JP2014153352A - Digital circuit having a recycling high-pressure chamber for environment monitoring - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a digital circuit having a recycling high-pressure chamber for environment monitoring.SOLUTION: The digital circuit includes: an integrator unit; a first diode connected to the integrator unit; a second diode connected to the integrator unit; a comparator connected to the integrator unit; a flip-flop connected to the comparator; a NOT gate connected to the flip-flop; a NAND element connected to the flip-flop and the NOT gate; a switch element connected to the NAND element; and an output drive unit connected between the NAND element and the switch element. As a result, the circuit can compensate a parasitic leak current with the use of an adjustable current source connected parallelly to an input current while retaining a similar temperature characteristic, effectively resolve a problem of a surface leak current and achieve elimination of influence of a bias current and improvement of atmospheric environment resistance because, after the compensation, the lowest applicable current is femtoampere (10-15A) and the result of temperature insensible measurement exceeds 50°C.

Description

The present invention relates to a digital circuit with a recycling high pressure chamber for environmental monitoring, and in particular, using a tunable current source connected in parallel to an input current while having similar temperature characteristics, parasitic leakage current After compensation, the lowest applicable current will be femtoampere (10-15A), and temperature numbness measurement will be over 50 ° C, effectively surface It is possible to eliminate the leakage current problem and to eliminate the influence of the bias current and to enhance the environmental air resistance.

The gamma ray chamber is the simplest but fastest emerging radiation detector, and the principle of normal work of the chamber is to concentrate all the charges generated by the ionization directly into the gas with an electric field. Its standard structure is composed of two basic electrodes, one of which is a high voltage electrode, and the other is a concentrated electrode. The chamber is filled with argon gas, which is a high pressure gas, and the outside is sealed. It becomes a stopped casing. When the incident γ rays enter the chamber sensitivity region, secondary electrons (photoelectrons and Compton electrons) are emitted from the electrodes and the walls of the chamber, the gas is ionized by the secondary electrons, and positive and negative ion pairs are generated. The When an electric field is present (when two electrodes have polarization voltages), ions and electrons are caused by the positive charge coasting toward the cathode and the negative charge coasting toward the anode. A current is constructed. When a gas having a predetermined volume is irradiated with a predetermined γ-ray, the generation rate of ion pairs becomes constant.

The advantages of the chamber are its simple structure, long-term work stability, long service life, and no maintenance during use, so it can operate stably even in bad work environments. Therefore, there are many types of radiation detectors used in nuclear radiation dashboards, most of which are, for example, ionizing radiation calibration, nuclear medicine equipment radiation quality measurement, high energy X radiation container detector, mill thickness Various volume chambers are used as detectors in gauges, continuous steel pouring liquid level control devices, nuclear power scales, and continuous liquid level detectors.

In 1981, the United States GE Company and the United States Department of Energy's Environmental Surveillance Laboratory collaborated to develop the world's first high-pressure Ion Chamber (HPIC) online environmental radiation monitoring system. The environmental monitor consists of an HPIC, a weak ammeter and a data processor, which has a stainless steel sphere with an argon gas of 25 atmospheric pressure inside, and a small ball with a diameter of 2 inches in the center of the sphere. Between the frame and the sphere, it is sealed with ceramic, and the sphere itself becomes the positive and negative electrodes of the detector. When operating as a gamma ray detector, the negative potential cathode plug is connected to the -400 Volt voltage, and the anode and leakage current suppression electrode ring are connected to the ground potential. When high-energy gamma rays enter the HPIC, they interact with the chamber walls and argon gas to ionize them, generating positively charged argon ions and negatively charged electrons. Charged particles are accelerated by the internal electric field, absorbed by the anode and the cathode, an electric current is formed and an electrostatic charge is deposited, and the physical quantity is directly proportional to the energy and flow rate of gamma rays.

According to the data published by GE company, if the HPIC radiation sensitivity is 2.6x10-14 amps / (μR / h) and under estimated environmental background radiation (~ 10μR / h), its output current Is approximately 0.26 pA, and if it is a conventional GE HPIC environmental monitor weak ammeter, when providing an analog output signal relative to the dose, the high-insulation and airtightness directly in the HPIC It is necessary to mount it on the electrode plug, which reduces the space leakage current noise, and the current output of the chamber is in the range of 10-14 to 10-11 amps (about 100 times less background environmental radiation intensity ), A very low resistance value of 5x1011 ohm is converted into a voltage and output. The range of 10-10 to 10-8 amperes is 109 ohms, converted to voltage and output.

However, the existing design that converts a weak current into a voltage with a conventional high-resistance resistor and then performs analog / digital conversion is based on the characteristics of the ADC integrated circuit element. According to the practical experience applied in the hot and humid climate of Taiwan, the contacts are not only very high failure rate due to oxidation and leakage current, but also ADC The high resistance voltage signal sent to is easily interfered with, so abnormal surge voltage often intrudes, making it difficult to analyze survey data.

