Coating layer monitoring device and operating method thereof for monitoring a barrier coating layer

Abstract

A device for monitoring corrosion on a coating layer 20, which includes: a signal generator 11, a signal receiver 12, and a processor 13. The signal generator generates at least 2 reference alternatin

Description

[1] The present invention relates to a coating layer monitoring device for monitoring a barrier coating layer, which applies to offshore wind power device. BACKGROUND OF RELATED ARTS [2] Nowadays, the energy need of human society has been getting gotten very huge with the explosive growth of global population and the industrialization of developing country. The huge consumption of energy results in a big problem for earth. As environmental issues are getting more and more attention, creating a net-zero and green power environment has become the goal in globalization development. Wind power is the electric power generated by the kinetic energy that is created by the rotation of big fans caused by wind, which is a kind of low-pollution energy. In the wind power station field, offshore power turbines have more advantages and potentials than onshore wind power turbines, because the consistent direction of offshore wind benefits the power generation efficiency. [3] Although there are many advantages of offshore wind power turbines, severe marine environment is still an issue to develop offshore wind power. Especially, high salinity environment makes marine engineering buildings (such as offshore wind turbines, or offshore platforms / foundations) corrode speedily. These buildings have to be protected by anti-corrosion process such as applying sacrificial anodes, cathodic protection, and / or coating a barrier protection layer to ensure the life and stability of the overall structure and generator set. 26 10 23 [4] Due to the high cost of the marine engineering, frequent check and maintenance of anti-corrosion means executed manually are thus limited during the whole operating life cycle of marine buildings. In other words, at the present time, to monitor the corrosion of coating layer, the inspection of corrosion condition of offshore wind power generator still needs to be operated by human eyes. Moreover, for the undersea objects (such as offshore foundation), it takes divers to dive undersea in order to do the inspection, which leads to not only the massive cost, but the elevated risk to the divers as well. [5] Metal corrosion monitoring is usually applied for the corrosion status of several kinds of objects in a corrosive environment such as undersea or underground. The purpose of monitoring the corrosion of each object is to replace them immediately before they are seriously damaged. However, most corrosion monitoring methods are only suitable in laboratory because various and complex apparatus are required in these methods. For example, in common electrochemical impedance measurement, power supplier with big volume, reference electrode, auxiliary electrode, and beaker need to be installed at the same time. Therefore, if the abovementioned corrosion measuring methods are applied in offshore wind turbine, there will be an issue to overcome the problems which are brought by the requirement of various and complex apparatus. Additionally, the corrosion measuring methods usually need to be operated manually. However, most of the offshore wind turbine is run by unmanned control systems and offshore wind power farm is far away to marine route. Thus, the fact that inspection and repairment staffs could not go to wind 26 10 23 power farm frequently thus makes corrosion monitoring with remote control and transmission functions an important issue. [6] A well-known method used for monitoring the anti-corrosion performance of coating layers is to monitor the electrochemical impedance of coating layer in a single frequency. Thereafter, the value of impedance determines whether the barrier protection performance of the coating layer is sufficient or not. The basic concept of the method is using a signal source to output a sinusoidal voltage signal with small amplitude in a single frequency to the coating layer, and then measuring the feedback impedance from the coating layer. The monitor frequency of common commercial coating layer monitoring instruments is mostly ranged from 0.1-1 Hz, and the impedance standard adopted in said monitoring devices is ranged from about 100 MQ-1 GQ, thus to determine whether the barrier protection performance of the coating layer is sufficient or not. The reason for choosing above range of frequency is that the low-frequency impedance usually decays faster in corrosion process. [7] However, the measured impedance of coating layer will be influenced in a single frequency by various factors besides corrosion. The factors include but not limit to the kinds of coating layer, the difference in thickness when the coating layer is applied, and non-uniform corrosion occurring in corrosive environment, etc.. Therefore, the common monitoring device measuring the impedance of coating layer only in a single frequency cannot accurately determine whether the barrier protection performance of the coating layer is sufficient or not. As a result, the inaccurately measured impedance will lead to a 26 10 23 wrong determination. If an intact coating layer is mistakenly determined to be a failed coating layer, unnecessary maintenance costs will be produced. If a failed coating layer is mistakenly determined to be an intact coating layer, the risk of possible accident with economic loss is elevated. SUMMARY [8] In order to solve the above problem in prior art, the present invention provides a coating layer monitoring device and operating method thereof for monitoring a barrier coating layer. [9] A coating layer monitoring device for monitoring a barrier coating layer includes a signal generator, a signal receiver, and a processor. The signal generator generates two reference alternating voltage signals and outputs the reference alternating voltage signals to a coating layer to be monitored. Each the reference alternating voltage signal is a sinusoidal wave and frequency of each the reference alternating voltage signal is different. The signal receiver is connected to the coating layer and the signal receiver receives two feedback current signals which are generated correspondingly after each reference alternating voltage signal passes through the coating layer. The processor computes a feedback current signal ratio between any two of the feedback current signals.

