JP2023087221A - Logarithmic conversion processing device - Google Patents

Abstract

To provide a highly productive logarithmic conversion processing device that performs logarithmic conversion and counting loss correction.SOLUTION: A logarithmic conversion processing device 50 includes: an integrated circuit 10 that receives a first signal 3a according to a count value of a detection signal corresponding to energy of an incident radiation, logarithmically transforms the first signal 3a and outputs it as a second signal 10a; and a count value correction circuit 20 that has control units 21, 22, 23 provided independently from the integrated circuit 10 in the subsequent stage of the integrated circuit 10 and corrects counting loss of the count values in second signals 10a, 40a output by the integrated circuit 10. In the count value correction circuit 20, a correction command for correcting the counting loss of the count value is stored in a storage device 25. The control units 21, 22, 23 A/D-convert the second signals 10a, 40a into digital signals based on a set resolution, and perform digital processing using the correction command on the digital signals to correct the counting loss of the count value.SELECTED DRAWING: Figure 1

Description

The present application relates to a logarithmic conversion processing device.

In measuring radiation such as neutrons emitted from radioactive substances, a radiation detector such as a proportional coefficient tube outputs a pulse signal having a pulse number corresponding to the radiation intensity of the radiation to be measured. Then, this pulse signal is converted into a current signal corresponding to the number of pulses, and is input to a logarithmic conversion circuit for radiation analysis. Signals output from such radiation detectors generally have a wide range of count rates of 6 digits or more, so signal compression is performed by logarithmic conversion to facilitate subsequent signal processing. . Furthermore, due to the characteristics of radiation detectors such as the dead time of radiation, as the count rate of the pulse signal being measured increases, the radiation count is lost. It is necessary to perform drop correction. This counting loss correction is generally performed by the calculation represented by the following equation.
Count drop correction formula: N=N0/(1-N0×τ)
However, N: Number of pulses actually generated
N0: number of pulses from the radiation detector
τ: resolution of the radiation detector Then, the following logarithmic conversion circuit is disclosed as a logarithmic conversion processing device that performs the above logarithmic conversion and counting loss correction using the logarithmic characteristics of the transistor. .

That is, a conventional logarithmic conversion circuit includes an operational amplifier, NPN first and second transistors, and a resistor. The collector of the first transistor is connected to the input terminal side (negative terminal) of the operational amplifier, the other input terminal side (positive terminal) of the operational amplifier is grounded, and the output terminal side (output terminal) of the operational amplifier is grounded. ) is connected to the base of the second transistor. One end of a resistor is commonly connected to the emitters of the first and second transistors, and the other end of the resistor is connected to the negative electrode of a DC power source. The base of the first transistor is grounded, and the collector of the second transistor is connected to the positive terminal of the DC power supply. If the current flowing through the resistor is If, the input current is Iin, and the current flowing through the second transistor is Ic, then Ic=If−Iin. Assuming that the voltage is Vout and ln is the natural logarithm, Vout=-ln{Iin/(If-Iin)} (2). On the other hand, the counting loss correction formula in the pulse system detector is given by the following formula. N=Nx/(1−Nx·τ) (3). Here, N is the number of pulses corrected for counting down, Nx is the number of pulses detected by the pulse system detector, and τ is the resolution of the pulse system detector. Taking the logarithm of both sides of equation (3), ln(N)=ln{(Nx)/(1/τ−Nx)}−ln(τ) (4). Comparing the first term on the right side of the above formula (2) and formula (4), if Iin = Nx and If = 1/τ, both are equivalent except for the difference in positive and negative polarities (for example, See Patent Document 1).

