JPS62228962A - Counting rate meter - Google Patents

Abstract

PURPOSE:To improve a response speed and accuracy by varying automatically a standard deviation according to variation in the difference between a radiation pulse counted value and a low counting rate limit value, calculating a time constant from the standard deviation, and determining a counting rate based on the time constant and an input counting value. CONSTITUTION:Radiation pulses from a radiation detector are counted by a counting means. A storage means is stored with a table wherein different standard deviations corresponding to various counting rates are stored. A standard deviation determining means finds a standard deviation in the table according to the difference between the input counted value and a low counting limit value. A counting rate arithmetic means finds the time constant from the determined standard deviation and calculates the counting the from the time constant and input counted value. This computed counting rate is outputted by an output means.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a radiation measuring device, and particularly to a digital radiation count rate meter.

(Conventional technology) Radiation monitoring of nuclear power stations and other nuclear facilities!
At position A, a count rate meter is used that processes the radiation pulses detected by the radiation detector and outputs the average value of counts at fixed time intervals. Conventionally, this J:Tuna M number rate meter is an analog type using a Cooke V-BO circuit, or a counter is connected to a radiation detector, and the contents of the counter are read at regular intervals and the average 1a is taken. The method and
Furthermore, an analog calculation method is used in which the time constant is changed according to the input capsule count value, and the counting rate is obtained by multiplying by the previous counting rate calculation value and (1) by multiplying it by the current counting rate.

However, in the conventional analog counting rate meter described above, since the time constant is uniquely determined by the capacitor and the resistor, there is a problem in that it cannot respond flexibly to pulse input fluctuations. In addition, count rate meters that use average value processing or analog calculation methods have problems such as slow response to changes in the count rate due to time constant constraints and counting time settings due to the relationship between standard deviation and time constant. There is. Furthermore, in radiation monitoring equipment that uses these calculation methods, the standard deviation with respect to the count rate is constant, so in order to maintain detection sensitivity, it is difficult to increase the thickness of the lead shield to match the detection sensitivity at the background (BG > level). Measures had to be taken.

In other words, the detection sensitivity of the radiation monitoring device is expressed by the following formula (1):
Because it depends on the BG count rate nβ and the standard deviation σ,
[3G: When the f-number rate nβ increases, detection sensitivity A cannot be maintained, and it is necessary to respond to the increase in BG level by replacing the sampler, reinforcing lead shielding, or changing the count rate meter circuit. It is.

A=3(2n a a/7)= (1) nβ : BG count rate σ : Standard deviation η : Detection efficiency (problem to be solved by the invention) As mentioned above, in the conventional count rate meter, radiation detection There have been problems in that flexible responses cannot be taken when there are large fluctuations in the input radiation pulses from the device, and that responsiveness to fluctuations in the Sl number rate is slow. In addition, in radiation monitoring equipment that uses a count rate meter that uses average value processing or an analog calculation method, the standard deviation for the count rate is constant, so in order to maintain detection sensitivity, lead shielding is thickened to match the detection sensitivity at the BG level. There were also problems that required time-consuming measures such as

This invention was made in view of such conventional problems, and uses the operation T7 function of a microcomputer to respond to changes in the difference between the radiation pulse count value and the BG level or the low count rate limit setting value. By automatically changing the standard deviation based on the standard deviation, determining a new time constant from that standard deviation, and calculating the counting rate, we have developed a counting rate meter that can improve response speed and measure with a certain level of accuracy. The purpose is to provide.

[Structure of the invention]

(Means for Solving the Problems) As shown in FIG. 1, the present invention has a means for counting radiation pulses from a radiation detector, a count value input, a low count rate limit value, and various count rates. storage means for storing a table in which different standard deviations are registered; means for determining the standard deviation from the table according to the difference between the input count value and the low count rate limit value; The gist of this invention is a count rate meter comprising means for determining a constant and calculating a count rate from this time constant and an input count value, and means for outputting the calculated count rate.

(Function) In the count rate meter of the present invention, the standard deviation is automatically changed according to the fluctuation of the difference between the radiation pulse count value and the low count rate limit value, and the time constant is calculated from the determined standard deviation. Then, the divisor rate is determined from the obtained time constant and the input value.

