CN114659439A - Novel pulse eddy current thickness measuring device and method - Google Patents
Novel pulse eddy current thickness measuring device and method Download PDFInfo
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- CN114659439A CN114659439A CN202210255326.3A CN202210255326A CN114659439A CN 114659439 A CN114659439 A CN 114659439A CN 202210255326 A CN202210255326 A CN 202210255326A CN 114659439 A CN114659439 A CN 114659439A
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- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B7/00—Measuring arrangements characterised by the use of electric or magnetic techniques
- G01B7/02—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring length, width or thickness
- G01B7/06—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring length, width or thickness for measuring thickness
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Abstract
The invention discloses a novel pulse eddy current thickness measuring device and a novel pulse eddy current thickness measuring method, wherein the novel pulse eddy current thickness measuring device comprises a thickness measuring instrument host and at least one probe; the thickness gauge host comprises a CPU, and a transmitting module and a receiving module which are respectively electrically connected with the CPU; the probe is electrically connected with the thickness gauge host, and comprises a transmitting coil and a receiving coil, wherein the transmitting coil is used for exciting a pulse eddy current signal to the pipeline to be measured, and the receiving coil is used for receiving a feedback signal of the pipeline to be measured. The novel pulse eddy current thickness measuring device is portable and efficient, does not need to polish a metal body or a coupling agent by using a medium-low frequency electromagnetic principle, does not fear high temperature and low temperature, realizes high-precision scanning, efficient positioning and quantitative metal loss, and provides accurate data for completely evaluating potential safety hazards caused by internal local corrosion.
Description
Technical Field
The invention relates to the technical field of pipeline detection, in particular to a novel pulse eddy current thickness measuring device and method.
Background
The conventional ultrasonic thickness measurement technology (generally, piezoelectric ultrasonic) which is used in a large amount at present needs to remove paint on the surface of a steel pipeline during detection, polish a metal body and need a coupling agent to measure the wall thickness. Although the method is high in precision, the detection efficiency is low, the coverage rate is very small, the dotting is mainly carried out through the experience of detection personnel, the method has great contingency, and the defect that the surface is covered by dots exists in the evaluation process.
The method utilizes the pulse eddy current detection technology to carry out scanning type wall thickness detection (forming current wall thickness A scanning, wall thickness continuous extension value B scanning and area C scanning) on the metal pipeline or equipment, and is a novel non-contact nondestructive detection technology developed in recent years. Different from the conventional eddy current detection technology (sine wave excitation is used), the pulse eddy current detection technology adopts square waves with different frequencies as an excitation mode, has stronger excitation energy and good penetrating performance, realizes scanning of the wall thickness of a pressure-bearing pipeline or equipment without shutdown, has the detection efficiency dozens of times of that of the conventional ultrasonic thickness measurement, and has good application prospect.
However, since the material permeability is different, the signal characteristics and the research method of the pulse eddy current are different between the ferromagnetic material and the non-ferromagnetic material. Different from the ferromagnetic material which generally adopts the inflection point time or the late signal attenuation rate in a double logarithmic coordinate system as the characteristic value, the non-ferromagnetic material generally adopts the peak value, the peak value time, the zero crossing point time or the lift-off crossing point of a differential signal as the characteristic value; among these characteristic values, the differential peak value, the peak time, etc. are influenced by the lift-off height, and the lift-off intersection is not influenced by the lift-off height, but the operation is complicated, which is not beneficial to the field application. The difference of signal characteristics and research methods limits the application range of the pulse eddy current detector, and most of the existing pulse eddy current detection systems cannot detect ferromagnetic materials and non-ferromagnetic materials at the same time.
Disclosure of Invention
The present invention is directed to solving at least one of the problems of the prior art. Therefore, the invention provides a novel pulse eddy current thickness measuring device and a novel pulse eddy current thickness measuring method, which can be used for realizing the defect detection function of ferromagnetic materials and non-ferromagnetic materials by using a pulse eddy current detection technology.