[10] The processor determines whether the barrier protection performance of the coating layer is sufficient or not according to the feedback current signal ratio as compared with a first end or a second end. Specifically, in the operating method of coating layer monitoring device in present invention, two reference alternating voltage signals comprise the first reference alternating voltage signal 26 10 23 and the second reference alternating voltage signal. The first reference alternating voltage signal has a first frequency and a first voltage. The second reference alternating voltage signal has a second frequency and a second voltage. The second frequency is higher than the first frequency. The reference signal frequency ratio is defined as the second frequency divided by the first frequency. Furthermore, the reference signal voltage ratio is defined as the second voltage divided by the first voltage. In addition, the two corresponding feedback current signals comprise the first feedback current signal and the second feedback current signal. The first feedback current signal has the first frequency and a first current. The second feedback current signal has the second frequency and a second current. The feedback current signal ratio is defined as the second current divided by the first current. Finally, the first end is a product of the reference signal frequency ratio and the reference signal voltage ratio. The second end is the reference signal voltage ratio. The processor determines the coating layer is effective if the feedback current signal ratio is closer to the first end; or the processor determines the coating layer is failed if the feedback current signal ratio is closer to the second end.

[11] The above-mentioned descriptions are only preferred embodiments of the present invention and are not intended to limit the scope of implementation of the present invention. Therefore, all the shapes, structures, features, and spirits described in the scope of the patent application of the present invention shall be regarded as equivalent to the changes and modifications per se, and be included in the scope of the patent application of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS 26 10 23

[12] FIG. 1 is a schematic diagram of an embodiment of the coating layer monitoring device of the present invention.

[13] FIG. 2 is a schematic diagram of the signal receiver circuit of the embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[14] In order to understand the technical features and practical effects of the present invention, and to implement it according to the contents of the specification, the preferred embodiment shown in the drawings will be described in detail as follows:

[15] The present invention provides a coating layer monitoring device for monitoring a barrier coating layer. The device can overcome the disadvantage of known coating layer monitoring instruments. The above disadvantage is that these instruments may provide mistaken determinations because they measure the impedance of the coating layer only in a specific frequency. As the above description, the coating layer monitoring device disclosed in the embodiment of the present invention can measure the impedance of a coating layer by signals in different frequencies to improve the accuracy of detecting the integrity of the coating layer.

[16] FIG. 1 is a schematic diagram of an embodiment of the coating layer monitoring device of the present invention. The coating layer monitoring device 10 of the present invention can be applied to an offshore wind power device. The above coating layer monitoring device 10 includes a signal generator 11, a signal receiver 12, and processor 13. 26 10 23

[17] The signal generator 11 supplies alternating voltage signals V and output V to a coating layer which is to be measured. The alternating voltage signal V comprises the first reference alternating voltage signal and the second reference alternating voltage signal. The waveform of each reference alternating voltage signal is sinusoidal. Furthermore, the first reference alternating voltage signal of this embodiment has a first frequency Fl and a first voltage VI, and the second reference alternating voltage signal of this embodiment has a second frequency F2 and a second voltage V2. The second frequency is higher than the first frequency (F2>F1).

