CN103234986B - An intelligent electronic device, a QXAFS (quick X-ray absorption fine structure) system and a data acquisition and motor control method - Google Patents

Abstract

This application discloses an intelligent electronic device, a QXAFS system and a data acquisition and motor control method. The intelligent electronic device replaces the stepper motor controller and the scaler in the conventional XAFS experimental system, and uses a programmable device as the core component. , the electronic equipment implements analog acquisition through a multi-channel ADC acquisition circuit combined with a current amplifier in a fast XAFS system, or uses the counting function of a programmable device combined with a V/F converter in a fast XAFS system to realize integral data acquisition. The programmable device controls the stepper motor by reading the control curve configured in the RAM, and at the same time performs data acquisition in the control section that allows data acquisition, realizing high-speed synchronization of stepper motor control and data acquisition, and through the control curve in the control curve Sampling data in the low-speed or static control section avoids energy movement in the process of collecting data, and obtains the best solution in the contradiction between scanning speed and energy movement.

Description

Intelligent electronic device, QXAFS system and data acquisition and motor control method

technical field

This application relates to the modern material structure analysis method - synchrotron radiation experiment method, especially to a kind of intelligent electronic equipment, fast XAFS experimental system and Data acquisition and stepper motor control methods in a fast XAFS experiment implemented using this smart electronics device.

Background technique

The modern XAFS experimental system is a tool for large-scale material structure analysis and research based on synchrotron radiation devices. Its basic principle is to irradiate the sample to be studied with single-energy X-rays, and gradually change the energy of single-energy X-rays within a specific X-ray energy range. Energy scanning is realized, and the intensity of X-rays before and after the sample is detected at the same time, so as to obtain the absorption line of the sample in a specific energy range, and the microstructure information of the sample can be obtained by analyzing the absorption line. The XAFS experimental method is widely used in the research of physics, chemistry, catalysis, materials, environment, biology and other multidisciplinary fields. It is one of the most widely used analytical methods among many synchrotron radiation experimental methods.

Fig. 1 schematically shows a structural block diagram of a conventional XAFS experimental system. In Fig. 1, synchrotron radiation X-rays are incident on a twin-crystal monochromator 101, and the twin-crystal monochromator 101 monochromatizes synchrotron radiation X-rays, for example, only monochromatic X-rays whose wavelength satisfies the Bragg relationship The rays are reflected, and when the twin-crystal monochromator 101 is rotated to change the incident angle of the X-rays, the wavelength of the outgoing light changes accordingly, so that the energy (wavelength) scanning of single-energy adjustable X-rays required by the XAFS experiment can be realized. The single-energy X-ray emitted from the twin-crystal monochromator 101 acts on the sample.

The single-energy X-ray enters the ionization chamber X-ray detector 103 located in front of the sample, the sample and the ionization chamber X-ray detector 103 located behind the sample (while detecting the standard sample, there may also be a third ionization chamber X-ray detector). The front and rear ionization chamber X-ray detectors 103 respectively measure the intensity of the X-rays before interacting with the sample and the intensity of the X-rays after interacting with the sample, so as to obtain the XAFS spectrum.

The weak current signal output by the detector 103 of the ionization chamber is fed into the current amplifier 105 . The current amplifier 105 amplifies and converts the current signal proportional to the X-ray intensity generated by the X-ray detectors before and after the sample into an analog voltage signal. The number of current amplifiers may be at least two. The analog voltage signal obtained by the current amplifier 105 corresponds to the intensity of the monoenergetic X-ray, and the intensity of the X-ray can be obtained based on the output value of the current amplifier 105 . The working state of the current amplifier 105 can be set by a computer through a general purpose interface bus (General Purpose interface Bus, GPIB).

Voltage/frequency (V/F) converter 106 converts the analog voltage signal output from current amplifier 15 into a pulse frequency signal, and scaler 107 counts the pulse frequency signal output by V/F converter 106, and counts the value Transfer to computer 108. The intensities of X-rays before and after interacting with the sample can be obtained through the count value of the scaler 107 .

The shaft angle encoder 109 reads the current angle of the twin crystal monochromator 101 , displays it on the display 110 and transmits it to the computer 108 . The computer 108 sends control signals to the linear motor driver 112 to control the roll angle and pitch angle of the twin-crystal monochromator 101 . The linear motor driver 112 is connected with the computer 108 to realize manual/automatic control.

The computer 108 sends a signal to the stepper motor controller 114, so that the stepper motor controller 114 generates a control pulse of the stepper motor driver 113, thereby prompting the motor driver 113 to drive the stepper motor to rotate and then drive the double crystal monochromator 101 to rotate. The stepper motor controller 114 can also send control signals to other controlled devices.

In addition, the current amplifier 105 and the stepper motor controller 114, and the computer and the current amplifier 105 can be connected through the GPIB bus to carry out various required communications. The computer 108 and the stepper motor controller 114, the linear motor driver 112 and The displays 110 can be connected via RS232.

When the system in Figure 1 is used for slow-speed spectrum acquisition, a spectrum acquisition process consists of the control and data acquisition of multiple energy points. For each energy point, the single-energy X-rays are generated step by step by the stepping motor first, and then start to collect data after the stepping motor stops moving and the X-ray energy is stable. The advantage of this method is that at the time of data acquisition, the X-ray energy has been stabilized, and the signal-to-noise ratio of the measurement results is high.

Quick XAFS (QXAFS) method is the development of conventional XAFS experimental technology, which can provide time-resolved structural information, so it is an important experimental method for studying chemical reaction mechanism, phase transition and kinetic process in the fields of materials, chemistry and catalysis. The QXAFS method is based on the conventional synchrotron radiation XAFS experimental system, and replaces the conventional step by step energy scanning mode with the continuous energy scanning mode (continuing mode), which reduces the spectral acquisition speed from the conventional XAFS experiment to the order of about 10 minutes. The spectrum is improved to a spectrum in seconds.

However, the improvement of spectral acquisition speed is at the expense of data quality. From the perspective of spectroscopy, the data quality of the original spectrum includes two aspects, XAFS oscillation information in the spectrum and statistical noise. The XAFS oscillation distortion leads to the distortion of the adjacent structure information, and the statistical noise is superimposed on the XAFS oscillation waveform, which makes it lose its analytical value. The currently published QXAFS implementation plans focus more on the improvement of the acquisition speed and ignore the methods and measures of the acquisition data quality. In essence, the QXAFS method cannot simply pursue speed. The purpose of QXAFS is to achieve a balanced optimization between spectrum acquisition speed and data quality.

