CN110763891A - Large-dynamic-range current conversion circuit and method for tritium measurement ionization chamber - Google Patents
Large-dynamic-range current conversion circuit and method for tritium measurement ionization chamber Download PDFInfo
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- CN110763891A CN110763891A CN201910868880.7A CN201910868880A CN110763891A CN 110763891 A CN110763891 A CN 110763891A CN 201910868880 A CN201910868880 A CN 201910868880A CN 110763891 A CN110763891 A CN 110763891A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R15/00—Details of measuring arrangements of the types provided for in groups G01R17/00 - G01R29/00, G01R33/00 - G01R33/26 or G01R35/00
- G01R15/08—Circuits for altering the measuring range
- G01R15/09—Autoranging circuits
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R1/00—Details of instruments or arrangements of the types included in groups G01R5/00 - G01R13/00 and G01R31/00
- G01R1/30—Structural combination of electric measuring instruments with basic electronic circuits, e.g. with amplifier
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
- G01R19/0092—Arrangements for measuring currents or voltages or for indicating presence or sign thereof measuring current only
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Abstract
The invention discloses a large dynamic range current conversion circuit and a method for measuring a tritium ionization chamber, wherein the circuit comprises the ionization chamber, a transimpedance amplification circuit, an ADC (analog to digital converter) circuit, a microprocessor, a signal output end and a transimpedance switching circuit, wherein the ionization chamber, the transimpedance amplification circuit, the ADC circuit, the microprocessor and the signal output end are sequentially connected; the method includes ionizing a chamber output current signal; the trans-impedance amplifying circuit performs I-V conversion; the ADC circuit converts the voltage signal into a digital signal and outputs the digital signal to the microprocessor; the microprocessor converts the received digital signal into a digital current value, and controls the transimpedance switching circuit to switch into the transimpedance in the transimpedance amplifying circuit; the signal output end outputs a digital current value obtained by carrying out digital filtering and signal noise reduction processing by the microprocessor. Through the scheme, the invention achieves the purpose of meeting the current signal processing requirement of the existing ionization chamber, and has very high practical value and popularization value.
Description
Technical Field
The invention belongs to the technical field of electronics, and particularly relates to a large-dynamic-range current conversion circuit and method for a tritium measuring ionization chamber.
Background
The intensity of the current generated by the ionization chamber in the tritium measuring instrument is usually between 1fA and 100nA, the requirement on the dynamic range of a corresponding ionization chamber current conversion circuit is high, the requirement on the sensitivity is also high, and the generated signal is easily influenced by external factors such as electromagnetic interference and the like due to low current lower line, so that the current conversion circuit is required to have good noise resistance.
In the conventional ionization chamber current signal processing method, in order to realize large dynamic range measurement, a multi-stage amplification method is generally adopted. Because the noise is introduced into the multistage amplifier, and the noise at the front stage is easily amplified by the rear stage, the measurement lower line is limited, the magnitude of 100fA is usually achieved, and the measurement lower limit and the measurement sensitivity of the tritium measuring instrument are directly influenced. Therefore, it is difficult to simultaneously implement the measurement of the switching of the weak circuit with large dynamic range and lower limit by the multi-stage amplification method, and therefore, how to solve the problems existing in the prior art is a problem that needs to be solved urgently by those skilled in the art.
Disclosure of Invention
The invention aims to provide a large dynamic range current conversion circuit and method for a tritium measurement ionization chamber, and mainly solves the problem that the conventional ionization chamber signal processing method in the prior art is difficult to realize large dynamic range and current conversion measurement simultaneously through a multi-stage amplification method.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a large dynamic range current conversion circuit for a tritium measuring ionization chamber comprises an ionization chamber, a transimpedance amplification circuit, an ADC (analog to digital converter) circuit, a microprocessor, a transimpedance switching circuit and a signal output end, wherein the ionization chamber is used for generating weak current signals; the transimpedance switching circuit comprises an amplifier ADA4530-1ARZ chip with an output end connected with a microprocessor, a relay K1 and a high-resistance resistor R11, wherein one end of the relay K1 and the other end of the relay R11 are connected with the negative input end of the ADA4530-1ARZ chip after being connected in series, one end of the relay K1 and the negative input end of the ADA4530-1ARZ chip are connected, the other end of the relay K1 and the high-resistance resistor R8 are connected with the output end of the ADA4530-1ARZ chip, the positive input end of the ADA4530-1ARZ chip is grounded, and the output end of the ADA4530-1ARZ chip is connected with the.