    The present inventor has carefully studied in order to eliminate the above-mentioned drawbacks, and can use the theory to effectively eliminate the above-mentioned disadvantages, and the digital circuit with a recycling high-pressure chamber for environmental monitoring that is rational in design. The present invention is proposed.

The main object of the present invention is to compensate for parasitic leakage current using an adjustable current source connected in parallel to the input current, with similar temperature characteristics, and the lowest after compensation The applicable current is set to femtoampere (10-15A), and the temperature insensitivity measurement exceeds 50 ° C. A digital circuit with a recycling high-pressure chamber is provided for environmental monitoring that eliminates the effects and enhances environmental air resistance.

In order to achieve the above object, the present invention is a digital circuit with a recycling high pressure chamber for environmental monitoring, comprising an integration unit, a first diode connected to the integration unit, and a first diode connected to the integration unit. Two diodes, a comparator connected to the integration unit, a flip-flop connected to the comparator, a negative gate connected to the flip-flop, and a negative AND element connected to the flip-flop and the negative gate, A switch element connected to the negative AND element and an output drive unit connected between the negative AND element and the switch element are included.

According to an embodiment of the present invention, the integration unit includes a charge / discharge capacity and an operational amplifier.

According to an embodiment of the present invention, the charge / discharge capacity is a glass charge / discharge capacity with an ultra-low leakage current.

According to an embodiment of the present invention, the operational amplifier is a CMOS operational amplifier.

According to an embodiment of the present invention, the first diode is a low leakage current diode.

According to an embodiment of the present invention, the second diode is an ultra low leakage current diode.

According to an embodiment of the present invention, the second diode is connected to the integrating unit by a current limiting resistor.

According to an embodiment of the present invention, the switch element is a CMOS switch.

According to an embodiment of the present invention, the CMOS switch is composed of an NMOS transistor and a PMOS transistor connected in parallel.

According to the embodiment of the present invention, an analog switch is further connected between the flip-flop and the negative gate.

    Hereinafter, the features and technical contents of the present invention will be described in detail with reference to the drawings. However, the drawings and the like are for reference and explanation, and the present invention is not limited thereby.

It is a basic structure conceptual diagram of the present invention.

FIG. 1 is a conceptual diagram of the basic structure of the present invention. As shown in the figure, the present invention is a digital circuit with a recycling high-pressure chamber for environmental monitoring, and includes at least an integration unit 1, a first diode 2, a second diode 3, a comparator 4, a flip-flop 5, It comprises a negative gate 6, a negative AND element 7, a switch element 8 and an output drive unit 9.

The integration unit 1 includes a charge / discharge capacity 11 and an operational amplifier 12. The charge / discharge capacity 11 is a glass charge / discharge capacity with an ultra-low leakage current, and the operational amplifier 12 is a CMOS operational amplifier.

The first diode 2 is connected to the integrating unit 1 and is a low leakage current diode.

The second diode 3 is connected to the integrating unit 1 by a current limiting resistor 31 and is an ultra-low leakage current diode.

The comparator 4 is connected to the integration unit 1.

The flip-flop 5 is connected to the comparator 4.

The negative gate 6 is connected to the flip-flop 5, and an analog switch A is further connected between the flip-flop 5 and the negative gate 6.

A flip-flop 5 and a negative gate 6 are connected to the negative AND element 7.

The switch element 8 is connected to the negative AND element 7 and is a CMOS switch. The CMOS switch includes an NMOS transistor and a PMOS transistor connected in parallel.

The output drive unit 9 is connected between the NAND element 7 and the switch element 8. The above design constitutes a new digital circuit with a recycling high pressure chamber for environmental monitoring.

According to the present invention, when the high energy gamma ray is incident on the high pressure chamber, it is ionized by acting on the wall of the chamber or argon gas to generate positively charged argon ions and negatively charged electrons. Accelerated by the internal electric field, absorbed by the anode and cathode, a current is formed, and soot charges are deposited, the physical quantity of which is directly proportional to the energy and flow rate of gamma rays, and the ion flow is integrated in the chamber in the integrating unit 1 When the charging is performed through the charging / discharging capacity 11 and the output of the integrating unit 1 is increased by charging with the chamber current and the voltage is increased to a predetermined level, the lower-level comparator 4 is driven to output a positive logic. A signal is generated, and the size of the output gate (Gate) of the comparator 4 is determined.

The high, medium and low frequency timings generated by the precise oscillator B are simultaneously supplied to the flip-flop 5 and the negative gate 6 as work timings. The comparator 4 is a circuit of the integration unit 1 for the chamber current. When the level rises to a predetermined level, when generating a positive logic output signal, the logic output signal is modulated by the flip-flop 5 and then delayed by the negation gate 6 to the negative AND element 7 in synchronism with the timing delayed. While the output of the flip-flop 5 is maintained at the high potential, the negative AND element 7 continuously outputs the timing to the analog switch A, and the flip-flop 5 outputs the low potential. The NAND element 7 stops the timing output.

