An Automatic Digital Pole-Zero Cancellation Method

Abstract

The present invention relates to the technical field of signal analysis, and specifically discloses an automatic digital pole-zero cancellation method; on the host computer operation software, a default threshold is set for pulse signal acquisition, and a default starting pole-zero parameter value is set; the host computer operation software sends a command to the digital pulse amplitude analyzer to collect the pulse waveform after pole-zero once; it is judged whether the pulse tail of the received waveform is lower than the baseline value; if the pulse tail is lower than the baseline value, the pole-zero parameter value is adjusted; if the pulse tail is not lower than the baseline value, it is judged whether the current adjustment is the minimum number of digits of the pole-zero parameter; if the current adjustment is not the minimum number of digits of the pole-zero parameter, the current adjustment digit is changed, and then the pole-zero parameter value is adjusted; if the current adjustment is the minimum number of digits of the pole-zero parameter, the optimal pole-zero parameter value is obtained, and the automatic pole-zero process ends; compared with the traditional manual operation and discrimination, the present invention has multiple advantages: fast, good consistency, low requirements for personnel, and realization of automatic linkage.

Description

Technical Field

[0001] The present invention relates to the technical field of signal analysis, and particularly to an automatic digital pole-zero cancellation method. Background Art

[0002] In the nuclear instrumentation industry, in the process of processing the exponentially decaying signal output by a detector, the pole-zero cancellation process is an important step. There may be two problems with the original signal output from the detector. One is that the output signal has an exponential tail undershoot due to various reasons, and the other is that some detector signals have a large time constant, that is, a large pulse signal width, and pulse pile-up is likely to occur when the counting rate is high. To solve these problems, in a traditional analog multi-channel pulse amplitude analyzer, a pole-zero cancellation circuit is used to process the input signal.

[0003] As Figure 2 shown, the pole-zero cancellation circuit is an improved differential circuit, and the undershoot caused by differentiation is improved through pole-zero cancellation. Compared with a simple differential circuit, the pole-zero cancellation circuit can improve the undershoot after signal differentiation and at the same time has the effect of reducing the pulse width of the differential circuit. The anti-pile-up effect of pole-zero cancellation is as Figure 3 shown. The original wider signal becomes narrower after processing, the piled-up pulses can also be distinguished, and the baseline shift is also improved.

[0004] The above introduces the processing scheme of the pole-zero cancellation circuit in an analog multi-channel. In a digital multi-channel, this process is implemented in the form of digital operations. In a digital multi-channel, the signal output by the detector is directly converted into discrete data through a high-speed ADC and achieves the effect of filtering and shaping through a series of operations. There are various digital pole-zero cancellation methods. The main idea is to perform mathematical modeling based on the analog circuit of pole-zero cancellation, establish a differential equation, transform the differential equation into an equation in the time series according to the discrete characteristics of ADC sampling, and transform to obtain the numerical sequence expression of the output and the input. There are relevant algorithms introduced in the existing published literature. One of the algorithm formulas is as follows:

[0005]

[0006] Where V2[n] is the data after pole-zero cancellation, and V1[n] is the original signal data before pole-zero cancellation. k1 and k2 are external input parameters, where k1 is determined by the exponential decay time constant of the input signal, and k2 determines the exponential decay time constant of the output signal.

[0007] In these algorithms, the above parameters need to be input from the outside to perform mathematical operations on the original pulse. In actual operation, generally, the exponential decay constant k2 of the pulse after pole-zero cancellation is fixed. Generally, there is only one external parameter input k1 for the algorithm related to pole-zero cancellation.

[0008] In the nuclear instrument industry for energy spectrum measurement, especially for digital multi-channel analyzers and their supporting software, current actual operations and public information show that confirming the pole-zero cancellation parameter value is the main purpose of the pole-zero debugging process of digital multi-channel analyzers. This process is manually completed by humans. The process of debugging pole-zero cancellation is as follows:

[0009] Manually set the pole-zero parameter value to the median, obtain the pulse waveform after real-time pole-zero cancellation, and adjust the pole-zero parameter value by manually observing the over-compensation and under-compensation forms of the waveform, ultimately achieving a reasonable waveform form. For example, when the pole-zero parameter value is too large, an under-compensation phenomenon will occur, such as Figure 4 shown, there is a downward overshoot in the tail of the pulse, resulting in the value of the tail being less than the baseline. It also causes the height of the second pulse to be distorted because it continues on the downward overshoot tail. When the pole-zero parameter value is too small, an over-compensation phenomenon will occur, such as Figure 5 shown, the tail of the pulse cannot return to the baseline along the predetermined trajectory but is higher than the baseline, resulting in the second pulse continuing on the tail of the first pulse and the pulse being distorted. When the pole-zero parameter is appropriate, the effect shown in Figure 6 is produced, where the tail of the pulse meets the theoretical requirements, quickly returns to the baseline, and does not affect subsequent pulses.

