JPH0541423Y2 - - Google Patents

Description

[Detailed description of the invention] [Technical field to which the invention pertains] This invention measures the amount of radiation over a wide range from small values to large values by switching the measurement range with one measuring instrument. The present invention relates to a multi-range radiation measuring device that can perform multiple ranges, and particularly to a radiation measuring device that does not require a special structure for a circuit switching mechanism for range switching.

[Prior art and its problems] FIG. 3 is a block diagram of a first example of a conventional multi-range radiation measuring device. In the figure, 1 is a radiation detector such as an ionization chamber that detects radiation and outputs a signal current I according to the amount of radiation; 2 is a radiation detector whose negative electrode is connected to the detector 1 and whose positive electrode is connected to a reference potential 4; 3 is a radiation detection section consisting of a detector 1 and a power source 2; Reference numeral 5 denotes an operational amplifier whose first input terminal 5a is connected to the reference potential 4 and whose second input terminal 5b receives the signal I.
, a plurality of resistors Q ₁ , Q ₂ , each one end of which is connected to the input terminal 5b and the other end of which is switched by a switch 6 and connected to the output terminal 5c of the amplifier 5. ...Q _o is provided as a feedback resistor. Assuming that the symbols Q ₁ , Q ₂ , ...Q _o represent resistance values, a relationship of Q ₁ >...>Q _o is established. 7 is a signal processing unit that processes the signal voltage output from the amplifier 5 in a predetermined manner and outputs a signal 7a corresponding to the signal Va;
This is the display unit that receives the information. Amplifier 5 and feedback resistor
Q ₁ , Q ₂ , . . . Q _o , the switch 6, the signal processing section 7, and the display section 8 constitute a receiving section 9. According to the configuration shown in FIG. 3, since the signal Va is proportional to the signal I, the amount of radiation detected by the detector 1 can be measured using the display section 8.

Since the measuring instrument shown in FIG. 3 is constructed as described above, the gain of the amplifier 5 can be changed by switching the resistors Q ₁ to Q _o using the switch 6, and as a result, the gain of the signal current I can be changed. Even if the value changes greatly, the amount of change in the signal voltage Va can be localized within a predetermined range, so the same signal processing unit 7 and display can be used for a wide range of current values from small to large values of current I. Section 8 can be used.
In other words, in this ^case , the resistors Q ₁ to Q _o and the switch 6 constitute a range switching mechanism in radiation measurement ^. Since the current is extremely weak such as ¹⁴ [A], the resistors Q ₁ to _{Q o} are all set to large values to increase the gain of the amplifier 5, and the voltage Va is proportional to the current I. In order to achieve this, amplifier 5 is constructed with a very large input impedance. Therefore, in a radiation measuring instrument having such a configuration, unless the insulation resistance of the switch 6 is made very high, for example, the output terminal 5c of the amplifier
A leakage current flows from the sensor 1 through the switch 6 to the detector 1, causing a measurement error. Furthermore, when switching circuits with switch 6, noise voltage may be generated due to changes in the value of capacitance existing between the fixed contact and the movable contact, or noise voltage may be generated due to friction between the two contacts. A noise current flows into the detector 1 due to the noise voltage, but even if this noise current is small, the current I is originally a weak current, so the radiation measuring instrument shown in Fig. 3 has a large measurement error due to the noise voltage. There is a problem in that it may cause According to experiments, due to the noise voltage, the indicator forming the display section 8 sometimes swings out of the indicated scale range for several minutes, and in such cases, radiation measurement becomes impossible.

