JP7047698B2 - Analysis equipment - Google Patents

Description

The present invention relates to an analyzer, and more specifically to a technique of data processing in the analyzer.

In an analyzer represented by a time-of-flight mass spectrometer (TOFMS), the output signal (ion signal) of a detector such as a mass spectrometer is amplified and integrated a predetermined number of times. However, there is a risk that systematic noise will be superimposed on the signal due to this data processing.

For example, in Japanese Patent No. 3741563 (Patent Document 1), a background spectrum shorter than the spectrum of the measurement data is prepared in advance, paying attention to the fact that the systematic noise has a relatively short period. In addition, a technique for suppressing periodic noise by repeatedly executing a process of subtracting the background from the spectrum of measurement data is described.

Japanese Patent No. 3741563

In the technique of Patent Document 1, it is necessary to prepare a background spectrum showing periodic noise in advance. Therefore, if there is a difference between the noise level prepared in advance and the actual noise spectrum, noise suppression may be insufficient or noise may be generated instead.

Further, in Patent Document 1, in order to perform phase matching of periodic noise, Fourier transform is performed, a high-pass filter is applied on the frequency plane, and then inverse Fourier transform is performed. There is also concern that it will become.

The present invention has been made to solve such a problem, and an object of the present invention is a simple calculation with a configuration capable of pipeline processing of periodic noise of a signal obtained by an analyzer. It is more surely suppressed by.

An analyzer according to the present invention includes a detector and a data processing unit that receives an output signal from the detector. The data processing unit includes a signal generation unit, an integration processing unit, and a periodic noise reduction unit. The signal generation unit generates a digital signal obtained by sampling the output signal. The integration processing unit executes integration processing a predetermined number of times for the digital signal. The periodic noise reduction unit removes periodic peak noise included in the digital signal train after the integration processing output from the integration processing unit. The periodic noise reduction unit includes a delay unit, a correction parameter calculation unit, and a correction processing unit. The delay unit delays the digital signal sequence from the signal generation unit according to the period of peak noise. The correction parameter calculation unit calculates the correction position where peak noise exists and the correction amount thereof by pipeline processing using the signal train in the non-signal section in which the analysis signal immediately after the signal is emitted does not exist in the digital signal train. The correction processing unit performs correction processing on the digital signal sequence to correct the digital signal value corresponding to the correction position calculated by the correction parameter calculation unit by the correction amount. The correction parameter calculation unit has a parameter calculation unit. The parameter calculation unit corresponds to the peak noise cycle according to the addition result of the absolute values of the digital signal values of the signal sequence of the non-signal section delayed by the delay section and the signal sequence of the non-signal section not passing through the delay section. The correction position is calculated by extracting the maximum value of the digital signal values of the number of samples, and the correction amount at the correction position is calculated.

Preferably, the parameter calculation unit calculates the correction amount based on at least the polarity of the digital signal value and the number of integration processes.

Alternatively, preferably, the delay section delays the digital signal sequence by the number of samples corresponding to the period of the peak noise. The number of samples that delay the digital signal sequence in the delay section is a predetermined fixed value.

Alternatively, preferably, the periodic noise removing unit further includes a noise period calculating unit. The noise cycle calculation unit calculates the peak noise cycle using the signal sequence (baseline signal) in the non-signal section that does not include the analysis signal. The delay section delays the digital signal sequence by the number of samples corresponding to the period of the peak noise. The number of samples that delay the digital signal sequence in the delay unit is set according to the period calculated by the noise period calculation unit.

Further, preferably, the delay unit imparts information indicating a reference position to each digital signal constituting the digital signal sequence to be output with a delay for each number of samples. The parameter calculation unit defines the correction position as a relative position with respect to the reference position. The correction processing unit executes the correction amount subtraction processing for the reference position and the digital signal specified by the correction position.

According to the present invention, the periodic noise of the signal obtained by the analyzer can be more reliably suppressed by a simple arithmetic processing.

It is a schematic block diagram explaining the structure of the analyzer according to embodiment of this invention. It is a block diagram explaining the structure of the data processing part shown in FIG. It is a figure which shows the observation example of a baseline signal waveform. It is a functional block diagram of the periodic noise reduction part according to Embodiment 1. FIG. It is a conceptual waveform diagram explaining the operation timing of the periodic noise reduction part shown in FIG. It is a figure which shows the observation example of the baseline signal waveform in the experiment for demonstrating the effect by a correction processing part. It is a functional block diagram of the periodic noise reduction part according to Embodiment 2. FIG.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following, the same or corresponding parts in the figure will be designated by the same reference numerals, and the explanations will not be repeated in principle.
[Embodiment 1]

FIG. 1 is a schematic block diagram illustrating a configuration of an analyzer 5 according to an embodiment of the present invention.

