Laser photoelectric sensor suitable for marine environment

Abstract

The invention relates to a laser photoelectric sensor suitable for a marine environment. The laser photoelectric sensor comprises an emitter and a receiver, the transmitter comprises a voltage stabilizing module, a control unit MCU module, a driving module, an optical signal amplitude modulation module and an optical signal transmitting module. The optical signal transmitting module comprises a high-power 532 nm laser light source. The receiver comprises a photosensitive component used for receiving optical signals, and a signal amplification circuit, an optical signal modulation and demodulation module and an output circuit which are connected with the photosensitive component. According to the laser photoelectric sensor suitable for the marine environment, modulation optical signals are transmitted in an amplitude modulation mode, and the received signals are demodulated and restored by using modulation carriers with the same frequency and the same phase and are compared with the transmitted signals; only an optical signal emitted by the sensor or completely reflected by a detected object can trigger the receiving end of the photoelectric sensor to change a control signal, so that the seawater interference resistance of the sensor is greatly improved.

Description

Technical Field

[0001] The invention relates to the technical field of sensors, and in particular to a laser photoelectric sensor suitable for marine environments. Background Art

[0002] Photoelectric proximity switch is a sensor that uses light as a transmission / detection medium, emits a light signal through a photodiode, and detects whether the light signal is blocked to detect the presence of an object. Photoelectric switches can be divided into short-range, medium-range, and long-range according to their uses, and can be divided into red light, infrared light, blue-violet light, etc. according to the wavelength of the emitted detection light. They are widely used to detect people, goods, machinery and equipment, etc., and have the advantages of high accuracy, fast response speed, and no need to contact the detected object. Therefore, they have been widely used in modern industrial production and logistics fields.

[0003] The ocean covers most of the earth's surface and contains immeasurable economic benefits and strategic significance. The development of marine resources is an inevitable requirement for national and social development. At present, the detection sensing method used in seawater is mainly acoustic sensing. However, the propagation of sound waves in seawater is not only affected by the various complex properties of seawater, but also the nature of the sound waves themselves determines that acoustic sensing has many inherent disadvantages. Compared with optical sensing, acoustic sensing has obvious shortcomings in speed, bandwidth, resolution, etc.

[0004] However, traditional photoelectric sensors are not suitable for underwater environments, especially seawater environments. The complex optical environment of the ocean and the high corrosiveness of seawater have greatly hindered the application of photoelectric sensors. Faced with the huge demand for ocean development, the market urgently needs a photoelectric sensor that can be used in seawater. Summary of the invention

[0005] Therefore, the technical problem to be solved by the present invention is to overcome the problem that the photoelectric sensors in the prior art have many restrictions when used in the marine environment, resulting in great limitations in the use of the photoelectric sensors.

[0006] In order to solve the above technical problems, the present invention provides a laser photoelectric sensor suitable for marine environment, including: a transmitter and a receiver; the transmitter includes: a voltage stabilizing module, a control unit MCU module, a driving module, an optical signal amplitude modulation module and an optical signal transmitting module, the optical signal transmitting module includes a high-power 532nm laser light source, the driving module includes an LED laser light source driving circuit, the optical signal amplitude modulation module is used to load the light signal into the carrier of different frequency components, when propagating in the water body, only the light wave emitted by itself or the echo reflected by the detected object can maintain the modulation information, and the echoes reflected by the water body at different distances will be superimposed on each other and lose the modulation information; the receiver includes: a photosensitive component for receiving the light signal and a signal amplification circuit connected to the photosensitive component, an optical signal modulation and demodulation module and an output circuit. The laser photoelectric sensor suitable for marine environment of the present invention relates to a series of photoelectric sensors suitable for marine environment with the technical characteristics of using a laser in the "blue-green window" wavelength that is not suitable for seawater absorption as a light source, applying amplitude modulation to the emitted light to remove the interference of seawater refraction, and adopting high-temperature vulcanization anti-corrosion measures.

[0007] In one embodiment of the present invention, the optical signal modulation and demodulation module can restore the original light signal when demodulating the light signal emitted by itself or the light signal reflected by the detected object, thereby effectively removing the interference of the refraction of the seawater on the light signal.

[0008] In one embodiment of the present invention, the output circuit can change the output mode of the sensor according to the initialization setting of the sensor and the comparison result between the demodulated signal and the signal before transmission modulation.

[0009] In one embodiment of the present invention, the optical signal amplitude modulation module can obtain the required modulation signal by simulating the multiplication of the original signal to be modulated A1 and the carrier signal f1, and adding a DC component Bias. The modulation depth of the amplitude modulation can be changed by controlling the amplitude of the original signal to be modulated A1. The frequency of the carrier signal f1 is the frequency of the modulation signal, and the DC component Bias is used to control the emission intensity of the above-mentioned optical signal transmitting module.