In a nutshell, when performing rapid spectrum acquisition based on the system shown in Figure 1, there are the following problems:

(1) stepper motor controller and data acquisition device (such as current amplifier 105, V/F converter 106 and scaler 107 etc. in Fig. Software synchronization is limited by the communication speed between the computer and peripherals, the internal working mechanism of peripherals, etc., and cannot achieve fast synchronization, thus limiting the spectrum acquisition speed.

(2) In order to achieve fast scanning, the continuous mode is adopted in the QXAFS experiment process, that is, the data is collected while the stepping motor is moving, so there must be energy movement ΔE (that is, energy change) within the data collection time t of a single energy point, This distorts the data, resulting in XAFS oscillating distortion.

(3) When data is collected at one energy point, the statistical error of the data is expressed as Formula 1: Where N is the amount of data collected at this energy point, I is the signal strength, and t is the data collection time at this point. Using the QXAFS method shortens the spectrum acquisition time, t will inevitably decrease, and the statistical error will inevitably increase.

(4) Different data acquisition circuit schemes, such as an analog-to-digital conversion (ADC) sampling scheme (i.e., adopting a current amplifier 105 in FIG. 1 to obtain a voltage value corresponding to the X-ray intensity) or an integral scheme (i.e., adopting The combination of V/F converter 106 + scaler 107 to obtain the count value corresponding to the intensity of X-rays) has different efficiencies, that is, the N values collected in the same time t are different. Therefore, establishing a reasonable data acquisition hardware is an important aspect of optimizing the QXAFS method.

(5) There are time constants in the detection system, such as the reaction speed of the ionization chamber detector 103, the rise time of the current amplifier 105, etc., which will affect the XAFS oscillation structure, resulting in distortion of the XAFS oscillation waveform and distortion of adjacent structure information. It can be seen that improving the hardware of the detection system is also an important aspect of optimizing the QXAFS method.

(6) Step loss and inaccurate stepping and sampling phases during the energy scanning process of the QXAFS experiment will cause the spectrum to be deformed on the energy axis, and also cause the XAFS oscillation waveform to be distorted, resulting in distortion of the adjacent structure information.

(7) In addition, in order to optimize the QXAFS method, the overall hardware system design should be able to compress the time overhead of signal processing and transmission to the greatest extent, so as to maximize the speed of spectrum acquisition.

Contents of the invention

In order to solve one or more of the above problems, the application provides an intelligent electronic device dedicated to QXAFS experiments, a fast XAFS experimental system, and data acquisition and stepping in the fast XAFS experiment implemented using the intelligent electronic device In the motor control method, the intelligent electronic device is used to replace the stepper motor controller and the scaler in the conventional XAFS experimental system.

This application discloses an intelligent electronic device dedicated to fast XAFS experiments, including: at least one of a multi-channel analog-to-digital conversion acquisition circuit and a multi-channel isolation circuit, a programmable device, a first isolation circuit, and a communication interface circuit:

The multi-channel analog-to-digital conversion acquisition circuit is used to convert the analog voltage signals from at least two current amplifiers into digital signals, and the at least two current amplifiers are used to connect the X-ray detectors before and after the sample in the fast XAFS experiment The current signal proportional to the X-ray intensity generated is amplified and converted into an analog voltage signal;

The multi-channel isolation circuit is used to realize the electrical isolation between the pulse frequency signal from the voltage/frequency converter and the programmable device, and the voltage/frequency converter is used to convert the analog voltage signal of the at least two current amplifiers into a pulse frequency signal;

The programmable device is connected to the multi-channel analog-to-digital conversion acquisition circuit and the multi-channel isolation circuit, and is used to receive the signal output by the multi-channel analog-to-digital conversion acquisition circuit, and the pulse frequency input to the voltage/frequency converter The signal is counted, and the signal output by the multi-channel analog-to-digital conversion acquisition circuit and the count value for counting the pulse frequency signal input by the voltage/frequency converter are stored in the first-in-first-out (First In First Out, FIFO) data buffer for computer reading;

The control curve of the stepper motor is pre-configured in the control curve configuration RAM carried by the programmable device, and the control curve is defined as the different control segments of the stepper motor and the stepper motor when data acquisition is performed at different energy points. Controlling the relationship between pulse frequencies, the different control sections include a static control section that allows data collection, a constant speed control section after deceleration or a constant speed control section after acceleration, and an acceleration control section that does not perform data collection;

The programmable device is used to send control pulses to the stepper motor driver to control the rotation of the stepper motor by reading the control curve of the stepper motor, and in the static control section, the constant speed control section after deceleration and the acceleration Data acquisition starts after a preset delay after the start of the last constant speed control segment;

The first isolation circuit is connected to the programmable device for realizing electrical isolation between the programmable device and the stepper motor driver;

The communication interface circuit is connected with the programmable device for realizing the communication between the programmable device and the computer.

The application also discloses a fast XAFS experimental system, including:

Synchrotron X-ray sources;

A twin-crystal monochromator monochromatizes the X-rays output by the synchrotron radiation X-ray source to obtain the single-energy X-rays required for fast XAFS experiments;

A shaft angle encoder for detecting the angle of the twin crystal monochromator;

A stepper motor is used to control the rotation of the twin crystal monochromator;

a stepper motor driver, electrically connected to the stepper motor, for driving the stepper motor to rotate;

At least two current amplifiers are used to amplify and convert the current signal proportional to the X-ray intensity generated by the X-ray detector before and after the sample in the fast XAFS experiment and convert it into an analog voltage signal;

A voltage/frequency converter, connected to the at least two current amplifiers, for converting the analog voltage signals of the at least two current amplifiers into pulse frequency signals;

a computer, configured to receive the angle of the dual crystal monochromator detected by the shaft encoder; and

Intelligent electronic equipment, including: at least one of a multi-channel analog-to-digital conversion acquisition circuit and a multi-channel isolation circuit, a programmable device, a first isolation circuit, and a communication interface circuit:

The multi-channel analog-to-digital conversion acquisition circuit is electrically connected to the at least two current amplifiers, and is used to convert the analog voltage signals from the at least two current amplifiers into digital signals;

A multi-channel isolation circuit is configured between the voltage/frequency converter and the programmable device, and is used to realize electrical isolation between the pulse frequency signal from the voltage/frequency converter and the programmable device;