With reference to FIG. 1, the analyzer 5 is typically a time-of-flight mass spectrometer (TOFMS), which includes a detector 10, an amplifier 20, and a data processing unit 100. For example, the detector 10 is a mass spectrometer including an ionization unit and a mass separation unit (analyzer) (not shown), and has a mass / charge ratio of atoms and molecules constituting an ionized (gas phase) sample to be analyzed. An analysis signal (analog signal) showing the mass spectrometry result based on the difference is output.

The amplifier 20 amplifies the analysis signal output from the detector 10. The data processing unit 100 collects the analysis signal amplified by the amplifier 20 by digital sampling, performs integration processing and correction noise processing on the digital signal, and performs an output signal from the analysis device 5 (hereinafter, “analysis output signal”). Also called). The analysis output signal corresponds to a signal showing a so-called mass spectrum.

FIG. 2 is a block diagram illustrating the configuration of the data processing unit 100. In addition, each functional block described in the block diagram described below including FIG. 2 realizes the function by at least one of hardware processing by FPGA (Field-programmable Gate Array) and software processing by a processor. can do.

With reference to FIG. 2, the data processing unit 100 includes an analog / digital (A / D) converter 110, a signal acquisition unit 120, an integration processing unit 130, a baseline correction unit 140, and a baseline correction unit 140, which are shown as functional blocks. , Includes a periodic noise reduction unit 150.

The A / D converter 110 converts the analysis signal (analog signal) amplified by the amplifier 20 into a digital value. The signal acquisition unit 120 generates a digital signal having a predetermined bit width (for example, 10 bits) at a predetermined sampling frequency (for example, 5 (GHz)). At each sample timing, each bit of the digital signal is determined by the quantization of the analog value of the analysis signal. As a result, a digital signal Sdg according to the voltage (analog) of the analysis signal is generated for each sampling cycle which is the reciprocal of the sampling frequency. That is, the function of the "signal generation unit" can be realized by the A / D converter 110 and the signal acquisition unit 120.

The integration processing unit 130 integrates the digital signal Sdg generated by the signal acquisition unit 120 for a predetermined number of times Ni, and outputs a digital signal sequence Sds indicating the integration result. The baseline correction unit 140 performs baseline correction on the digital signal sequence Sds after the integration process, and outputs the digital signal sequence Sds * after the baseline correction.

Baseline correction is a correction process for adjusting the analysis signal to zero level. As for the baseline correction, a known method can be appropriately used, and detailed description thereof will be omitted. Hereinafter, the signal section of the digital signal sequence Sds * output from the baseline correction unit 140 that does not include the analysis signal immediately after emission is also referred to as a “baseline signal” in particular.

FIG. 3 is a waveform diagram showing an observation example of the baseline signal waveform. The horizontal axis of FIG. 3 is the time axis (number of samples), and the vertical axis plots the digital signal value represented by the predetermined bit width of the digital signal for each sample. FIG. 3 shows an example when periodic peak noise is observed when the number of integrations is large (for example, about 1000 times).

With reference to FIG. 3, it is understood that the baseline signal waveform exhibits a noise-like behavior with an average value of zero due to the effect of the baseline correction. However, when the number of integrations is large, peak noise that periodically occurs on the time axis is observed on the baseline signal waveform. For example, in the example of FIG. 3, noise having a peak is generated every 64 samples, that is, at a frequency of 78.125 (MHz) at a sampling frequency of 5 (GHz). In FIG. 3, the peak noise is shown in a circle. In the following, the noise period (Nz) is shown in units of the number of samples of the digital signal generated by the A / D converter 110 and the signal acquisition unit 120. For example, in the example of FIG. 3, Nz = 64.

It is predicted that the peak noise is generated due to the hardware on the substrate on which the component of the data processing unit 100 is mounted, and it is an invention that the frequency of the peak noise is usually substantially constant for each individual. Found by those. Further, such peak noise is more prominent as the number of integration processes (hereinafter, also referred to as “integration number Ni”) increases.

In the analysis output signal, there is a concern that the peak noise is erroneously recognized as a spectrum, or that the true spectrum cannot be detected due to the influence of the peak noise.

Therefore, in the analyzer according to the present embodiment, as shown in FIG. 2, in order to remove the periodic peak noise (FIG. 3) from the baseline corrected digital signal sequence Sds * by arithmetic processing, the periodic period A noise removing unit 150 is further provided. In the first embodiment, it is assumed that the peak noise generation cycle Nz (noise cycle Nz) is known by observing the baseline signal waveform (FIG. 3).