FIG. 4 is a block diagram of the main parts of a second conventional example of a radiation measuring device designed to improve the problems in the radiation measuring device as described above.
FIG. 2 is an explanatory diagram of the vicinity of a switch 10 corresponding to switch 6 in the figure. In the figure, F ₁ to _{F o} are the fixed contacts of the switch 10 connected to the resistors Q ₁ to Q _o , respectively, P ₁ to _{P o} are the intermediate contacts corresponding to the contacts F ₁ to _{F o} , respectively, and M is the shaft 11. The contacts P ₁ to P _o and M are also contacts of the switch 10 . Contacts (not shown)
F ₁ to F _o are supported by elastic members, and their positions can be changed by pressing them.
Since the shaft 11 is connected to the output terminal 5c of the amplifier 5, the contact M is a contact that attempts to feed back the voltage Va to the input terminal 5b of the amplifier via the resistors _Q1 to _Qo . Intermediate points P ₁ to P _o are all hemispherical head 1
2 and a columnar body 13, each body 13 being fixed to the free end of a cantilever-like elastic body 14. Then, the movable contact M and the intermediate contact
P ₁ ~ P _o and fixed contacts F ₁ ~ _{F o} are
When rotated around the head 12, the contact M rides on the head 12 and presses the contacts P ₁ to _{P o} in the axial direction of the body 13, and as a result, the end surface 13a of the body 13 moves to the contact F ₁
~F _o , so that electrical continuity between the contact M and the contacts F ₁ ~ _{F o} is established. When the contact M presses the contacts P ₁ to _{P o} , the elastic body 14 is deflected, so when the contact M leaves the position of the contacts P ₁ to _{P o} , the contacts P ₁ to _{P o} move in the axial direction of the body 13 return to its old position.

In FIG. 4, the switch 10 is configured as described above, and furthermore, when switching the contact M from the contact P ₁ to the contact P ₂ , for example, there is a state in which M, P ₁ and F _{1 are in contact, and a state in which M and P 1} are in contact with each other. The main parts are configured so that a state in which P ₂ and F ₂ are in contact exists simultaneously for a predetermined period of time or longer. In other words, in FIG. 4, not only in the above case, but when switching M,
The switch 10 is configured so that there always exists a time period in which the conduction state before switching and the conduction state after switching between M and F ₁ to F _o exist at the same time. Therefore, when using such a switch 10,
When switching circuits, no noise voltage is generated due to the change in capacitance as described above. Further, in the switch 10, a sliding state occurs between the contact M and the contacts P ₁ to _{P o} , but the sliding state occurs between the contacts P ₁ to P _o and the contacts F ₁ to _{F o}
No sliding condition will occur between the two. Then, after M and P ₁ to P _o come into contact, P ₁ to _{P o} and F ₁ to F _o come into contact, and after P ₁ to P _o and F ₁ to F _o are separated, M and P ₁
~P _o is becoming more distant. Therefore, in the switch 10, when switching circuits, no noise voltage is generated due to friction between the contacts as described above.

Since the switch 10 has the above-mentioned characteristics, it is effective in preventing the generation of noise voltage during circuit switching, but as is clear from the above, the structure is complicated. Therefore, such a switch 10 has the problem that it is large in size and has more movable parts than the above-mentioned switch 6, so that it is more likely to break down. Another problem, similar to the switch 6, is that the insulation resistance of each part must be made very large.

[Purpose of invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a multi-range radiation measuring instrument that eliminates the above-mentioned problems with conventional measuring instruments and does not require a special structure for the circuit switching mechanism for range switching.

[Key points of the idea]

In order to achieve the above object, the present invention includes a radiation detection section that outputs a signal current according to the amount of radiation, an amplifier circuit that outputs a signal voltage when a signal current is input to an input terminal, and an input terminal of the amplifier circuit. A plurality of series circuits each having one end connected to a circuit, a circuit switching device that switches each other end of the series circuit and connects it to the output terminal of the amplifier circuit, and a ground that connects each other end of the series circuit to a reference potential. In a device that is equipped with a resistor and a voltage correction circuit that performs a predetermined correction on the signal voltage, and in which radiation measurement is performed based on the output signal of the voltage correction circuit, the grounding resistor must have a low resistance value. The series circuit is formed of a feedback resistor and a diode having different resistance values for each series circuit to constitute a multi-range radiation measuring instrument. With this configuration, when the other end of the series circuit is switched by the circuit switch for range switching,
Even if a noise voltage occurs, most of the noise current based on this noise voltage flows to the reference potential via the grounding resistor, and the influence of the noise voltage no longer appears on the signal voltage or the output signal of the voltage correction circuit. Therefore, this makes it possible to obtain a multi-range radiation measuring instrument that does not require a special structure for the circuit switcher for range switching. Furthermore, with the above configuration, the series circuits that are not selected by the circuit switcher are reliably separated from the feedback circuit of the amplifier circuit by the function of the diode, so from this point of view as well, the circuit switcher can be highly isolated. This makes it possible to obtain a radiation measuring instrument that does not require a special resistor structure.