[18] In the embodiment, signal generator 11 is electrically connected to a coating layer 20 to be measured, and another end of the coating layer 20 is electrically connected to the signal receiver 12. The signal receiver 12 receives the corresponding feedback current signal I which is generated after alternating voltage signal V passes through the coating layer 20. The feedback current signal I comprises the first feedback current signal and the second feedback current signal. The first feedback current signal has the first frequency Fl and a first current II. The second feedback current signal has the second frequency F2 and a second current 12. Finally, after the processor 13 in the FIG. 1 computes and gets a feedback current signal ratio Ir, the barrier protection performance of the coating layer 20 can be thus determined whether to be sufficient or not accordingly. The feedback current signal ratio IrIs the second current 12 divided by the first current II.

[19] Furthermore, the description hereinafter explains that how the processor 13 of this embodiment is able to determine whether the barrier protection performance of the coating layer 20 is sufficient or not. In the beginning, 26 10 23 processor 13 computes the data measured by coating layer monitoring device 10 to get a first end and a second end. By comparing the feedback current signal ratio iRwith said first end and second end, the processor 13 determines whether the barrier protection performance of the coating layer 20 is sufficient or not. Specifically, the value of the first end is the product of the reference signal frequency ratio Fr and reference signal voltage ratio Vr. The reference signal frequency ratio FrIs the second frequency F2 divided by the first frequency Fl. The reference signal voltage ratio VrIs the second voltage V2 divided by the first voltage VI. The value of the second end is the reference signal voltage ratio Vr. After computing the two ends, the processor 13 determines the coating layer 20 is effective if feedback current signal ratio is close to the first end. On the contrary, the processor 13 determines the coating layer 20 is failed if feedback current signal ratio Ir is closer to the second end.

[20] The signal generator 11 of this embodiment is a voltage signal generator which can output a preset waveform. In the other words, any voltage signal generator which can output a preset waveform can be used as the signal generator. In addition, because coating layer monitoring is a non-destructive measuring method, said alternating voltage signal V with preset waveform has to avoid high voltage signals making coating layer failed. Hence, the suggested range of voltage amplitude of V used in this embodiment is 5-20 mV, and the better range is 10-20 mV.

[21] Basically, the waveform of said alternating voltage signal V of this embodiment comprises at least two sine waves with different frequencies, which includes but not limited to square wave, pulse wave, triangle wave, sawtooth wave, and various waveforms composed by sine waves. The waveforms in which the 26 10 23 amplitude of each sine wave comprised within has a specific functional relationship to their frequency are suggested, and square wave is recommended.

[22] The range of frequencies of this embodiment is defined by the first frequency Fl and the second frequency F2. Although the low-frequency signal of detected coating layer is more sensitive when the coating layer is failed, the operation time required accordingly in on single monitoring period is longer. Therefore, considering both the monitoring efficiency and the detection sensitivity, the suggested range of the first frequency Fl of this embodiment is 0.05-5 Hz, and the better range is 0.1-2 Hz. The range of the reference signal frequency Fr is 5-30.

[23] The coating layer to be measured in this embodiment is a barrier layer, the material may be commercial epoxy.

[24] The signal receiver 12 of this embodiment is a signal receiver capable of receiving AC signal waveforms (including amplitude and frequency). In other words, anyone signal receiver which can receive AC signal waveform can be a signal receiver of this embodiment. The signal receiver 12 receives the corresponding feedback current signal I which is generated after alternating voltage signal V passes through the coating layer 20, and outputs the corresponding feedback current signal I to the processor 13. FIG. 2 is a schematic diagram of the signal receiver circuit of the embodiment. The signal receiver 12 comprises a reference resistance Rref. The reference resistance Rref is configured between two voltage sensors outputting a first voltage signal SI and a second voltage signal S2. The feedback current signal I is generated after alternating voltage signal V passes through the coating layer 20 and can be obtained by the following formula: 26 10 23 1 = ( Sl-S2) / Rref SI is the first voltage signal in the circuit diagram. S2 is the second voltage signal in the circuit diagram. In this embodiment, the suggested range of reference resistance Rref is less than 12% of estimated minimum resistance in coating layer measuring frequency, and the better range is less than 6%.