FIG. 4 is a functional block diagram of the periodic noise reduction unit 150 shown in FIG.
With reference to FIG. 4, the periodic noise reduction unit 150 includes delay units 160 and 180, a correction parameter calculation unit 170, and a correction processing unit 200. The correction parameter calculation unit 170 includes an addition unit 172, a peak detection unit 174, and a parameter calculation unit 175.

The delay unit 160 outputs the digital signal sequence Sds # after the baseline correction output from the baseline correction unit 140, and the digital signal sequence Sds # delayed by the Nz sample corresponding to the period of the peak noise. For example, in the delay unit 160, in order to synchronize with the signal transmitted to the addition unit 172, the digital signal sequence Sds # may be output after adding information indicating the reference position to each Nz sample. can.

The addition unit 172 executes an addition operation between the absolute values of the digital signal values between the digital signal sequence Sds * that does not pass through the delay unit 160 and the digital signal sequence Sds # delayed by the Nz sample. As a result, it is possible to obtain a digital signal sequence in which the addition result is significantly enlarged as compared with other samples, corresponding to the position of the peak noise shown in FIG. 3 for each Nz sample. Further, the addition unit 172 stores information indicating the polarity (positive / negative) of the digital signal value before it is converted into an absolute value.

The peak detection unit 174 extracts the maximum value of the addition result between the absolute values from the Nz sample of the digital signal sequence obtained by the addition unit 172. Thereby, the position of the peak noise can be specified by specifying the digital signal corresponding to the maximum value from the digital signal sequence for the Nz sample. For example, the position of the peak noise can be indicated by the number of samples from the above-mentioned reference position, that is, the position relative to the reference position.

The parameter calculation unit 175 acquires information (position in the Nz sample) for specifying the position of the peak noise from the peak detection unit 174, and also obtains the digital signal value (peak noise value) corresponding to the peak noise from the addition unit 172. Acquires information indicating the polarity (positive / negative) before making it an absolute value. Further, as information indicating the magnitude of the peak noise, it is also possible to further acquire the addition value of the absolute values corresponding to the peak noise.

The parameter calculation unit 175 calculates the correction position Nh and the correction amount Sh for removing the peak noise for each Nz sample, and outputs the correction processing unit 200 to the correction processing unit 200. The correction position Nh can be information indicating the number of samples from the reference position for specifying one of the digital signals in the Nz sample. Since the correction means to bring the peak noise value close to the noise effective value, the correction amount Sh corresponds to (detected peak noise-noise effective value). For example, when the noise effective value estimated in advance is Nr, it can be set to be √ (Ni) times Nr (Ps (LSB) = Nr * √ (Ni)). The correction value Ps is calculated based on the information from the addition unit 172 so as to have the polarity (positive / negative) of the noise peak value before being converted into an absolute value. In this way, the correction parameter calculation unit 170 calculates the correction position Nh and the correction amount Sh for removing the peak noise by the pipeline processing.

The delay unit 180 further delays the digital signal sequence Sds # delayed by the number of Nz samples in the delay unit 160 by a predetermined number of samples. The delay unit 180 acts as a buffer for waiting for the correction calculation process by the correction processing unit 200. Therefore, the number of delayed samples by the delay unit 180 can be appropriately designed according to the time required for the correction calculation in the correction processing unit 200. Even in the delay unit 180, the information indicating the reference position given to each Nz sample by the delay unit 160 is maintained.

The correction processing unit 200 executes periodic peak noise correction processing on the digital signal sequence output from the delay unit 180. Specifically, among a plurality of digital signals constituting the digital signal sequence, the correction amount Sh is subtracted from the digital signal to which the information indicating the reference position is added to the digital signal delayed by the Nh sample indicating the correction position. The correction process is executed as follows. That is, for each Nz sample, correction by the correction amount Sh is executed in order to remove the peak noise. If the correction value Ps is calculated so as to have a polarity opposite to the polarity of the noise peak value, the correction process can be executed by adding the correction amount Sh.

FIG. 5 shows a time chart illustrating the operation timing of the periodic noise reduction unit 150.

With reference to FIG. 5, the analyzer 5 is turned on and off, and the emitted analysis signals are integrated for the number of integrations. Immediately after the injection, there is no signal that does not include the analysis signal, so this period is used as the reference signal used for periodic noise reduction. At the time of data transmission after the integration process, the digital signal sequence Sds * with baseline correction, that is, the above-mentioned baseline signal is input to the periodic noise reduction unit 150. The baseline signal does not contain a component indicating a mass spectrum, but contains noise generated by the data processing unit 100, particularly periodic peak noise generated by integration processing.