JP 2009-300293 A (paragraphs [0019] to [0026], FIG. 1)

The logarithmic conversion circuit as the conventional logarithmic conversion processing device is constructed using discrete parts such as resistors and transistors, which are individual single parts. Utilizing the fact that the output of the logarithmic conversion circuit is equivalent to the calculation formula for the counting loss correction, the logarithmic conversion circuit simultaneously performs the logarithmic conversion and the counting loss correction collectively.
However, in the logarithmic conversion circuit with such a configuration, for example, due to the shortage of supply of semiconductors in recent years or the discontinuation of production, etc., it is difficult to obtain discrete parts that are single parts. When it becomes necessary to use alternative discrete parts supplied by the manufacturer, it is necessary to review the entire circuit due to variations in the characteristics of the alternative parts, making new production difficult. In addition, due to variations in the characteristics of the substitute parts, errors may occur in both the logarithmic conversion and counting correction. Therefore, there is a problem that productivity and performance are lowered.
The present application discloses a technique for solving the above problems, and an object of the present application is to provide a highly productive and high-performance logarithmic conversion processing apparatus.

The logarithmic conversion processing device disclosed in the present application is
an integrated circuit for receiving a first signal corresponding to a count value of a detection signal corresponding to the energy of incident radiation, logarithmically transforming the first signal and outputting it as a second signal;
a count value correction circuit provided after the integrated circuit and independently of the integrated circuit, and having a control unit that corrects the counting loss of the count value in the second signal output by the integrated circuit;
In the count value correction circuit, a correction command for correcting the counting loss of the count value is stored in a storage device,
The control unit A/D-converts the second signal into a digital signal based on the set resolution, performs digital processing on the digital signal using the correction command, and counts down the count value. to correct the
It is.

According to the logarithmic conversion processing device disclosed in the present application, a high-productivity and high-performance logarithmic conversion processing device can be obtained.

1 is a block diagram showing a schematic configuration of a logarithmic conversion processing device according to Embodiment 1; FIG. 2 is a circuit block diagram showing the circuit configuration of a logarithmic conversion circuit according to Embodiment 1; FIG. 2 is a circuit block diagram showing the circuit configuration of an amplifier circuit according to Embodiment 1; FIG. FIG. 4 is a flowchart showing a processing flow of an undercount correction circuit according to Embodiment 1; 3 is a diagram showing an example of a circuit configuration around an input terminal of the logarithmic conversion circuit according to Embodiment 1; FIG.

Embodiment 1.
FIG. 1 is a block diagram showing a schematic configuration of a logarithmic conversion processing device 50 according to Embodiment 1. As shown in FIG.
FIG. 2 is a circuit block diagram showing the circuit configuration of the logarithmic conversion circuit 10 included in the logarithmic conversion processing device 50 shown in FIG.
FIG. 3 is a circuit block diagram showing the circuit configuration of the amplifier circuit 30 included in the logarithmic conversion processing device 50 shown in FIG.
FIG. 4 is a flowchart showing the processing flow of the counting loss correction circuit 20 shown in FIG.
The logarithmic conversion processing device 50 of the present embodiment compresses the detection signal, which detects radiation such as neutrons emitted from a radioactive substance, by logarithmic conversion, and causes the radiation due to the characteristics of the radiation detector. It corrects the counting loss of the counting rate.

As shown in FIG. 1, the logarithmic conversion processing device 50 of this embodiment is provided with a detector 1 for detecting radiation, a preamplifier 2, and a wave height discrimination shaper 3 on its input side.
The detector 1 is, for example, a proportional coefficient tube, and when radiation is incident, it outputs a pulse signal 1a as a detection signal having a wave height corresponding to the energy of the incident radiation.
The pulse signal 1a output in this way has a dynamic range of the radiation count rate per second of about 1 to 10̂6 cps.

The preamplifier 2 amplifies each input pulse signal 1a and outputs it as a pulse signal 2a.
The wave height discrimination shaper 3 outputs a current signal 3a as a first signal of about 100 pA to 0.1 mA, which indicates the count for each energy value of each input pulse signal 2a. The output current signal 3 a is input to the logarithmic conversion processor 50 .

Next, the configuration of the logarithmic conversion processing device 50, which is the main part of the first embodiment, will be described.
As shown in FIG. 1, the logarithmic conversion processing device 50 includes a logarithmic conversion circuit 10, a counting loss correction circuit 20 as a count value correction circuit provided independently of the logarithmic conversion circuit 10, and the logarithmic conversion circuit 10 and an undercount correction circuit 20, and an amplifier circuit 30 and a test circuit 40.

