JPH0735568A - Trigger device - Google Patents

Abstract

PURPOSE:To provide a trigger device having the capability of completely preventing the occurrence of malfunction while setting a short measurement time for following up a natural phenomenon, and ensuring a burst to be properly detected, regarding a trigger device for measuring a random phenomenon in the natural world and detecting bursted state. CONSTITUTION:The occurrence of radiation or the like is measured repeatedly over the prescribed time in a counting circuit 2, and the results of the measurement are compared in a comparator 4 to process the results on the basis of the Poisson's distribution. The comparison result is flagged in a shift register 5 and saved. Then, the number of flags over a plurality of consecutive times is measured with a flag check circuit 6, and processed on the basis of the binominal distribution for comparison with a reference flag number established with a flag comparator 7. As a result, the probability where the flag number in the shift register 5 is equal to or above the prescribed value, can be made zero and, therefore, the occurrence of malfunction can be completely prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the structure of a trigger device used for activating a fault recorder, a transient recorder, etc., and more particularly to a trigger device for detecting and triggering discrete phenomena such as particles and radiation. It is a thing.

[0002]

2. Description of the Related Art FIG. 4 shows a schematic configuration of an apparatus for recording the progress of a time series phenomenon such as a transient recorder.
First, the input signal I is input to the trigger circuit 11 and the delay circuit 12
To the input signal I in the trigger circuit 11.
Is determined to satisfy a predetermined condition. When the trigger circuit 11 determines that the predetermined condition is satisfied, the recorder 13 is activated. As a result, the input signal I arriving at the recorder 13 after a delay from the delay circuit 12 is stored in the recorder 13, and the state of the input signal I at that time can be analyzed later.

The signal used as a trigger may be an analog signal such as a voltage signal, but when connected to a radiation detecting device or the like, a natural random digital signal is targeted.

For example, a transient recorder is arranged around a linac, a nuclear reactor, a cyclotron accelerator, etc., and detects and records the environmental radiation level or the counting level when the counting level is higher than the allowable counting level. May be used. In such an apparatus, it is general that a radiation detector such as a GM tube counts for a certain period of time, and when the value exceeds a certain value, it is detected as a burst, and a trigger is applied based on this. There is.

[0005]

However, if a burst is detected based on such measurement of a certain time, the following problems will occur. That is, when a random count is measured, if the measurement period is long and a sufficient number of counts can be obtained as a population, a normal distribution is exhibited. But,
It is known that the Poisson distribution is followed when the measurement period is short. The approximate formula in Poisson distribution is as follows.

[0006]

[Equation 1]

Here, λ is the average number of input pulses per unit time, and x is the number that actually occurs (the number of pulses actually input). What happens when the Poisson distribution is followed under the condition that one is stochastically input during a certain measurement period when the measurement time is long enough (this is also called statistical probability)? Substitutes 1 for λ and sets x to 0
It can be understood by changing the value between 10 and solving the equation (1).
The results are shown in Table 1 below.

[0008]

[Table 1]

From Table 1, it can be seen that under the condition that one is stochastically input, the probability that the count is 0, that is, x = 0 is approximately 36.8%. At the same time, under the condition that one is stochastically input, the probability that the count shows 9
It can be seen that there is a 1 / 1,000,000 possibility of x = 9.
Furthermore, the probability that the count shows 10, x = 10, is not completely zero. So, for example, in burst detection,
Even when the trigger level, which is a threshold value, is set to the count value x = 9 to 10, a condition (λ = 1) in which one is stochastically input is detected and it is determined that a burst occurs, and a malfunction occurs. It shows that there is a possibility.

Generally, the count P0 is the trigger level Pt.
In many cases, the burst is determined by comparing whether or not h has been reached, that is, P0> Pth or P0 ≧ Pth. The integrated expected value (expected value integration) used when judging a burst based on the comparison of P0 ≧ Pth, and the expected value in each case of x = 1 to 10 up to λ = 1 to 10 are summarized below. There is. In this Table 2, for example, if λ = 1 and Pth = 2 is set,
It can be seen that the probability of reaching this trigger level is about 92%, which is the sum of the expected values of x = 0, 1, and 2.

