrated operational amplifier AU4A, and the emitter is connected to test point 2. Figure 2 The lower part is a logarithmic amplification circuit, including an integrated operational amplifier AU2 and a triode AU1A. The test point 2 is connected to the positive electrode of the integrated operational amplifier AU2 and the base of the triode AU1A. The output terminal of the ionization chamber is denoted as test point 0. Test point 0 is connected to the negative electrode of the integrated operational amplifier AU2 and the collector of the triode AU1A through resistors AR8 and AR9. The output terminal of the integrated operational amplifier AU2 is used as the output terminal of the logarithmic amplification circuit through a limiting protection circuit, denoted as test point 1. The emitter of the triode AU1A is connected to test point 1. The execution process of this circuit is as follows:

[0023] 11. The reference voltage source outputs a reference voltage (provided by the reference chip) and is connected from the Figure 2 upper left corner position. A reference current is formed through resistors AR19 and AR17. The integrated operational amplifier AU4A and the triode AU1D form an I-V conversion, and the reference current Iref = 2.5 / (AR17 + AR19).

[0024] 12. The ionization chamber outputs a current signal I between 1 pA and 100 nA, that is, at the position of test point 0 shown in the figure. Test point 0 is connected to the logarithmic amplification circuit, and at the same time, the bias generation circuit provides the biased test point 2 to provide a bias voltage for the logarithmic amplification circuit. The logarithmic amplifier converts the input current into a voltage signal. Specifically:

[0025] According to the triode PN junction characteristic formula Ic = Is * [exp(Vbe / Vt) - 1]. Where Is is the reverse saturation current of the triode, Ic is the collector junction current, Vbe is the be junction voltage of the triode, Vt is the voltage equivalent of temperature, Vt = kt / q. At 25 °C, Vt ≈ 26 mV. The deformation formula gives Vbe = In(Ic / Is) * Vt.

[0026] As can be seen from the circuit diagram, the reference current input to the integrated operational amplifier AU4A is Iref2.5 / (AR17 + AR19). Therefore, the voltage V0 at test point 2 is Vbe = Ln(Iref / Is)*Vt. For the logarithmic amplifier circuit composed of the integrated operational amplifier AU2 and the triode AU1A, the voltage V1 at test point 1 is V1 = Vt*Ln(I*I / Iref). In the figure, a RC filter circuit is also connected to the test point 1. The limiting protection circuit includes resistors AR2 and AR7 connected in series. The node between the resistors AR2 and AR7 is connected to the ground through the voltage stabilizing diode TD1. The RC filter circuit is connected in series with the resistor AR12 and the capacitor AC20 connected to the ground. The RC filter circuit further processes the signal stability. The limiting protection circuit prevents the voltage from being too large.

[0027] In the design of this circuit structure, the output voltage of AU4A is affected by the temperature drift of AU1D, providing a bias voltage under the same temperature influence for the logarithmic amplifier composed of AU2, so that the influence of temperature on AU1A and the temperature influence of AU1D cancel each other out. In addition, an effective bias voltage of -0.6V is provided to AU2, so that the output offset of the logarithmic amplifier circuit composed of AU2 starts from 0. However, in a conventional logarithmic amplifier, it starts from 0, resulting in a large signal noise for signals greater than 0 and approaching 0, and it is also difficult for the subsequent stage to measure. In this embodiment, the reference voltage source provides a reference current with the same temperature coefficient as the logarithmic amplifier circuit and provides a negative bias voltage to ensure that the output signal is unipolar.

[0028] As Figure 3 shown, the square root amplifier circuit includes the integrated operational amplifier AU8B, the integrated operational amplifier AU4B, and the triodes AU1B and AU1C. After the reference voltage source passes through a voltage follower, it is divided by the resistors DR6 and DR7 and connected to the positive terminal of the integrated operational amplifier AU8B. The bias voltage provided by the microprocessor through the DAC bias circuit is connected to the negative terminal of the integrated operational amplifier AU8B through the resistors DR11 and DR8. The integrated operational amplifier AU8B is connected with a feedback resistor DR9. The output terminal of the integrated operational amplifier AU8B is divided by the resistors DR5 and DR10 and then connected to the positive terminal of the integrated operational amplifier AU4B. The integrated operational amplifier AU8B is connected with a feedback resistor AR3 (in the figure, AR16 is also connected in series, and its resistance value is much smaller than AR3 and can be ignored). The test point 1 is connected to the negative terminal of the integrated operational amplifier AU4B after being amplified by the square root formed by the triodes AU1B and AU1C. The execution process of this circuit is as follows:

[0029] 13. The reference voltage source follows and outputs the reference voltage through a voltage follower ( Figure 3 not shown in the figure), and divides the voltage by the resistors DR6 and DR7 to about 0.5V and inputs it to the positive terminal of the integrated operational amplifier AU8B.

[0030] 14. The bias voltage provided by the microprocessor through the DAC bias circuit, namely the marked MCU_P20 in the figure, with the voltage denoted as Vp20, is connected to the negative pole of the integrated operational amplifier AU8B through the resistor DR11 and the resistor DR8. The output voltage of the integrated operational amplifier AU8B is V7 = 1 - Vp20. Then, through the voltage division of the resistors DR5 and DR10, a voltage bias is provided to AU4B, with the voltage denoted as V3, to ensure that the square root circuit of AU4B is in the positive direction. At the same time, the system noise of the microprocessor is introduced into this circuit loop. In the measurement circuit at the later stage of the microprocessor, the system noise can cancel out this noise with each other.