[0010] From the above process, it can be known that debugging the pole-zero parameters is a cumbersome and complex process, and it requires human participation. Moreover, the experience of the participants has a great impact on the speed of debugging. The so-called under-compensation and over-compensation are both forms of description, and there is no precise determination method. Summary of the Invention

[0011] Aiming at the problems existing in the prior art, the purpose of the present invention is to provide an automatic digital pole-zero cancellation method.

[0012] The technical solution adopted by the present invention to solve its technical problems is: an automatic digital pole-zero cancellation method, including the following steps:

[0013] Step 1) The digital pulse amplitude analyzer cooperates with the upper computer operation software. The digital pulse amplitude analyzer collects the output signal of the detector, and clicks the automatic pole-zero button on the upper computer operation software to start the automatic pole-zero process;

[0014] Step 2) Set the default threshold for obtaining the pulse signal and set the default initial pole-zero parameter value on the upper computer operation software;

[0015] Step 3) The upper computer operation software sends a command to the digital pulse amplitude analyzer to collect the pulse waveform after one-time pole-zero cancellation. After the digital pulse amplitude analyzer waits for the signal to trigger the threshold, it performs one-time data acquisition and uploads it to the upper computer operation software;

[0016] Step 4) After the host computer operation software receives the spectral line, it determines the received waveform and whether its pulse tail is lower than the baseline value;

[0017] Step 5) If the pulse tail is lower than the baseline value, adjust the pole-zero parameter value, and then the host computer operation software sends the command to obtain the spectral line after pole-zero to the digital pulse amplitude analyzer again;

[0018] Step 6) If the pulse tail is not lower than the baseline value, it is judged whether the current adjustment is the minimum number of digits of the pole-zero parameter;

[0019] Step 7) If the current adjustment is not the minimum number of digits of the pole-zero parameter, change the current adjustment digit, then adjust the pole-zero parameter value, and then the host computer operation software sends the command to obtain the spectral line after pole-zero to the digital pulse amplitude analyzer again;

[0020] Step 8) If the current adjustment is the minimum number of digits of the pole-zero parameter, obtain the optimal pole-zero parameter value, restore the threshold, and the automatic pole-zero process ends.

[0021] Specifically, the digital pulse amplitude analyzer in the step 1) is provided with a lower computer program, and the lower computer program collects the waveform signal of the exponentially decaying signal output by the detector and performs digital pole-zero cancellation processing on it to generate the signal after pole-zero.

[0022] Specifically, the default threshold of the pulse signal in the step 2) is selected to be not less than 50% of the sampling signal amplitude to ensure a good signal-to-noise ratio.

[0023] Specifically, after setting the default starting pole-zero parameter value in the step 2), the fractional position of the currently adjusted value is saved, and the fractional position starts from the highest bit of the value.

[0024] Specifically, for the pole-zero pulse waveform collected in the step 3), the baseline waveform for a certain time before the trigger threshold needs to be retained, which is implemented by the queue buffering method for subsequent operation to judge the baseline value.

[0025] Specifically, the method for determining whether the pulse tail in step 4) is lower than the baseline value is as follows: First, read a section of the baseline waveform before the waveform threshold trigger after the poles and zeros, extract the minimum value m of this section of the waveform, and take p = m - s * |m| as the theoretical minimum value of the baseline, where s is a preset default parameter, and s is generally taken as 0.5. Then, read the subsequent waveform starting from the trigger threshold, extract the minimum value n, and calculate the difference n - p; when n - p is negative, the pulse tail is lower than the baseline value, and when n - p is positive, the pulse tail is not lower than the baseline value; according to the above rule, when the poles and zeros value is greater than the theoretical value, the pulse is undercompensated, and the pulse tail must be lower than the baseline value. Because the set initial default poles and zeros parameter is a relatively large value, the obtained waveform must be undercompensated, so it can be determined for the first time that the pulse tail is lower than the baseline value.