[Example of idea]

FIG. 1 is a block diagram of an embodiment of the present invention. In the figure, reference numeral 15 denotes an operational amplifier corresponding to the operational amplifier 5 in FIG. 3, and this amplifier 15 is provided with a variable resistor 16 for adjusting offset voltage. Similarly to the amplifier 5, in the amplifier 15, the reference potential 4 is input to the first input terminal 15a, and the signal current I is input to the second input terminal 15b. In this case, the switch 6 is designed to switch between four circuits. R ₁ is output terminal 1 of amplifier 15
5c and the first feedback resistor connected between the input terminal 15b. 17 is diode D ₂ and resistor R ₂
18 is a diode D ₃
19 is a _third series circuit consisting of a diode D ₄ and a resistor R ₄ ,
Diodes D ₂ , D ₃ , D ₄ in series 17, 18, 19
The side ends are all connected to the input terminal 15b of the amplifier 15, and the other ends of the series circuits 17, 18, and 19 are connected to the fixed contacts F ₂ , F ₃ , and F ₄ of the switch 6, respectively, and are connected to the ground resistor R. It is also connected to the reference potential 4 via _{R 5} , R ₆ , and R ₇ . Each of the resistors R ₅ to _{R 7} is a resistor having a resistance value of several [kΩ] to several tens of [kΩ]. The fixed contact F ₁ is connected to a fixed contact F ₁ c of a switch 23, which will be described later.

In this case, the signal voltage Va output from the amplifier 15 is applied to a series circuit consisting of a diode Dc and a resistor _R8 , and the voltage Vb generated at the resistor _R8 is inputted to the amplifier circuit 20 with a gain of 1. There is. 21 is a DC power supply 22 having a voltage E, and variable resistors R ₉ - each end of which is connected to the negative electrode of the power supply 22.
R ₁₁ , a four-circuit changeover switch 23 having fixed contacts F ₁ c to F ₄ c, and a resistor R ₁₂ whose one end is connected to the positive terminal of the power supply 22. Variable resistors R ₉ to _{R 11} Each other end is a contact point F ₂ c ~ _{F 4}
c, and is connected to the fixed contact side terminal 2 of the switch 23.
3a is connected to the other end of resistor _R12 . Contact F ₁
c is connected to contact _F1 as described above.
The switch 23 is a switch that operates in conjunction with the switch 6, and the negative pole of the power supply 22 is connected to the output terminal 20c of the amplifier circuit 20. Vc is terminal 23
This voltage Vc is inputted to an impedance conversion amplifier circuit 24 with a gain of 1, and the output voltage of this circuit 24 is inputted to an indicator 25. 26 is a diode
Dc, resistor _R8 , amplifier circuit 20, and voltage generation circuit 21
The operation and function of this circuit will be described later.

Next, the operation of the radiation measuring device shown in FIG. 1 will be explained.
That is, when measuring radiation using this measuring device, first connect the movable contact _M6 of the switch 6 to the contact _F1 , and operate the variable resistor 16 with the radiation entering the detector 1 blocked. so that the voltage Vi at the input terminal 15b of the amplifier becomes zero. As a result, the series circuit 1 connected to the terminal 15b
The potentials at the ends of 7, 18, and 19 become equal to the reference potential 4. On the other hand, the other ends of the series circuits 17-19, that is, the ends connected to the contacts _F2 - _F4 , are connected to the reference potential 4 through grounding resistors _R5 - _R7 , respectively. Therefore, since the voltage applied to each of the diodes D ₂ , D ₃ , and D ₄ becomes zero volts, the diodes D _{2 , D 4} , and
The currents I _{2 ,} I ₃ , and I ₄ flowing through each of D 3 and D ₄ become infinitely small. Therefore, the current I ₁ flowing from the output terminal 15c of the amplifier through the first resistor R ₁ is equal to the signal current I output by the detector 1 when radiation is incident on the detector 1, and as a result, the amplifier The signal voltage Va output by the circuit 15 is a voltage Va ₁ expressed by equation (1). However, in this case amplifier 1
5 is assumed to be not yet saturated.

