A control method for complex spatially distributed electrical capacitance tomography system

Abstract

The present invention discloses a complex space distributed capacitance tomography system and control method, the imaging system includes an imaging computer, a timing controller, and multiple capacitance tomography data acquisition systems; the timing controller simultaneously sends a timing control signal to the capacitance tomography data acquisition system; the timing controller provides the capacitance tomography data acquisition system with an electrode switching control signal including independent K pulses to control electrode switching; the capacitance tomography data acquisition system immediately reads the synchronization frame number signal after obtaining the frame start signal of the timing controller, so that the capacitance data of the capacitance tomography data acquisition system is synchronized; the imaging computer reconstructs the capacitance data uploaded by the capacitance tomography data acquisition system into ECT images respectively, and splices all the ECT sub-images to form a complete ECT image in the frame period. The present invention can realize full-cycle, three-dimensional, and transient imaging of complex spaces or complex structures.

Description

Technical Field

[0001] The invention relates to the technical field of circulating fluidized bed imaging, and in particular to a control method for a complex spatially distributed capacitance tomography system. Background Art

[0002] With the advancement of science and technology, the field of imaging detection technology has developed rapidly. Imaging detection technology has the advantages of high detection efficiency, visualization, non-destructive detection, and high precision. Various imaging detection technologies represented by X-ray imaging technology and infrared thermal imaging technology are widely used in military, industrial testing, medical and other fields, greatly improving people's detection capabilities, improving people's living standards, and promoting the development of science and technology.

[0003] The circulating fluidized bed is a typical complex space. It is a circulation loop formed by connecting and combining multiple units. The structure is complex, and the units are coupled and influenced by each other. The gas-solid flow between the units in the system has an interactive relationship. The gas-solid flow in each unit in the loop will affect the pressure balance and material balance of the system. The particles in the circulating fluidized bed are mostly opaque media and distributed in three dimensions. The light beam cannot effectively penetrate the bed material, so the optical method can only be used for two-dimensional measurement or point measurement. Nuclear magnetic resonance, PEPT, and ray methods have satisfactory measurement accuracy, but the structure is complex and the cost is high. Most of them have radiation, and sensors cannot be customized for complex fluidized bed structures. At present, most fluidized bed measurement methods can only measure gas-solid flow parameters at local positions (units) or even single points, and most of them use two-dimensional measurement methods in three-dimensional fluidized beds. Most measurements are average signals over a period of time. Therefore, the existing fluidized bed measurement methods cannot take into account the full cycle, three-dimensional, and transient measurements required for the complex structure of the fluidized bed.

[0004] Capacitance tomography can realize non-contact imaging of the internal flow of two-phase flow and measure the flow characteristics of particles in the fluidized bed, such as solid concentration, particle velocity, bubbling, etc. It is an ideal gas-solid fluidized bed measurement technology. The two-dimensional / three-dimensional ECT currently used in fluidized beds also has certain shortcomings. Two-dimensional ECT can only image regular cross sections and provide the average solid concentration distribution within a certain axial length of the local key cross section. Two-dimensional ECT requires that the fluid flow does not change much along the axial direction, that is, the actual three-dimensional flow can be equivalent to two-dimensional flow, and requires that the electric field generated by the excitation signal of the detection circuit is relatively uniform along the axial direction in the imaging area. Usually, the axial driving electrode can be added to increase the uniformity of the electric field in the axial direction, effectively reducing the influence of the edge effect on the two-dimensional ECT. Even if the influence of the edge effect is not considered, the measurement result of the two-dimensional ECT is also the average signal of the concentration within the axial length range of the measuring electrode. Due to the complex structure of the fluidized bed, the structure of the units such as the riser outlet, the return port, and the cyclone separator in the flow direction is irregular and cannot be equivalent to a two-dimensional structure. To achieve imaging of the entire fluidized bed, three-dimensional imaging must be used. Three-dimensional ECT (Electrical Capacitance Volume Tomography, also known as ECVT) can be used to image the interior of any three-dimensional object. Theoretically, it is not limited by the shape of the object being measured and can measure the three-dimensional flow conditions of complete bubbles and irregular positions in the fluidized bed.

[0005] Prior art publication number CN109900751B discloses a portable capacitance tomography measurement device, which adopts modular design, and a complex programmable logic device (CPLD) chip calculates the voltage signal of each electrode of the capacitance array in the capacitance measurement module to realize the shaping and demodulation of the measurement signal, and uploads the on-chip storage data to the host computer through a serial bus communication circuit. However, this application only controls a single capacitance tomography device, and does not disclose how the specific control signal is controlled, and cannot be detected in a complex space. Summary of the invention

[0006] 1. Technical problems to be solved:

[0007] In response to the above technical problems, the present invention provides a complex space distributed capacitance tomography method, in which multiple ECT systems are deployed for complex space or complex structure to realize segmented synchronous three-dimensional imaging, and the images collected by each ECT system are spliced ​​to realize full-cycle, three-dimensional, transient measurement imaging of the complex space or complex structure.