Further, the current output by the ionization chamber spans 7 orders of magnitude, wherein the switching of the measuring range is realized by controlling a high-resistance resistor R11 in the transimpedance amplification circuit through a microprocessor.
Further, the transimpedance amplification circuit is a current-voltage conversion circuit.
Specifically, the ADC circuit adopts a 24-bit analog-to-digital conversion chip ADS1255, wherein the ADC circuit is configured to collect a voltage signal converted by the transimpedance amplification circuit.
A method for measuring a large dynamic range current switching circuit of a tritium ionization chamber, comprising the steps of:
(S1) the ionization chamber outputting a current signal between 10fA and 100 nA;
(S2) the transimpedance amplification circuit converts the current signal output from the ionization chamber into a voltage signal;
(S3) the ADC circuit converting the voltage signal into a digital signal and outputting the digital signal to the microprocessor;
(S4) the microprocessor converts the received digital signal into a digital current value, and simultaneously controls the transimpedance switching circuit to switch into the transimpedance in the transimpedance amplifying circuit;
(S5) the signal output end outputs a digital current value obtained by carrying out digital filtering and signal noise reduction processing by the microprocessor.
Compared with the prior art, the invention has the following beneficial effects:
the invention carries out current-voltage conversion on the current generated by the ionization chamber through the transimpedance amplification circuit, the converted voltage is converted into a digital signal by the ADC circuit, the digital signal is converted into a digital current value through the microprocessor, meanwhile, the microprocessor carries out digital filtering and signal noise reduction processing and then passes through a digital current value at the signal output end, and the microprocessor simultaneously controls the transimpedance of the transimpedance switching circuit to be connected into the transimpedance amplification circuit, thereby switching the measuring range of the output current of the ionization chamber. The large dynamic range current conversion circuit and the conversion method for signal processing of the ionization chamber, which are provided by the invention, can automatically realize current measurement of 10 fA-100 nA level, can meet the current signal processing requirement of the existing ionization chamber, and have stronger practicability.
Drawings
Fig. 1 is a schematic block diagram of the circuit of the present invention.
Fig. 2 is a flow chart of the operation of the present invention.
Fig. 3 is a schematic diagram of a transimpedance switching and amplifying circuit according to the present invention.
Fig. 4 is a schematic diagram of an ADC circuit of the present invention.
FIG. 5 is a comparison graph of the current conversion circuit results of the circuit of the present invention and a TYNE 7045 type tritium measuring instrument.
Detailed Description
The present invention is further illustrated by the following examples and figures, and embodiments of the present invention include, but are not limited to, the following examples.
Examples
As shown in fig. 1 to 5, a large dynamic range current conversion circuit for a tritium measuring ionization chamber includes an ionization chamber for generating a weak current signal, a transimpedance amplification circuit for receiving a current generated by the ionization chamber, an ADC circuit connected to the transimpedance amplification circuit and having high precision, a microprocessor connected to the ADC circuit, a transimpedance switching circuit connected to the microprocessor and returning a signal to the transimpedance amplification circuit, and a signal output terminal connected to the microprocessor.
The transimpedance amplification circuit connected with the ionization chamber and used for receiving the current signal generated by the ionization chamber is a current-voltage conversion circuit (shown in figure 3), and the working effect of the transimpedance amplification circuit directly influences the detection lower limit and the sensitivity of the preamplifier circuit to weak current. The invention realizes the amplification of a current signal with 10fA magnitude, so the bias current requirement of the selected operational amplifier U5 is less than 10 fA. The invention adopts ADA4530-1ARZ type extremely low input bias current operational amplifier produced by Analog Devices company as an I-V conversion chip, and the main technical indexes are that the typical input bias current is 1fA, the maximum input bias current is +/-20 fA, the input impedance is more than 100T omega, the current noise density is 0.07fA √ Hz, and the input offset voltage is 50 muV.