(Example) Hereinafter, this invention will be explained in detail based on embodiments shown in the drawings.

FIG. 2 shows a circuit block diagram of an embodiment of the present invention, and shows a radiation detector 3 installed in a lead shield 2 of a radiation dust cleaner 1 included in an 11ml radiation monitoring device. detects the radiation level and outputs a layer pulse signal for the IIi line to the count rate meter 4 according to the embodiment of the present invention.

The count rate meter 4 includes a pulse count module 5 that receives a count pulse signal from the radiation detector 3 and outputs a count value, and a memory 6 that stores the count value output from the pulseless count 7 joules 5. . The memory 6 also stores a low count rate limit value and a standard deviation table 8 as shown in FIG. 3 via an external input device 7.

The counting rate meter 4 further includes a microprocessor 9 and a clock generator 10. This microprocessor 9 reads the radiation pulse count value from the memory 6 every period, calculates the difference from the low count rate limit value also stored in the memory 6, and calculates the standard deviation value also stored in the memory 6. From Table 8, as shown in FIG. 3, the measurement allowable standard deviation value σi is extracted according to the magnitude of the difference value. Furthermore, a time constant is determined from the extracted standard difference σi and the previous count rate calculation value, and a new count rate is calculated.

The counting rate meter 4 further includes an output interface 11.
is equipped with an external display device 12 and an external recording device 13.
The current counting rate calculated by the microprocessor 9 is outputted to the display device 12 and/or the external recording device 13 through the output interface 11.

Standard deviation table 8 for determining the standard deviation σ1
The counting rate limit value can be updated by the operator from the outside using the external input device 7.

Next, the count rate calculation operation by the count rate meter with the above configuration is performed in the fourth step.
This will be explained based on the flowchart shown in the figure.

The microprocessor 9 calculates the counting rate using the following counting rate calculation formula (2).

RE = C+ (Rt -1-C) e -1/τ...
...(2) R It varies depending on the standard deviation σ and the count value C.

τ = 1/2σ2C (3) Therefore, in the conventional calculation method, the standard deviation σ was fixed and the time constant τ was changed only by fluctuations in the count value C to obtain the counting rate R. However, it is known that random numbers such as radiation pulse counts follow a Poisson distribution statistically.
Moreover, the following equation (4) holds true between the standard deviation σ and the standard deviation σ.

σ=1/Fjiwani (3) From this formula (4), the larger the count value C, the smaller the standard deviation σ of the count value itself, and conversely, the smaller the count value mc, that is, It is clear that the standard deviation σ increases when the count rate is low.

Therefore, in order to guarantee the highest detection sensitivity of radiation monitoring equipment, the initial BG level, etc. is used as the count rate level to fix the standard deviation during count rate calculation to a minimum of 1 = standard deviation, and the low count rate limit value is set. Establish.

When a count value less than that is measured, the standard deviation is kept constant and the counting rate is calculated from the above equations (2) and (3), but when a count value greater than that is measured, the standard deviation is varied according to the count value, and the counting field is calculated.

The flow of this calculation will be explained based on FIG.
Step 21: Then, this count value C is compared with the low count rate limit value RO stored in the memory 6,
If the input count value C is larger, the difference Δ between the input count value C and the low count rate limit value RO is calculated, and as shown in FIG. One step of determining the corresponding standard deviation σi 22-24゜ In the comparison in step 22, if the count value C is smaller than the low count rate limit value RO, one step in which the standard deviation is automatically set to the minimum standard deviation σ0 25゜ Calculate the time constant τ from the standard deviation σ1 thus determined and the input count value C based on the above formula (3) - Step 2
6゜Next, the counting rate Rt is calculated based on the above formula (2) using the calculated time constant and the input count value C - Step 27゜The new R [calculated in this way is stored in the memory. 6 is stored as the previous count rate result Rt-1 and simultaneously output to the display device 12 and/or external recording device 13 - step 28. In this way, the difference between the input count value C and the low count value limit value RO is Δ is calculated, and the standard deviation σ is calculated from the standard deviation registration table 8 stored in the memory 6 based on the size of the difference Δ.
i is found, the time constant τ is determined based on this newly set standard deviation σ1, and a new counting rate R[ is calculated. This standard deviation σ1 varies depending on the difference value Δ,
The larger the difference Δ, that is, the higher the counting rate, the larger the value. This is because, as is clear from equation (4), the higher the counting rate, the smaller its own standard deviation becomes, and even if the measurement standard deviation σ1 is increased, there is almost no effect on detection sensitivity. be.