[25] The processor 13 of this embodiment is a processor capable of capturing the amplitudes of sinusoidal signals in specific frequencies from the received current waveform and getting the result of a following division operation. For example, the processor has some electronic circuits including a Fourier transform calculator (for capturing the amplitude of the sinusoidal signal in specific frequencies), a signal recorder (for recording II and 12), and a division calculator (for calculating Ir).

[26] After the coating layer monitoring device 10 is installed on offshore wind generator, the control center on the land can get the result of whether the barrier protection performance of the coating layer is sufficient or not transported via wireless communication. Thus, the real-time monitoring on the structure of the offshore wind turbine can be facilitated to ensure the system safety and make the offshore wind turbine work normally.

[27] In this embodiment, the used experimental parameters are as follows: First, the waveform of the alternating voltage signal V input is square wave, and the frequency and the amplitude are 0.1 Hz and 20 mV, respectively. Next, the receiver adopted is a circuit designed as FIG.2. The reference resistance Rref is 26 10 23 10 MQ, which is 1 / 100 of 1 GQ (the common impedance standard adopted in commercial monitoring devices).

[28] The frequencies used in this embodiment are: the first frequency Fl of the first group is 0.1 Hz, the second frequency F2 of the first group is 0.5 Hz, the reference signal frequency Fr of the first group is 5, and the reference signal voltage ratio Vr of the first group is 1 / 5. The first frequency Fl of the second group is 0.1 Hz, the second frequency F2 of the second group is 2.7 Hz, the reference signal frequency Fr of the second group is 27, and the reference signal voltage ratio Vr of the second group is 1 / 27.

[29] The determination standard of whether the barrier protection performance of the coating layer is sufficient or not is set by calculating Vr and Fr. In the first group, the standard of an intact coating layer is 1, which is the product of Vr and Fr. The standard of a failed coating layer is 0.2, which is Vr. In the second group, the standard of an intact coating layer is 1, which is the product of Vr and Fr. The standard of failed coating layer is 0.037, which is Vr.

[30] The monitoring frequency for the control group 1 and group 2 is set at 0.5 Hz and 2.7 Hz, respectively, in order to correspond to that for the embodiment groups. Hence, the determination standard of the coating layer impedance for the control group 1 is 1 GQ at 0.5 Hz, which is a common standard used in commercial monitoring devices. The determination standard of the coating layer impedance for the control group 2 is 180 MQ at 2.7 Hz because the impedance of an intact coating layer will decrease proportionally as the monitoring frequency increases.

[31] The experimental data of the embodiment and control groups are described as 26 10 23 follows: Table 1 shows the inspection results acquired by a common commercial coating layer monitoring instrument (Coating Impedance Detector, CID) and the embodiment of this present invention, in which the experimental data are the results of intact coating layers with different impedance (sample 1 with relatively high impedance -21.7 GQ at 0.1 Hz / sample 2 with relatively low impedance -3.29 GQ at 0.1 Hz) inspected by embodiment groupl (embodiment 1 and 3 in the table), embodiment group 2 (embodiment 2 and 4 in the table), control group 1 (control 1 and 3 in the table), and control group 2 (control 2 and 4 in the table). Prior to the inspection, both samples are checked by electrochemical impedance spectroscopy technique to ensure that both samples are coated by coating layers with sufficient barrier protection performance. As shown by Table 1, the control groups get the incorrect result of an intact coating layer when that coating layer has a relatively low impedance, even if it still has sufficient barrier protection performance, and the embodiment groups get the correct results whether coating layer impedance is high or low.

[32] Table 1: Sample 1 (intact coating layer with high impedance) Control 1 (F2=0.5 Hz) Embodiment 1 (F2=0.5 Hz) Impedance detected by CID Determined result Measured value Ir Determined result 4.29 GQ OK(>1 GQ) 0.99 OK(~1) Control 2 (F2=2.7 Hz) Embodiment 2 (F2=2.7 Hz) Impedance detected by CID Determined result Measured value Ir Determined result 850 MQ OK(>180 MQ) 0.98 OK(~1) Sample 2 (intact coating layer with low impedance) Control 3 (F2=0.5 Hz) Embodiment 3 (F2=0.5 Hz) Impedance detected by CID Determined result Measured value Ir Determined result 690 MQ NG(<1 GQ) 0.97 OK(~1) Control 4 (F2=2.7 Hz) Embodiment 4 (F2=2.7 Hz) Impedance detected by CID Determined result Measured value Ir Determined result 170 MQ NG(<180 MQ) 0.96 OK(~1) 26 10 23