The voltage signal output by the transimpedance amplification circuit is connected to the input end of an ADC (analog-to-digital converter) circuit of the high-precision analog-to-digital conversion circuit, the ADC circuit samples and converts the voltage signal into a digital signal, and the sampling precision requirement is guaranteed to be below 10 muV. According to the invention, a 24-bit analog-to-digital conversion chip ADS1255IDBR produced by Texas Instruments is selected to realize the acquisition of the output voltage signal of the I-V conversion circuit. The main technical parameters of the ADS1255 are that the ADC acquisition digit is 24 bits, the maximum nonlinear error is +/-0.001%, and the maximum sampling rate is 30 kSPS. To optimize the ADS1255 performance, the design provides a 2.5V external voltage reference generated by an ultra-low noise high precision 2.5V reference voltage chip ADR4525 manufactured by Analog Devices, the ADR4525 output noise is less than 1.25 μ Vp-p, the temperature coefficient is less than 2 ppm/deg.C, and the output current can reach + -10 mA.
And the voltage digital signal output by the ADC is transmitted to the microprocessor, digital filtering and current calculation are executed in the microprocessor, and the relay is controlled by feedback to switch the trans-resistance. The specific operation steps are as follows: firstly, receiving a digital signal output by the ADC, carrying out coding conversion to a decimal voltage value V0, reading a current relay state register, correspondingly selecting a conversion formula of the voltage value and an actual current value, and then calculating an actual current value I1. And then, sequentially storing the ADC voltage values, constructing a digital low-pass filter with the bandwidth of 10Hz, and filtering the current value I1 to obtain a filtered voltage value I2. And finally, presetting two voltage thresholds T1 and T2(T1> T2) for judging whether the relay needs to be switched or not. When the relay is in the off state (which is a low range current transition), if I2> T1, the relay is on; when the relay is in the on state, if I2< T2, the relay is open.
The microprocessor is also used for controlling the trans-resistance switching circuit to switch the trans-resistance connected into the trans-resistance amplifying circuit, so that 7 orders of magnitude crossed output current of the ionization chamber are switched, the relay K1 is normally opened, and the microprocessor MCU is used for controlling the switch of the relay K1. Initial state input IinThe current is converted into an output voltage V through a high-resistance resistor R8 with the resistance value of 10G omegaoAs shown in the formula (1),
Vo＝Iin·R2(1)
when the output voltage reaches a certain threshold value, the microprocessor MCU controls the relay K1 to be closed, the resistance value of the high resistance becomes the parallel value of R8 and R11, and the output voltage achieves the purpose of switching the measuring range as shown in the formula (2).
When the relay is selected, the insulation resistance of the relay is at least two orders of magnitude (1T omega) larger than the high resistance R8 so as to prevent larger leakage current.
And (3) experimental verification: the ionization chamber current conversion circuit provided by the invention is used for testing a wire-drawing ionization chamber tritium-measuring signal with the volume of 0.5L, and a 7045 type tritium measuring instrument produced by a Canada TYPE Engineering company is adopted to compare with the current conversion circuit designed by the patent. In the experiment, an exhaust port of the wire-drawing ionization chamber is connected with an air inlet of a TYNE 7045 type tritium measuring instrument and is placed in an air environment containing tritium. The tritium concentration in the experiment is changed within the range of 5 x 105Bq/m3To 6X 106Bq/m3In the meantime. The response curves obtained by the two measuring instruments are shown in figure 5, the change trends and absolute measurement values of the two response curves in the graph are very close, and the response delay of the TYNE 7045 type tritium measuring instrument is about 10s mainly because the measuring instrument is connected to the rear end of the tritium concentration on-line monitor. Experiments show that the tritium concentration on-line monitor has the same measurement effect as a TYNE 7045 type tritium measurement instrument in a low concentration range.
