JP2001051062A - Radiation measuring device and noise elimination method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To exclude a noise caused by a radio wave and vibration or the like from a detection signal, in a radiation measuring device (especially, a personal dosimeter). SOLUTION: In the noise elimination method, a noise is reduced by utilizing that a noise signal is generated at both the polar sides of a baseline while a radiation signal is generates on one polar side of the baseline. A comparator 22 extracts a signal component at one polar side in a detection signal, namely it outputs a signal 100 including both of the radiation signal and noise. A comparator 24 extracts merely the signal constituent at the other polar side in the detection signal. More specifically, a signal 102 including merely the noise is outputted. A counter operation part 26 subtracts the signal 102 from the signal 100, thus reducing the noise.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a radiation measuring apparatus and a method for removing noise, and more particularly, to the removal of noise caused by vibrations and external electromagnetic waves.

[0002]

2. Description of the Related Art For example, in a radiation measuring device such as a personal dosimeter, radiation is detected by a semiconductor sensor, and the detection signal is counted and displayed as a dose.
In recent years, various safety standards have been proposed, and it is required that radiation measuring devices such as personal dosimeters also satisfy various strict safety standards.

When a physical impact is applied to a semiconductor sensor or a substrate on which the semiconductor sensor is mounted, noise is generated due to physical distortion, and this causes erroneous counting. In addition, when an electromagnetic wave is received, noise is generated due to the electromagnetic wave, which also causes erroneous counting.

[0004]

Therefore, in order to ensure highly reliable measurement, it is necessary to reduce the erroneous counting as described above as much as possible. It is conceivable to mold the inside of the device or put a cushion material in the device against impact, but the effect is not sufficient. Although shielding is effective for electromagnetic waves, there is still a need for a method for more reliably removing noise.

[0005] The present invention has been made in view of the above-mentioned conventional problems, and has as its object to remove noise and perform highly reliable radiation measurement.

It is another object of the present invention to pay attention to the difference between a radiation signal and a noise signal and to specify and exclude the noise signal.

[0007]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a detection circuit having a radiation sensor for detecting radiation and an amplifier for amplifying a radiation detection signal, and a detection circuit for detecting the detection signal from the detection circuit. And a signal processing circuit for removing noise according to the difference between the signal component of one polarity and the signal component of the other polarity.

According to the above configuration, even if noise occurs due to electromagnetic waves or vibrations in a detection circuit including a radiation sensor and an amplifier, the noise is detected based on the difference between the radiation detection signal and the noise waveform. By excluding it, it becomes possible to specify only the radiation detection signal.

That is, according to the experimental study by the present inventors, the original detection signal of radiation has a waveform component appearing only in one polarity as shown in FIG. On the other hand, it has been confirmed that noise due to electromagnetic waves and vibration has waveform components in both polarities as shown in FIG. Therefore, the present invention is to specify and remove noise using such a difference in waveform.

[0010] Various safety standards require that the noise level be reduced as much as possible. For example, even if multiple electromagnetic shields are provided, it is not easy to completely shield the electromagnetic noise, and moreover, it is difficult for portable individuals. Adopting a complicated shield structure in a dosimeter goes against the demand for miniaturization. As for vibration, if measures such as resin molding of the inside of the device are taken, the weight of the device increases and maintenance becomes difficult. According to the present invention, even if noise is induced in a detection signal, it can be eliminated by electrical processing only by adding a simple circuit configuration. In addition, there is an advantage that high-accuracy measurement can be realized.

Preferably, the signal processing circuit counts the one-polarity signal component to calculate a first count value.
A counter for counting the signal component of the other polarity to calculate a second count value; and a subtractor for subtracting the second count value from the first count value.

Preferably, the signal processing circuit comprises: a difference device for calculating a difference between the signal component of one polarity and the signal component of the other polarity after the delay; a counter for counting the signal after the difference calculation; including.

Preferably, the signal processing circuit compares a detection signal from the detection circuit with a first reference value set on one polarity side of a baseline to detect the signal component of one polarity. And comparing a detection signal from the detection circuit with a second reference value set on the other polarity side of the baseline to detect a signal component of the other polarity.
And a comparator.

