JPH058789B2 - - Google Patents

Description

[Detailed description of the invention] [Technical field to which the invention pertains] The present invention is a radiation measuring device using an ionization chamber, particularly for environmental monitoring in nuclear power plants, etc. This invention relates to a measuring device that can perform measurements over a wide range of levels up to a certain level.

[Prior art and its problems]

When measuring the radiation dose rate, it is extremely advantageous if the measuring device has a wide measuring range when the measuring device is to be used for radiation monitoring. For this reason, conventional radiation measurement devices using an ionization chamber that detects radiation and outputs a current proportional to its dose rate use a logarithmic amplifier to convert the output current of the ionization chamber into a signal proportional to the logarithm of the current. However, the dose rate is usually measured based on this signal, and an amplifier using a semiconductor element such as a silicon diode or a silicon transistor, or a vacuum tube as a feedback element is used as the logarithmic amplifier. Such radiation measuring devices have the following problems.

(1) The maximum measurement range is about 6 digits, and if the measurement range is made wider than this, the measurement error will increase and it cannot be used practically.

(2) The accuracy of radiation dose rate measurement is poor because the logarithm of this current is measured instead of directly measuring the output current of the ionization chamber.

(3) Since the temperature coefficient of the logarithmization circuit of a logarithmic amplifier is large, in practice a temperature compensation circuit is built into the logarithmic amplifier, but measurement errors still increase depending on the ambient temperature.

(4) Logarithmic amplifiers that use vacuum tubes have a wider conversion range than those that use semiconductor elements, but there has been a strong tendency in recent years for vacuum tube manufacturing to be discontinued, making it difficult to obtain vacuum tubes. be. For this reason, if logarithmic amplifiers were not used, there was a problem that the measurement equipment would become bulky as a result of requiring multiple linear amplifiers with different gains in order to be able to measure over a wide range of radiation levels. .

[Purpose of the invention]

The present invention solves the problems with conventional radiation measurement devices as described above, and measures radiation dose rates with high accuracy over a wide measurement range, for example, a 10-digit measurement range, without using a logarithmic amplifier. The purpose of the present invention is to provide a compact radiation measuring device that can be used to measure radiation.

[Key points of the invention]

In order to achieve the above object, the present invention provides a radiation measuring device including an ionization chamber, an amplifier that amplifies the output current of the ionization chamber and converts it into a voltage, and an upper limit that compares the output voltage of the amplifier with an upper limit setting voltage. a comparator, a lower limit comparator that compares the output voltage of the amplifier with a lower limit setting voltage, a reversible counting circuit that performs addition and subtraction operations based on the output signals of both the comparators, and a decoder that decodes the contents of the reversible counting circuit;
It consists of a resistor switching circuit that connects the feedback resistor to the feedback circuit of the amplifier according to the output signal of the decoder. By configuring the radiation measurement device in this way, the radiation dose rate detected by the ionization chamber, and therefore the output voltage of the amplifier, changes. When the upper limit set voltage or lower limit set voltage is exceeded, feedback resistors with different resistance values are automatically connected to the feedback circuit via a resistor switching circuit to change the gain of the amplifier, and the amplifier output voltage in this case is changed. The radiation dose rate can be measured with high precision over a wide measurement range by using the output signal of the decoder and the output signal of the decoder, without using a logarithmic amplifier or multiple linear amplifiers as in conventional radiation measurement equipment. It is something.

[Embodiments of the invention]