The relation between the tritium concentration in the ionization chamber and the output current of the ionization chamber is that the number of pairs of ions produced by β rays emitted by tritium in the ionization chamber is directly proportional to the energy and the intensity of radiation, and when the radiation energy deposition of the wall of the ionization chamber is neglected, the relation between the saturation current I of the ionization chamber and the tritium concentration C is shown in a formula (3):
wherein E represents the average energy of tritium decay deposition and has a value of 5.7 keV; veRepresents the effective volume of the ionization chamber in m3(ii) a e represents an electronic charge and has a value of 1.6X 10-19C; w represents the average work of ionization, approximately 33.7eV in air.
When the input tritium concentration is 5X 105Bq/m3The saturated output current of the ionization chamber with a volume of 0.5L was calculated to be 6.8fA according to equation (4).
And (3) calculating:
the current conversion circuit proposed by this patent is proven to be able to reach the lower measurement limit of 10 fA.
The above embodiments are only preferred embodiments of the present invention, and are not intended to limit the scope of the present invention, but all changes that can be made by applying the principles of the present invention and performing non-inventive work on the basis of the principles shall fall within the scope of the present invention.
Claims (5)
1. A large dynamic range current conversion circuit for a tritium measuring ionization chamber is characterized by comprising an ionization chamber for generating a weak current signal, a transimpedance amplification circuit for receiving current generated by the ionization chamber, an ADC (analog to digital converter) circuit which is connected with the transimpedance amplification circuit and has high precision, a microprocessor which is connected with the ADC circuit, a transimpedance switching circuit which is connected with the microprocessor and returns a signal to the transimpedance amplification circuit, and a signal output end which is connected with the microprocessor; the transimpedance switching circuit comprises an amplifier ADA4530-1ARZ chip, a relay K1 and a high-resistance resistor R11, wherein the output end of the amplifier ADA4530-1ARZ chip is connected with a microprocessor, one end of the relay K1 and the other end of the relay R11 are connected with the negative input end of the ADA4530-1ARZ chip after being connected in series, one end of the high-resistance resistor R8 is simultaneously connected with the negative input end of the relay K1 and the negative input end of the ADA4530-1ARZ chip, the other end of the high-resistance resistor R8 is connected with the output end of the ADA4530-1ARZ chip, the positive input end of the ADA4530-1 AR.
2. The large dynamic range current conversion circuit for tritium measurement ionization chamber according to claim 1, wherein the current output by the ionization chamber spans 7 orders of magnitude, and wherein switching of the measurement range is realized by controlling the connection of a high resistance value resistor R11 in the transimpedance amplification circuit through a microprocessor.
3. The large dynamic range current-to-voltage conversion circuit for a tritium-measuring ionization chamber of claim 2, wherein the transimpedance amplification circuit is a current-to-voltage conversion circuit.
4. The large dynamic range current conversion circuit for tritium measuring ionization chamber according to claim 3, wherein the ADC circuit employs a 24-bit analog-to-digital conversion chip ADS1255, wherein the ADC circuit is used for collecting the voltage signal converted by the transimpedance amplification circuit.
5. A method for a large dynamic range current transformation circuit for a tritium ionization chamber according to any one of claims 1 to 4, comprising the steps of:
(S1) the ionization chamber outputting a current signal between 10fA and 100 nA;
(S2) the transimpedance amplification circuit converts the current signal output from the ionization chamber into a voltage signal;
(S3) the ADC circuit converting the voltage signal into a digital signal and outputting the digital signal to the microprocessor;
(S4) the microprocessor converts the received digital signal into a digital current value, and simultaneously controls the transimpedance switching circuit to switch into the transimpedance in the transimpedance amplifying circuit;
(S5) the signal output end outputs a digital current value obtained by carrying out digital filtering and signal noise reduction processing by the microprocessor.
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| CN114660215A (en) * | 2022-05-25 | 2022-06-24 | 山东科技大学 | FID detection circuit of gas chromatograph |
| CN115575688A (en) * | 2022-09-29 | 2023-01-06 | 北京航天计量测试技术研究所 | Weak current detection circuit |
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