[0014] Preferably, the radiation measuring device is a portable personal dosimeter with a built-in battery. For example, even when a personal dosimeter is inserted into a breast pocket together with a mobile phone or the like, the present invention can effectively remove electromagnetic noise caused by radio waves.

Since the device according to the present invention is extremely resistant to vibration in terms of noise, the device may be used for a moving body such as a vehicle.

According to another aspect of the present invention, there is provided a method for removing noise included in a detection signal from a radiation detection circuit, the method comprising the steps of: The noise is specified based on a difference in waveform between signal components of the other polarity, and the noise is excluded from the detection signal.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a preferred embodiment of the radiation measuring apparatus according to the present invention, and FIG. 1 is a circuit diagram showing the entire configuration. This radiation measuring instrument is, for example, a portable personal dosimeter.

The radiation sensor 10 is composed of, for example, a semiconductor detector. External radiation is detected by the radiation sensor 10. The detection signal is amplified by the preamplifier 12 and then further amplified by the amplifier 14, and the amplified detection signal is input to the signal processing circuit 16.

As will be described later with reference to FIG. 2 and the like, the signal processing circuit 16 excludes a noise component contained in the detection signal and removes only the radiation signal based on the difference between the properties of the radiation signal and the noise signal. It is a circuit for counting. The counting result is output to the display 18, that is, the display 18 displays, for example, the dose. When the radiation measuring device shown in FIG. 1 is configured as a personal dosimeter, a battery 20 is provided inside the device, and the battery 20 supplies power to each circuit.

FIG. 2 shows the signal processing circuit 16 shown in FIG.
Is shown. Here, the detection signal from the detection circuit is input to the two comparators 22 and 24 via the capacitor C1. Incidentally, the detection circuit is constituted by the radiation sensor 10 and the amplifiers 12 and 14 in FIG.

The comparator 22 is a circuit for extracting only a signal component of one polarity with reference to a baseline.
More specifically, the detection signal is input to the negative input terminal of the comparator 22, and the first reference voltage signal 104 is input to the other positive input terminal. Here, the first reference voltage signal 104 is determined by the reference power supply and the resistor R7, and the reference voltage is set to a level close to the base line on the polarity side. In the comparator 22, a detection signal exceeding the first reference voltage signal 104 is extracted, and a pulse corresponding to the extracted signal component is output to the counting operation unit 26. In FIG. 2, the pulse is shown as signal 100, which includes both a radiation signal and a noise signal.

The above-mentioned detection signal is input to the + input terminal of the comparator 24, and the second input terminal is connected to the-input terminal of the comparator 24.
The reference voltage signal 106 is input. Here, the second reference voltage signal 106 is set by the reference power supply and the resistor R8. The second reference voltage is set to a level near the baseline on the other polarity side. When the comparator 24 receives a detection signal exceeding the second reference voltage on the other polarity side, a signal component exceeding the second reference voltage is extracted, and a pulse corresponding to the signal component is output to the counting operation unit 26. The signal is signal 1 in FIG.
The signal 102 has only a noise component. Incidentally, in FIG. 2, the resistors R1, R2, R3, R4, R5, R6 determine the operating conditions of the comparators 22, 24.

Therefore, according to the circuit shown in FIG. 2, a signal including a true signal component and noise can be generated by one comparator, and a signal including only noise can be generated by the other comparator.

The counting operation section 26 shown in FIG.
Then, noise is excluded from the detection signal by subtracting the signal 102 from the detection signal, a necessary operation is performed on the signal from which the noise has been excluded, and the operation result is output to the display 18.

FIG. 3 shows a first example of the counting operation section 26 shown in FIG. In this first example, the signal 10
0 is input to the counter A28, and this counter A
The signal 100 is counted by 28. Further, the signal 102 is input to the counter B30, and the signal 102 is counted by the counter B30. The arithmetic unit 32 performs an operation of subtracting the count result of the counter B from the count result of the counter A. This removes noise from the detection signal. Specifically, the arithmetic unit 32
Subtracts the value obtained by multiplying the count value of the counter B by a constant coefficient α from the count value of the counter A. Here, the coefficient α is set as a weight so as not to make an erroneous count. The arithmetic unit 32 resets each of the counters A and B every predetermined time, for example, the time interval is 1 second.