The timing output from the NAND element 7 is output to the lower 32bits high-speed addition counter via the output drive unit 9 for pulse counting, and the number of discharge pulses generated per unit time is the chamber current. The digital detection function of “current / frequency conversion” is realized, the switch element 8 is controlled at a fixed cycle timing, and the charge / discharge capacity 11 is unidirectionally controlled by the second diode 3. On the other hand, the amount of the stable pulse current is determined by the magnitude of the value of the current limiting resistor 31 and the Vref reference voltage until the output of the integration unit 1 becomes a low voltage by performing pulse discharge quantitatively. In addition, the discharge frequency of the switch element 8 is determined by the magnitude of the ion flow.

In the current / frequency analog-digital conversion ammeter, when the forward voltage of the second diode 3 is reduced due to an increase in temperature, the resistance of the insulation characteristic of the charge / discharge capacitor 11 is reduced, the capacitance value is also reduced, and the capacitance value is reduced. Is negatively affected by charging efficiency, and the integral value of capacity value and median dissipation factor (DF) fluctuates with changes in temperature. The present invention uses a switch element 8 of a CMOS switch as a discharge switching element, and in this way, in the cut-off state, mainly the leakage current is sub-threshold current (Sub-threshold
The leakage current and subthreshold slope St (Sub-threshold Slope) increase rapidly when VG = 0V with increasing temperature. When the temperature rises from 0 ° C to 50 ° C, the leakage current increases 20 times.

    In the current frequency conversion design circuit using the first diode 2 as the temperature compensated current source, it is connected to the recycling high-pressure chamber under background radiation (signal current is about 0.2 pA) and compensated by the first diode 2 When the leakage current compensation is applied to a low Vc voltage and works at a high voltage, the leakage current and the compensation current are balanced at room temperature and the temperature rises. The rate of current rise is faster than the leakage current, and a characteristic inversion phenomenon occurs. Under a low voltage (for example, 65mV), the leakage current and compensation current are balanced at a temperature of 40-45 ° C. At this time, by adding a simple compensation circuit, the current-frequency conversion design circuit temperature rises. Saturation cutoff phenomenon can be prevented.

As described above, the digital circuit with a recycling high-pressure chamber for environmental monitoring according to the present invention can effectively eliminate the conventional drawbacks and has a similar temperature characteristic and is connected in parallel to the input current. Can be compensated for parasitic leakage currents, and after compensation, the lowest applicable current is femtoampere (10-15A), and temperature insensitive measurement However, it is possible to effectively overcome the surface leakage current problem, eliminate the influence of bias current, and enhance the environmental air resistance. Therefore, the present invention is more progressive and more Apply for patents according to law, practical.

The above is merely a better embodiment of the present invention, and the present invention is not limited thereby, and equivalent changes made based on the scope of the claims and the description of the present invention. All modifications are within the scope of the claims of the present invention.

DESCRIPTION OF SYMBOLS 1 Integration unit 11 Charging / discharging capacity 12 Operational amplifier 2 1st diode 3 2nd diode 31 Current limiting resistor 4 Comparator 5 Flip-flop 6 Negative gate 7 Negative AND element 8 Switch element 9 Output drive unit A Analog type switch B Precise oscillator

Claims (10)

An integration unit;
A first diode connected to the integration unit;
A second diode connected to the integrating unit;
A comparator connected to the integration unit;
A flip-flop connected to the comparator;
A negative gate connected to a flip-flop;
A negative AND element connected to the flip-flop and the negative gate;
A switch element connected to a negative AND element;
An output drive unit connected between the negative AND element and the switch element;
Contains,
A digital circuit with a recycling high-pressure chamber for environmental monitoring. The digital circuit with a recycling high-pressure chamber for environmental monitoring according to claim 1, wherein the integration unit includes a charge / discharge capacity amount and an operational amplifier. 3. The digital circuit with a recycling high-pressure chamber for environmental monitoring according to claim 2, wherein the charge / discharge capacity is a glass charge / discharge capacity with an ultra-low leakage current. The digital circuit with a recycling high-pressure chamber for environmental monitoring according to claim 2, wherein the operational amplifier is a CMOS operational amplifier. The digital circuit with a recycling high-pressure chamber for environmental monitoring according to claim 1, wherein the first diode is a low-leakage current diode. The digital circuit with a recycling high pressure chamber for environmental monitoring according to claim 1, wherein the second diode is an ultra-low leakage current diode. The digital circuit with a recycling high pressure chamber for environmental monitoring according to claim 1, wherein the second diode is connected to the integrating unit by a current limiting resistor. 2. The digital circuit with a recycling high-pressure chamber for environmental monitoring according to claim 1, wherein the switch element is a CMOS switch. 9. The digital circuit with a recycling high-pressure chamber for environmental monitoring according to claim 8, wherein the CMOS switch comprises an NMOS transistor and a PMOS transistor connected in parallel. 2. The digital circuit with a recycling high-pressure chamber for environmental monitoring according to claim 1, further comprising an analog switch connected between the flip-flop and the negative gate.