[33] Table 2 shows the inspection results acquired by a common commercial coating layer monitoring instrument (Coating Impedance Detector, CID) and the embodiment of this invention, in which the experimental data are the results of failed coating layers with different impedance (sample 3 with relatively high impedance -2.13 GQ at 0.1 Hz / sample 4 with relatively low impedance -0.09 GQ at 0.1 Hz) inspected by embodiment group 1 (embodiment 5 and 7 in the table), embodiment group 2 (embodiment 6 and 8 in the table), control group 1 (control 5 and 7 in the table), and control group 2 (control 6 and 8 in the table). Prior to the inspection, both samples are checked by electrochemical impedance spectroscopy technique to ensure that the coating layers on both samples are already corroded and not able to perform sufficient barrier protection. As shown by Table 2, the control groups get the incorrect result of a failed coating layer when that coating layer has a relatively high impedance, even if it cannot provide sufficient barrier protection performance, and the embodiment groups get the correct results whether coating layer impedance is high or low.

[34] Table 2: 26 10 23 Sample 3 (failed coating layer with high impedance) Control 5 (F2=0.5 Hz) Embodiment 5 (F2=0.5 Hz) Impedance detected by CID Determined result Measured value Ir Determined result 1.70 GQ OK(>1 GQ) 0.2 NG(~0.2) Control 6 (F2=2.7 Hz) Embodiment 6 (F2=2.7 Hz) Impedance Determined Measured value Determined detected by CID result Ir result 410 MQ OK(>180 MQ) 0.05 NG(~0.037) Sample 4 (failed coating layer with low impedance) Control 7 (F2=0.5 Hz) Embodiment 7 (F2=0.5 Hz) Impedance detected by CID Determined result Measured value Ir Determined result 85 MQ NG(<1 GQ) 0.2 NG(~0.2) Control 8 (F2=2.7 Hz) Embodiment 8 (F2=2.7 Hz) Impedance detected by CID Determined result Measured value Ir Determined result 81 MQ NG(<180 MQ) 0.036 NG(~0.037)

[35] In Table 1 and Table2, while the first frequency Fl in both embodiment group 1 and 2 are set as 0.1Hz, the second frequency F2 varies from 0.5 Hz (embodiment group 1) to 2.7 Hz (embodiment group 2). As shown by the results, 14 26 10 23 the embodiment of this present invention can correctly determine whether the barrier protection performance of the coating layer is sufficient or not.

[36] Although the results in Table 1 and 2 prove this present invention can correctly determine whether the barrier protection performance of the coating layer is sufficient or not, as described above, one can find that the feedback current signal ratio Ir measured by the embodiment of this present invention is more accurate in embodiment group 1 (the second frequency F2 set as 0.5 Hz), as compared to that in embodiment group 2 (F2 set as 2.7 Hz). In other words, the measured feedback current signal Ir in Table 1 and Table 2 shows that Ir recorded in embodiment group 1 (with F2 at 0.5 Hz) is closer to its ideal value, which is 1 in Table 1 and 0.2 in Table 2, respectively. To disclose a suggested measuring frequency range, an experiment is conducted (as shown in Table 3), in which sample 4 (-0.09 GQ at 0.1 Hz) is inspected by the embodiment groups of this present invention with different Fl and F2.

[37] By comparing the measured values of Ir in embodiment 7, 9, 11, and 13, it can be found that all these embodiments can correctly determine the coating layer to be failed as the first frequency Fl ranging from 0.05 - 5 Hz and the reference signal frequency ratio Fr set at 5. However, the deviation between Ir and the ideal value (0.2) is small when Fl is set from 0.1 Hz (embodiment 7) to 2 Hz (embodiment 11), and gets larger when Fl is set at 0.05 Hz (embodiment 9) and 5 Hz (embodiment 13). Similar phenomenon can be also found in embodiment 8, 10, 12, and 14. Thus, to get more accurate inspection results, the suggested range of the first frequency Fl is 0.05 - 5 Hz, and a better range of Fl is 0.1 - 2 Hz.