In one aspect, a novel pulsed eddy current thickness measuring device according to an embodiment of the present invention includes: the thickness gauge host comprises a CPU, and a transmitting module and a receiving module which are respectively electrically connected with the CPU; the thickness gauge comprises at least one probe, the probe with the calibrator host electricity is connected, the probe includes transmitting coil and receiving coil, transmitting coil is used for arousing pulse eddy current signal to the pipeline that awaits measuring, receiving coil is used for receiving the feedback signal of the pipeline that awaits measuring.
The novel pulse eddy current thickness measuring device provided by the embodiment of the invention has at least the following beneficial effects: CPU sends detection signal to the probe through the emission module, so that the emission coil of the probe excites impulse type attenuation eddy current signal to the pipe to be detected, and then the receiving coil of the probe is utilized to receive attenuation magnetic field signal (namely feedback signal) generated by attenuation eddy current in the pipe wall of the pipe to be detected; then the thickness gauge host receives the feedback signal through the receiving module, and after A/D conversion (analog-digital conversion) is carried out on the feedback signal, the CPU analyzes and processes the received signal through an algorithm, so as to calculate the relative wall thickness value of the pipeline to be measured; the scanning type detection is carried out on the pipeline to be detected through the probe, and the change condition of the wall thickness value of each detection point of the pipeline to be detected can be observed, so that the defect position of the pipeline to be detected can be effectively detected and positioned. The novel pulse eddy current thickness measuring device is suitable for rapidly scanning bare stainless steel pipes (non-ferromagnetic materials) and ferromagnetic material pipelines, and the specific position of a metal loss abnormal area of the pipeline is rapidly found by displaying the data change of the wall thickness value of each detection point; the device is portable high-efficient, utilizes well low frequency electromagnetism principle, need not polish the metal body, need not the couplant, does not fear high temperature and low temperature, realizes that high accuracy is swept and is examined, high-efficient location and quantitative metal loss, provides accurate data for the potential safety hazard that the inside local corrosion of complete aassessment leads to then.
According to some embodiments of the invention, the number of probes is plural, and a plurality of probes are disposed on the flexible connection mount.
According to some embodiments of the invention, the probe is electrically connected to the thickness gauge host through a cable.
According to some embodiments of the invention, the thickness gauge host is provided with a display screen.
According to some embodiments of the invention, the thickness gauge host is provided with a plurality of function keys.
According to some embodiments of the invention, the thickness gauge main body further comprises at least one of a power panel module and a battery pack module.
On the other hand, the novel pulse eddy current thickness measuring method comprises the following steps: the probe is close to the surface of the pipeline to be detected; the probe excites a pulse eddy current signal to the pipeline to be detected and receives a feedback signal of the pipeline to be detected; acquiring a middle-term signal slope maximum value of the feedback signal, and taking the middle-term signal slope maximum value as a characteristic value; obtaining the wall thickness value of the pipeline to be detected at the current position of the probe according to the relation between the preset characteristic value and the wall thickness value; and displaying the wall thickness value on a display screen of the thickness gauge host.
The novel pulse eddy current thickness measuring method provided by the embodiment of the invention has at least the following beneficial effects: the maximum value of the middle signal slope of the pulse eddy current is used as a characteristic value, and a relation between different wall thicknesses and corresponding characteristic values is fitted through a standard template test method, so that quantitative and rapid scanning detection on the wall thickness value of the pipeline to be detected is realized.
According to some embodiments of the present invention, the number of the probes is a plurality, a plurality of the probes are arranged on the flexible connecting support, and the novel pulsed eddy current thickness measuring method further comprises the following steps: controlling the plurality of probes to be switched in sequence to work so as to obtain wall thickness values of different positions of the pipeline to be detected; and moving a plurality of probes to obtain the measured wall thickness extension values when the probes are continuously moved.
According to some embodiments of the invention, the relationship between the preset characteristic value and the wall thickness value is obtained by: and obtaining characteristic values of a plurality of standard sample plates with different thicknesses, and fitting the thickness values of the plurality of standard sample plates with the corresponding plurality of characteristic values to obtain the relation between the preset characteristic values and the wall thickness values.