[0008] 2. Technical solution:

[0009] A control method for a complex spatial distributed capacitance tomography system, characterized in that: the distributed capacitance tomography system comprises an imaging computer, a timing controller, and N capacitance tomography data acquisition systems, where N is an integer greater than 1; the imaging computer comprises a data communication system and an image reconstruction system; the timing controller sends a timing control signal to control the N capacitance tomography data acquisition systems, specifically comprising the following steps:

[0010] Step 1: The timing controller sends the N capacitance tomography data acquisition systems ECTDAQ x , x=1,…,N, and simultaneously send a timing control signal; the timing control signal includes a frame start signal, a synchronization frame number, and an electrode switching signal; wherein the frame start signal sent to each capacitance tomography data acquisition system is the same; the synchronization frame number sent to each capacitance tomography data acquisition system is the same; the capacitance data collected by each capacitance tomography data acquisition system within a frame period under the same frame number can reconstruct a complete image;

[0011] The electrode switching control signal is sent to each capacitance tomography data acquisition system in turn, specifically: the nth capacitance tomography data acquisition system ECTDAQ is preset n The first electrode switching control signal is at t n At the moment, the n+1th capacitance tomography data acquisition system ECT n+1 The first electrode switching control signal is at t n+1 Time is issued, where t n+1 With t n is a phase difference of one imaging sub-period T sub ; The data acquisition time of each capacitance tomography data acquisition system occupies one imaging sub-cycle T of the frame cycle sub , the time T required for the distributed electrical capacitance tomography system to collect a complete frame of data fr =T sub *N;

[0012] The electrode switching control signal provided by the timing controller to each capacitance tomography data acquisition system includes K independent pulses to control the electrode switching; the kth electrode switching control signal of any capacitance tomography data acquisition system is preset at t k The k+1th electrode switching is controlled at t k+1 Switching is performed at the moment t k+1 With t k The difference is one electrode switching cycle T sw , and T sw The product of K is less than T sub ;

[0013] Step 2: Each capacitance tomography data acquisition system receives and reads the timing control signal of the timing controller; immediately reads the synchronization frame number signal after obtaining the frame start signal of the timing controller, so that the capacitance data of each capacitance tomography data acquisition system is synchronized; each capacitance tomography data acquisition system controls the K-time electrode switching of the data acquisition system according to the received electrode switching control signal and collects capacitance data, and uploads it to the imaging computer;

[0014] Step 3: The imaging computer reconstructs N ECT sub-images from the capacitance data uploaded by N capacitance tomography data acquisition systems, and splices the N ECT sub-images to form a complete ECT image in the frame period.

[0015] Furthermore, the synchronization frame number is J digital signal lines, where J is greater than or equal to 12; providing J-bit frame number data for each capacitance tomography data acquisition system.

[0016] Furthermore, each capacitance tomography data acquisition system includes a single-chip microcomputer, a capacitance detection circuit, a switch switching circuit, and an array capacitance sensor; the switch switching circuit is respectively connected to the array capacitance sensor and the capacitance detection circuit; the single-chip microcomputer controls the switch switching circuit to switch the electrodes of the array capacitance sensor to realize the capacitance connection between different electrodes so that the capacitance detection circuit can be used for measurement, and the data of the capacitance detection circuit is transmitted unidirectionally to the single-chip microcomputer.

[0017] Furthermore, in step 2, each capacitance tomography data acquisition system generates an image including the following steps:

[0018] S21: Use a 250KHz AC signal to excite the capacitance measurement circuit;

[0019] S22: The single-chip microcomputer of the capacitance tomography data acquisition system controls the switch circuit of the system to switch the electrodes of the array capacitance sensor according to the electrode switching signal received from the timing controller, reads the J-bit synchronization frame number under the trigger of the rising edge of the frame start signal, and enters the data acquisition state. The electrode switching signal realizes the capacitance connection between different electrodes so that the capacitance measurement circuit can be used for capacitance measurement. The single-chip microcomputer collects the data of the capacitance measurement circuit and transmits the data to the imaging computer through the network port.

[0020] Furthermore, when reconstructing and stitching the images in step three, the order of the images sent by the capacitance tomography data acquisition system is identified based on the received synchronization frame number, and the images of different capacitance tomography data acquisition systems with the same frame number are reconstructed and stitched into the same frame image.