Using the data of the non-signal period immediately after the injection, the correction parameter calculation unit 170 is operated, while the correction processing unit 200 is stopped. As a result, the correction position Nh and the correction amount Sh for removing the peak noise for each Nz sample are calculated in the no-signal period.

Continuing as it is, the correction processing unit 200 executes correction processing in order to remove the periodic peak noise superimposed on the digital signal sequence based on the analysis signal. That is, the digital signal sequence Sds * after the baseline correction is corrected according to the correction position Nh and the correction amount Sh calculated in the no-signal period. This makes it possible to suppress periodic peak noise in the output signal from the data processing unit 100.

FIG. 6 shows an observation example of the baseline signal waveform in an experiment for explaining the effect of the correction processing unit 200. As mentioned above, the baseline signal waveform is a set of digital signals at each sample timing during the no-signal period. Also in FIG. 6, the horizontal axis is the time axis (number of samples), and the vertical axis is the digital value for each sample.

6 (a1), (b1), and (c1) show baseline signal waveforms obtained when the correction processing unit 200 is stopped in a no-signal period on different substrates. In each of (a1), (b1), and (c1), it is understood that the average value of the digital values is approximately 0 due to the effect of the baseline correction. Further, due to the difference in the characteristics of each substrate, periodic peak noise is generated in (a1) and (b1), but no remarkable peak noise is observed in (c1).

In FIG. 6A2, the output signal from the data processing unit 100 when the correction processing unit 200 is experimentally operated with respect to the baseline signal waveform of (a1) in the no-signal period, that is, The baseline signal waveform after the peak correction processing is shown. Similarly, (b2) shows the baseline signal waveform after the peak correction processing with respect to the baseline waveform of (a2) in the no-signal period.

As can be understood from the comparison of (a1) and (a2) and the comparison of (b1) and (b2), the correction processing unit 200 removes the periodic peak noise having a large negative value. Understood. The standard deviation (σ) of each digital signal value constituting the baseline signal waveform is 67.34 in (a1) and 56.42 in (a2), whereas the standard deviation (σ) after the peak correction process is (a1). In a2), it is improved to 58.61, and in (b2), it is improved to 46.74.

On the other hand, the baseline signal waveform after the peak correction processing with respect to the baseline signal waveform of (c1) in which no remarkable peak noise is observed is shown in (c2). As can be understood from the comparison of (c1) and (c2), even if the correction processing unit 200 is operated for the baseline signal waveform in which the periodic peak noise is inconspicuous, the noise does not deteriorate. The standard deviation (σ) of each digital signal value constituting the baseline signal waveform is 53.80 in (c1), which is equivalent to (a2) and (b2) after peak correction processing. The standard deviation (σ) in (c2) is 54.64, and it is understood that the deterioration of noise does not occur even when viewed from the quantitative value (standard deviation).

As described above, according to the analyzer according to the present embodiment, the data processing is performed by the integration processing by performing the correction processing according to the extraction of the periodic peak noise from the actual baseline signal in the non-signal period such as immediately after the injection. Periodic peak noise generated in the process can be suppressed. As a result, since it can be processed in real time, it is possible to suppress noise more reliably and accurately with respect to the strength and weakness of the noise due to the change with time, as compared with the method of creating a noise pattern in advance.

In particular, noise can be suppressed by relatively simple digital signal processing such as maximum value extraction and addition / subtraction without performing conversion to the frequency domain. Further, as can be understood from the comparison of (c1) and (c2) of FIG. 6, the influence on the signal before correction is also suppressed.

[Embodiment 2]
FIG. 7 is a schematic block diagram illustrating the configuration of the periodic noise reduction unit according to the second embodiment. In the analyzer according to the second embodiment, in the configurations of FIGS. 1 and 2, the periodic noise reduction unit 150a having the configuration of FIG. 7 is arranged in place of the periodic noise reduction unit 150 (FIG. 4).

The periodic noise removing unit 150a is different from the periodic noise removing unit 150 shown in FIG. 4 in that it further includes a noise period calculating unit 190. The noise cycle calculation unit 190 calculates the noise cycle by inputting the digital signal sequence Sds * after the baseline correction output from the baseline correction unit 140. That is, in the first embodiment, the noise cycle calculation unit 190 measures the number of samples Nz indicating the noise cycle, which is a known value by the waveform observation (FIG. 3) in advance, online.