[0031] 15. The output terminal of the logarithmic amplifier circuit, namely the test point 1, is connected from Figure 3 the lower right corner. Two triodes AU1B and AU1C and AU4B form a square root amplifier to perform square root operation on the input current signal. Under the automatic bias condition provided by the microprocessor, the current signal is converted into a voltage signal.

[0032] Finally, the output voltage V5 (i.e., the voltage of the test point 5 in the figure) = (AR3) * sqrt(Vref / (AR17 + AR19)) * sqrt(I) + V3. AR3 is the feedback resistor of AU4B, with a resistance value of 150K, and the total resistance value of AR17 and AR19 is 25K.

[0033] 16. Finally, a high-precision ADC (model AD7124 - 4BRUZ, 24 bits) samples the voltage V5, and the microprocessor can obtain the magnitude of the input current through simple calculation. The calculation of the current by the microprocessor is not the inventive point of the present utility model and can be realized by using the existing MCU (model Stm 32g030 in this embodiment), which will not be elaborated here.

[0034] Finally, for the thermal noise analysis of the entire circuit, from the transfer function, the component noise of the entire circuit mainly comes from AR17 + AR19 and AR3. Compared with the traditional multi-stage amplification or transimpedance amplification, the resistance value has decreased by at least 10 times. According to the Johnson noise formula <Vn = 4kTRB^0.5>, where k is the Boltzmann constant (1.38×10^-23 J / K), T is the temperature of the resistor, B is the bandwidth, and R is the resistance value of the resistor. The empirical rule shows that a 1kohm resistor has a noise of 4nV / Hz^1 / 2 at room temperature. It can be seen that the thermal noise of this circuit is reduced by at least 10 times compared with the traditional circuit.

[0035] In addition, from the transfer function, and because AU1D, AU1A, AU1B, and AU1C select triodes of the same crystal, that is, under the condition that their temperature coefficients and parameters are the same, it can be known that they perform temperature compensation on each other and eliminate the temperature error.

[0036] Moreover, for the bias voltage V3, it is indirectly input under the control of the microprocessor. That is, at the time of factory shipment, the microprocessor automatically adjusts V3 to make the output voltage of the ADC close to 0, thus avoiding the instability of the adjustable resistor.

[0037] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A large dynamic range current conversion circuit for hydrogen flame ion measurement, characterized in that: The invention comprises a logarithmic amplifier circuit connected to the ionization chamber, wherein the input end of the logarithmic amplifier circuit is also connected to a logarithmic amplifier bias generating circuit, the logarithmic amplifier bias generating circuit is connected to a reference voltage source, the output end of the logarithmic amplifier circuit is sequentially connected to a square root amplifier circuit, a high-precision ADC, and a microprocessor, the reference voltage source is also connected to the square root amplifier circuit, and the microprocessor is also connected to the square root amplifier circuit through a DAC bias circuit.

2. The large dynamic range current conversion circuit for hydrogen flame ion measurement as claimed in claim 1, characterized in that: The logarithmic amplification bias generating circuit includes an integrated operational amplifier AU4A and a transistor AU1D, wherein the positive electrode of the integrated operational amplifier AU4A is grounded, and the negative electrode is connected to the reference voltage source through resistors AR19 and AR17. The output end of the integrated operational amplifier AU4A is used as the output end of the logarithmic amplification bias generating circuit through resistor AR15, which is recorded as test point 2. The base of the transistor AU1D is grounded, the collector is connected to the negative electrode of the integrated operational amplifier AU4A, and the emitter is connected to the test point 2.

3. The large dynamic range current conversion circuit for hydrogen flame ion measurement as claimed in claim 2, characterized in that: The logarithmic amplifier circuit includes an integrated operational amplifier AU2 and a transistor AU1A. The test point 2 is connected to the positive electrode of the integrated operational amplifier AU2 and the base of the transistor AU1A. The output end of the ionization chamber is recorded as test point 0. Test point 0 is connected to the negative electrode of the integrated operational amplifier AU2 and the collector of the transistor AU1A through resistors AR8 and AR9. The output end of the integrated operational amplifier AU2 is used as the output end of the logarithmic amplifier circuit through a limiting protection circuit, which is recorded as test point 1. The emitter of the transistor AU1A is connected to test point 1.

4. The large dynamic range current conversion circuit for hydrogen flame ion measurement as claimed in claim 3, characterized in that: The test point 1 is also connected to an RC filter circuit.

5. The large dynamic range current conversion circuit for hydrogen flame ion measurement as claimed in claim 4, characterized in that: The amplitude limiting protection circuit includes a resistor AR2 and a resistor AR7 connected in series, a node between the resistor AR2 and the resistor AR7 is connected to the ground through a voltage regulator tube TD1, and the RC filter circuit is connected in series to a resistor AR12 and a capacitor AC20 connected to the ground.

6. A large dynamic range current conversion circuit for hydrogen flame ion measurement as claimed in claim 5, wherein the square root amplification circuit comprises an integrated operational amplifier AU8B, an integrated operational amplifier AU4B, and triodes AU1B and AU1C; the reference voltage source is connected to the positive electrode of the integrated operational amplifier AU8B through resistors DR6 and DR7 after voltage follower; the bias voltage provided by the microprocessor through the DAC bias circuit is connected to the negative electrode of the integrated operational amplifier AU8B through resistors DR11 and DR8; the integrated operational amplifier AU8B is connected to a feedback resistor DR9; the output end of the integrated operational amplifier AU8B is connected to the positive electrode of the integrated operational amplifier AU4B after voltage division through resistors DR5 and DR10; the integrated operational amplifier AU8B is connected to a feedback resistor AR3; and the test point 1 is connected to the negative electrode of the integrated operational amplifier AU4B after square root amplification composed of triodes AU1B and AU1C.

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