[0021] 3. Beneficial effects:

[0022] (1) A control method for a complex spatial distributed capacitance tomography system of the present invention comprises deploying a plurality of ECT devices in a complex space as required, and connecting them with a timing controller to form a complex spatial distributed capacitance tomography system. Each ECT device, as one of the capacitance tomography data acquisition systems, transmits the image of the space in which it is located to an imaging computer; the timing controller sends a control signal to coordinate each ECT device to collect data in different time periods within a frame cycle; after completing the acquisition of a frame of data, each capacitance tomography data acquisition system uploads the collected capacitance data to the imaging computer to realize three-dimensional imaging of N subsystems, and splices them to form a complete three-dimensional full-cycle image, thereby solving the problem that a single ECT device cannot image complex structures due to limited measurement scale.

[0023] (2) In the present invention, the imaging method of the distributed three-dimensional capacitance tomography system performs segmented imaging of the structure or space to be imaged, and synchronously obtains the capacitance data of sensors at different positions. This not only reduces the requirements for the data transmission speed of the ECT subsystem, but also reduces the instability and computational complexity of the imaging algorithm. This makes it possible to perform full-cycle three-dimensional imaging of complex structures or spaces. If a capacitance tomography system is decomposed into N subsystems of comparable size, the sensitive field matrix is ​​also decomposed into N sub-sensitive field matrices, and the condition number of the sensitive field matrix is ​​reduced, which effectively improves the stability of image reconstruction. The total computational complexity of the N subsystems is only 1 / N of that before decomposition.

[0024] (3) In the present invention, a timing controller sends a start signal, a synchronization frame number, and a control signal to the ECT devices of each data acquisition system, thereby coordinating multiple ECT devices to complete the capacitance data acquisition of their respective imaging areas.

[0025] (4) In the present invention, each capacitance tomography data acquisition system obtains the frame number in real time according to the timing control signal provided by the timing controller, and performs K electrode switching according to the electrode switching signal to complete the data acquisition of the ECT device and upload it to the imaging computer.

[0026] (5) In the present invention, the image reconstruction system of the imaging computer uses the synchronous frame number information sent to all ECT devices as a reference when reconstructing and splicing pictures, identifies the image order of each ECT device, ensures that the spliced ​​multiple ECT images are in the same frame, and avoids image misalignment. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a schematic diagram of a distributed three-dimensional electrical capacitance tomography system taking a circulating fluidized bed as an example in a specific embodiment;

[0028] Figure 2 This is a diagram of control signals sent in one frame period in a specific embodiment. DETAILED DESCRIPTION

[0029] The present invention will be described in detail below with reference to the accompanying drawings. Specific embodiment:

[0031] This embodiment takes a circulating fluidized bed as an example to explain this solution.

[0032] To perform full-cycle three-dimensional ECT imaging of complex structures such as circulating fluidized beds, a huge number of sensor electrodes are required. However, the detection channels of the current common ECT measurement system are limited, and a single ECT system cannot meet the requirements of full-cycle three-dimensional imaging of fluidized beds. The distributed three-dimensional ECT architecture of the present invention decomposes the large and complex three-dimensional imaging system into several moderately sized subsystems, realizes segmented synchronous three-dimensional imaging of complex structures and complex spaces, and splices the images of each subsystem into a complete three-dimensional image of the structure or space.

[0033] As attached Figure 1 The middle part is a typical structure of a circulating fluidized bed. Five capacitance tomography systems are deployed around the structure in a complex position according to the imaging needs and are numbered respectively. The boxes deployed around the fluidized bed in the figure represent the array capacitance sensor electrodes of the capacitance tomography system. The timing controller sends the following Figure 2 The control signals shown are sent to each capacitance tomography system; the five ECT subsystems realize the whole-bed full-cycle imaging of the circulating fluidized bed under the coordination of the timing controller, among which ECT1, ECT2 and ECT5 are used for imaging of key positions or irregular structures, while ECT3 and ECT4 are used for imaging of regular straight pipe sections. Since the flow of regular straight pipe sections is relatively stable, the axial length of its electrodes can be greater than the length of the ECT sensor electrodes at key positions. As shown in the attached figure Figure 2 The figure shows the control signals sent by the timing controller of the imaging system in a frame cycle; the timing controller controls the operation timing of all ECT subsystems, including the real-time data frame number, the start signal for the acquisition of capacitance data in each frame, and the electrode switching signal under each excitation state in the frame cycle. After receiving the start signal, each ECT subsystem switches the electrode, sets its own excitation electrode and detection electrode according to the requirements of full-cycle imaging, and collects the capacitance data of the corresponding detection channel after the electrode switching. The imaging computer reconstructs the three-dimensional image of the subsystem based on the collected capacitance data, and splices it to form a complete full-cycle three-dimensional image.