A logarithmic conversion IC (Integrated Circuit), which is a general-purpose integrated circuit, is used for the logarithmic conversion circuit 10 .
As shown in FIG. 2, the logarithmic conversion IC includes an input resistor 10Rin, an operational amplifier 10Amp, a capacitor 10C, and a logarithmic conversion transistor 10Tr. A plurality of these electronic components are formed on a silicon wafer and integrated.

An input resistor 10Rin is connected in series to the negative input terminal of the operational amplifier 10Amp.
The logarithmic conversion transistor 10Tr has its collector side connected to the connection point between the input resistor 10Rin and the negative input terminal of the operational amplifier 10Amp, and its emitter side connected to the output terminal of the operational amplifier 10Amp. A positive input terminal of the operational amplifier 10Amp is grounded. A capacitor 10C is connected in parallel with the logarithmic conversion transistor 10Tr.

The logarithmic conversion circuit 10 configured in this manner logarithmically converts the input current signal 3a and outputs a voltage signal 10a as a second signal of about 0 to 2.5V.
A capacitor (not shown) is externally attached to the logarithmic conversion circuit 10 in order to adjust the response time.
Note that the logarithmic conversion circuit 10 is not limited to the logarithmic conversion IC having the circuit configuration shown in FIG.
A voltage signal 10a that has been signal-compressed by the logarithmic conversion circuit 10 is input to the amplifier circuit 30 in the subsequent stage.

As the circuit configuration of the amplifier circuit 30 is shown in FIG. 3, the amplifier circuit 30 has an operational amplifier 30Amp, an input resistor 30Rs, and a feedback resistor 30Rf. Then, the amplifier circuit 30 converts the voltage signal 10a, which is the input signal, to 0 to 10 V according to the processing in the counting loss correction circuit 20 at the subsequent stage, with the amplification factor set by the input resistor 30Rs and the feedback resistor 30Rf. Amplifies to about voltage. A voltage signal 30a as a second signal amplified by the amplifier circuit 30 is input to the counting loss correction circuit 20 in the subsequent stage.

As shown in FIG. 1, the count value correction circuit 20 includes an A/D conversion circuit 21 as a control section, a processor 22 as a control section, and a D/A conversion circuit 23 as a control section. and a storage device 25 .

Here, the storage device 25 includes a volatile storage device such as a random access memory (not shown) and an auxiliary storage device such as a non-volatile EEPROM such as a flash memory.
Also, an auxiliary storage device such as a hard disk may be provided instead of the flash memory.
The processor 22 executes a later-described program input from the storage device 25 . In this case, the program is input to the processor 22 from an auxiliary storage device such as an EEPROM through a volatile storage device. Further, the processor 22 may output data such as calculation results to the volatile storage device of the storage device 25, or may store the data in an auxiliary storage device via the volatile storage device.

Details of the processing performed by the counting loss correction circuit 20 configured as described above will be described below.
In describing this process, the flow chart shown in FIG. 4 will be used.
First, the voltage signal 30a is input to the A/D conversion circuit (step S001).

The A/D conversion circuit 21 performs A/D conversion on the input voltage signal 30a based on the set resolution, and converts the input voltage signal 30a of 0 to 10 VD into 0 to 32767 (0000h to 7FFFh). 16-bit digital signal.
Here, the storage device 25 stores first data 25D in which the resolution in A/D conversion corresponding to the magnitude of the input voltage signal 30a is recorded in advance. The A/D conversion circuit 21 determines the resolution in A/D conversion based on this first data 25D (steps S002, S003). For example, when the amplitude of the input voltage signal 30a is large, the A/D conversion circuit 21 performs A/D conversion with high resolution based on the first data 25D, and when the amplitude of the voltage signal 30a is small, performs A/D conversion at low resolution.