The programmable device is connected to the multi-channel analog-to-digital conversion acquisition circuit and the multi-channel isolation circuit, and is used to receive the signal output by the multi-channel analog-to-digital conversion acquisition circuit, and the pulse frequency input to the voltage/frequency converter The signal is counted, and the signal output by the multi-channel analog-to-digital conversion acquisition circuit and the count value for counting the pulse frequency signal input by the voltage/frequency converter are stored in the first-in-first-out in a data cache for the computer to read;

The control curve of the stepper motor is pre-configured in the control curve configuration RAM carried by the programmable device, and the control curve is defined as the different control segments of the stepper motor and the stepper motor when data acquisition is performed at different energy points. Controlling the relationship between pulse frequencies, the different control sections include a static control section that allows data collection, a constant speed control section after deceleration or a constant speed control section after acceleration, and an acceleration control section that does not perform data collection;

The programmable device is used to send control pulses to the stepper motor driver to control the rotation of the stepper motor by reading the control curve of the stepper motor, and in the static control section and the constant speed control section after deceleration And start data acquisition after a preset delay after the accelerated constant speed control segment starts;

The first isolation circuit is connected to the programmable device for realizing electrical isolation between the programmable device and the stepper motor driver;

The communication interface circuit is connected with the programmable device for realizing the communication between the programmable device and the computer.

The present application also discloses a method for data acquisition and stepping motor control in the fast XAFS experiment implemented by the aforementioned fast XAFS experiment system, including the following steps:

Receive all the operating parameters required for the fast XAFS experiment through the human-computer interaction interface installed in the computer, format the operating parameters and transmit them to the intelligent electronic device, and the intelligent electronic device stores the operating parameters in the programmable In the configuration RAM related to energy scanning and stepper motor homing of the device, the control curve is generated by the programmable device, and the control curve is stored in the control curve configuration RAM of the programmable device;

When starting spectrum acquisition, the current angle of the twin-crystal monochromator is detected by the shaft angle encoder and displayed through the display and transmitted to the computer, and the programmable device reads the control curve configuration RAM. Control the curve, and send control pulses to the stepper motor driver to control the rotation of the stepper motor, so as to realize monochromatic X-ray scanning;

And while performing the stepping motor control step, the programmable device constantly checks the current time, the static control segment in the stepping motor control curve pre-configured in the control curve configuration RAM in the current time, the constant speed after deceleration When the difference between the start times of the control segment or the accelerated constant speed control segment reaches a preset delay, data acquisition is started, so that the signals output by the multi-channel analog-to-digital conversion acquisition circuit corresponding to different energy points and/or The count value of counting the pulse frequency signal input by the voltage/frequency converter is stored in the first-in-first-out data buffer of the programmable device to form initial data;

At the end of the spectrum collection, the angle of the twin-crystal monochromator is detected by the shaft angle encoder again and displayed on the display and transmitted to the computer;

After the spectrum acquisition is finished, the initial data in the first-in-first-out data buffer is sent to the computer, and the computer organizes the initial data, and corrects the The energy calibration in the initial data finally generates a formal fast XAFS experimental data file, and the collected fast XAFS spectrum is displayed on the human-computer interaction interface in the computer installation.

The intelligent electronic equipment provided by the application replaces the stepper motor controller and the scaler in the conventional XAFS experimental system (if the intelligent electronic equipment does not include the device for the integral sampling scheme, the intelligent electronic equipment can also instead of the V/F converter), the control curve and data acquisition of the stepper motor are synchronously carried out by reading the control curve pre-stored in the RAM through the programmable device, realizing fast synchronization, and then overcoming the problem of the inability to quickly synchronize in the prior art The problem caused by the limited acquisition speed.

Moreover, the control curve of the stepping motor is pre-configured in the RAM, and the control area includes a static control section for data acquisition, a constant speed control section after acceleration, or a constant speed control section after deceleration, that is, the stepping motor Run at a fluctuating speed, collect data at low speed or at rest, and run at high speed in the non-data collection interval. Using the wave rotation mode can reduce or eliminate the energy shift ΔE during fast data acquisition, and can obtain the best solution in the contradiction between the scanning speed and ΔE.

In the following embodiments, it will be further described in detail how to solve various problems mentioned in the background technology by using the embodiments of the present application.

The above and other objects, features and advantages of the present application will be more apparent through the following description of preferred embodiments with reference to the accompanying drawings.

Description of drawings

Fig. 1 schematically shows a structural block diagram of a conventional XAFS experimental system;

Fig. 2 schematically shows a structural block diagram of the QXAFS experimental system of the embodiment of the present application;

Fig. 3 schematically shows the structural block diagram of the intelligent electronic device dedicated to the QXAFS experiment in the embodiment of the present application;

Fig. 4 shows the logical block diagram of the analog data acquisition and integral form data acquisition of the intelligent electronic device in the embodiment of the present application;

Fig. 5 schematically shows the firmware (firmware) block diagram of the programmable device in the embodiment of the present application;

Fig. 6 schematically shows a kind of control curve pre-configured in RAM;

Fig. 7 schematically shows another control curve pre-configured in RAM;

Fig. 8 schematically shows another control curve pre-configured in RAM;

Fig. 9 schematically shows a setting method of a preset delay in a control curve;

Fig. 10 schematically shows a schematic diagram of a segmented configuration in RAM;

Fig. 11 schematically shows a schematic diagram of the configuration of the control curve in the RAM;

Fig. 12 schematically shows another structural block diagram of the QXAFS experimental system in the embodiment of the present application;

FIG. 13 schematically shows a schematic structural diagram of another intelligent electronic device according to an embodiment of the present application;

Fig. 14 schematically shows the K-edge EXAFS spectrum of Cu (copper) in K-space acquired by the system shown in Fig. Comparison effect between K-edge EXAFS spectra of Cu.

Detailed ways

Fig. 2 schematically shows the structural block diagram of the QXAFS experimental system of the embodiment of the present application. Synchrotron radiation X-rays are incident on the twin-crystal monochromator 101, and monochromatic monochromatic X-rays through the twin-crystal monochromator 101 enter the ionization chamber detector 103 located in front of the sample, the sample, and the ionization chamber detector located behind the sample 103 (can also have a third ionization chamber X-ray detector to detect the standard sample at the same time).