According to some embodiments of the invention, the obtaining of the mid-term signal slope maximum of the feedback signal comprises: said feedback signal representing a set of induced voltage values decaying with time, denoted by (T)i，Vi) Represents; wherein, TiDenotes the decay time, ViRepresents TiThe induced voltage value at the moment, i represents the number of time windows, and i is a positive integer; logarithm of said induced voltage values to obtain a set of time-decaying induced voltage logarithm values, denoted by (T)i，log Vi) Represents; according to formula Ki＝(log Vi+1-log Vi)/(Ti+1-Ti) Calculating the slope between each two adjacent points and obtaining the maximum slope value Kmax，KmaxNamely the maximum value of the slope of the middle signal.
Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Drawings
The above and/or additional aspects and advantages of the present invention will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:
FIG. 1 is a schematic structural diagram of a novel pulsed eddy current thickness measuring device according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of an internal structure of a thickness gauge main unit according to an embodiment of the present invention;
FIG. 3 is a diagram illustrating a display result of a display screen according to an embodiment of the present invention;
FIG. 4 is a flow chart illustrating the steps of a novel pulsed eddy current thickness measurement method according to an embodiment of the present invention;
reference numerals:
the thickness gauge comprises a thickness gauge host 100, a CPU110, a transmitting module 120, a receiving module 130, a display screen 140, function keys 150, a power panel module 160, a battery pack module 170, a probe 200, a pipeline 300 to be measured, a flexible connecting bracket 400 and a cable 500.
Detailed Description
Reference will now be made in detail to the present preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout.
In the description of the present invention, a plurality of means is one or more, a plurality of means is two or more, and greater than, less than, more than, etc. are understood as excluding the essential numbers, and greater than, less than, etc. are understood as including the essential numbers. If the first and second are described for the purpose of distinguishing technical features, they are not to be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated or implicitly indicating the precedence of the technical features indicated.
In the description of the present invention, unless otherwise explicitly limited, terms such as arrangement, installation, connection and the like should be understood in a broad sense, and those skilled in the art can reasonably determine the specific meanings of the above terms in the present invention in combination with the specific contents of the technical solutions.
In one aspect, as shown in fig. 1 and 2, the novel pulsed eddy current thickness measuring device according to the embodiment of the invention comprises a thickness gauge main body 100 and at least one probe 200; the thickness gauge main body 100 comprises a CPU110, and a transmitting module 120 and a receiving module 130 which are respectively electrically connected with the CPU 110; the probe 200 is electrically connected with the thickness gauge main body 100, the probe 200 comprises a transmitting coil and a receiving coil, the transmitting coil is used for exciting a pulse eddy current signal to the pipeline 300 to be measured, and the receiving coil is used for receiving a feedback signal of the pipeline 300 to be measured.
Specifically, according to the novel pulsed eddy current thickness measuring device of the embodiment of the present invention, in practical application, the CPU110 sends a detection signal to the probe 200 through the transmitting module 120, so that the transmitting coil of the probe 200 excites a pulsed attenuated eddy current signal to the pipe 300 to be measured, and then the receiving coil of the probe 200 is utilized to receive an attenuated magnetic field signal (i.e., a feedback signal) generated by the attenuated eddy current in the pipe wall of the pipe 300 to be measured. Then, the thickness gauge main unit 100 receives the feedback signal through the receiving module 130, and performs a/D conversion (analog-to-digital conversion) on the feedback signal, and then the CPU110 performs an algorithm analysis process on the received signal, thereby calculating a relative wall thickness value of the pipe 300 to be measured. The probe 200 is used for scanning detection of the pipeline 300 to be detected, so that the change of the wall thickness value of each detection point of the pipeline 300 to be detected can be observed, and the defect position of the pipeline 300 to be detected can be effectively detected and positioned.
In some embodiments of the present invention, the number of probes 200 is plural, and a plurality of probes 200 are disposed on the flexible connection mount 400.