Va ₁ = I・R ₁ (1) In other words, when the contact M ₆ of the switch 6 is connected to the contact F ₁ , each resistance of the diodes D 2 to _{D 4} has an extremely large value, so the resistance of the diodes D ₂ to D 4 is extremely large. circuit 17
19 and the resistors R ₅ to R ₇ are in a state of being disconnected from the input terminal 15b. In addition, in Figure 1
R ₂ ≫ R ₅ , R ₃ ≫ R ₆ , R ₄ ≫ _{R 7} . When contacts M ₆ and F ₁ are connected, switch 23
Since the contact F ₁ c and the movable contact M ₂₃ are connected, the input voltage Vc of the amplifier circuit 24 is Va ₁ in equation (1).
is equal to Therefore, the indicator 25 has a voltage Va ₁
Therefore, from this instruction, the value of the current I, and therefore the amount of radiation corresponding to I, can be measured.

When the amount of radiation incident on the detector I increases and the current I increases, the amplifier 15 will eventually become saturated and the voltage Va will no longer be proportional to I, so connect the contact _M6 to the contact _F2 as shown. to reduce the gain of the amplifier 15. Next, the operation of each part at this time will be explained. That is, when contacts M ₆ and F ₂ are connected, diode D ₂ becomes conductive and current I ₂ increases. Therefore, equations (2) and (3) hold, and from these equations, equation (4) can be obtained.

I=I ₁ +I ₂ …(2) Va ₂ =I ₁・R ₁ =Vd ₂ +I ₂・R ₂ …(3) I={(R ₁ +R ₂ )/(R ₁ R ₂ )}・Va _{2 -Vd2} / _R2
...(4) Here, Va ₂ is the value of the signal voltage Va when the contacts M ₆ and F ₂ are connected, and Vd ₂ is the voltage across the diode D ₂ . In this case, since R ₁ ≪ R ₂ , equation (5) can be obtained from equation (4). Since R ₂ and Vd ₂ are set so that Va ₂ < Va ₁ when the contact M ₆ is switched from F ₁ to F ₂ , the gain of the amplifier circuit including the amplifier 15 is reduced at this time. As a result, the saturated state of the amplifier 15 before the switching of the contact _M6 is released.

Va ₂ =I·R ₂ +Vd ₂ (5) Now, in this case, since the voltage Va ₂ is applied to the diode DC, equation (6) holds true, and as a result, equation (7) holds true. Here, Vdc is the voltage across the diode DC.

Vb=Va ₂ −Vdc (6) Vc=Vd+{R ₉ /(R ₉ +R ₁₂ )}·E (7) Equation (8) is obtained from equations (5) to (7).

Vc=I・R ₂ +Vd ₂ −Vdc+{R ₉ /(R ₉ +
R ₁₂ )}・E...(8) Now, in Figure 1, diodes D ₂ and Dc have the same specifications, and the currents I ₂ and Ic flowing through these diodes are shown in Figure 2. Since the current is in the small current region, equation (9) holds true, and (9)
From the formula, formula (10) is established. Here K ₁ and K ₂ are constants.

Vd ₂ =K ₁・logI ₂ +K ₂ Vdc=K ₁・logIc+K ₂ …(9) Vdc−Vd ₂ =K ₁・log(Ic/I ₂ ) …(10) However, in Fig. 1, Va changes. Since it is clear that the currents I ₂ and Ic change in proportion to this, equation (11) holds true with A ₂ as a proportionality constant, and from equations (10) and (11), equation (12) can be obtained. is obtained. In equation (12), K ₃₂ is a constant.