The processor 22 performs a digital processing operation for correcting counting loss of the counting rate on the A/D converted digital signal 21a (step S004).
A correction command for correcting the counting loss is stored as a program in the storage device 25 and is expressed by the following equation.
N=N0/(1-N0×τ))
However, N: Number of pulse signals actually generated
N0: the number of pulse number signals measured from the radiation detector
τ: Resolution of the detector that detects radiation

In this case, the calculation for the counting loss correction by the processor 22 is performed for each bit value that has been A/D converted. Therefore, as the input voltage signal 30a is A/D-converted with higher resolution by the A/D conversion circuit 21, more correction calculations are performed, and the correction precision of the count-off correction becomes higher.

The digital signal 22a that has undergone the count-down correction is output to the D/A conversion circuit 23 in the subsequent stage.
The D/A conversion circuit 23 performs D/A conversion on the input digital signal 22a, converts the digital signal into an analog signal, and outputs the analog signal (step S005).
In this way, the logarithmic conversion processing device 50 outputs an analog signal that has undergone logarithmic conversion and counting loss correction processing.

By converting a digital signal into an analog signal by the D/A conversion circuit 23, it can be applied to existing radiation measuring instruments that often use analog signals, but the D/A conversion circuit 23 is not provided. As a configuration, it may be configured to output a digital signal.

Next, the test circuit 40 provided in the logarithmic conversion processing device 50 will be described with reference to FIGS. 1 and 5. FIG.
FIG. 5 is a diagram showing an example of the peripheral circuit configuration of the input terminals of the logarithmic conversion circuit 10 for explaining the test circuit 40 of the present embodiment.
As shown in FIG. 1, test circuit 40 includes test input circuit 41 and adjustment circuit 42 . The test circuit 40 is not used for actual radiation measurement, but is used for prior operation confirmation of the logarithmic conversion processing device 50 and adjustment of circuit constants.

The test input circuit 41 inputs to the logarithmic conversion circuit 10 a test signal 41 t simulating the current signal 3 a which is the first signal output from the wave height discrimination shaper 3 .
Further, the adjustment circuit 42 adjusts the bias and gain for at least one of the voltage signal 10a output from the logarithmic conversion circuit 10 and the voltage signal 30a output from the amplifier circuit 30 in response to the input of the test signal 41t. , perform zero adjustment.

The amplification factor of the amplifier circuit 30 may be adjusted according to the value of at least one of the voltage signals 10a and 30a obtained by inputting the test signal 41t.
Further, according to the value of at least one of the voltage signals 10a and 30a obtained by inputting the test signal 41t, as shown in FIG. You may adjust the value of electronic components, such as resistor 10R, connected externally.

In this way, the test input circuit 41 confirms the operation of the logarithmic conversion circuit 10 under the condition that radiation is detected in a pseudo manner. Then, the adjustment circuit 42 adjusts the voltage signal from at least one of the logarithmic conversion circuit 10 and the amplifier circuit 30 and inputs it to the counting loss correction circuit 20 . In this way, it is possible to confirm the operation of the counting loss correction circuit 20 in a state in which radiation is detected in a pseudo manner.
As a result, for example, even when the logarithmic conversion IC used in the logarithmic conversion circuit 10 is in short supply and is replaced with another general-purpose logarithmic conversion IC, the logarithmic conversion processing device 50 can easily use the replaced general-purpose IC. , and adjustment of the logarithmic conversion processing device 50 according to the replaced general-purpose IC becomes possible.

The logarithmic conversion processing device of this embodiment configured as described above is
an integrated circuit for receiving a first signal corresponding to a count value of a detection signal corresponding to the energy of incident radiation, logarithmically transforming the first signal and outputting it as a second signal;
a count value correction circuit provided after the integrated circuit and independently of the integrated circuit, and having a control unit that corrects the counting loss of the count value in the second signal output by the integrated circuit;
In the count value correction circuit, a correction command for correcting the counting loss of the count value is stored in a storage device,
The control unit A/D-converts the second signal into a digital signal based on the set resolution, performs digital processing on the digital signal using the correction command, and counts down the count value. to correct the
It is.