Specifically, as shown in fig. 1, the number of the probes 200 is three (the actual number is not limited), the three probes 200 are disposed on the flexible connecting support 400, and the curvature of the flexible connecting support 400 is adjustable, so that the flexible connecting support can meet pipelines with different pipe diameters, and the applicability is high. Meanwhile, by arranging a plurality of probes 200, the wall thickness values of a plurality of positions of the pipeline 300 to be detected can be detected simultaneously (similar to C-scan), so that the detection efficiency is improved; when the plurality of probes 200 are continuously moved and detected, a result of the wall thickness extension value (i.e., B-scan) can be obtained. Furthermore, the sequential switching between the three probes 200 is realized by a program preset inside the CPU110, namely: the probe 1 is switched on, and the probe 2 and the probe 3 are switched off; the probe 2 is switched on, and the probe 1 and the probe 3 are switched off; probe 3 is on and probe 1 and probe 2 are off. The design enables the probes 200 to be sequentially conducted, so that the mutual interference of magnetic fields among the probes 200 when a plurality of probes 200 are simultaneously turned on or off is avoided. The embodiment of the invention adopts three high-precision miniature probes of stainless steel bare tubes, so that the time delay of conduction between the probes 200 is very short (the measurement time of each probe 200 is controlled to be about 125 us).
As shown in FIG. 1, in some embodiments of the present invention, probe 200 is electrically connected to thickness gauge mainframe 100 via cable 500. The thickness gauge main body 100 transmits a detection instruction to the probe 200 through the cable 500, and receives detection data of the probe 200.
As shown in fig. 1 and 3, in some embodiments of the present invention, a display screen 140 is further disposed on the thickness gauge main body 100. When the thickness gauge host 100 calculates the wall thickness value of the detection position, the detection result can be displayed in real time through the display screen 140, so that a user can visually observe the wall thickness value of each position of the pipeline 300 to be detected, and the position of the defect can be found and positioned in time.
As shown in fig. 1, in some embodiments of the present invention, a plurality of function buttons 150 are provided on the thickness gauge main body 100. For example, functional keys 150 such as "measure", "set", and "reset" are provided below the display screen 140 of the thickness gauge main body 100, and parameter setting can be performed on the thickness gauge main body 100; functional keys 150 for 'viewing' and 'amplifying' are arranged at two sides of the display screen 140, and the display interface can be adjusted. It is to be understood that the specific type and location of the function keys 150 are not limiting.
As shown in fig. 2, in some embodiments of the present invention, thickness gauge host 100 further includes at least one of a power strip module 160 and a battery pack module 170. The power panel module 160 can be used to connect an external power source, so as to supply power or charge the thickness gauge main body 100; the battery module 170 can be used to supply power to the thickness gauge main body 100, and the battery replacement is convenient.
On the other hand, as shown in fig. 4, the novel pulsed eddy current thickness measuring method according to the embodiment of the invention comprises the following steps:
step S100: the probe 200 is brought close to the surface of the pipe 300 to be measured.
Step S200: the probe 200 excites the pulsed eddy current signal to the pipe 300 to be measured and receives the feedback signal of the pipe 300 to be measured.
Specifically, the CPU110 sends a detection signal to the probe 200 through the transmitting module 120, so that the transmitting coil of the probe 200 excites a pulsed attenuated eddy current signal to the pipe 300 to be tested, and then receives an attenuated magnetic field signal (i.e., a feedback signal) generated by the attenuated eddy current in the pipe wall of the pipe 300 to be tested by using the receiving coil of the probe 200.
Step S300: and acquiring the maximum value of the slope of the middle-term signal of the feedback signal, and taking the maximum value of the slope of the middle-term signal as a characteristic value.
Specifically, the thickness gauge host 100 receives the feedback signal sent by the probe 200 through the receiving module 130, and after a/D conversion (analog-to-digital conversion) is performed on the feedback signal, the CPU110 performs algorithm analysis processing on the received signal, so as to obtain a middle-term signal slope maximum value of the feedback signal, and uses the middle-term signal slope maximum value as a characteristic value.
In order to obtain the maximum value of the slope of the mid-term signal of the feedback signal, the following method can be adopted: the feedback signal is represented as a set of induced voltage values decaying with time, denoted by (T)i，Vi) Represents; wherein, TiRepresents the decay time, ViRepresents TiThe induced voltage value at the moment, i represents the number of time windows, and i is a positive integer; logarithm of the induced voltage value to obtain a set of time-decaying induced voltage logarithm values, using (T)i，log Vi) Represents; according to formula Ki＝(log Vi+1-log Vi)/(Ti+1-Ti) Calculating the slope between each two adjacent points and obtaining the maximum slope value Kmax，KmaxI.e. the maximum value of the slope of the signal in the middle period. The feedback signal received by the CPU110 is a differential signal subjected to a logarithmic superposition process, and the number of time windows is generally about 20 to 128 (equal interval logarithmic time).