The current angle of the twin crystal monochromator 101 can be detected by the shaft angle encoder 109 and displayed by the display 110 and transmitted to the computer 108 .

The roll angle and pitch angle of the twin-crystal monochromator 101 are driven by a linear motor driver 112, which is connected with a computer 108 to realize manual/automatic control.

The weak current signal output by the ionization chamber detector is fed into at least two current amplifiers 105, and the working state of the current amplifiers can be set by the computer 108 through the GPIB bus.

For example, the smart electronic device 200 is connected to the computer 108 through a USB bus, and performs command and data transmission with the computer 108. The smart terminal electronic device 200 is connected to the stepper motor driver 113, and sends out control pulses, so that the stepper motor is driven according to a preset program. The twin-crystal monochromator 101 rotates at a Bragg angle, thereby realizing monochromatic light energy scanning. The intelligent electronic device 200 is connected to the current amplifier 105, and under the control of the intelligent electronic device, it coordinates the Bragg angle rotation of the twin crystal monochromator 101 and the reading of the output signal of the current amplifier 105, thereby completing the data collection of the sample .

After data collection, the spectrum data is transmitted from the intelligent electronic device 200 to the computer 108 .

Comparing Fig. 2 and Fig. 1, it can be seen that the difference between the QXAFS experimental system of the embodiment of the present application and the conventional XAFS experimental system is that the stepper motor controller 114 in the conventional XAFS experimental system is replaced by an intelligent electronic device 200 and scaler 107 .

FIG. 3 schematically shows a structural block diagram of an intelligent electronic device 200 dedicated to QXAFS experiments in the embodiment of the present application.

The intelligent electronic device 200 includes: a multi-channel analog-to-digital conversion (ADC) acquisition circuit 201 , a multi-channel isolation circuit 202 , a programmable device 203 , a first isolation circuit 204 and a communication interface circuit 205 .

The multi-channel ADC acquisition circuit 201 is used to convert the analog voltage signals from at least two current amplifiers into digital signals. At least two current amplifiers (for example, current amplifier 105 in FIG. 1 ) are used to amplify and convert the current signal proportional to the intensity of X-rays generated by the X-ray detectors before and after the sample in the fast XAFS experiment and convert it into an analog voltage signal .

The multi-channel isolation circuit 202 realizes electrical isolation between the pulse frequency signal from the V/F converter 106 and the programmable device 203 . The V/F converter 106 is used to convert the analog voltage signals of the at least two current amplifiers into pulse frequency signals.

The programmable device 203 may have multiple random access memories (Random Access Memory, RAM) and FIFO data buffers. The programmable device 203 is connected with the multi-channel ADC acquisition circuit 201 and the multi-channel isolation circuit 202, and is used to receive the signal output by the multi-channel ADC acquisition circuit 201, count the pulse frequency signal input by the V/F converter 106, and multiple The signal output by the channel ADC acquisition circuit 201 and the counted value of the pulse frequency signal input by the V/F converter 106 are stored in the FIFO data buffer of the programmable device 203 .

Fig. 4 shows a logic block diagram of analog data acquisition and integral form data acquisition of the intelligent electronic device in the embodiment of the present application. The multi-channel ADC acquisition circuit 201 converts the analog voltage signal of the current amplifier 105 into a digital signal, and the programmable device 203 stores the signal input by the multi-channel ADC acquisition circuit 201 into the FIFO data buffer, which is equivalent to data acquisition in the form of ADC. The programmable device 203 uses its own counting module to count the pulse frequency signal input by the V/F converter 106, and stores the count value in the FIFO data buffer, which is equivalent to replacing the function of the scaler in the conventional XAFS system, And it realizes data collection in integral form. These two data acquisition paths are parallel and do not interfere with each other.

Fig. 5 schematically shows a firmware block diagram of the programmable device in the embodiment of the present application. For example, the programmable device is a field-programmable gate array (FPGA), and the logic of the FPGA can be mainly composed of 3 configuration RAMs, several registers (not shown in the figure), 4 logic function modules, and 6 FIFO data buffers, etc. constitute. All signals marked in italics in the figure can be set by registers; all signals marked in bold can be read by registers. Each logical function module, RAM, and FIFO can communicate through the ECS interface.

The energy scanning process and homing process are completely defined by 3 configuration RAMs.

(1) Control curve configuration RAM: The control curve of the stepping motor includes acceleration curve and deceleration curve, etc. The acceleration curve and deceleration curve can be regarded as two opposite processes. Incrementally, when decelerating, the pulse frequency decreases. Therefore, the acceleration and deceleration curves use the same RAM configuration.

(2) Energy scanning configuration RAM: This RAM defines the running process of the energy scanning control module.

(3) Operation configuration RAM of homing control module: This RAM defines the running process of stepper motor homing.

Registers can be divided into two categories: control registers and status registers, which are used for control and monitoring of intelligent electronic devices, respectively. For example, through the stepper motor control register, an energy scan operation request can be issued.

Four logical function modules realize the control of the stepper motor and the collection of data.

(1) Energy scanning control module

The energy scanning control module can access the energy scanning configuration RAM and the control curve configuration RAM. According to the configuration of the two RAMs, the acceleration and deceleration control of the stepping motor is completed, and a data acquisition request is sent at a low speed or at a standstill to complete the energy scanning process. .

The energy scan control module can be started by writing the control register.

(2) Homing control module

The homing control module can access the operating configuration RAM and the control curve configuration RAM of the homing control module. According to the configuration of the two RAMs, the acceleration and deceleration control of the stepping motor is completed, so that the stepping motor returns to the initial position.

The homing control module can be enabled by writing to the control register.

(3) Stepper motor pulse modulation module

The functions of the stepping motor pulse modulation module include: stretching the pulse signal, controlling the direction signal of the stepping motor, counting the pulse signal of the stepping motor, and detecting whether the pulse count of the stepping motor exceeds the limit, etc.

When the stepper motor pulse modulation module detects an overrun error in the pulse count of the stepper motor, it will stop the operation of the stepper motor and play a protective role, that is, if an overrun error is detected, the energy scanning control module or homing control If the module is running, the running process will be stopped immediately.

(4) Data acquisition module

The data acquisition module receives the data acquisition request sent by the energy scanning control module, and can perform data acquisition according to the data acquisition delay and the data acquisition width. After the data acquisition is completed, the acquisition results are stored in the FIFO data buffer for caching data, and are read by the computer. The data acquisition module has a counting module, which can count the pulse frequency signal sent by the V/F converter.