As described above, the logarithmic conversion processing apparatus of the present embodiment uses an integrated circuit to perform logarithmic conversion of the first signal according to the count value of the incident radiation. In the subsequent stage of this integrated circuit, a count value correction circuit for correcting counting loss is provided independently of the integrated circuit.
In this way, the circuit that performs logarithmic conversion and the circuit that performs count-off correction are configured independently of each other, and their functions are separated. , it is possible to suppress errors in the correction accuracy on the counting loss correction circuit side. In this way, it is possible to eliminate the need to review the circuit of the entire logarithmic conversion processing device, thereby ensuring high production continuity and at the same time maintaining high correction accuracy.

In general, the logarithmic characteristics of discrete component transistors change with temperature, but the logarithmic conversion circuit of the present embodiment does not use discrete component transistors that are highly temperature dependent, but uses an integrated circuit. Therefore, it is possible to suppress the instability of the proportional voltage due to the characteristic variation of the discrete components.
As a result, signal compression can be performed while maintaining high logarithmic conversion characteristics without depending on the ambient environment such as the temperature of the place where radiation measurement is performed. Therefore, it is possible to obtain a highly reliable logarithmic conversion processing apparatus suitable for measuring neutron beams having a wide energy range.
Also, there is no need to separately provide a circuit for compensating temperature dependence. This makes it possible to reduce the size and cost of the logarithmic conversion processor.

In addition, since an integrated circuit is used, it is not necessary to use a poorly workable connection method such as aerial wiring as a connection method between elements in consideration of reducing the influence of noise and the like. As a result, the noise reduction effect can be ensured, and high productivity and workability can be obtained. In addition, performance can be improved by eliminating the influence of leakage current.
Furthermore, since the counting loss correction circuit is provided after the logarithmic conversion circuit, the counting loss correction circuit can perform the counting loss correction based on the easy-to-process signal with a compressed counting rate range.

In addition, a correction command for correcting counting loss of the count value is stored in the storage device. Then, the control unit A/D-converts the signal-compressed second signal into a digital signal based on the set resolution, performs digital processing using this correction command, and corrects counting loss of the count value. ing. By using digital signals in this way, signals with less noise, distortion and interference can be transmitted.
Furthermore, by performing a count-off correction calculation by digital processing on this digital signal, an ideal count-off correction formula: N=N0/(1-N0×τ) that does not depend on temperature, humidity, noise, etc. Curve correction becomes possible.

Further, in the logarithmic conversion processing device of the present embodiment configured as described above,
The storage device stores first data in which the resolution in the A/D conversion is recorded according to the magnitude of the second signal,
In the A/D conversion of the second signal, the control unit determines the resolution based on the first data according to the magnitude of the second signal, and the value of each bit after A/D conversion. performing digital processing using the correction instructions on each of
It is.

In this way, the first data in which the resolution corresponding to the magnitude of the second signal is recorded is stored in the storage device. Then, the control unit determines the resolution based on the first data according to the magnitude of the second signal. As a result, for example, when the amplitude of the second signal to be input is large, A/D conversion can be performed with high resolution, thereby suppressing the occurrence of resolution-dependent errors.
Then, digital processing using a correction command is performed on each bit value that has been A/D converted while suppressing the error. As a result, a high counting loss correction accuracy is obtained even in a high counting rate region.

Also, for example, when an integrated circuit that performs logarithmic conversion is replaced with an integrated circuit of another semiconductor manufacturer, even if the magnitude of the output voltage and current changes, A/D conversion can be performed using an appropriate resolution. Therefore, high correction accuracy can be maintained without depending on the characteristics of the replaced integrated circuit.

Further, in the logarithmic conversion processing device of the present embodiment configured as described above,
An amplifier circuit that adjusts the amplification factor of the second signal is provided between the integrated circuit and the count value correction circuit,
It is.

In this way, by providing an amplifier circuit between the integrated circuit and the count value correction circuit, in the same manner as described above, for example, an integrated circuit that performs logarithmic conversion can be used as an integrated circuit of another semiconductor manufacturer. Even if it is replaced, its output can be adjusted. This makes it possible to maintain high correction accuracy without depending on the characteristics of the replaced integrated circuit.

