JP7027963B2 - Current measuring device and radiation detection device - Google Patents

Description

The present invention relates to, for example, a current measuring device for measuring a minute current such as an ionization current in an ionizing box type radiation detecting device, and a radiation detecting device using this current measuring device.

FIG. 5 is a conventional technique of a current measuring device applied to an ionization chamber type radiation detector, which is described in Patent Document 1.
The current measuring device 1 includes a charge integrating circuit 3 that integrates the measured current (ionized current) I _in input from the input terminal 2, and its output signal (integrated voltage signal) _Vo is the low range side current measuring unit 4. And is input to the high range side current measuring unit 5. The measured values _{Im and ImH calculated} by these current measuring units 4 and 5 are input to the measured value determining unit 6 to determine the final current measured value _Im .
A pumping circuit 7 for discharging the charge accumulated in the integrating capacitor is connected to the input side of the charge integrating circuit 3, and a pulse signal P1 from the high range side current measuring unit ₅ is input to the pumping circuit 7. There is.

FIG. 6 is a detailed configuration diagram of the current measuring device 1 shown in FIG.
The charge integration circuit 3 includes an operational amplifier 31 and an integrating capacitor 32, and the integrated voltage signal Vo output from the operational amplifier 31 is converted _{into a digital signal V od by} the A / D conversion circuit 41 of the low range side current measuring unit 4. It is input to the operation processing circuit 42 including the low range side measurement value calculation unit 42a and the high range side measurement value calculation unit 42b.

Further, the integrated voltage signal _Vo is input to the voltage comparison circuit 51 in the high range side current measuring unit ₅ , and the comparison signal _Sc is output according to the comparison result with the reference voltage V1. The comparison signal Sc is input to a pulse signal generation circuit 52 composed of a _monostable multivibrator, and the output pulse signal P ₁ is input to the counter circuit 53 and the pumping circuit 7.
The counter circuit 53 counts the count value N corresponding to the cycle of the pulse signal P ₁ sequentially input, that is, the cycle T of the integrated voltage signal _Vo , and calculates the high range side measurement value in the low range side current measurement unit 4. Output to unit 42b.
Note that FIG. 7 shows the operation of each unit constituting the high range side current measuring unit 5 together with the measured current I _in and the integrated voltage signal _Vo .

As described above, the pulse signal P ₁ is input to the pumping circuit 7 including the capacitor 71, the resistor 73 and the diode 72, and the output of the pumping circuit 7 is applied to the inverting input terminal of the operational amplifier 31 in the charge integrating circuit 3. There is.

The low range side measurement value calculation unit 42a of the calculation processing circuit 42 performs timer interruption processing in a cycle equal to the sampling cycle of the A / D conversion circuit 41 (for example, 1 [s]), and digital signals of the integrated voltage signal _Vo . Multiply the rate of change of V _od by the conversion factor to calculate the low range side current measurement value I _mL .
On the other hand, the measured value calculation unit 42b on the high range side _obtains the frequency of the integrated voltage signal Vo based on the period T taken in from the counter circuit 53 by the timer interruption processing of a predetermined period (for example, 125 [ms]), and uses this frequency. Multiply the conversion factor to calculate the high range side current measurement value _ImH .
FIG. 8A shows the relationship between the measured current I _in ( _IML ) calculated by the low range side measurement value calculation unit _42a and the time change rate of the integrated voltage signal Vo, and FIG. 8B shows the relationship. , The relationship between the measured current I _in ( _ImH ) calculated by the measured value calculation unit 42b on the high range side and the frequency of the integrated voltage signal _Vo is shown.

When the measured value determination unit 6 in FIG. 5 can calculate the high range side current measured value _ImH according to the desired output request timing by the high range side current measuring unit 5, the high range side current measured value _ImH is calculated. It is determined as the current measured value _Im with respect to the measured current I _in . If the high range side current measurement value _ImH cannot be calculated at the desired output request timing, the low range side current measurement value I _mL calculated by the low range side current measurement unit 4 is measured with respect to the measured current I _in . Determined as the value _Im .
In this way, the current measurement value _Im is obtained by selecting either I _mL or _ImH depending on whether or not the high range side current measurement value _ImH can be calculated within the desired output request timing. It is possible to accurately measure a minute measured current I _{in in} a wide range according to a desired output request timing without causing a loss time due to range switching.

International Publication No. 2015/01/916 (paragraphs [0009] to [0011], [0041] to [0046], Fig. 1, Fig. 2, Fig. 7, etc.)

In the above-mentioned prior art, as shown in _FIG . 7, a pulse signal P ₁ is generated by a comparison signal Sc output when the integrated voltage signal _Vo exceeds the reference voltage V ₁ , and this pulse signal P ₁ is generated. It is supplied to the pumping circuit 7 to discharge the integrating capacitor 32 of the voltage integrating circuit 3. Specifically, at the rising edge of the pulse signal P1, the electric charge of the capacitor 71 flows to the _ground side via the resistor 73, and the voltage drop generated in the resistor 73 at that time causes a current to flow to the voltage integrating circuit 3 side via the diode 72. By flowing, the electric charge accumulated in the integrating capacitor 32 is discharged (reset).