Ic＝A ₂・I ₂ ...(11) Vdc−Vd ₂ =K ₃₂ ...(12) Therefore, from equations (8) and (12), equation (13) is obtained,
If the resistance R ₉ is adjusted and the equations (14) are arranged, the equation (13) becomes the equation (15).

Vc=I・R ₂ −K ₃₂ + {R ₉ /(R ₉ +R ₁₂ )}・E
…(13) K ₃₂ {R ₉ /(R ₉ +R ₁₂ )}・E …(14) Vc=IR ₂ …(15) Therefore, the indicator 25 indicates Vc of equation (15), and also the above-mentioned As before, in this case amplifier 15
is not saturated, the value of the current I, and hence this I, is produced by the indication of the indicator 25. It is possible to measure more radiation than in the case of equation (1). In other words, by switching contact _M6 from _F1 to _F2 , the gain for converting current I to voltage Vc is made smaller than in equation (1), and the measurement range can be changed. .

As is clear from the above, the signal voltage Va in this case is expressed by equation (5), and the indicator 25 indicates the voltage according to equation (15). Therefore, the signal Va
In the process of converting to Vc, the voltage correction circuit 26 corrects the signal Va so that Vd ₂ becomes zero. Therefore, the correction circuit 26 is a circuit that performs the above-described predetermined correction on the signal voltage Va.

When contact M ₆ and contact F ₂ are connected, when a larger current I can be measured, contact M ₆ is switched to contact F ₃ . At this time, since R ₁ ≫ R ₃ , equation (16) holds true. Va ₃ is the value of the signal voltage Va in this case, and Vd ₃ is the voltage across the diode D ₃ .

Va ₃ = I・R ₃ + Vd ₃ …(16) Then, when contact M ₆ is switched from F ₂ to F ₃
Since R ₃ and Vd ₃ are set so that Va ₃ <Va ₂ , the gain of the amplifier circuit including the amplifier 15 is further reduced at this time. Also, in this case, the relationship of equation (17) is similar to that of equation (11). A ₃ is the constant of proportionality.

A ₃ = Ic/I ₃ (17) In this case as well, the resistance R ₁₀ is adjusted by 0 so that equation (18) holds true.

Therefore, the voltage Vc input to indicator 25 is (19)
Expressed by the formula.

_K1・_logA3 ={ _R10 /( _R10 + _R12 )}・E...(18) Vc=I・_R3 ...(19) Therefore, the current I can be measured by the indicator 25, and this In this case, since R ₃ < R ₂ , the gain for converting current I to voltage Vc is smaller than in equation (15), and the current I is larger than when contact M ₆ is connected to F ₂ . can be measured.

When contact M ₆ is switched from contact F ₃ to F ₄ , R ₁ ≫
Since R is ₄ , formula (20) holds true. Here
Va ₄ is the value of Va, and Vd ₄ is the voltage across diode D ₄ .

Va ₄ =I·R ₄ +Vd ₄ (20) R ₄ and Vd ₄ are set so that when the contact M ₆ is switched, Va ₄ < Va ₃ . Also, in this case, there is the relationship of equation (21) with A ₄ as a proportionality constant,
Furthermore, by adjusting the resistance _R11 , equation (22) is made to hold true. Therefore, Vc in this case is as shown in equation (23).

A ₄ = Ic/I ₄ …(21) K ₁・logA ₄ = {R ₁₁ / (R ₁₁ + R ₁₂ )}・E…(22) Vc=I・R ₄ …(23) Therefore, according to the indicator 25, In this case, since R ₄ < R ₃ , the contact M ₆ is
A larger current I can be measured than when connected to F ₃ .