A known technique can be applied to the process for calculating the noise cycle by the noise cycle calculation unit 190. For example, Japanese Patent Application Laid-Open No. 2008-252190 or Japanese Patent Application Laid-Open No. 2007-151051 can be used. The techniques described can be used.

The noise cycle calculation unit 190 described with reference to FIG. 7 operates at a timing earlier than that of the delay unit 160. Thereby, before the correction parameter calculation is executed, the number of samples Nz indicating the period of the peak noise can be automatically calculated based on the digital signal sequence Sds * in the no-signal period. Since the subsequent processing is the same as that of the first embodiment, the detailed description will not be repeated.

According to the data processing apparatus according to the second embodiment, the period of the peak noise can be set according to the online measurement result. As a result, even if the peak noise cycle changes due to temperature conditions or the like, noise suppression can be achieved with the correct cycle.

In the present embodiment, an example in which correction processing is performed only for one piece corresponding to the peak noise in the digital signal of the Nz sample has been described, but the same applies to the second, third, and the like louder noises. It is also possible to perform the correction processing of. In this case, the peak detection unit 174 detects a plurality of peaks including the maximum value, and calculates correction parameters (correction position Nh and correction amount Sh) corresponding to each peak.

Further, the present embodiment has been described with TOFMS in mind as the analyzer to which the present invention is applied, but if a periodic peak noise is generated by the integration process even in an analyzer of a method other than TOFMS, it is detected. Regardless of the type of the device, it is possible to perform correction processing for periodic peak noise according to the present embodiment.

It should be considered that the embodiments disclosed this time are exemplary in all respects and not restrictive. The scope of the present invention is shown by the scope of claims rather than the above description, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

5 Analyzer, 10 detector, 20 amplifier, 100 data processing unit, 110 converter, 120 signal acquisition unit, 130 integration processing unit, 140 baseline correction unit, 150, 150a periodic noise removal unit, 160, 180 delay unit. , 170 correction parameter calculation unit, 172 addition unit, 174 peak detection unit, 175 parameter calculation unit, 190 noise cycle calculation unit, 200 correction processing unit, Nh correction position, Ni integration frequency, Nr noise effective value, Nz noise cycle (sample). Number), Ps correction value, Sdg digital signal, Sds digital signal sequence, Sds * digital signal sequence (after baseline correction), Sdg # digital signal (after delay), Sh correction amount.

Claims (5)

With the detector,
It is equipped with a data processing unit that receives an output signal from the detector.
The data processing unit
A signal generation unit that generates a digital signal obtained by sampling the output signal, and
An integration processing unit that executes integration processing a predetermined number of times for the digital signal, and
It includes a periodic noise removing unit that removes periodic peak noise included in the digital signal train after integration processing output from the integration processing unit.
The periodic noise reduction unit is
A correction parameter calculation unit that calculates the correction position and correction amount of the peak noise using the signal train in the non-signal section of the digital signal train.
A delay unit that delays the digital signal sequence from the signal generation unit according to the period of the peak noise, and a delay unit.
The digital signal train during the operation period of the detector includes a correction processing unit that corrects the digital signal value corresponding to the correction position calculated by the correction parameter calculation unit by the correction amount. ,
The correction parameter calculation unit is
According to the addition result of the absolute values of the digital signal values of the signal train delayed by the delay unit and the signal train not passing through the delay unit, the digital signal value of the number of samples corresponding to the period of the peak noise An analyzer having a parameter calculation unit that calculates the correction position by extracting the maximum value among them and also calculates the correction amount at the correction position. The analyzer according to claim 1, wherein the parameter calculation unit calculates the correction amount based on at least the polarity of the digital signal value and the number of times of the integration processing. The delay portion delays the digital signal sequence by the number of samples corresponding to the period of the peak noise.
The analyzer according to claim 1 or 2, wherein the number of samples is a predetermined fixed value. The periodic noise reduction unit is
It further includes a noise period calculation unit for calculating the period of the peak noise using the signal sequence of the non-signal section.
The delay portion delays the digital signal sequence by the number of samples corresponding to the period of the peak noise.
The analyzer according to claim 1 or 2, wherein the number of samples is set according to a cycle calculated by the noise cycle calculation unit. The delay unit adds information indicating a reference position for each number of samples to the digital signal constituting the digital signal sequence to be output with a delay.
The parameter calculation unit defines the correction position as a relative position with respect to the reference position.
The analyzer according to any one of claims 1 to 4, wherein the correction processing unit corrects the reference position and the digital signal value specified by the correction position.

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