Step S400: and obtaining the wall thickness value of the pipeline 300 to be detected at the current position of the probe 200 according to the relation between the preset characteristic value and the wall thickness value.
After the characteristic value of the detection position is obtained, the wall thickness value of the pipe 300 to be detected at the current position of the probe 200 can be obtained according to the preset relationship between the characteristic value and the wall thickness value. In order to obtain the relationship between the preset characteristic value and the wall thickness value, the following method can be adopted: and obtaining characteristic values of a plurality of standard sample plates with different thicknesses, and fitting the thickness values of the plurality of standard sample plates with the corresponding plurality of characteristic values to obtain a relation between a preset characteristic value and a wall thickness value. For example, assuming that a nondestructive inspection 304 stainless steel sample plate having a thickness of 4mm, 6mm, 8mm, 10mm, 12mm, 16mm, 20mm or the like is selected as a test object, characteristic values of the respective standard sample plates are obtained by the above-described method, and a relationship between the characteristic values and the wall thickness values is finally obtained by fitting a plurality of thickness values and a plurality of characteristic values. In the implementation of the invention, through practical tests, the relation between the characteristic value and the wall thickness value is obtained as follows: d (K)max)＝24.44×Kmax -1The degree of fit R is required2>0.998. Where the constant 24.44 is related to the configuration of the probe 200, d (K)max) Is the wall thickness value, K, of the current position of the pipe 300 to be measuredmaxIs a characteristic value (i.e., the maximum value of the slope of the signal in the middle period). From this relational expression, if the feature value of each detection point can be acquired, the wall thickness value corresponding to each detection point can be calculated.
Step S500: the wall thickness value is displayed on the display screen 140 of the thickness gauge main body 100.
After the wall thickness value of the detection point is obtained, the wall thickness value is displayed on the display screen 140 of the thickness gauge main body 100 in real time.
In addition, as shown in fig. 1, in the embodiment of the present invention, the number of the probes 200 is three (the actual number is not limited), the three probes 200 are disposed on the flexible connecting support 400, and the curvature of the flexible connecting support 400 is adjustable, so that the flexible connecting support can meet pipelines with different pipe diameters, and the applicability is strong. Meanwhile, by arranging a plurality of probes 200, the wall thickness values of a plurality of positions of the pipeline 300 to be detected can be detected simultaneously (similar to C-scan), so that the detection efficiency is improved; when the plurality of probes 200 are continuously moved and detected, the result of the wall thickness extension value (i.e., B-scan) can be obtained. Furthermore, by means of a program preset inside the CPU110, sequential switching between the three probes 200 can be achieved, namely: the probe 1 is switched on, and the probe 2 and the probe 3 are switched off; the probe 2 is switched on, and the probe 1 and the probe 3 are switched off; probe 3 is on and probe 1 and probe 2 are off. The design enables the probes 200 to be sequentially conducted, so that the mutual interference of magnetic fields among the probes 200 when a plurality of probes 200 are simultaneously turned on or off is avoided.
The novel pulse eddy current thickness measuring device and the novel pulse eddy current thickness measuring method are suitable for fast scanning of the exposed stainless steel pipe (non-ferromagnetic material) and the ferromagnetic material pipeline, and the specific position of the metal loss abnormal area of the pipeline is fast searched by displaying the data change of the wall thickness value of each detection point. The device is portable high-efficient, utilizes well low frequency electromagnetism principle, need not polish the metal body, need not the couplant, does not fear high temperature and low temperature, realizes that high accuracy is swept and is examined, high-efficient location and quantitative metal loss, provides accurate data for the potential safety hazard that the inside local corrosion of complete aassessment leads to then. Because the device is used for scanning and measuring the relative wall thickness value on the surface of a stainless steel bare pipe (the lift-off height is small), and the size and the power of the probe 200 are small, the scanning precision (or the resolution) for the defects of the inner wall of the wall thickness is very high, and the device can be used for quickly positioning the defects of the area type metal loss of the inner wall of the stainless steel pipeline. The method adopts the maximum value of the mid-term signal slope of the pulse eddy current as the characteristic value, and fits the relation between different wall thicknesses and corresponding characteristic values through a standard template test method, thereby realizing quantitative and rapid scanning detection of the wall thickness of the pipeline 300 to be detected. Further, by providing three probes 200, the wall thickness values and the wall thickness extension values of the three channels can be detected and displayed simultaneously.
