JPH053549B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention provides a method for correcting a true ground level for correcting an apparent ground level to a true ground level when, for example, a preamplifier and a linear amplifier are AC-coupled. Regarding estimation method.

[Technical background of the invention]

In the radiation estimating device, as shown in FIG. 1, radiation emitted from a radiation source 11 is detected using a detector 12 such as a germanium detector. This detection output is weak, on the order of μV. The preamplifier 13 amplifies this to about mV and also shapes the waveform using a built-in RC circuit. A linear amplifier (main amplifier) 14 amplifies this to a voltage level suitable for a measuring device 15 such as a pulse height analyzer, and also shapes the waveform.

Now, when the preamplifier 13 and the linear amplifier 14 are AC-coupled by the capacitor 16 as shown in the figure, the ground level on the linear amplifier 14 side varies depending on the state of the signal output from the preamplifier 13. Generally, if a pulse signal as shown by the solid line 18 in FIG. 2A is output from the preamplifier, the ground level on the linear amplifier side will be as shown by the broken line 19. Further, when the frequency of the pulse signal increases as shown by a solid line 21 in FIG. 2B, the ground level increases as shown by a broken line 22.

In the radiation estimating device shown in Fig. 1, each time radiation is detected, pulse signals 24 ₁ , 24 ₂ . . . which decrease exponentially as shown in Fig. 3 are outputted one by one. It is. The generation status of these pulse signals 24 ₁ , 24 ₂ . . . depends on the state of the radiation source 11, and is, of course, undetermined. Therefore, in the conventional measuring device of this type, the true ground level cannot be estimated on the linear amplifier side, which causes an error in the estimation result of a subsequent measuring device such as a pulse height analyzer.

[Purpose of the invention]

In view of the above-mentioned circumstances, an object of the present invention is to provide a method capable of estimating the true ground level on the linear amplifier side and stabilizing the baseline after waveform shaping.

[Structure of the invention]

In the present invention, an input signal is detected by the rise or fall of its waveform, a signal that simulates the signal is generated after a predetermined period of time has elapsed, and the difference between these two signals is calculated by a calculator. In a waveform shaping device that shapes the pulse signal into a pulse signal having a time width equal to the predetermined time, the difference between the ground level on this device side and the level of the signal output from the arithmetic unit is detected, and This difference during the period is fed back to the arithmetic unit as an error in the signal level output from the arithmetic unit, and the level is corrected. The ground level after this correction is estimated to be the true ground level on the waveform shaping device side.

〔Example〕

The present invention will be explained in detail with reference to Examples below.

FIG. 4 shows the main parts of a linear amplifier using the true ground level estimation method of this embodiment. A signal 32 having a waveform as shown in FIG. 5a, for example, is input to an input terminal 31 of this linear amplifier. At this time, the preamplifier outputs a signal 33 having a waveform as shown in FIG. In other words, the level l _p of signal 32 is the ground level of the preamplifier, and the ground level of the linear amplifier side.
l A predetermined level difference exists between _L and L.

The signal 32 passes through the arithmetic unit 34 and is sent to the signal detection circuit 35.
is input. The signal detection circuit 35 detects the rise of the signal 32 and sends the detected signal to the switch circuit 3.
Supply to 6. In the switch circuit 36, when a predetermined time T has elapsed from this rising point,
A simulated signal transmission start control signal 39 is sent to the simulated signal generation circuit 37.

The simulated signal generation circuit 37 includes, for example, an exponential function generation circuit consisting of a capacitor and a resistor, and charges are stored in the capacitor in response to the signal 32. Then, from the time when the simulated signal transmission start control signal 39 is input, the simulated signal 41 decreases exponentially.
(Fig. 5c) is generated. The waveform of the signal 32 input to the input terminal 31 is determined in advance by the preamplifier. Therefore, when a preamplifier that outputs a pulse signal that decreases exponentially is used, a similar waveform as described above will be output as the simulated signal 41. Further, when a waveform in which the DC level changes stepwise as shown in FIG. 6 is input, the simulated signal 41 also has a stepwise waveform simulating this. In the case of the simulated signal 41 shown in the figure, the voltage at which the signal level is lowered (or increased) by the offset ΔV on the linear amplifier side becomes the apparent ground level l _L ' of the linear amplifier.

Now, the arithmetic unit 34 calculates the difference between the simulated signal 41 outputted from the simulated signal generation circuit 37 and the signal 32 inputted from the input terminal 31. The resulting output signal 42 is supplied to an output terminal 43, from which it is sent to a subsequent circuit section.

By the way, FIG. 5d shows the output signal 42' assuming that no ground level correction is performed.
This represents the waveform of . As can be understood from this figure, the output signal 42 falls at once by the difference in response to the rise of the waveform of the simulated signal 41 (c in the same figure), but even after that, the apparent ground level of the linear amplifier l _L ' decreases exponentially towards . Therefore, for such an output signal 42',
It is not possible to obtain a pulse signal with a wave height that accurately corresponds to the wave height of the signal 33 output from the preamplifier side.

Therefore, in this embodiment, the error detection circuit 45 is used to correct the ground level. Error detection circuit 4
5 receives the waveform passing signal 46 (FIG. 5e) from the switch circuit 36, and corrects the ground level during other periods. Here, the waveform passing signal 46 is a pulse signal that is generated for a period of time T from the rising edge of the signal 32. That is, the error detection circuit 45 compares the potential of the ground and the output side of the arithmetic unit 34, and matches the level of the simulated signal 41 outputted from the simulated signal generation circuit 37 with the ground level L _L of the linear amplifier side. As a result, the zero level of the output signal becomes the true ground level l _L as shown in FIG. 5f, and its wave height corresponds exactly to the wave height of the signal 33.

〔Effect of the invention〕

As described above, according to the present invention, the error obtained by the comparison calculation of the arithmetic unit is fed back to the arithmetic unit to estimate the true ground level. Therefore, as shown in the embodiment, it is possible to effectively deal with not only ground level fluctuations due to AC coupling, but also offsets on the preamplifier and linear amplifier side due to causes such as temperature, improving the accuracy of pulse height analysis, etc. be able to.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing the general configuration of a radiation measuring device, Figure 2 A and B are waveform diagrams showing the relationship between the duty of the pulse signal and the ground level, and Figure 3 is the waveform diagram of the signal output from the preamplifier. A waveform diagram showing an example, FIG. 4 is a block diagram showing the main parts of a linear amplifier to which the true ground level estimation method is applied in one embodiment of the present invention, and FIG. 5 is a diagram for explaining the circuit operation in this embodiment. FIG. 6 is a waveform diagram showing other examples of input signals. 32...Input signal, 34...Arithmetic unit, 4
1...Simulated signal, 42...Output signal, 45...Error detection circuit, l _L ...Ground level on the linear amplifier side.

Claims (1)

[Claims] 1. Detect an input signal by the rising or falling edge of its waveform, generate a signal that simulates the signal after a predetermined period of time has elapsed, and calculate the difference between these two signals using a calculator to detect the signal for the predetermined period of time. A waveform shaping device that shapes the pulse signal into a pulse signal having a time width equal to This difference in the signal level output from the arithmetic unit is returned to the arithmetic unit as an error in the signal level, and the level is corrected, and the signal level of this part after correction is estimated as the true ground level.True ground level estimation Method.