FIG. 1 is a configuration diagram of one embodiment of the radiation measuring device according to the present invention, in which 1 is an ionization chamber that detects radiation and outputs a current proportional to its dose rate;
is an amplifier that amplifies the output current of the ionization chamber 1 and outputs a DC voltage 2a proportional to the magnitude of this current, and 3 to 7 are resistance values R ₁ , R ₂ , R ₃ , R ₄ , respectively.
feedback resistors with R ₅ , 8a-12a are contacts driven by each of relay coils 8-12, 13 are feedback resistors 3-7 are connected to contacts 8a-12a, respectively;
Amplifier 2, connected in a switched manner by 12a
This is the feedback circuit. In this case R ₁ : R ₂ : R ₃ : R ₄ :
The resistance values of resistors 3 to 7 are selected so that the following relationship exists: R ₅ =1:10 ² :10 ⁴ :10 ⁶ :10 ⁸ . 14
is a frequency conversion circuit which receives the output voltage 2a of the amplifier and outputs a pulse frequency signal 14a proportional to this voltage. 15 is the variable upper limit setting voltage Vh
16 is the lower limit setting voltage that outputs the variable lower limit setting voltage Vl, 17 is the voltage 2a into which the output voltage 2a and the upper limit setting voltage Vh are input.
An upper limit comparator that outputs an H signal among binary signals consisting of an H signal and an L signal when the magnitude of exceeds the voltage Vh, 18 is the output voltage 2a and the lower limit setting voltage
This is a lower limit comparator which outputs the H signal among the binary signals as described above when the voltage 2a is inputted with Vl and the magnitude of the voltage 2a becomes smaller than the voltage Vl. In this case, it is set so that (Vh/Vl)≈100.
19 is a two-input one-shot circuit into which each output signal of the comparators 17 and 18 is input;
This circuit outputs one pulsed H signal when either of its two inputs becomes an H signal. 20 is the output signal of the upper limit comparator 17 and the one shot circuit 19
A two-input first AND circuit 21 outputs an H signal when the output signal of the lower limit comparator 18 and the output signal of the one-shot circuit 19 are input and both signals are H. This is a two-input second AND circuit that outputs an H signal if it is a signal. The first and second AND circuits 20 and 21 may be configured to have similar functions using other logic elements. 22 is a two-input reversible counting circuit having an addition terminal 22a and a subtraction terminal 22b; in this case, the terminal 22a has a first AND
The output terminal of the circuit 20 is connected to the terminal 22b.
The output terminal of the 2AND circuit 21 is connected. 2
3 is a decoder that receives the output signal of the reversible counting circuit 22 and outputs a plurality of binary signals according to the contents of the counting circuit 22; in this case, the output signal of the decoder is five binary signals that are output in parallel. Signal 23a, 2
It is composed of 3b, 23c, 23d, and 23e. Note that the signal 23a means the range 1 signal,
Similarly, the signal 23b is the range 2 signal, and the signal 23
c is range 3 signal, signal 23d is range 4 signal,
Signals 23e each represent a range 5 signal.
In this way, this example has a five range configuration. 24 to 28 are relay drive circuits that operate to excite relay coils 8 to 12 when each H signal of signals 23a to 23e is input, and feedback resistors 3 to 7 operate to excite relay coils 8 to 12. When the contacts 8a to 12a operate, they are connected to the feedback circuit 13. Therefore, the drive circuits 24 to 28, the relay coils 8 to 12, and the contacts 8a to 12a are connected to the feedback resistor according to the output signals 23a to 23e of the decoder 23. 3 to 7 constitute a resistor switching circuit 29 that connects the resistors 3 to 7 to the feedback circuit 13. In this case, feedback resistor 3
-7, output signals 23a-23e and a resistor switching circuit 29 are configured such that one of them is connected to the feedback circuit 13.

Next, the operation of the measuring device shown in FIG. 1 will be explained. 1st
In the figure, each part is configured as described above, so that, for example, the feedback resistor 5 is connected to the feedback circuit 13 by the relay contact 10a, and the magnitude of the output voltage 2a of the amplifier is equal to the set voltage Vh and Vl. If the dose rate of the radiation detected by the ionization chamber 1 increases and the magnitude of the output voltage 2a becomes larger than the set voltage Vh in a state between , the upper limit comparator 17 outputs an H signal. Therefore, one pulse-like H signal is output from the one-shot circuit 19, and since the output signal of the lower limit comparator 18 is an L signal at this time, the first AND circuit 20
One pulse is output to the reversible counting circuit 22, and as a result, the contents of the counting circuit 22 are incremented by one. The decoder 23 is configured to make the output signal 23b an H signal and the output signal 23c an L signal, depending on the count contents of the counting circuit 22 at this time.
Therefore, the feedback resistor 4 is connected to the feedback circuit 1 by the relay drive circuit 25, relay coil 9, and contact 9a.
3 and the feedback resistor 5, which has been connected to the feedback circuit 13, is separated from the feedback circuit 13 by the relay drive circuit 26, relay coil 10, and contact 10a. At this time, the value of the feedback resistor of the amplifier 2 changes from _R3 to _R2 , so the gain of the amplifier becomes 1/100, and therefore the value of the output voltage 2a becomes a value near the lower limit setting voltage Vl. The voltage Vl is set to a value slightly smaller than the magnitude of the output voltage 2a at this time. When the feedback resistor 4 is connected to the feedback circuit 13, the gain of the amplifier 2 is 1/100 compared to when the feedback resistor 5 is connected, so the output voltage 2a at this time is equal to the latter. It represents an output current that is 100 times larger than the output current of the ionization chamber 1 when the output voltage 2a is the same in the connected state. In this state, when the radiation dose rate increases further and the output voltage 2a becomes larger than the lower limit set voltage Vh again, the upper limit comparator 1
7, one-shot circuit 19, first AND circuit 20,
The counting circuit 22 operates in the same manner as described above, and at this time, the signal 23b becomes an L signal and the signal 23a becomes an H signal. Therefore, the feedback resistor 3 is connected to the feedback circuit 13, and the feedback resistor 4 is disconnected, so that the output voltage 2a represents the output current of the ionization chamber 1 which is further increased by 100 times.