[0011]

[Table 2]

In such a burst detector, for example, it is assumed that Pth is set to 9 under the condition of λ = 1 while permitting a malfunction of one part per million. Then, it is assumed that an abnormality occurs in the accelerator and a state where five pieces are stochastically input, that is, a state of λ = 5 is entered. In this case, there is almost a possibility of reaching Pth, x = 9, from the expected value integration.
%. Therefore, it is not possible to detect an increase with a probability of only 3%. As described above, in the simple digital comparison circuit as described above, reliable burst detection is impossible with a small number of counts. Of course, it is possible to handle as a normal distribution by lengthening the measurement time and increasing the count value, but the detection speed will decrease and it will be difficult to function as a trigger device used for transient recorders. Becomes

Therefore, in view of the above problems, it is an object of the present invention to realize a trigger device which has a high detection speed and is capable of detecting bursts while surely preventing malfunction. .

[0014]

In order to solve the above-mentioned problems, in the present invention, the comparison result by the Poisson distribution is further processed by using the binomial distribution to surely detect the burst while maintaining the detection speed. It is possible. That is, the trigger device according to the present invention comprises a counting means capable of continuously counting for a predetermined time, and a flag setting means for setting a flag when the count value of the counting means and a preset reference count value or more. An evaluation based on the Poisson distribution is performed, and further, flag holding means capable of holding the states of the plurality of flags set by the flag setting means, a flag counting means for counting the flags held by the flag holding means, and The evaluation by the binomial distribution is carried out by the flag number comparing means for comparing the number of flags counted by the flag counting means with the preset reference number of flags.
Further, it has a judging means for outputting a trigger signal based on the result of the flag number comparing means.

In such a trigger device, it is desirable to have a reference count value setting means capable of variably setting the reference count value, and it is also effective to have a reference flag number setting means capable of variably setting the reference flag number. .

[0016]

Embodiments of the present invention will be described below based on circuits actually used. FIG. 1 shows the configuration of a trigger device according to an embodiment of the present invention. The present apparatus includes a counting circuit 2 capable of detecting and counting radiation for a predetermined time under the control of a reference clock 1, a count P measured by the counting circuit 2 and a trigger level Pth preset by a threshold setting unit 3. And a comparison circuit 4 for comparing
When the count P ≧ Pth is satisfied, the 8-bit shift register 5 is set, a flag check circuit 6 for checking the number of flags set in the shift register, and a flag counted by the flag check circuit 6. A flag comparison circuit 7 that compares the number F with the reference flag number Fth preset by the reference flag setting unit 8.
And a signal transmission circuit 9 that outputs a burst signal based on the result of the flag comparison circuit 7.

The counting circuit 2 is based on the reference clock 1 and
Measure the number of detected radiation events for a given period,
The count value P is output to the comparison circuit 4. After that, the count is reset, the measurement is performed again for a predetermined period, and this operation is repeated. The comparator circuit 4 compares the count P input from the counter circuit 2 with the trigger level Pth, and count P ≧ Pth.
When is satisfied, a flag is set in the shift register 5 that is performing the synchronous operation with the same reference clock 1. Since the shift register 5 is an 8-bit shift register and incorporates the presence or absence of a flag in accordance with the reference clock 1, it is possible to go back in the past and accumulate the results of the comparison circuit 2 in eight counting periods. Then, the flag check circuit 6
Is the number of flags F recorded in this shift register 5.
Therefore, the flag check circuit 6 can refer to the results of the past eight counting periods.

For example, assume that the statistical probability of the counted input pulses is 1 within a predetermined period. This condition is the above-described average number of input pulses per unit time and corresponds to the condition that λ is 1. Then, Pth is set to 4. Under this condition, the probability that the flag is set in the shift register 5 by the comparison circuit 4 is an expected value in which the number of actually input pulses is 4 or more, and 1 to x shown in Table 1
= 0 is a probability obtained by subtracting an integrated value of expected values. That is, the probability F (Pth) that a flag is set in the register is F (Pth) = 1- (expected value integration of x = 3) = 1-0.981012 = 0.018988 (2). This corresponds to the shaded portion 21 of the Poisson distribution (λ = 1) shown in FIG.

When a flag is raised with such a statistical probability,
Of the 8-bit shift register 5, the number of registers with flags and their probabilities follow a binomial distribution. Therefore, the probability R (y) of flagging the y registers R is

[0020]

[Equation 3]

Here, N is 8 because the shift register has 8 bits, and 0.018988 obtained by the equation (2) is used as F (Pth). The values of R (y) when the value of y is changed from 0 to 8 are summarized in Table 3 below.