Each of the above four modules has a basic error detection function, and all error information can be queried through registers.

6 FIFO data buffers are used to buffer the results of data acquisition, corresponding to 3 analog voltage acquisition channels and 3 V/F pulse counting channels.

The control curve of the stepper motor is pre-configured in the control curve configuration RAM of the programmable device. The control curve defines the relationship between the different control segments of the stepper motor and the control pulse frequency of the stepper motor when data acquisition is performed at different energy points. These different control segments include a static control segment that allows data collection, a constant speed control segment after deceleration or a constant speed control segment after acceleration, and an acceleration control segment that does not perform data collection.

Fig. 6 schematically shows a control curve pre-configured in RAM. In the control curve, the abscissa t represents the running time of the stepping motor, and the ordinate fs represents the control pulse frequency of the stepping motor. The speed of the stepping motor is related to the control pulse frequency. When the stepping motor accelerates, the control pulse frequency increases; when the stepping motor decelerates, the control pulse frequency decreases.

Different control sections corresponding to a single energy point (that is, a single-energy energy point obtained through a twin-crystal monochromator, such as the first energy point) include a decelerated constant-velocity control section that allows data collection and an acceleration control section that does not perform data collection .

The acceleration control section without data acquisition is essentially a high-speed control section, in which the stepper motor is accelerated to make the stepper motor rotate to the required angle, and then obtain the required single-energy X-ray.

After the acceleration control segment, there may be an accelerated constant speed control segment and a deceleration control segment. After the deceleration control section, enter the deceleration constant speed control section. The decelerated constant-velocity control section is a low-speed control section, and data acquisition in the control section can reduce the energy transfer of single-energy X-rays, thereby improving the quality of spectrum collection.

It can be seen that by controlling the stepper motor through the control curve shown in Figure 6, the stepper motor can be cycled to perform acceleration operation, uniform speed operation after acceleration (high speed operation), deceleration operation, and uniform speed operation after deceleration (low speed operation), realizing The "fluctuating" operation control of the stepping motor is realized.

One of the key points in the solution proposed by this application for the problems existing in the prior art is to let the stepping motor run in a "fluctuating" manner, that is, the stepping motor is allowed to rotate rapidly when the data is not being collected, while the data is being collected. The acquisition phase turns the stepper motor at a low speed. In this way, on the one hand, the stepping motor can be quickly rotated to the required position to achieve the purpose of fast speed; on the other hand, the stepping motor can be run at a low speed during data collection, reducing the energy movement of single-energy X-rays and improving The signal-to-noise ratio of the system ensures the quality of the spectrum.

Fig. 7 schematically shows another control curve pre-configured in RAM. In the control curve, the abscissa t represents the running time of the stepping motor, and the ordinate fs represents the control pulse frequency of the stepping motor.

In Fig. 7, different control segments corresponding to a single energy point include a static control segment that allows data collection and an acceleration control segment that does not perform data collection.

The acceleration control section without data acquisition is essentially a high-speed control section, in which the stepper motor is accelerated to make the stepper motor rotate to the required angle, and then obtain the required single-energy X-ray.

After the acceleration control segment, there may be an accelerated constant speed control segment and a deceleration control segment. Enter the stationary control segment after the deceleration control segment. The data acquisition in the static control section can reduce the energy shift of the single-energy X-ray, thereby improving the quality of the spectrum.

It can be seen that by controlling the stepper motor through the control curve shown in Figure 7, the stepper motor can be cycled to perform acceleration operation, uniform speed operation after acceleration (high-speed operation), deceleration operation, and stand still, realizing the "wave type" of the stepper motor. "Operational control.

In the control curves shown in Fig. 6 and Fig. 7, the process of fast start-stop control is similar to that of the traditional XAFS experimental system, but because data collection is allowed in the low-speed control section or static control section, the fast start-stop of the stepper motor is The process can be highly synchronized with the data collection process. Therefore, compared with the traditional XAFS experimental system, the embodiment of the present application can complete data collection in less time under the premise of ensuring the quality of spectrum collection.

Fig. 8 schematically shows another control curve pre-configured in RAM. In the control curve, the abscissa t represents the running time of the stepping motor, and the ordinate fs represents the control pulse frequency of the stepping motor.

Different control segments corresponding to a single energy point include a constant speed control segment after acceleration that allows data collection and an acceleration control segment that does not perform data collection.

In the curve shown in Figure 8, the data acquisition is completed during the high-speed operation of the stepper motor. This control curve is used to control the stepper motor. Since the stepper motor runs at high speed during the data acquisition process, the energy shift of the single-energy X-ray is slightly larger. However, since the data acquisition is allowed in the uniform speed control section after acceleration, the The high-speed synchronization of stepper motor control and data acquisition is achieved, so it still has a fast advantage compared with the conventional XAFS experimental system.

In the control curves shown in Figures 6 to 8, the effective data collection interval corresponding to each energy point can be set, that is, after the start of the static control section, the decelerated constant speed control section, or the accelerated constant speed control section, etc. Data acquisition begins after a preset delay. For example, FIG. 9 schematically shows a setting manner of a preset delay in a control curve. In FIG. 9 , data collection starts after a preset delay Td after the start of the decelerated constant-speed control section (ie, the low-speed section). The duration of the valid data collection interval is Ts.

In the embodiment of this application, the control of the stepper motor and data acquisition adopts segment control. A spectrum acquisition process includes multiple control segments. The control section can have various types, for example, as shown in the control curves in Figure 6 to Figure 8, it can include a single-step control section, an acceleration control section, a constant speed control section, a deceleration control section, a static control section, etc., which are used to control The stepper motor moves one step, the stepper motor accelerates, the stepper motor runs at a constant speed, the stepper motor decelerates, the stepper motor stands still, etc. Multiple control segments included in a spectrum acquisition process can be stored in the control curve configuration RAM of the programmable device or can be directly accessed by the programmable device. FIG. 10 schematically shows a schematic diagram of a segmented configuration in RAM. The control curve configuration RAM is configured with control segment 1, control segment 2, ... control segment N, and each control segment can be configured with the duration Ts of the effective data collection interval and the preset delay Td for starting data collection.