With the feedback resistor 3 connected to the feedback circuit 13, when the radiation dose rate decreases and the output current of the ionization chamber 1 becomes smaller, the magnitude of the output voltage 2a of the amplifier decreases, and finally this magnitude increases. When the voltage becomes smaller than the set voltage Vl, the lower limit comparator 18 outputs an H signal. As a result, one pulse-shaped H signal is output from the one shot circuit 19, and since the output signal of the upper limit comparator 17 is an L signal at this time, one pulse is output from the second AND circuit 21 to the reversible counting circuit 22. Therefore, the counting circuit 2
The content of 2 is decreased by 1. Therefore, the content of the counting circuit 22 at this time is that the feedback resistor 4 is switched to the feedback circuit 1 by the decoder 23 and the resistor switching circuit 29.
3, the output signal 23b of the decoder becomes an H signal, and the output signal 23a becomes an L signal. Therefore, in this case, the feedback resistor of the feedback circuit 13 is switched from resistor 3 to resistor 4 by the resistor switching circuit 29, so that the output voltage 2a after switching is equal to that of the ionization chamber 1 represented by the output voltage 2a before switching. This represents an output current that is 1/100 of the output current, and since the set voltage Vl is set as described above at the time of this switching, the magnitude of the output voltage 2a is equal to the upper limit set voltage.
The voltage becomes smaller than Vh near Vh. In this state, when the radiation dose rate further decreases and the output voltage 2a becomes smaller than the lower limit setting voltage Vl, the lower limit comparator 18, the one-shot circuit 19, the second AND
The circuit 21 and the counting circuit 22 operate in the same manner as described above,
At this time, the signal 23b becomes an L signal and the signal 23c becomes an H signal.
It becomes a signal. Therefore, at this time, the measuring device shown in FIG. 1 is in the initial state of this operation description, in which the feedback resistor 5 is connected to the feedback circuit 13.

As described above, in the measuring device shown in FIG. 1, the connection of the feedback resistors 3 to 7 is automatically switched every time the output current of the ionization chamber 1 increases by 100 times, and the gain of the amplifier 2 is changed to 1/1. 100, and the magnitude of the gain of the amplifier 2 corresponds to the states of the output signals 23a to 23e of the decoder 23. Therefore, the state of the output signal of the decoder 23 and the output voltage 2
From the size of a, the size of the output current of the ionization chamber 1,
Therefore, the dose rate of radiation can be measured, and in this case, the gain of amplifier 2 is increased by 5 times by 100.
Since the measuring device can be switched in stages, it has a measuring range of 10 digits. Decoder 2
Since the states of the output signals 23a to 23e of No. 3 correspond to the magnitude of the gain of the amplifier 2, these signals also represent the measurement range. As described above, the output signal 14a of the frequency conversion circuit is a pulse whose frequency is proportional to the output voltage 2a. Therefore, the output signal 23a~ of the decoder 23 is added to the signal 14a.
By multiplying the weights represented by each of 23e, the radiation dose rate can be directly measured over a 10-digit measurement range without using a logarithmic amplifier or multiple linear amplifiers.