[0026] Specifically, after determining that the pulse tail is lower than the baseline value in step 5), the method for adjusting the poles and zeros parameter value is to query the fraction at the currently saved numerical position and subtract 1 from the value at this fraction position to obtain the new poles and zeros parameter value.

[0027] Specifically, the method for changing the current adjustment digit and adjusting the poles and zeros parameter value in step 7) is to lower the digit and take the maximum value of 9.

[0028] The present invention has the following beneficial effects:

[0029] The automatic digital poles and zeros cancellation method designed by the present invention has multiple advantages over the traditional manual operation and discrimination:

[0030] 1) Fast: For traditional manual operation, it is necessary to manually modify the poles and zeros parameters, manually obtain the waveform after poles and zeros, and manually magnify the waveform for judgment, which takes a long time. The automated process can perform each judgment and change in milliseconds, which can greatly improve the efficiency.

[0031] 2) Good consistency: For traditional manual operation, due to the limitations of the operator's own level, operation state, or differences between different operators, different optimal values may be generated. The automated process can ensure good consistency.

[0032] 3) Low requirements for personnel: The automated process can automatically optimize after replacing the detector, without the need for manual participation, reducing the requirements for users.

[0033] 4) Realize automated linkage: In the case of needing to switch different detector signals, it can be linked with other automated processes to further improve the overall automation level. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a flowchart of the automatic digital poles and zeros cancellation method.

[0035] Figure 2 It is a comparison circuit diagram of an ordinary differential circuit and a differential circuit with pole-zero cancellation.

[0036] Figure 3 It is a waveform diagram of the pole-zero cancellation anti-piling-up effect.

[0037] Figure 4 It is a waveform diagram of the under-compensation phenomenon when the pole-zero parameter value is too large.

[0038] Figure 5 It is a waveform diagram of the over-compensation phenomenon when the pole-zero parameter value is too small.

[0039] Figure 6 It is a waveform diagram of the effect when the pole-zero parameter is appropriate. Specific implementation mode

[0040] The following will further clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings in the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0041] As Figure 1 shown, an automatic digital pole-zero cancellation method, the carrier is a digital pulse amplitude analyzer and its supporting lower computer program and upper computer operation software. In the digital multi-channel pulse amplitude analyzer and its supporting software, during the implementation of the function of determining the digital pole-zero cancellation parameters, a software function and method for automatically determining the pole-zero parameters, which is applicable to the automatic digital pole-zero cancellation function for exponentially decaying signals.

[0042] The user clicks the automatic pole-zero button to start the automatic pole-zero process.

[0043] Set a suitable default threshold for pulse acquisition. Generally, it is selected to be not less than a certain proportion of the sampling signal amplitude, such as not less than 50% of the sampling signal amplitude. For example, for the case where the maximum amplitude of the signal is 1V, the threshold is generally set to 0.5V to ensure a good signal-to-noise ratio. Set a default starting pole-zero parameter value and save the position of the fractional digit of the currently adjusted value (default starting from the highest digit). Generally, a relatively large pole-zero parameter is selected. For example, the theoretically matching pole-zero parameter for the detector output signal is generally 17000 - 22000, set the default initial pole-zero parameter to 30000, and the position of the current numerical adjustment is the ten-thousandth digit.

[0044] The host computer operation software (host computer) sends a command to the digital multi-channel pulse amplitude analyzer (lower computer) to collect the pulse waveform after the pole-zero once. After the lower computer waits for the signal trigger threshold, it performs a data collection and uploads it to the host computer. For the collected waveform after the pole-zero, the waveform for a certain period of time before the trigger threshold needs to be retained for subsequent operation to judge the baseline value. This function can be achieved by methods such as queue buffering.

[0045] After the host computer receives the spectral line, it judges the received waveform to see if the pulse tail is lower than the baseline value. The specific judgment method is as follows: First, read a section of the baseline waveform before the threshold trigger of the waveform after the pole-zero, extract the minimum value m of this section of the waveform, and take p = m - s * |m| as the theoretical minimum value of the baseline, where s is the preset default parameter, generally taking 0.5. Then read the subsequent waveform starting from the trigger threshold, extract the minimum value n, and calculate the difference n - p. When n - p is negative, the pulse tail is lower than the baseline; if n - p is positive, the pulse tail is not lower than the baseline. According to the above rules, when the pole-zero value is greater than the theoretical value, the pulse is under-compensated and the pulse tail must be lower than the baseline value. Since the set initial default pole-zero parameter is a relatively large value, the obtained waveform must be under-compensated, so it can be determined for the first time that the pulse tail is lower than the baseline.