The acceleration and deceleration process of the stepper motor can actually be completed by sending out the stepper motor control pulse signal according to a series of predetermined time intervals. This series of time intervals can be stored in a control curve configuration RAM built into the programmable device or in a RAM that can be directly accessed by the programmable device. FIG. 11 schematically shows the configuration diagram of the control curve in the RAM. The pulse period corresponding to each pulse frequency is configured in the RAM. The reciprocal of this series of time intervals is the frequency of a series of control pulse signals to be generated. When accelerating, the frequency of this series of pulses becomes larger, and when decelerating, the frequency of the pulses becomes smaller.

The time interval of a series of pulses in the acceleration and deceleration process is calculated in advance by a computer or a programmable device, and written into the control curve configuration RAM. Using the control curve to configure the time interval stored in RAM can accelerate the stepping motor from rest to the highest operating speed of the stepping motor, and can also decelerate the stepping motor from the highest operating speed to the static state. Of course, an acceleration or deceleration process from any speed to another speed can also be realized.

The acceleration control section can be all or part of the acceleration curve stored in the control curve configuration RAM, and can be specifically determined by the start speed and end speed specified by the acceleration control section. The start speed and end speed determine the start speed and end speed of the acceleration process.

The deceleration control section is similar to the acceleration control section, but it is used in reverse to realize a deceleration process.

The acceleration and deceleration curves can be calculated by the computer according to the torque, speed and other parameters of the stepping motor as well as the structure and load of the transmission device, and written into the RAM of the programmable device.

In order to synchronize the operation of the stepper motor with data acquisition, data acquisition can be started in the acceleration control section, constant speed control section, deceleration control section and static control section of the stepper motor's operating state. Of course, these control sections can also prohibit data collection, which can be determined by the definition of the control section. Preferably, in order to avoid large single-energy X-ray energy shifts during data collection, the data collection can be started in the constant speed control section and the static control section after deceleration. In the acceleration control segment, data acquisition is prohibited.

For the control segment with the data acquisition function turned on, a delay time Td can be defined between the execution start time of the control segment and the start time of data acquisition, as shown in FIG. 9 .

The intelligent electronic device shown in FIG. 3 includes a multi-channel ADC acquisition circuit 201 and can count pulse frequency signals through a programmable device 203, so that two data sampling modes of ADC data sampling and integral sampling can be performed. Certainly, the device may also have one of the two sampling modes of ADC sampling and integral sampling. Fig. 12 schematically shows another structural block diagram of the QXAFS experimental system in the embodiment of the present application. Compared with the structure shown in Fig. 2, this structure saves the V/F converter, which is equivalent to that the intelligent electronic device 200 replaces the stepper motor controller, scaler and V/F converter in the conventional XAFS system device. Accordingly, the multi-channel isolation circuit may not be included in the intelligent electronic device 200 . The structure shown in Figure 12 can only realize the ADC sampling mode.

If the intelligent electronic device 200 counts the pulse frequency signal without including the multi-channel ADC acquisition circuit 201, the V/F converter cannot be omitted in the system shown in FIG. Stepper motor controller and scaler in the system.

The working process of the QXAFS experimental system of the present application will be described below in conjunction with FIG. 2 to FIG. 12 .

Before starting the QXAFS experiment, the relevant general control program is installed in the computer (for example, the general control program can be implemented through Labview), and the user inputs all the operating parameters of the spectrum acquisition through the human-computer interaction interface of the general control program, and after formatting, download transmitted to intelligent electronic devices. The intelligent electronic device stores the operating parameters in the configuration RAM (for example, the energy scanning configuration RAM and the homing operation RAM in Fig. 5 ) related to the energy scanning and the homing of the stepping motor that the programmable device carries, and is controlled by The programmable device generates a control curve, and the control curve is stored in the control curve configuration RAM of the programmable device.

A pre-scan can be performed before the QXAFS experiment, allowing users to observe the size of the white noise in the K-space, and determine the duration of data acquisition by observing the noise in the K-space and combining factors such as light intensity, sample state, and statistical errors allowed by the analysis data. , that is, the size of Ts in FIG. 9 , and input the determined size of Ts to the intelligent electronic device. Based on the magnitude of Ts input by the user, the intelligent electronic device can form a sampling plan, that is, multiple control curves of the stepping motor.

At the beginning of spectrum acquisition, the current angle of the double crystal monochromator is detected by the shaft angle encoder and displayed on the display and transmitted to the computer, and the programmable device reads the control curve and configures the control curve in the RAM, and sends it to the stepping motor The driver sends out control pulses to control the rotation of the stepper motor, so as to realize monochrome X-ray scanning.

And while the stepper motor control step is being performed, the programmable device constantly checks the current time, and the static control segment, the constant speed control segment after deceleration or the acceleration in the stepper motor control curve pre-configured in the current time and control curve configuration RAM When the difference between the start times of the subsequent constant speed control segments reaches a preset delay, data acquisition is started, so that the signals output by the multi-channel analog-to-digital conversion acquisition circuit corresponding to different energy points and/or the voltage/frequency converter The count value counted by the input pulse frequency signal is stored in the first-in-first-out data buffer of the programmable device to form the initial data.

At the end of the spectrum collection, the angle of the double crystal monochromator is detected by the shaft angle encoder again, displayed on the display and transmitted to the computer.

After the spectrum acquisition is finished, the initial data in the FIFO data buffer is sent to the computer, and the computer arranges the initial data, and corrects the energy calibration in the initial data according to the value of the shaft angle encoder obtained at the beginning and end of the spectrum acquisition , and finally generate a formal fast XAFS experimental data file, and display the collected fast XAFS spectrum on the human-computer interaction interface installed in the computer.

In particular, it should be noted that in the embodiments of the present application, the stepping motor control step and the data collection step are performed simultaneously, and the rapid synchronization between these two steps can be realized through intelligent electronic devices based on programmable devices.

In the embodiment of the present application, the number of ADC channels included in the multi-channel ADC acquisition circuit may be no less than 2 channels, and the number of acquisition bits for analog-to-digital conversion may be no less than 10 bits. The multi-channel isolation circuit may be an optical isolation circuit or a magnetic isolation circuit. FIG. 13 schematically shows a schematic structural diagram of another intelligent electronic device according to an embodiment of the present application. In this device, the multi-channel ADC acquisition circuit 201 includes three ADC acquisition channels 201a, and the multi-channel optical isolation circuit 202 includes a three-channel optical isolation circuit 202a.