This measuring device has a measurement range of 10 digits, but if the frequency conversion circuit 14 is capable of outputting a pulse signal with a frequency proportional to the input signal over this entire measurement range, then If the frequency of the pulse signal corresponding to the starting point of is 10 ^m [Hz], the frequency of the pulse signal corresponding to the end point of the measurement range is 10 ^{m + 10} [Hz], and by counting such pulse signals, for example, Since the radiation dose rate can be directly measured, if the measurement error in this case is α [%] with respect to the full scale, the absolute value of this error is 10 ^{m + 10} × α × 10 ^-2 [Hz ]
This value is α × 10 ¹⁰ [%] for the pulse signal frequency 10 ^m [Hz] corresponding to the starting point of the measurement range.
becomes. Conventional radiation measurement equipment using a logarithmic amplifier had an error of α×10 ¹⁰ [%], but in the measurement equipment shown in Figure 1, it is possible to The output signal of the frequency conversion circuit corresponding to the starting point of the measurement range, that is, the minimum value of the output voltage 2a of the amplifier 2 when one of the amplifiers is connected to the feedback circuit 13 and the gain of the amplifier 2 is set to one value G. 14a frequency
If it is set to 10n [Hz], the frequency of the output signal 14a corresponding to the end point of the measurement range with the gain of amplifier 2 set to value G is 10n ⁺² [Hz]
Assuming that this 10 ⁿ⁺² [Hz] includes a radiation dose rate ^measurement error of α [%], this error will be α ×
10 ² [%], and the percentage of this error is α×10 ² [%]
does not change regardless of which of the feedback resistors 3 to 7 is connected to the feedback circuit. In other words, in a conventional radiation measurement device using a logarithmic amplifier, the measurement error at the starting point of the measurement range is α × 10 ¹⁰ [%], whereas the
In the measuring device shown in the figure, the measurement error at the starting point of the measurement range is α×10 ² [%], so the measurement accuracy is significantly improved.

In the embodiment described above, the ratio between the upper limit setting voltage Vh and the lower limit setting voltage Vl is set to approximately 10 ² , and the gain of the amplifier 2 is set to 1, 10 ² , 10 ⁴ , 10 by the feedback resistors 3 to 7. ⁶ , 10, ⁸ , the present invention is not limited to this embodiment, and the upper limit voltage Vh and the lower limit voltage Vl
^{The ratio of} Of course, in this case, the decoder 23 outputs s output signals, and the resistor switching circuit 29 outputs s output signals.
is configured to connect s feedback resistors to the feedback circuit 13 of the amplifier 2 by this output signal. Therefore, in the radiation measuring device configured in this way, the gain of the amplifier 2 is automatically switched every time the input signal of the amplifier 2 increases by R times.
This switching takes place over s stages, so
The total measurement range of such a radiation measuring device depends on R ^s , and the measurement accuracy of the above-mentioned measuring device, which switches the gain of the amplifier every time the input signal increases by R times, depends on R ^s . It is clear from the above that the measurement accuracy is better than that of an apparatus that measures the entire measurement range according to the measurement using a logarithmic amplifier.

Further, in the embodiment shown in FIG. 1, the gain switching of the amplifier 2 is performed by connecting one feedback resistor to the feedback circuit, but the present invention is not limited to such an embodiment; The gain switching may be performed by connecting a plurality of feedback resistors to the feedback circuit by appropriately setting the resistance value of each feedback resistor.

Furthermore, in the embodiment of FIG.
The output signal of the circuit 20 is input to the addition terminal 22a and
Although the output signal of the 2AND circuit 21 is inputted to the subtraction terminal 22b, the present invention may also be configured such that the output signal of the first AND circuit 20 is inputted to the subtraction terminal 22b and the output signal of the second AND circuit 21 is inputted to the addition terminal 22a. Of course, in this case the resistor switching circuit 29 is arranged to reduce the gain of the amplifier 2 as the content of the reversible counting circuit 22 decreases.

In the embodiment shown in FIG. 1, the addition/subtraction direction switching circuit of the reversible counting circuit 22 is composed of a one-shot circuit 19 and AND circuits 20, 21. A one-shot circuit may be connected to each of the one-shot circuits, and the output signal of each one-shot circuit may be directly led to the addition terminal 22a and the subtraction terminal 22b of the reversible counting circuit 22. Alternatively, the output signals of the two comparators 17 and 18 may be connected to A differentiating circuit may be connected to each, and only the positive pulse of the differential output may be guided to the reversible counting circuit 22 via, for example, a waveform shaping circuit.