[0046] If the pulse tail is lower than the baseline, adjust the pole-zero parameter value, and then send a command to the lower computer to obtain the spectral line after the pole-zero.

[0047] If the pulse tail is not lower than the baseline, judge whether the current adjustment is the minimum digit of the pole-zero parameter.

[0048] If the current adjustment is not the minimum digit of the pole-zero parameter, change the current adjustment digit, then adjust the pole-zero parameter value, and then send a command to the lower computer to obtain the spectral line after the pole-zero.

[0049] If the current adjustment is the minimum digit of the pole-zero parameter, then obtain the optimal pole-zero parameter value.

[0050] After obtaining the optimal pole-zero parameter value, restore the threshold, and the automatic pole-zero process ends.

[0051] After determining that the pulse tail is lower than the baseline, the method of adjusting the pole-zero parameter value is to query the fractional digit of the currently saved numerical position and subtract 1 from the value at this fractional digit position, that is, to obtain the new pole-zero parameter value. For example, if the currently saved value is 30000 and the fractional digit is the ten-thousandth digit, so subtract 1 from the value 3 at the ten-thousandth digit position to get the new value 2. Thus, the new pole-zero parameter is 20000.

[0052] After changing the current digit, the method to adjust the pole-zero parameter value is to lower the digit and take the maximum value of 9. For example, if the current pole-zero value is 24000 and the current saved adjustment position is in the thousands place. After changing the current adjustment digit, the pole-zero parameter is adjusted to 24900.

[0053] Specific embodiments are described as follows for a certain operation process:

[0054] Starting from automatic pole-zero, set the initial time constant to 30000, set the threshold to 0.5V, and at this time the adjustment position is in the ten-thousands place. Send a command to the lower computer to obtain the spectrum after pole-zero, obtain the signal after pole-zero, determine that the pulse tail is lower than the baseline, and adjust the pole-zero parameter value to 20000.

[0055] Send a command to the lower computer to obtain the spectrum after pole-zero, obtain the signal after pole-zero, determine that the pulse tail is not lower than the baseline, determine that the current adjustment position is in the ten-thousands place and not the smallest digit, change the current adjustment position to the thousands place, and adjust the pole-zero parameter value to 29000.

[0056] Send a command to the lower computer to obtain the spectrum after pole-zero, obtain the signal after pole-zero, determine that the pulse tail is lower than the baseline, adjust the pole-zero parameter value to 28000, and repeat this process 7 times. The current parameter value is 21000.

[0057] Send a command to the lower computer to obtain the spectrum after pole-zero, obtain the signal after pole-zero, determine that the pulse tail is not lower than the baseline, determine that the current adjustment position is in the thousands place and not the smallest digit, change the current adjustment position to the hundreds place, and adjust the pole-zero parameter value to 21900.

[0058] Repeat the above process until the current parameter value is 21634. Send a command to the lower computer to obtain the spectrum after pole-zero, obtain the signal after pole-zero, determine that the pulse tail is not lower than the baseline, determine that the current adjustment position is in the units place and is the smallest digit, obtain the optimal pole-zero parameter value 21634, restore the threshold, and the automatic pole-zero process ends.

[0059] In the above process, it should be noted that:

[0060] The selection and setting of the threshold are necessary. Generally, under normal circumstances, the threshold is a very small value, about one-thousandth to one-hundredth of the signal amplitude. In this method, a relatively large threshold must be set, fully considering the influence of the signal-to-noise ratio. In this method, it is necessary to ensure the accuracy of the difference judgment to ensure that the automatic process will not be interrupted accidentally. And the accuracy of the difference judgment mainly comes from the signal-to-noise ratio of the original signal. If a smaller threshold is selected, the signal-to-noise ratio of the signal is poor, and the waveform will be distorted due to the influence of noise, resulting in misjudgment.

[0061] End judgment of the automatic process. In the real world, the actual pole-zero value is an analog value with an infinite number of decimal places. In digital operations, the input pole-zero parameters must have a finite number of decimal places or be integers, resulting in discontinuous time. The discrete time parameters cause the waveforms generated by the operations to be either over-compensated or under-compensated. Therefore, the judgment condition for the end of the automatic process can be achieved.