[0022]

[Table 3]

As can be seen from Table 3, when y = 6 or more, R
(Y) becomes 0 up to about 8 digits after the decimal point, and can be regarded as 0 in measurement. Therefore, the number of flags counted in the flag check circuit 6 is set to 6 as the reference flag number Fth set in the reference flag number setting unit.
As described above, by comparing in the flag comparison circuit 7, the statistical probability of the previously set counted input pulse is 1
It is possible to completely prevent the trigger device from malfunctioning in a condition corresponding to the above condition, that is, a condition corresponding to the condition of λ = 1.

As described above, in the trigger device of this example, the random natural phenomenon measured by the radiation measuring device from the counting circuit 2 and the comparison circuit 4 is processed based on the Poisson distribution, and the result is further processed by the shift register. 5 and the flag check circuit 6 can perform processing based on the binomial distribution. As a result, it can be seen that it is possible to detect a random natural phenomenon that occurs with a predetermined statistical probability without malfunction. Of course, even in the conventional device that triggers only based on the Poisson distribution, it is possible to reduce the probability of malfunction to one part per million or one part per million by making Pth sufficiently large. Therefore, at first glance, this difference is considered to be negotiable small.
However, if the probability of miscalculation is 1 / million or 1 / million in the present condition that a computer that calculates once every 1 μs is normal, the result of the calculation is 1 second or 1
A malfunction will occur once every 0 seconds. Therefore, there is a large difference between the probability of malfunction being very small and the probability of malfunction being 0.

Thus, by using this device,
It is possible to detect bursts by shortening the measurement time and preventing malfunctions while following natural phenomena.

As explained above, each count rate (λ)
Input, F (Pth) = 4, reference flag number Fth
The following table 4 shows the result of calculating the expected value at = 6.

[0027]

[Table 4]

As can be seen from this table, an input count of 5 or higher shows a high probability. The purpose of this device is to detect the transition to the steady state or the transient state reliably and as soon as possible, and further, the malfunction in the steady state is not allowed. Therefore, as described above, when the input count is 5 or more, the burst can be reliably detected by adjusting the measurement time, Pth, Fth, and the number of memories.

In the trigger device of this embodiment, the reference flag number Fth can be freely set by using the reference flag setting section 8, and the trigger level Pth can be set.
Can also be freely set by the threshold setting unit 3. Further, when measuring the natural decrease, the average number of input pulses per unit time of the Poisson distribution can be freely selected by changing the measurement time. Therefore, in such a trigger device, first, it is desirable that the number of reference flags is about 80% of the number of measurements that can be stored in the shift register, and in this example, about 6 per 8-bit register. Then, the trigger level Pth, which is the threshold value of the Poisson distribution, may be set to a value at which the repetition number y in the binomial distribution is regarded as 0 at the previously set Fth.
Furthermore, by setting the measurement time to a time at which the trigger level Pth can be measured in the Poisson distribution measurement, the number of input pulses can be averaged, so that the above-described trigger device can detect a random natural phenomenon without malfunction. Become.

[0030]

As described above, the trigger device according to the present invention processes a comparison result by Poisson distribution using a binomial distribution for a random natural phenomenon, and has a short detection time, It is possible to prevent malfunction and surely detect a burst. Therefore, in a device where it is difficult to secure a large count value to be detected based on an accurate normal distribution from the measurement time, it is possible to replace the conventional trigger device consisting only of Poisson distribution with an accurate and high-speed trigger. can do.

[0031]

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a trigger device according to an embodiment of the present invention.

FIG. 2 is a graph showing Poisson distribution.

FIG. 3 is a graph showing a binomial distribution.

FIG. 4 is a block diagram showing an outline of functions of a transient recorder.

[Explanation of symbols]

 1 ... Reference clock 2 ... Counting circuit 3 ... Threshold setting circuit 4 ... Comparison circuit 5 ... Shift register 6 ... Flag check circuit 7 ... Signal output circuit 11 ... Trigger Circuit 12 ... Delay circuit 13 ... Recorder

Claims (3)

[Claims] 1. A counting means capable of continuously counting for a predetermined time, a flag setting means for setting a flag when the count value of the counting means is equal to or larger than a preset reference count value, and the flag setting means. Flag holding means capable of holding the states of a plurality of set flags, flag counting means for counting the flags held by the flag holding means, the number of flags counted by the flag counting means, and a preset reference A trigger device, comprising: a flag number comparing means for comparing the number of flags; and a determining means for outputting a trigger signal based on a result of the flag number comparing means. 2. The trigger device according to claim 1, further comprising a reference count value setting means capable of setting the reference count value. 3. The trigger device according to claim 1, further comprising a reference flag number setting means capable of setting the reference flag number.