However, immediately after discharging the integrating capacitor 32, the electric charge does not become completely zero due to the influence of the dielectric absorption of the integrating capacitor 32, which causes a problem that an error is included in the current measured value.

Therefore, the problem to be solved of the present invention is to provide a current measuring device that reduces the error of the current measured value by appropriately correcting the current measured value immediately after the discharge of the integrating capacitor, and to use this current measuring device. The purpose is to provide a radiation detector.

In order to solve the above problem, the current measuring device according to claim 1 is a charge integrating means that integrates the measured current and outputs an integrated voltage signal, and is measured based on the time change rate of the integrated voltage signal. In a current measuring device including a current measuring means for calculating a current and a pumping means for discharging an integrating capacitor in the charge integrating means when the integrated voltage signal reaches a reference voltage.
The error between the measured current whose value is known and the current measured value by the current measuring means when the measured current is input to the charge integrating means is measured immediately after the discharge of the integrating capacitor by the pumping means. And a compensation function creating means that generates a charge reset compensation function that is close to the error.
It is characterized by comprising a measured value correction means for calculating a current measured value from which the error is removed by correcting the current measured value using the charge reset compensation function.

In the current measuring device according to claim 2, the compensation function creating means synthesizes a plurality of compensation functions including an initial current value, an attenuation coefficient, and an elapsed time after the start of discharge of the integrating capacitor, and the charge reset compensation is performed. It is characterized by creating a function.

The current measuring device according to claim 3 is the current measuring device according to claim 1 or 2, wherein the measured current is an ionization current for measuring a dose rate of radiation.

The radiation detection device according to claim 4 includes the current measuring device according to any one of claims 1 to 3, and detects a radiation dose rate using a current measurement value output from the measured value correction means. It is characterized by doing.

According to the present invention, the current measurement value after discharging the integrating capacitor of the voltage integrating circuit into which the measured current flows is corrected by the charge reset compensation function, thereby reducing the error caused by the dielectric absorption of the integrating capacitor. It is possible to realize a current measuring device. Further, if this current measuring device is applied to a radiation detecting device, it is possible to accurately measure the dose rate of radiation.

It is a block diagram which shows the main part of the Embodiment of this invention. In the embodiment of the present invention, it is a figure which shows the data (part) when the synthetic compensation function which approximated the measurement error of the current measuring apparatus is obtained as the addition value of three compensation functions 1 to 3. It is a waveform diagram which shows the measurement error, the compensation function 1 to 3, and the composite compensation function in FIG. It is a waveform diagram which showed the relationship between the elapsed time after the integrated charge discharge and the current measured value in the case of with / without integrated charge reset compensation based on the data of FIG. It is a block diagram of the current measuring apparatus described in Patent Document 1. It is a detailed block diagram of FIG. It is a waveform diagram which shows the operation of the prior art. In the prior art, the relationship between the measured current measured by the low range side measurement value calculation unit and the rate of change of the integrated voltage signal (FIG. 8A), and the measured current and integrated voltage signal by the high range side measurement value calculation unit. It is a figure which shows the relationship with the frequency (FIG. 8 (b)), respectively.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, the present invention defines a charge integrating means for inputting a measured current to perform an integrating operation, a current measuring means for calculating the measured current based on the integrated voltage signal, and an integrating capacitor for the charge integrating means. The target is a current measuring device equipped with a pumping means for discharging at a timing.
Therefore, the present invention can be applied to, for example, the current measuring device described in Patent Document 1, but the function of switching between the low range side current measuring unit and the high range side current measuring unit described above is not always necessary. is not it.

First, FIG. 1 is a block diagram showing a main part of an embodiment of the present invention.
In FIG. 1, for example, a measured current Iin such as an ionization current _in an ionization chamber type radiation detection device is input to a charge integrating means 11 provided with an operational amplifier and an integrating capacitor as shown in FIG. The integrated voltage signal _Vo output from the charge integrating means 11 is input to the current measuring means 12, and the current measuring means 12 is based on the integrated voltage signal _Vo , the capacity of the integrating capacitor, and the elapsed time from the start of measurement. The measured current value _Im'is calculated by a well-known calculation.

Further, when the integrated voltage signal _Vo exceeds the reference voltage, the current measuring means 12 generates a pulse signal P and outputs the pulse signal P to the pumping means 13. The pumping means 13 is configured in the same manner as the pumping circuit 7 of FIG. 6, for example, and has a function of discharging the charge accumulated in the integrating capacitor of the charge integrating means 11 when the pulse signal P is input.

Due to the influence of the dielectric absorption of the integrating capacitor described above, the integrated voltage signal Vo does not become zero immediately after the integrating capacitor is discharged, and as a result, the measured value _Im'output from the current _measuring means 12 includes an error. There is.
Therefore, in the present embodiment, the error of the measured value _Im'is corrected by the measured value correcting means 15 to obtain an accurate measured value _Im , and in order to make this correction, a synthesis means as a compensation function creating means. The synthetic compensation function SC _n generated by 14 is used.