[38] Table 3: Sample 4 (failed coating layer with low impedance) Embodiment 9 (F 1=0.05 Hz, Fr=5) Embodiment 7(Fl=0.1 Hz, Fr=5) Measured value Ir Determined result Measured value Ir Determined result 0.24 NG(~0.2) 0.2 NG(~0.2) Embodiment 10 (F 1=0.05 Hz, Fr=25) Embodiment 8 (Fl=0.1 Hz, Fr=27) Measured value Ir Determined result Measured value Ir Determined result 0.049 NG(~0.04) 0.036 NG(~0.037) 26 10 23 Sample 4 (failed coating layer with low resistance) Embodiment 11 (Fl =2 Hz, Fr=5) Embodiment 13 (Fl=5 Hz, Fr=5) Measured value Ir Determined result Measured value Ir Determined result 0.22 NG(~0.2) 0.47 NG(~0.2) Embodiment 12 (Fl =2 Hz, Fr=25) Embodiment 14 (Fl=5 Hz, Fr=25) Measured value Ir Determined result Measured value Ir Determined result 0.052 NG(~0.04) 0.16 NG(~0.04)

[39] In addition, comparing the data measured by the embodiments with the same first frequency Fl in table 3, it can be found that: between embodiment 7 and 8, the deviation in embodiment 7 is 0%, the deviation in embodiment 8 is 10%; between embodiment 9 and 10, the deviation in embodiment 9 is 20%, the 26 10 23 deviation in embodiment 10 is 32%; between embodiment 11 and 12, the deviation in embodiment 11 is 10%, the deviation in embodiment 12 is 30%; between embodiment 13 and 14, the deviation in embodiment 13 is 135%, the deviation in embodiment 14 is 300%. By analyzing the data above, it can be concluded that with the same Fl, the deviation of measured Ir from its ideal value will increase by reference signal frequency ratio Fr increasing.

[40] Furthermore, the reference signal frequency ratio Fr represents the monitoring frequency range, which is defined by the first frequency Fl and the second frequency F2. Hence, from the experimental data in Table 3, it can be found that when the reference signal frequency ratio Fr is larger, the deviation of the detected data is larger. However, a small reference signal frequency ratio Fr means a small monitoring frequency range, which is also affect the inspection. In an extreme condition, if the reference signal frequency ratio Fr is 1 (which means F1=F2), the measurement method described in the embodiment of this invention will fail to function normally, and the coating layer monitoring method thereof will fail as well. Thus, the reference signal frequency ratio Fr must be greater than 1, which means the second frequency F2 must be greater than the first frequency Fl. In order to get a balance between the data quality in inspection and the monitoring frequency range, a preferred range of Fr in the present invention is 5-30; with a Fr out of this range, although the method described in the embodiment of this invention can still function normally (as long as Fr greater than 1), the data measured will have larger deviation.

[41] Specifically, the coating layer monitoring device of this present invention is better than the common monitors which monitor the electrochemical impedance of coating layer in a single frequency. The advantage of this present invention is 26 10 23 that it can eliminate the interference of external factors such as coating layer thickness difference and non-uniform corrosion, and accurately reflect whether the coating layer still has a good barrier protection ability at present. Furthermore, with a more accurate inspection ability, the present invention can avoid the incorrect determination which mistake an intact coating layer with good barrier protection performance to be an invalid one just because the coating layer is thinner in thickness, thereby reducing unnecessary maintenance costs during the operation of marine engineering buildings. On the other hand, the present invention can avoid the coating that has been damaged by non-uniform corrosion (such as pitting corrosion) from being misjudged as a good one only because its impedance value has not declined significantly yet, thereby preventing engineering accidents and economic losses caused by subsequent unforeseen rapid corrosion damage to marine engineering buildings.