[0062] This method has multiple advantages over the traditional manual operation and discrimination. When using a digital multi-channel and its supporting software for measurement, it is necessary to determine the pole-zero parameters in advance. The existing operation is to manually set a pole-zero parameter, manually obtain the spectral line, manually judge the waveform after pole-zero, and manually modify the pole-zero parameter in a continuous cycle until a suitable pole-zero parameter is obtained. The software function implemented by this method can liberate manpower, and only by clicking a button, a fully automated automatic optimization process of pole-zero parameters can be implemented.

[0063] The present invention is not limited to the above embodiments. Anyone should know that structural changes made under the inspiration of the present invention, as long as they have the same or similar technical solutions as the present invention, fall within the protection scope of the present invention.

[0064] The technologies, shapes, and structures not described in detail in the present invention are all well-known technologies.

Claims

1. An automatic digital pole-zero cancellation method, characterized in that, It includes the following steps: Step 1): The digital pulse amplitude analyzer cooperates with the upper computer operation software. The digital pulse amplitude analyzer collects the output signal of the detector, and clicks the automatic pole-zero button on the upper computer operation software to start the automatic pole-zero process; Step 2): Set the default threshold for obtaining the pulse signal and set the default initial pole-zero parameter value on the upper computer operation software; Step 3): The upper computer operation software sends a command to the digital pulse amplitude analyzer to collect the pulse waveform after one-time pole-zero. After the digital pulse amplitude analyzer waits for the signal to trigger the threshold, it performs one-time data acquisition and uploads it to the upper computer operation software; Step 4): After the upper computer operation software receives the spectrum line, it judges the received waveform. The method for judging whether the pulse tail is lower than the baseline value is as follows: First, read a section of the baseline waveform before the waveform threshold trigger after pole-zero, extract the minimum value m of this section of the waveform, and take p = m - s * |m| as the theoretical minimum value of the baseline, where s is the preset default parameter and s takes 0.

5. Then read the subsequent waveform starting from the trigger threshold, extract the minimum value n, and calculate the difference n - p; when n - p is negative, the pulse tail is lower than the baseline value, and if n - p is positive, the pulse tail is not lower than the baseline value; When the pole-zero value is greater than the theoretical value, the pulse is under-compensated, and the pulse tail must be lower than the baseline value. Because the set initial default pole-zero parameter is a relatively large value, the obtained waveform must be under-compensated, so it can be determined for the first time that the pulse tail is lower than the baseline value; Step 5): If the pulse tail is lower than the baseline value, adjust the pole-zero parameter value, query the fractional position of the currently saved numerical position, and subtract 1 from the value at this fractional position to obtain the new pole-zero parameter value. Then the upper computer operation software sends a command to the digital pulse amplitude analyzer again to obtain the spectrum line after pole-zero; Step 6): If the pulse tail is not lower than the baseline value, judge whether the current adjustment is the minimum digit of the pole-zero parameter; Step 7): If the current adjustment is not the minimum digit of the pole-zero parameter, change the current adjustment digit, then adjust the pole-zero parameter value, and then the upper computer operation software sends a command to the digital pulse amplitude analyzer again to obtain the spectrum line after pole-zero; Step 8): If the current adjustment is the minimum digit of the pole-zero parameter, obtain the optimal pole-zero parameter value, restore the threshold, and the automatic pole-zero process ends.

2. The automatic digital pole-zero cancellation method according to claim 1, wherein The digital pulse amplitude analyzer in the above step 1) is provided with a lower computer program. The lower computer program collects the waveform signal of the exponentially decaying signal output by the detector and performs digital pole-zero cancellation processing to generate the signal after pole-zero.

3. The automatic digital pole-zero cancellation method according to claim 1, wherein The default threshold of the pulse signal in the above step 2) is selected to be not less than 50% of the sampling signal amplitude to ensure a good signal-to-noise ratio.

4. The automatic digital pole-zero cancellation method according to claim 1, wherein After setting the default initial pole-zero parameter value in the above step 2), save the fractional position of the currently adjusted numerical value, and the fractional position starts from the highest digit of the value.

5. The automatic digital pole-zero cancellation method according to claim 1, wherein For the pulse waveform after pole-zero collected in the above step 3), it is necessary to retain the baseline waveform for a certain time before the trigger threshold, which is realized by the queue buffer method for subsequent operation to judge the baseline value.

6. The automatic digital pole-zero cancellation method according to claim 1, characterized in that The method of changing the current adjustment digit and adjusting the pole-zero parameter value in step 7) is to lower the digit and take the maximum value 9 of this digit.

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