JPH0337147B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the number of signal generation per unit time of a signal source that generates signals periodically or randomly, for example (but not limited to) in the case of radiation measurement. The present invention relates to a device for measuring Since this device inputs signals from such a signal source and counts the number of input signals per unit time, this device will be referred to as a counting rate meter here.

Typical examples of such count rate meters include frequency meters and rotation rate meters that correspond to periodic signal generation rates, and examples that correspond to random signals such as radiation measurement , and various others.

For example, in environmental radiation monitors used around nuclear reactor facilities, a Geiger-Mueller tube or a scintillation detector is used as a radiation detector to constantly measure the count rate. Under normal circumstances, only natural radioactivity existing on the ground or in space is measured.
Count rate values are stable. If an abnormal count rate value is counted during measurement, it is necessary to issue an alarm because radioactive contamination has occurred for some reason.

In this kind of radioactivity measurement, conventionally, the first
A count rate meter of the circuit type shown in the figure is generally used. Referring to the figure, the output signal of the detector is inputted by shaping it into a constant amplitude pulse, and this is applied to the capacitor 1. The capacitor 1 converts a signal into a constant amount of charge according to its capacitance and input amplitude. This amount of charge charges capacitor 2, but
At the same time, a discharge occurs through the resistor 3. Capacitor 2 and resistor 3 form a time constant circuit. When the capacitor 2 is charged, the voltage increases and is output, but on the other hand, the voltage decreases due to discharge. This voltage drop curve is the result of capacitor 2 and resistor 3.
Determined by CR time constant. If there is an input again during discharging, charging is performed and then discharged again. This output voltage reaches equilibrium at a voltage that depends on the number of signals that fall within the time constant, ie, the count rate meter. The counting rate can be determined by reading this voltage with a meter. The operational amplifier 4 is used to improve linearity and increase the dynamic range.

In the case of radiation measurements, the input is random, ie, has no synchronization. Therefore, if the measured value of the counting rate is N, it has a standard deviation of ±√. To be more specific, if the measured value is 100, it will have a standard deviation value of 10. Therefore, in order to reduce the deviation value, the time constant must be increased. Particularly in the case of counting at a low counting rate, increasing the size of the capacitor 2 and resistor 3 causes deterioration of measurement accuracy for various reasons. That is, if the capacitor 2 is made larger, the leakage current of the capacitor causes deterioration of accuracy, and the output capacity necessary for charging the operational amplifier 4 may be exceeded, resulting in deterioration of accuracy. Furthermore, if the resistor 3 is made larger, the temperature stability will deteriorate due to the influence of the offset current of the operational amplifier 4, resulting in a decrease in measurement accuracy. Furthermore, since the capacitor 2 and resistor 3 themselves change due to temperature, the time constant changes and the measured counting rate changes. Furthermore, since the operational amplifier 4 itself is a DC amplifier, the problem of drift always accompanies it.

Even apart from these various problems, essential problems remain. That is, the originally digital counting is approximated and realized using an analog circuit. Now, assume that an input signal exists, a certain equilibrium state is reached, and then there is no input signal at all. In this case, since it is a count rate meter, the voltage should drop linearly over time, but in reality, the capacitor 2
And there is a drawback that it falls along a curve determined by the time constant determined by the resistor 3.

In this way, conventional radiation measurement count rate meters have been effective for measuring periodic signals with a certain range of count rates, but when it comes to measuring random signals with low count rates, Accurate measurements were impossible.

On the other hand, some frequency meters are of a digital type that count signal waves with a counter over a unit time and measure the frequency as the counted value. However, although it is possible to identify frequency changes between one measurement time and the next measurement time, it is not possible to detect frequency fluctuations within each measurement time or across both measurement times. Therefore, it is unsuitable for measuring randomly generated signals, and is particularly unsuitable for measuring signals with a low counting rate.

In view of the above points, it is an object of the present invention to provide a digital count rate meter that can accurately measure the counting rate of both periodic and random signals and also accurately capture changes over time. do.

In a count rate meter that measures the number of signal waves generated per unit time, the present invention provides a counting means that counts the number of input signals within a predetermined minute time, resets it at the end of the minute time, and performs the counting operation again. and temporary storage means for storing the count values counted by the counting means within each minute time for a predetermined period of time; the input signal wave is used as an addition input, and the output of the temporary storage means is used as a subtraction input. The digital count rate meter has an addition/subtraction counting means, and obtains the number of signal waves within the certain time period as a count value of the addition/subtraction counting means.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

Referring to FIG. 2, the illustrated embodiment has a counting circuit 7 that receives and counts an input signal from a signal source (not shown). The counting circuit 7 is reset by the clock pulse of the clock circuit 8. Therefore, the counting circuit 7 performs a new count every clock pulse. At the time of reset, the count value of the counting circuit 7 is transferred to a temporary storage circuit 9 such as a shift register and stored for a certain period of time. For example n
When a stage shift register is used, clock pulses from the clock circuit 8 are used to sequentially send clocks from the first stage and sequentially from the last stage. As a result, the temporarily stored time is expressed as (number of stages of shift register) x (clock pulse period).

In addition, in FIG. 2, the output of the counting circuit 7 is depicted as being such that all digits are outputted to the temporary storage circuit 9 in parallel. Therefore, when shift registers are used in the temporary storage circuit 9, shift registers (each having n stages) as many as the number of digits in the counting circuit 7 are provided in parallel corresponding to each digit.