In each embodiment of the present application, the communication interface circuit connected to the programmable device may be a USB interface, a network port, a serial port, a wireless interface, and the like. The multi-channel isolation circuit and the first isolation circuit may be optical isolation circuits or magnetic isolation circuits. The programmable device may be one of a field programmable gate array (FPGA), a microprocessor (MPU), a microcontroller (MCU), and a digital signal processor (DSP).

The following explains why the problems (1) to (7) in the prior art mentioned above can be solved by adopting the intelligent electronic device, the QXAFS experimental system and the corresponding data acquisition and stepping motor control method provided by the embodiment of the present application .

1. In the intelligent electronic equipment provided by this application, the counting of the pulse frequency signal is realized by a programmable device instead of a discrete scaler, and the control of the stepping motor is realized by a programmable device instead of a discrete scaler. The implementation of the stepper motor controller, that is to say, the intelligent electronic device provided by this application replaces the stepper motor controller and scaler in the conventional XAFS experimental system. In this way, the control curve of the stepper motor and the data acquisition are performed synchronously by reading the control curve pre-stored in the RAM through the programmable device, realizing fast synchronization, thereby overcoming the acquisition speed caused by the lack of fast synchronization in the prior art Restricted problem (1).

2. In the embodiment of the present application, the control curve of the stepper motor is pre-configured in the RAM, and the control curve includes a static control section for data collection or a constant speed control section after deceleration, that is to say, a stepping motor The motor runs at a fluctuating speed, and collects data at low speed or at rest, and runs at high speed in the non-data collection interval. Using this wave rotation mode can reduce or eliminate the energy movement ΔE during fast data acquisition, and can obtain the best solution in the contradiction between the scanning speed and ΔE, thus solving the problem of factors affecting the quality of QXAFS data (2) .

3. Through the pre-scanning program of the host computer and the setting of related analysis steps, the user can observe the size of the white noise in the K-space through the pre-scanning at the beginning of the spectrum collection. By observing the noise size of the K-space and combining the light intensity and the state of the sample And factors such as the statistical error allowed by the analysis data determine the duration of data acquisition, and quickly determine the minimum sampling time t of each energy point under the premise of ensuring data quality (that is, the duration Ts of data acquisition in Figure 7), Furthermore, the spectrum acquisition speed is optimized, and the problems affecting the quality of QXAFS data are solved (3).

4. According to an embodiment of the present application, in the intelligent electronic device, the data acquisition can be realized with the ADC sampling scheme through the multi-channel ADC acquisition circuit, and the data acquisition can be realized through the integration scheme by counting the pulse frequency signal through the programmable device, That is to say, the intelligent electronic device provides two data acquisition methods, thus, it provides flexibility for further comparing the advantages and disadvantages of different data acquisition circuit schemes, and adopting different improved detector system hardware under different experimental conditions. Issues (4) and (5) of factors affecting QXAFS data quality are addressed.

5. The intelligent electronic device of this application is based on programmable devices to realize the control and data acquisition of stepping motors, which has extremely high execution and timing accuracy, ensures the accurate phase of stepping and sampling in scanning, and solves the problem of affecting QXAFS data. Question of quality factor (6).

6. The intelligent terminal electronic equipment provided by this application integrates sampling and stepping drive, overcomes the time overhead of signal transmission, conversion, and host operation between multiple devices in the conventional XAFS system, and maximizes the overall spectrum acquisition speed of the system. Addressed issues with factors affecting QXAFS data quality (7).

Fig. 14 schematically shows the K-edge EXAFS spectrum of Cu (copper) in K-space acquired by the system shown in Fig. The comparison effect between the K-edge extended XAFS (extend X-ray Absorption FineStructure, EXAFS) spectrum of Cu, the sample is a standard copper foil of 5 microns. The black solid line in FIG. 14 represents the standard Cu K-edge EXAFS spectrum, and the gray solid line represents the Cu K-edge EXAFS spectrum obtained by the system shown in FIG. 2 . From the comparison of these two curves, it can be seen that the two spectra match well within 12K in K space, and the spectrum acquisition time is only 15 seconds, which shows that the application of the QXAFS system of the present application can have higher spectrum acquisition quality and faster The spectrum acquisition speed.

It should be noted that the QXAFS experimental system provided by this application is not limited to the structure of the shaft angle encoder, display, and linear motor driver in Figure 2, and those skilled in the art can design other structures. The focus of this application is on intelligent electronics. An electronic device and components associated with the intelligent electronic device.

While the present application has been described with reference to several exemplary embodiments, it is understood that the words which have been used are words of description and illustration, rather than of limitation. Since the present application can be embodied in various forms without departing from the spirit or essence of the invention, it should be understood that the above-described embodiments are not limited to any of the foregoing details, but should be construed broadly within the spirit and scope of the appended claims. , all changes and modifications falling within the scope of the claims or their equivalents shall be covered by the appended claims.

Claims (10)