As is clear from the above, the radiation measuring instrument shown in FIG. 1 has four measurement ranges. Therefore, one and the same indicator 25 can perform radiation measurements over a wide measurement range. Then in this case,
When switching the contacts F ₁ to _{F 4} by the switch 6, for example, even if a noise voltage is generated at the contact F ₂ , the noise current based on this noise voltage is
As mentioned above, since R ₂ >>R ₅ , most of the current flows to the reference potential 4 via R ₅ , and only a small amount of noise current flows through R ₂ . Therefore, with the configuration shown in Figure 1, even if a noise voltage is generated in switch 6 when changing the range, the effect will hardly appear on Va or Vb, so switch 6 has no special structure but an ordinary structure. A switch can be used. Also switch 6
When range switching is performed at switch 23, circuit switching is also performed in conjunction with switch 23. In this case, the noise voltage generated at contacts F ₂ c to F ₄ c is transferred to switch 23 and variable resistors R ₉ to R _11. and power supply 22
By simply passing a noise current through the closed circuit consisting of the resistor _R12 and the resistor R12, it has almost no effect on the voltage Vc. Therefore,
This switch 23 can also be of a normal structure.

In addition, in Fig. 1, as mentioned above, the contact points
Series circuits 17-1 not selected by _M6
9 is the amplifier 1 by the function of the diodes D ₂ to _{D 4} .
5 will be reliably disconnected from the input terminal 15b. Therefore, from this point of view as well, it is clear that the switch 6 does not need to have a special structure with special consideration given to insulation resistance, and may be of a normal structure.

[Effect of idea]

As mentioned above, the present invention includes a radiation detection section that outputs a signal current according to the amount of radiation;
An amplifier circuit that outputs a signal voltage when a signal current is input to an input terminal, a plurality of series circuits each having one end connected to the input terminal of the amplifier circuit, and an amplifier circuit that outputs a signal voltage by switching the other ends of the series circuits. The output of the voltage correction circuit is equipped with a circuit switch connected to the output terminal, a grounding resistor that connects each other end of the series circuit to a reference potential, and a voltage correction circuit that performs a predetermined correction to the signal voltage. In a radiation measuring instrument that measures radiation based on a signal, each grounding resistor has a low resistance value, and the series circuit has a feedback resistor and a diode each having a different resistance value for each series circuit. A multi-range radiation measuring instrument was constructed by forming a multi-range radiation measuring instrument. With this configuration, even if a noise voltage is generated when the other end of the series circuit is switched by a circuit switcher for range switching, most of the noise current based on this noise voltage is flows to the reference potential via the grounding resistor, and the influence of noise voltage does not appear on the output signal of the voltage correction circuit. The effect is that there is no need to make it into something.

Furthermore, with the above configuration, the series circuit not selected by the circuit switch is reliably separated from the feedback circuit of the amplifier circuit by the function of the diode, etc. From this point of view, the present invention has the following features: This has the advantage that there is no need for the circuit switch to have a special structure with high insulation resistance.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an embodiment of the present invention, Fig. 2 is a diagram explaining the voltage/current characteristics of a diode, Fig. 3 is a block diagram of the first example of a conventional multi-range radiation measuring instrument, and Fig. 4 is a block diagram of the first example of a conventional multi-range radiation measuring instrument. FIG. 6 is an explanatory diagram of main parts in a second example of a conventional multi-range radiation measuring device. 3...Radiation detection section, 4...Reference potential, 5,1
5...Operation amplifier, 5b...Second input terminal, 5c
...Output terminal, 6...Switch, 17-19...
Series circuit, 26...voltage correction circuit, I...signal current, Va...signal voltage, _R2 to _R4 ...feedback resistor,
_R5 to _R7 ...Grounding resistor, _D2 to _D4 ...Diode.

Claims (1)

[Scope of utility model registration request] a radiation detection unit that detects radiation and outputs a signal current according to the amount of radiation; and an input terminal into which the signal current is input, and when the signal current is input, a signal voltage according to the signal current. a plurality of series circuits each having one end connected to the input terminal of the amplifier circuit; and a circuit switching device switching each other end of the series circuit to connect the other end of the series circuit to the output terminal of the amplifier circuit. and a grounding resistor connecting each other end of the series circuit to a reference potential, respectively;
and a voltage correction circuit that performs a predetermined correction on the signal voltage, and measures the amount of radiation based on the output signal of the voltage correction circuit,
A multi-range radiation measurement characterized in that the grounding resistor is given a low resistance value, and the series circuit is formed of a feedback resistor and a diode each having a different resistance value for each series circuit. vessel.