Note that it is also possible to use a storage device as the temporary storage circuit 9. In this case, reading from the storage device is carried out by providing a counter that is reset when n clock pulses of the clock circuit 8 are counted and outputs the reset signal to the storage device as a readout signal. It's obvious what you should do.

The output of the temporary storage circuit 9 is sent to the addition/subtraction counting circuit 10.
The input signal from the signal source is applied to the addition input.

Now, assume that the contents of the counting circuit 7, addition/subtraction counting circuit 10, and temporary storage circuit 9 are cleared and an input signal is applied. Addition/subtraction counting circuit 10
continues to add and count the input signals. On the other hand, the counting circuit 7 repeats the operation of counting the input signals within the clock period and sending the counted value to the temporary storage circuit 9. After a predetermined period of time has elapsed, that is, when the temporary storage circuit 9 reaches its storage capacity in the case of a shift register, its contents are sequentially outputted and given as subtraction inputs to the addition/subtraction counting circuit 10, thereby performing addition/subtraction counting. The count value of circuit 10 is subtracted by the subtraction input value. Therefore, the count value of the counting circuit 7 for each clock cycle from the start of operation is sequentially C ₁ ,
C ₂ , C ₃ , ...C _k , ..., _Co ..., and the number of stages of the shift register as the temporary storage circuit 9 is, for example, 3.
In the case of a stage, the counting operation in the counting circuit 7 is the first 4 stages.
There is no subtraction input to the addition/subtraction counting circuit 10 until the fourth cycle is completed, and the first count value C ₁ is applied to the subtraction input at the end of the fourth cycle. Therefore, the count value A of the addition/subtraction counting circuit 10 at this time is (C ₁ +C ₂ +C ₃ +C ₄ )−
C becomes ₁ , and addition and subtraction are performed thereafter. Generally, the count value A at the end of n-th counting is given by A= 〓 ⁿ⁼¹ C _o − 〓 ⁿ⁼⁴ C _o-3 . That is, A indicates the sum of the previous three counts, which then indicates the number of signals within 3t time (where t is a clock period and 3t is a unit time).

If the input signal is periodic, the addition and subtraction values for each clock cycle are the same (i.e., C ₁ =C ₂ =...=C _o ), so the addition and subtraction counting circuit 1
A count value A of 0 reaches equilibrium. In the case of no periodicity, generally C ₁ ≠C ₂ ≠C ₃ ...≠C _o , so
The count value A of the addition/subtraction counting circuit 10 changes with the clock cycle. That is, changes in the counting rate over a short period of time, such as within a clock cycle, can be accurately captured.

In addition, by changing the clock cycle, the counting time can be set to match the generation rate of the target signal, and the storage time of the temporary memory circuit can be adjusted to maintain a constant unit time, so even low counting rates can be achieved. It can also be applied to measurements with high counting rates with high accuracy.

Furthermore, the standard deviation that accompanies random signal measurement can be easily reduced by increasing the storage capacity of the temporary storage circuit 9.

Note that the contents of the addition/subtraction counting circuit 10 indicate a count integral value with respect to a unit time, and the content of the counting circuit 7 indicates a differential count value with respect to a reference time. That is, the counting circuit 7 counts the signals randomly inputted between clock pulses without any dropout. Therefore, by measuring the count value of the counting circuit 7, there is an advantage that the presence or absence of disturbance can be quickly determined. In addition, the counting circuit 7 also has the addition/subtraction counting circuit 1.
Since 0 also counts all randomly generated input signals without any omissions, it is possible to obtain a counting rate meter that can accurately count not only regular input signals but also randomly generated input signals. This is one of the features not found in conventional methods. In this way, by using stable digital technology, there is no need to pay attention to the disadvantages of conventional methods, such as element temperature changes and operational amplifier drifts, and there is no need for offset level adjustment, etc., which is required with analog methods. . The circuit configuration according to the present invention not only solves the drawbacks of the conventional system and eliminates the troublesome work of adjustment, but also provides extremely great industrial benefits as it is constructed with a stable and economical digital circuit.
Further, when the present invention is used for monitoring the vicinity of a nuclear reactor, pollution monitoring, etc., it is possible to quickly determine the presence or absence of disturbance, which brings about a beneficial effect.

Note that although the present invention can be realized by a computer, it does not go beyond the scope of the present invention.

[Brief explanation of drawings]

Figure 1 is a diagram showing the circuit of a conventional count rate meter.
FIG. 2 is a block diagram showing an embodiment of the present invention. 7... Counting circuit, 8... Clock circuit, 9... Temporary memory circuit, 10... Addition/subtraction counting circuit.

Claims (1)

[Claims] 1. In a count rate meter that measures the number of signal waves generated per unit time, a counting means that counts the number of input signals within a predetermined minute time, resets it at the end of the minute time, and performs the counting operation again; Temporary storage means for storing the count values counted by the counting means within each minute time for a predetermined fixed period of time, and addition/subtraction using the input signal wave as an addition input and the output of the temporary storage means as a subtraction input. a counting means, the digital count rate meter is configured to obtain the number of signal waves within the certain time period as a count value of the addition/subtraction counting means.