1. An intelligent electronic device dedicated to fast XAFS experiments, comprising: at least one of a multi-channel analog-to-digital conversion acquisition circuit and a multi-channel isolation circuit, a programmable device, a first isolation circuit and a communication interface circuit: The multi-channel analog-to-digital conversion acquisition circuit is used to convert the analog voltage signals from at least two current amplifiers into digital signals, and the at least two current amplifiers are used to connect the X-ray detectors before and after the sample in the fast XAFS experiment The current signal proportional to the X-ray intensity generated is amplified and converted into an analog voltage signal; The multi-channel isolation circuit is used to realize the electrical isolation between the pulse frequency signal from the voltage/frequency converter and the programmable device, and the voltage/frequency converter is used to convert the analog voltage signal of the at least two current amplifiers into a pulse frequency signal; The programmable device is connected to the multi-channel analog-to-digital conversion acquisition circuit and the multi-channel isolation circuit, and is used to receive the signal output by the multi-channel analog-to-digital conversion acquisition circuit, and the pulse frequency input to the voltage/frequency converter The signal is counted, and the signal output by the multi-channel analog-to-digital conversion acquisition circuit and the count value for counting the pulse frequency signal input by the voltage/frequency converter are stored in the first-in-first-out In the data buffer for computer reading; The control curve of the stepper motor is pre-configured in the control curve configuration RAM carried by the programmable device, and the control curve is defined as the different control segments of the stepper motor and the stepper motor when data acquisition is performed at different energy points. Controlling the relationship between pulse frequencies, the different control sections include a static control section that allows data collection, a constant speed control section after deceleration or a constant speed control section after acceleration, and an acceleration control section that does not perform data collection; The programmable device is used to send control pulses to the stepper motor driver to control the rotation of the stepper motor by reading the control curve of the stepper motor, and in the static control section, the constant speed control section after deceleration and the acceleration Data acquisition starts after a preset delay after the start of the last constant speed control segment; The first isolation circuit is connected to the programmable device for realizing electrical isolation between the programmable device and the stepper motor driver; The communication interface circuit is connected with the programmable device for realizing the communication between the programmable device and the computer. 2. The intelligent electronic device of claim 1, wherein the programmable device is one of a field programmable gate array, a microprocessor, a microcontroller, and a digital signal processor. 3. The intelligent electronic device according to claim 1, wherein the different control sections corresponding to a single energy point include a static control section that allows data collection and an acceleration control section that does not perform data collection. 4. The intelligent electronic device according to claim 1, wherein the different control sections corresponding to a single energy point include a decelerated constant speed control section that allows data collection and an acceleration control section that does not perform data collection. 5. The intelligent electronic device according to claim 1, wherein the number of analog-to-digital conversion channels included in the multi-channel analog-to-digital conversion acquisition circuit is not less than 2 channels, and the number of analog-to-digital conversion acquisition bits is not less than 10 . 6. The intelligent electronic device according to claim 1, wherein the multi-channel isolation circuit is an optical isolation circuit or a magnetic isolation circuit. 7. A fast XAFS experimental system, comprising: Synchrotron X-ray sources; A twin-crystal monochromator monochromatizes the X-rays output by the synchrotron radiation X-ray source to obtain the single-energy X-rays required for fast XAFS experiments; A shaft angle encoder for detecting the angle of the twin crystal monochromator; A stepper motor is used to control the rotation of the twin crystal monochromator; a stepper motor driver, electrically connected to the stepper motor, for driving the stepper motor to rotate; At least two current amplifiers are used to amplify and convert the current signal proportional to the X-ray intensity generated by the X-ray detector before and after the sample into an analog voltage signal in the fast XAFS experiment; A voltage/frequency converter, connected to the at least two current amplifiers, for converting the analog voltage signals of the at least two current amplifiers into pulse frequency signals; a computer, configured to receive the angle of the dual crystal monochromator detected by the shaft encoder; and Intelligent electronic equipment, including: at least one of a multi-channel analog-to-digital conversion acquisition circuit and a multi-channel isolation circuit, a programmable device, a first isolation circuit, and a communication interface circuit: The multi-channel analog-to-digital conversion acquisition circuit is electrically connected to the at least two current amplifiers, and is used to convert the analog voltage signals from the at least two current amplifiers into digital signals; A multi-channel isolation circuit is configured between the voltage/frequency converter and the programmable device, and is used to realize electrical isolation between the pulse frequency signal from the voltage/frequency converter and the programmable device; The programmable device is connected to the multi-channel analog-to-digital conversion acquisition circuit and the multi-channel isolation circuit, and is used to receive the signal output by the multi-channel analog-to-digital conversion acquisition circuit, and the pulse frequency input to the voltage/frequency converter The signal is counted, and the signal output by the multi-channel analog-to-digital conversion acquisition circuit and the count value for counting the pulse frequency signal input by the voltage/frequency converter are stored in the first-in-first-out in a data cache for the computer to read; The control curve of the stepper motor is pre-configured in the control curve configuration RAM carried by the programmable device, and the control curve is defined as the different control segments of the stepper motor and the stepper motor when data acquisition is performed at different energy points. Controlling the relationship between pulse frequencies, the different control sections include a static control section that allows data collection, a constant speed control section after deceleration or a constant speed control section after acceleration, and an acceleration control section that does not perform data collection; The programmable device is used to send control pulses to the stepper motor driver to control the rotation of the stepper motor by reading the control curve of the stepper motor, and in the static control section and the constant speed control section after deceleration And start data acquisition after a preset delay after the accelerated constant speed control segment starts; The first isolation circuit is connected to the programmable device for realizing electrical isolation between the programmable device and the stepper motor driver; The communication interface circuit is connected with the programmable device for realizing the communication between the programmable device and the computer. 8. The system of claim 7, wherein the programmable device is one of a field programmable gate array, a microprocessor, a microcontroller, and a digital signal processor. 9. a kind of data collection and the stepping motor control method in the fast XAFS experiment implemented by the fast XAFS experiment system described in claim 7 or 8, comprise the steps: Receive all the operating parameters required for the fast XAFS experiment through the human-computer interaction interface installed in the computer, format the operating parameters and transmit them to the intelligent electronic device, and the intelligent electronic device stores the operating parameters in the programmable In the configuration RAM related to energy scanning and stepper motor homing of the device, the control curve is generated by the programmable device, and the control curve is stored in the control curve configuration RAM of the programmable device; When starting spectrum acquisition, the current angle of the twin-crystal monochromator is detected by the shaft angle encoder and displayed through the display and transmitted to the computer, and the programmable device reads the control curve configuration RAM. Control the curve, and send control pulses to the stepper motor driver to control the rotation of the stepper motor, so as to realize monochromatic X-ray scanning; And while performing the stepping motor control step, the programmable device constantly checks the current time, the static control segment in the stepping motor control curve pre-configured in the control curve configuration RAM in the current time, the constant speed after deceleration When the difference between the start times of the control segment or the accelerated constant speed control segment reaches a preset delay, data acquisition is started, so that the signals output by the multi-channel analog-to-digital conversion acquisition circuit corresponding to different energy points and/or The count value of counting the pulse frequency signal input by the voltage/frequency converter is stored in the first-in-first-out data buffer of the programmable device to form initial data; At the end of the spectrum collection, the angle of the twin-crystal monochromator is detected by the shaft angle encoder again and displayed on the display and transmitted to the computer; After the spectrum acquisition is finished, the initial data in the first-in-first-out data buffer is sent to the computer, and the computer organizes the initial data, and corrects the The energy calibration in the initial data finally generates a formal fast XAFS experiment data file, and the collected fast XAFS spectrum is displayed on the human-computer interaction interface installed in the computer. 10. The method according to claim 9, wherein the different control segments corresponding to a single energy point include a static control segment that allows data collection and an acceleration control segment that does not perform data collection; or Different control segments corresponding to a single energy point include a deceleration constant speed control segment that allows data collection and an acceleration control segment that does not perform data collection.