FIG. 4 shows a second example of the counting operation section 26 shown in FIG. In FIG. 4, a signal 100 is input to a delay unit 40 for performing timing adjustment, where a predetermined delay processing is performed. On the other hand, the signal 102 is input to the gate signal generator 42, and the signal 102
Gate signal G in the gate signal generator 42 based on
Has been generated. Here, the gate width of the gate signal is set as a pulse having a certain width to prevent erroneous counting. The delay time in the delay unit 40 is set in consideration of the generation of such a gate signal.

The gate circuit 44 outputs the output signal 100A from the delay unit 40 only during a period when the gate signal G is not output. Conversely, when the gate signal G is generated, the output signal 10
The passage of 0A is blocked, thereby eliminating a signal component corresponding to noise.

The counter 46 counts the signals passing through the gate circuit 44, and outputs the counting result to the calculator 48. Here, the arithmetic unit 48 is configured by a microcomputer that performs calculation such as dose based on the count result of the counter 46, for example. This is the same for the arithmetic unit 32.

As described above, according to the radiation measuring apparatus to which the above-described noise elimination method is applied, noise can be effectively eliminated based on the waveform difference between the radiation signal and the noise signal. There is an advantage that radiation measurement can be realized. Further, in the conventional apparatus, the apparatus tends to be large-sized and complicated for measures against electromagnetic waves and vibrations. However, according to the present embodiment, there is an advantage that such a problem can be solved. As a result, there is an advantage that, for example, a portable personal dosimeter can be reduced in size and weight. Further, there is an advantage that radiation measurement can be performed with high reliability even in an environment where, for example, electromagnetic waves exist.

[0031]

As described above, according to the present invention,
Radiation can be measured with high accuracy by excluding noise caused by radio waves, vibrations, and the like from the detection signal.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a preferred embodiment of a radiation measuring apparatus according to the present invention.

FIG. 2 is a circuit diagram showing an embodiment of the signal processing circuit shown in FIG.

FIG. 3 is a circuit diagram showing a first example of a counting operation unit shown in FIG. 2;

FIG. 4 is a circuit diagram showing a second example of the counting operation unit shown in FIG. 2;

FIG. 5 is a diagram showing a difference between the waveforms of a radiation signal and a noise signal.

[Explanation of symbols]

Reference Signs List 10 radiation sensor, 12 preamplifier, 14 amplifier, 16 signal processing circuit, 18 display, 20 battery, 22, 24 comparator, 26 counting operation unit, 2
8 counter A, 30 counter B, 32 arithmetic unit, 4
0 delay unit, 42 gate signal generator, 44 gate circuit, 46 counter, 48 arithmetic unit.

Claims (6)

[Claims] 1. A detection circuit comprising: a radiation sensor for detecting radiation; and an amplifier for amplifying a radiation detection signal; and a detection signal from the detection circuit in accordance with a difference between a signal component of one polarity and a signal component of the other polarity. A signal processing circuit for removing noise; 2. The apparatus according to claim 1, wherein the signal processing circuit counts the one-polarity signal component to calculate a first count value, and counts the other-polarity signal component. A second counter for calculating a second count value, and a subtractor for subtracting the second count value from the first count value. 3. The apparatus according to claim 1, wherein the signal processing circuit calculates a difference between the signal component of one polarity and the signal component of the other polarity, and counts the signal after the difference calculation. A radiation measuring device, comprising: a counter; 4. The signal processing circuit according to claim 1, wherein the signal processing circuit compares the detection signal from the detection circuit with a first reference value set on one polarity side of a baseline. A first comparator for detecting a component, and a second comparator for detecting a signal component of the other polarity by comparing a detection signal from the detection circuit with a second reference value set on the other polarity side of the baseline. A radiation measurement device characterized by including: 5. The radiation measuring apparatus according to claim 1, wherein said radiation measuring apparatus is a portable personal dosimeter having a built-in battery. 6. A method for removing noise included in a detection signal from a radiation detection circuit, wherein the noise is determined based on a difference in waveform between a signal component of one polarity and a signal component of another polarity in the detection signal. And removing the noise from the detection signal.