The embodiments of the present invention have been described in detail with reference to the accompanying drawings, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge of those skilled in the art without departing from the gist of the present invention.
Claims (10)
1. A novel pulse eddy current thickness measuring device is characterized by comprising:
the thickness gauge host comprises a CPU, and a transmitting module and a receiving module which are respectively and electrically connected with the CPU;
the thickness gauge comprises at least one probe, the probe with the calibrator host electricity is connected, the probe includes transmitting coil and receiving coil, transmitting coil is used for arousing pulse eddy current signal to the pipeline that awaits measuring, receiving coil is used for receiving the feedback signal of the pipeline that awaits measuring.
2. The novel pulsed eddy current thickness measuring device according to claim 1, wherein the number of the probes is multiple, and a plurality of the probes are arranged on the flexible connecting bracket.
3. The novel pulsed eddy current thickness measuring device according to claim 1, wherein the probe is electrically connected with the thickness gauge main machine through a cable.
4. The novel pulsed eddy current thickness measuring device according to claim 1, wherein a display screen is arranged on the thickness gauge main machine.
5. The novel pulsed eddy current thickness measuring device according to claim 4, wherein a plurality of function keys are arranged on the thickness gauge main machine.
6. The novel pulsed eddy current thickness gauge device according to claim 1, wherein the thickness gauge main unit further comprises at least one of a power panel module and a battery pack module.
7. A novel pulse eddy current thickness measuring method is characterized by comprising the following steps:
the probe is close to the surface of the pipeline to be detected;
the probe excites a pulse eddy current signal to the pipeline to be detected and receives a feedback signal of the pipeline to be detected;
acquiring a middle-term signal slope maximum value of the feedback signal, and taking the middle-term signal slope maximum value as a characteristic value;
obtaining the wall thickness value of the pipeline to be detected at the current position of the probe according to the relation between the preset characteristic value and the wall thickness value;
and displaying the wall thickness value on a display screen of the thickness gauge host.
8. The novel pulsed eddy current thickness measuring method according to claim 7, wherein the number of the probes is plural, and a plurality of the probes are arranged on the flexible connecting support, and the novel pulsed eddy current thickness measuring method further comprises the following steps:
controlling the plurality of probes to be switched in sequence to work so as to obtain wall thickness values of different positions of the pipeline to be detected;
and moving a plurality of probes to obtain the measured wall thickness extension values when the probes are continuously moved.
9. The novel pulsed eddy current thickness measuring method according to claim 7, wherein the relationship between the preset characteristic value and the wall thickness value is obtained by the steps of:
and obtaining characteristic values of a plurality of standard sample plates with different thicknesses, and fitting the thickness values of the plurality of standard sample plates with the corresponding plurality of characteristic values to obtain the relation between the preset characteristic values and the wall thickness values.
10. The novel pulsed eddy current thickness measuring method according to claim 7, wherein the step of obtaining the maximum value of the slope of the mid-period signal of the feedback signal comprises the following steps:
said feedback signal representing a set of induced voltage values decaying with time, denoted by (T)i，Vi) Represents; wherein, TiRepresents the decay time, ViRepresents TiThe induced voltage value at the moment, i represents the number of time windows, and i is a positive integer;
logarithm of the induced voltage value to obtain a set of induced electricity decaying with timeLogarithmic value of (T)i，log Vi) Represents;
according to formula Ki＝(log Vi+1-log Vi)/(Ti+1-Ti) Calculating the slope between each two adjacent points and obtaining the maximum slope value Kmax，KmaxNamely the maximum value of the slope of the middle signal.
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