Conversely, the time constant determined from the standard deviation σ1 determined in this manner becomes smaller as the standard t$ interval difference σi increases, and as a result, the response to a high count rate becomes faster.

In the above embodiment, the limit value is changed by the operator using the external input device 7, but it is also possible to set the low count rate limit value RO automatically. In that case, by periodically flowing clean water or purge gas to Nampura 1 and measuring the 8G level, and applying the average value to the low count rate limit value, it will automatically respond to fluctuations in the 8G level. It becomes something that can be handled.

Furthermore, although the standard deviation registration table 8 was changed by the operator using the external input device 7, the BG
The level is measured regularly, and if the G level on that day becomes higher than the specified range from the previous time, the Rin standard deviation registration table is automatically changed to ensure that measurements always exceed the detection sensitivity. It is possible. That is, as shown in FIG. 5, the detector 3 measures the BG level, the microprocessor 9 calculates the counting rate of the BG level, and calculates the average value - step 31.32. Calculate the difference between the average value of the rate and the current BG count rate and compare whether the difference exceeds the specified range - Step 33.
34° In this comparison, if the difference exceeds the specified range, the minimum standard deviation σβ is newly calculated based on the following equation (5), which is a modification of the above equation (1), and this new minimum standard 1t! i(Q difference σ
The contents of the standard deviation registration table 8 are changed according to β.

- Step 35.36゜In the comparison in step 34 above, if the difference does not exceed the specified width, the previous BG
One step 37° using the count rate average value and standard deviation table as is.New minimum target obtained in this way! 1! The eccentric stop and standard deviation registration table is stored in the memory 6 and used for calculating the counting rate 'tJ - step 38. In this way,
By automatically changing the low count rate limit value and standard deviation registration table, even if the BG level is too high, measurements can always be made above the detection sensitivity even if the BG level of sampler 1 is not lowered due to lead shielding or other reasons. This makes it possible to extend the life of the sampler.

〔Effect of the invention〕

Since this invention has the above configuration, when the radiation level becomes high, it is possible to change the standard (Iai difference), shorten the time constant, and improve responsiveness. Since the standard deviation is automatically changed according to the change in the standard deviation, it is possible to measure the counting rate with high accuracy.

Furthermore, if the configuration is configured to automatically change the minimum standard deviation in the standard deviation registration table according to fluctuations in the 8G level, even if the BG level exceeds the upper limit, the lead shielding of the radiation monitoring device can be improved. There is no need to take time-consuming measures such as increasing the thickness or changing the circuit configuration of the count rate meter, and the life of the device can be extended.

[Brief explanation of drawings]

Fig. 1 is a diagram corresponding to the claims of this invention, Fig. 2 is a block diagram of an embodiment of this invention, Fig. 3 is an explanatory diagram of the operation of the above embodiment, and Fig. 4 is an explanation of the operation of the above embodiment. The flowchart in FIG. 5 shows the J! y is a flowchart showing an automatic correction operation of the minimum standard deviation value. 1... Sampler 3... Detector 4... Count rate meter 5... Pulse count module 6... Memory 7... External human power device 8... Standard deviation table 9... Microprocessor 10...Clock oscillator 11...Output output face 12...Display device 13...External recording device
Text Figure 4 Figure 5

Claims (1)

[Claims] (1) A count rate meter that counts radiation pulses and outputs the counting rate, which includes a radiation pulse counting means, a count value by the counting means, and a low count rate limit value;
and storage means for storing a table in which different standard deviations are registered according to various count values, and a storage means for storing a table in which different standard deviations are registered according to various count values; a means for determining a time constant from the determined standard deviation, a means for calculating a counting rate from this time constant and the input count value, and a means for outputting the calculation result of the counting rate. Count rate meter.