[0034] Although the present invention has been disclosed as above in terms of preferred embodiments, they are not intended to limit the present invention. Anyone skilled in the art can make various changes or modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection defined by the claims of this application.

Claims

1. A control method for a complex spatially distributed electrical capacitance tomography system, characterized in that: The distributed capacitance tomography system includes an imaging computer, a timing controller, and N capacitance tomography data acquisition systems, where N is an integer greater than 1; the imaging computer includes a data communication system and an image reconstruction system; the timing controller sends a timing control signal to control the N capacitance tomography data acquisition systems, specifically including the following steps: Step 1: The timing controller sends the N capacitance tomography data acquisition systems ECTDAQ x , x=1,…,N, and simultaneously send a timing control signal; the timing control signal includes a frame start signal, a synchronization frame number, and an electrode switching signal; wherein the frame start signal sent to each capacitance tomography data acquisition system is the same; the synchronization frame number sent to each capacitance tomography data acquisition system is the same; the capacitance data collected by each capacitance tomography data acquisition system within a frame period under the same frame number can reconstruct a complete image; The electrode switching control signal is sent to each capacitance tomography data acquisition system in turn, specifically: the nth capacitance tomography data acquisition system ECTDAQ is preset n The first electrode switching control signal is at t n At the moment, the n+1th capacitance tomography data acquisition system ECT n+1 The first electrode switching control signal is at t n+1 Time is issued, where t n+1 With t n is a phase difference of one imaging sub-period T sub ; The data acquisition time of each capacitance tomography data acquisition system occupies one imaging sub-cycle T of the frame cycle sub , the time T required for the distributed electrical capacitance tomography system to collect a complete frame of data fr =T sub *N; The electrode switching control signal provided by the timing controller to each capacitance tomography data acquisition system includes K independent pulses to control the electrode switching; the kth electrode switching control signal of any capacitance tomography data acquisition system is preset at t k The k+1th electrode switching is controlled at t k+1 Switching is performed at the moment t k+1 With t k The difference is one electrode switching cycle T sw , and T sw The product of K is less than T sub ; Step 2: Each capacitance tomography data acquisition system receives and reads the timing control signal of the timing controller; immediately reads the synchronization frame number signal after obtaining the frame start signal of the timing controller, so that the capacitance data of each capacitance tomography data acquisition system is synchronized; each capacitance tomography data acquisition system controls the K-time electrode switching of the data acquisition system according to the received electrode switching control signal and collects capacitance data, and uploads it to the imaging computer; Step 3: The imaging computer reconstructs N ECT sub-images from the capacitance data uploaded by N capacitance tomography data acquisition systems, and splices the N ECT sub-images to form a complete ECT image in the frame period.

2. The control method of a complex spatial distributed electrical capacitance tomography system according to claim 1, characterized in that: The synchronization frame number is J digital signal lines, where J is greater than or equal to 12; and J-bit frame number data is provided for each capacitance tomography data acquisition system.

3. The control method of a complex spatial distributed electrical capacitance tomography system according to claim 1 or 2, characterized in that: Each capacitance tomography data acquisition system includes a single-chip microcomputer, a capacitance detection circuit, a switch switching circuit, and an array capacitance sensor; the switch switching circuit is respectively connected to the array capacitance sensor and the capacitance detection circuit; the single-chip microcomputer controls the switch switching circuit to switch the electrodes of the array capacitance sensor to realize the capacitance connection between different electrodes so that the capacitance detection circuit can be used for measurement, and the data of the capacitance detection circuit is transmitted unidirectionally to the single-chip microcomputer.

4. The control method of a complex spatial distributed electrical capacitance tomography system according to claim 3, characterized in that: In step 2, each electrical capacitance tomography data acquisition system generates an image including the following steps: S21: Use a 250KHz AC signal to excite the capacitance measurement circuit; S22: The single-chip microcomputer of the capacitance tomography data acquisition system controls the switch circuit of the system to switch the electrodes of the array capacitance sensor according to the electrode switching signal received from the timing controller, reads the J-bit synchronization frame number under the trigger of the rising edge of the frame start signal, and enters the data acquisition state. The electrode switching signal realizes the capacitance connection between different electrodes so that the capacitance measurement circuit can be used for capacitance measurement. The single-chip microcomputer collects the data of the capacitance measurement circuit and transmits the data to the imaging computer through the network port.

5. The control method of a complex spatial distributed electrical capacitance tomography system according to claim 1, characterized in that: When reconstructing and stitching the images in step 3, the order of the images sent by the capacitance tomography data acquisition system is identified based on the received synchronization frame number, and the images of different capacitance tomography data acquisition systems with the same frame number are reconstructed and stitched into the same frame image.

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