Further, in the logarithmic conversion processing device of the present embodiment configured as described above,
A test circuit for inputting a test signal simulating the first signal to the count value correction circuit,
an amplification factor of the amplifier circuit is adjusted based on the second signal output from the integrated circuit in response to the input of the test signal;
It is.

In this way, a pseudo-detection of radiation can be achieved by inputting the test signal from the test circuit. Then, the amplification factor of the amplifier circuit is adjusted according to the output signal output by the input of this test signal.
As a result, for example, even if the integrated circuit that performs logarithmic conversion is replaced with an integrated circuit from another semiconductor manufacturer, the operation of the logarithmic conversion processing device can be easily checked, and the circuit of the logarithmic conversion processing device can be adjusted accordingly. can. Therefore, high correction accuracy can be maintained without depending on the characteristics of the integrated circuit.

Further, in the logarithmic conversion processing device of the present embodiment configured as described above,
Based on the second signal from the integrated circuit output by the input of the test signal,
A configuration of an electronic component connected to at least one of an input terminal for inputting the first signal and an output terminal for outputting the second signal in the integrated circuit is adjusted;
It is.

As a result, for example, even when an integrated circuit that performs logarithmic conversion is replaced with an integrated circuit of another semiconductor manufacturer, the operation of the logarithmic conversion processing device can be easily checked, and the input and output terminals of the replaced integrated circuit can be connected. In addition, circuit constants of electronic components such as resistors are adjusted. Therefore, high correction accuracy can be maintained without depending on the characteristics of the integrated circuit.

Although the present application has described exemplary embodiments, the various features, aspects, and functions described in the embodiments are not limited to application of particular embodiments, alone or Various combinations are applicable to the embodiments.
Therefore, countless modifications not illustrated are envisioned within the scope of the technology disclosed in the present application. For example, the modification, addition, or omission of at least one component shall be included.

1a pulse signal (detection signal), 3a current signal (first signal),
10 logarithmic conversion circuit (integrated circuit), 10a voltage signal (second signal),
21 A/D conversion circuit (control unit), 22 processor (control unit),
23 D/A conversion circuit (control unit), 25 storage device, 30 amplifier circuit,
30a voltage signal (second signal), 40 test circuit, 50 logarithmic conversion processor.

Claims (5)

an integrated circuit for receiving a first signal corresponding to a count value of a detection signal corresponding to the energy of incident radiation, logarithmically transforming the first signal and outputting it as a second signal;
a count value correction circuit provided after the integrated circuit and independently of the integrated circuit, and having a control unit that corrects the counting loss of the count value in the second signal output by the integrated circuit;
In the count value correction circuit, a correction command for correcting the counting loss of the count value is stored in a storage device,
The control unit A/D-converts the second signal into a digital signal based on the set resolution, performs digital processing on the digital signal using the correction command, and counts down the count value. to correct the
Logarithmic conversion processor. The storage device stores first data in which the resolution in the A/D conversion is recorded according to the magnitude of the second signal,
In the A/D conversion of the second signal, the control unit determines the resolution based on the first data according to the magnitude of the second signal, and the value of each bit after A/D conversion. performing digital processing using the correction instructions on each of
2. A logarithmic transformation processing device according to claim 1. An amplifier circuit that adjusts the amplification factor of the second signal is provided between the integrated circuit and the count value correction circuit,
3. A logarithmic conversion processing device according to claim 1. A test circuit for inputting a test signal simulating the first signal to the count value correction circuit,
an amplification factor of the amplifier circuit is adjusted based on the second signal output from the integrated circuit in response to the input of the test signal;
4. A logarithmic transformation processing device according to claim 3. Based on the second signal from the integrated circuit output by the input of the test signal,
A configuration of an electronic component connected to at least one of an input terminal for inputting the first signal and an output terminal for outputting the second signal in the integrated circuit is adjusted;
5. A logarithmic transformation processing device according to claim 4.

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