That is, when the measured current I _in of which the value is known is input to the current measuring device used for the measurement and the measured value _Im'is obtained via the charge integrating means 11 and the current measuring means 12, the pumping means The time change of the error (measurement error) between the measured current I _in and the measured value _{Im'immediately} after the integrating capacitor is discharged (reset) by 13 is measured. If a compensation function (integral charge reset compensation function) that approximates this measurement error is created in advance and the measured value _Im'is corrected using this integrated charge reset compensation function, the effect of dielectric absorption by the integrating capacitor is removed. It is possible to obtain an accurate measured value _Im .
Since it is difficult to realize the integrated charge reset compensation function by a single function, the synthetic compensation function SC _n obtained by synthesizing a plurality of compensation functions is used in this embodiment.

In FIG. 2, a known measured current I _in is input to the current measuring device to obtain a measurement error, and the combined compensation function SC _n approximated to this measurement error is referred to as three compensation functions 1 to 3 (C _1n to C _{3 n} ). The data (part) when it is obtained as the added value of) is shown.
Here, about 326 [fA] of the measured current I _in is input to the current measuring device, and for each measurement from the first to the fourth, about 50 in the elapsed time for each 1 [s] after the integrating capacitor is discharged. The average value of each measured value (data without reset compensation) _Im'and the four measured values _Im ', and the measurement error of this average value with respect to the measured current I _in are obtained, and each measurement error is obtained. The synthetic compensation function close to is calculated as the addition value of the compensation functions 1 to 3.
In FIG. 2, the shaded data No. 0-No. Reference numeral 3 is a portion in which the integrating capacitor is discharged after confirming the value of the measured current I _in , and the data No. 3 is used. The time point 3 is the discharge timing (elapsed time = 0).

The following equation 1 is a setting example of the compensation functions ₁ to ₃ , and the compensation peak current initial values a1 to a3 and the attenuation coefficients τ1 to _τ3 can be adjusted for _each current measuring device to be used.

FIG. 3 is a waveform diagram showing a synthetic compensation function (broken line) approximated to the measurement error (solid line) in FIG. 2 and compensation functions 1 to 3 (dashed-dotted line, two-dot chain line, dotted line).
Since the synthetic compensation function SC _n is obtained by the synthetic means 14 of FIG. 1 described above, the measured value correction means 15 adds or subtracts the synthetic compensation function SC _n to the measured value _Im'to perform integrated charge reset compensation. Thereby, the measured value _Im from which the error due to the dielectric absorption of the integrating capacitor is removed can be obtained.

FIG. 4 is a waveform diagram showing the relationship between the elapsed time after the integrated charge discharge and the current measured value in the case where the integrated charge reset compensation of the present embodiment is performed and the case where the integrated charge reset compensation is not performed, based on the data of FIG. be.
In the waveform without reset compensation (dashed line) in FIG. 4, the four peak values from the one whose elapsed time is closer to 0 are the data Nos. in FIG. It is the first to fourth measured values of No. 5, and about 50 measured values between each peak value are the data without reset compensation in FIG. 2.
When there is no reset compensation, the measured value fluctuates greatly, but in the waveform with reset compensation (solid line) according to this embodiment, the fluctuation range of the measured value is small, and it can be seen that the compensation effect is remarkable. ..

INDUSTRIAL APPLICABILITY The present invention can be used in various current measuring devices for measuring minute currents, including ionizing currents of radiation detection devices.

11: Charge integrating means 12: Current measuring means 13: Pumping means 14: Synthesis means 15: Measured value correction means

Claims (4)

The charge integrating means that integrates the measured current and outputs the integrated voltage signal, the current measuring means that calculates the measured current based on the time change rate of the integrated voltage signal, and the integrated voltage signal have reached the reference voltage. In a current measuring device including a pumping means for discharging an integrating capacitor in the charge integrating means at times.
The error between the measured current whose value is known and the current measured value by the current measuring means when the measured current is input to the charge integrating means is measured immediately after the discharge of the integrating capacitor by the pumping means. And a compensation function creating means that generates a charge reset compensation function that is close to the error.
A measurement value correction means for calculating a current measurement value from which the error is removed by correcting the current measurement value using the charge reset compensation function, and a measurement value correction means.
A current measuring device characterized by being equipped with. In the current measuring device according to claim 1,
The current compensation function creating means is characterized in that a plurality of compensation functions including an initial current value, an attenuation coefficient, and an elapsed time after the start of discharge of the integrating capacitor are combined to create the charge reset compensation function. measuring device. In the current measuring device according to claim 1 or 2.
A current measuring device, characterized in that the measured current is an ionizing current for measuring a dose rate of radiation. A radiation detection device comprising the current measuring device according to any one of claims 1 to 3, wherein the dose rate of radiation is detected by using the current measured value output from the measured value correcting means.

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