FIG. 2 is a block diagram of another embodiment of the present invention.
In this embodiment, an ionization chamber 1 is constituted by an ionization chamber 1, an amplifier 2, feedback resistors 3-7, and relay coils 8-12, and a frequency conversion circuit 14, setting devices 15, 16, Comparator 1
7, 18, one shot circuit 19, AND circuit 2
0, 21, a reversible counting circuit 22, a decoder 23, and relay drive circuits 24 to 28 constitute a measuring section. The ionization chamber section and the measurement section are connected by a cable.

According to this embodiment of the configuration, the following advantages can be obtained. That is, the radiation ionization chamber often measures minute currents, and the ionization chamber is usually housed in a shield case so as not to be affected by external induction. Further, it is housed in a moisture-proof case to prevent the insulation resistance of the insulating material from decreasing due to moisture in the air. Therefore, if the ionization chamber section and the measurement section are separated and only the ionization chamber section is housed in a moisture-proof case with an electrostatic shield, the size of the housing case can be reduced and it can be manufactured at low cost.

In the embodiment shown in FIG. 2, the ionization chamber 1 and the amplifier 2 may be further separated into independent units. According to an embodiment with such a configuration, when the radiation ionization chamber is used at high temperature or under high radiation, only the ionization chamber 1 is installed at high temperature or under high radiation, and the output signal is guided to a place with favorable conditions by cable. Therefore, it can be used even at high temperatures or under high radiation conditions.

FIG. 3 is a block diagram of still another embodiment of the present invention. In this embodiment, the output signal of the AND circuit 20 is transmitted to the subtraction terminal 2 of the reversible counting circuit 22.
2b, and the output signal of the AND circuit 21 is input to its addition terminal 22a. Therefore, in the decoder 23, the position at which the output range is taken out is opposite to that of the embodiment shown in FIG.

〔Effect of the invention〕

As explained above, the present invention includes an ionization chamber, an amplifier that amplifies the output current of the ionization chamber and converts it into a voltage, an upper limit comparator that compares the output voltage of the amplifier with an upper limit set voltage, and an amplifier that A lower limit comparator that compares the output voltage of the output voltage with the lower limit setting voltage, a reversible counting circuit that adds and subtracts based on the output signals of both comparators, a decoder that decodes the contents of the reversible counting circuit, and a feedback circuit that performs feedback according to the output signal of the decoder. A radiation measuring device is constituted by a resistor switching circuit that connects the resistor to the feedback circuit of the amplifier, and the output signal of the decoder is extracted as a range signal for the selected feedback resistor. When the dose rate of the radiation detected by the ionization chamber changes and the output voltage of the amplifier increases or decreases, and this voltage exceeds the upper or lower set voltage, the amplifier gain is automatically adjusted by the resistor switching circuit. In this case, the amplifier output voltage and the decoder output signal can be used to measure the radiation dose rate. This has the advantage that it can be performed without using a logarithmic amplifier or a plurality of linear amplifiers, and as a result, the measurement accuracy can be improved and the measurement device can be made smaller.

[Brief explanation of the drawing]

1 to 3 are configuration diagrams of different embodiments of the radiation measuring device according to the present invention. 1...Ionization chamber, 2...Amplifier, 3-7...Feedback resistor, 1...Feedback circuit, 15...Upper limit setter,
16... Lower limit setter, 17... Upper limit comparator, 18... Lower limit comparator, 19... One-shot circuit, 20... First logic circuit as the first logic circuit.
1AND circuit, 21...the second logic circuit
2AND circuit, 22... Reversible counting circuit, 23... Decoder, 29... Resistor switching circuit, Vh... Upper limit set voltage, Vl... Lower limit set voltage.

Claims (1)

[Claims] 1. An ionization chamber that detects radiation and outputs a current proportional to its dose rate; and an amplifier that includes a feedback circuit to which a plurality of feedback resistors are switched and connected, and that converts the output current of the ionization chamber into a voltage. , an upper limit comparator that compares the output voltage of the amplifier with an upper limit setting voltage, a lower limit comparator that compares the output voltage of the amplifier with a lower limit setting voltage, and a reversible counting circuit that performs addition and subtraction operations based on the output signals of both the comparators. The output of the decoder includes a decoder that outputs a signal according to the contents of the reversible counting circuit, and a resistor switching circuit that connects at least one of the feedback resistors to the feedback circuit according to the output signal of the decoder. A radiation measuring device characterized in that the signal is extracted as a range signal for the selected feedback resistor, and the dose rate of the radiation is measured based on the output voltage of the amplifier.