[42] The above-mentioned descriptions are only preferred embodiments of the present invention and are not intended to limit the scope of implementation of the present invention. Therefore, all the shapes, structures, features, and spirits described in the scope of the patent application of the present invention shall be regarded as equivalent to the changes and modifications per se, and be included in the scope of the patent application of the present invention.

Claims

26 10 231. A coating layer monitoring device for monitoring a barrier coating layer, comprising:a signal generator to generate at least two reference alternating voltage signals, and output the reference alternating voltage signals to a coating layer to be monitored, wherein each of the reference alternating voltage signal is a sinusoidal wave, and the frequency of each of the reference alternating voltage signal is different;a signal receiver connected to the coating layer to receive at least two feedback current signals which are generated correspondingly after the reference alternating voltage signal passes through the coating layer; and a processor to compute a feedback current signal ratio between any two of the feedback current signals;the processor determines whether the barrier protection performance of the coating layer is sufficient or not according to the feedback current signal ratio as compared with a first end or a second end;wherein the at least two reference alternating voltage signals comprise at least:a first reference alternating voltage signal having a first frequency and a first voltage;a second reference alternating voltage signal having a second frequency and a second voltage, with the second frequency higher than the first frequency;a reference signal frequency ratio defined as the second frequencydivided by the first frequency;26 10 23a reference signal voltage ratio defined as the second voltage divided by the first voltage;wherein the at least two feedback current signals comprises at least:a first feedback current signal having the first frequency and a first current;a second feedback current signal having the second frequency and a second current; anda feedback current signal ratio defined as the second current divided by the first current;wherein the first end is a product of the reference signal frequency ratio and the reference signal voltage ratio;wherein the second end is the reference signal voltage ratio;wherein the processor determines the coating layer is effective if the feedback current signal ratio is closer to the first end; or the processor determines the coating layer is failed if the feedback current signal ratio is closer to the second end.

2. The coating layer monitoring device as claimed in claim 1, wherein the first frequency is between 0.05 and 5 Hz.

3. The coating layer monitoring device as claimed in claim 2, wherein the first frequency is between 0.1 and 2 Hz.

4. The coating layer monitoring device as claimed in claim 1, wherein the reference signal frequency ratio is between 5 and 30.

5. The coating layer monitoring device as claimed in claim 1, wherein each of the reference alternating voltage signal is between 5 and 20 mV.

6. The coating layer monitoring device as claimed in claim 1, wherein the26 10 23processor comprises a Fourier transform calculator, a signal recorder, and a division calculator.

7. The coating layer monitoring device as claimed in claim 1, wherein the signalreceiver further comprises a reference resistance configured between the at least two voltage sensors.

8. An operating method of coating layer monitoring device, comprises at least: generating at least two reference alternating voltage signal and outputting to a coating layer; wherein each the reference alternating voltage signal is a sinusoidal wave, and the frequency of each the reference alternating voltage signal is different;wherein the at least two reference alternating voltage signals comprise at least:a first reference alternating voltage signal having a first frequency and a first voltage;a second reference alternating voltage signal having a second frequency and a second voltage, with the second frequency higher than the first frequency;a reference signal frequency ratio defined as the second frequency divided by the first frequency;a reference signal voltage ratio defined as the second voltage divided by the first voltage;receiving at least two corresponding feedback current signals which are generated after the at least two alternating voltage signal passes through the coating layer, wherein the at least two corresponding feedback current signals comprise at least:a first feedback current signal having the first frequency and a first current;26 10 23a second feedback current signal having the second frequency and a second current;a feedback current signal ratio defined as the second current divided by the first current;computing the feedback current signal ratio and determining whether the barrier protection performance of the coating layer is sufficient or not;wherein the first end is a product of the reference signal frequency ratio andthe reference signal voltage ratio;wherein the second end is the reference signal voltage ratio;wherein a value of a computing result determines the coating layer is effective if the feedback current signal ratio is closer to the first end; or the processor determines the coating layer is failed if the feedback current signal ratio is closer to the second end.

9. The operating method as claimed in claim 8, wherein the computing result which determines whether the barrier protection performance of the coating layer is sufficient or not is output to a remote external system by wireless transmission.

Images