[0010] In one embodiment of the present invention, the optical signal amplitude modulation module includes a control unit MCU, a high-frequency sine wave generator, an integrated analog multiplier and a peripheral voltage regulator circuit; the peripheral voltage regulator circuit provides a positive power supply VDD and a negative power supply VSS to the optical signal amplitude modulation module, and the circuit reference provided by the peripheral voltage regulator circuit can obtain the proportional parameter SF and the DC component Bias required by the optical signal amplitude modulation module through voltage division; the control unit MCU outputs the original signal to be modulated A1 through the built-in DAC digital-to-analog converter; the high-frequency sine wave generator is used to configure the output carrier signal f1, and the signal expression function is ; Where f is the frequency of the sine wave signal, t1 and are respectively the time and phase of the carrier signal; the output function of the integrated analog multiplier is: , where X1 and X2, Y1 and Y2 represent the input quantities of the two differential multiplier input ports of the analog multiplier, respectively, and Z1 and Z2 represent the input quantities of the differential bias input ports of the analog multiplier, the same below. By configuring the peripheral circuit of the integrated analog multiplier, the output function of the analog integrated multiplier can be changed to achieve the required function, and its target output function is: , and then provide the original modulated signal A1 and the carrier signal f1 to the integrated analog multiplier, and the output is the required amplitude modulation signal.

[0011] In one embodiment of the present invention, the optical signal amplitude modulation module modulates any original signal to be modulated A1 and a carrier signal f1 of any frequency into an amplitude modulation signal AM1 with adjustable amplitude and offset. The mathematical expression is: .

[0012] In one embodiment of the present invention, the optical signal modulation and demodulation module multiplies the demodulated signal obtained after processing by the optical signal amplification circuit with the carrier signal f1 used by the optical signal amplitude modulation module. Since the frequency and phase of the carrier signal f1 used by the optical signal amplitude modulation module and the optical signal modulation and demodulation module are the same, the multiplied signal can be restored to the original undistorted modulated signal A1 by low-pass filtering.

[0013] In one embodiment of the present invention, the optical signal modulation and demodulation module includes a high-frequency sine generator, a high-pass filter, an integrated analog multiplier and a low-pass filter.

[0014] In one embodiment of the present invention, the high-frequency sine generator is the high-frequency sine generator used in the optical signal amplitude modulation module, and the signal function generated by the high-frequency sine generator is: ; The mathematical expression of the demodulated signal AM2 after amplification by the optical signal amplifier circuit is: ; Wherein, A1 is the original signal to be modulated, a is the amplitude coefficient of the received light signal after being amplified by the optical signal amplifying circuit, and Z is the DC offset coefficient of the received light signal after being amplified by the amplifying circuit. The DC offset coefficient can be removed by high-pass filtering the signal AM2 to obtain the received light amplified signal AM3 with the DC offset removed. The mathematical expression is: ; The output function of the integrated analog multiplier is: , by configuring the peripheral circuit of the integrated analog multiplier, changing the function to obtain the desired output function The input of the integrated analog multiplier is the light-receiving amplified signal AM3 with the DC offset removed and the carrier signal f1. AM3 is multiplied by the carrier signal f1 through the analog multiplier. Since the cosine component of AM3 and the cosine component of the carrier signal have the same frequency and phase, the output signal can be obtained after multiplication: , the signal is the original signal to be modulated A1 and the high frequency component The signal is filtered through a low-pass filter to remove the high-frequency component, and the original modulated signal A1 can be restored.

[0015] In one embodiment of the present invention, the interior of the laser photoelectric sensor adopts a vacuum glue potting process to provide waterproof and pressure-resistant protection for electronic components, and the external structure of the laser photoelectric sensor adopts a high-temperature vulcanized rubber process to provide waterproof and corrosion-resistant protection.

[0016] The above technical solution of the present invention has the following beneficial effects compared with the prior art: The laser photoelectric sensor suitable for marine environment described in the present invention adopts a 532nm wavelength blue-green laser as the transmitter, which is not easily absorbed or reflected by seawater. In addition, in order to avoid optical interference caused by the light signal reflected by seawater, the modulated light signal is emitted in an amplitude modulation manner, and the received signal is demodulated and restored using a modulated carrier with the same frequency and phase and compared with the emitted signal. Only the light signal emitted by itself or completely reflected by the detected object can trigger the receiving end of the photoelectric sensor to change the control signal, which greatly improves the sensor's ability to resist seawater interference. In view of the high pressure and high corrosiveness of seawater, the photoelectric sensor adopts a vacuum glue filling process and a high-temperature vulcanized rubber process for waterproof, pressure-resistant and corrosion-resistant protection, so that it can have high reliability and a long service life in seawater. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below according to specific embodiments of the present invention in conjunction with the accompanying drawings, wherein Figure 1 This is a schematic diagram of an amplitude modulation circuit in a preferred embodiment of the present invention; Figure 2A schematic diagram of a modulation and demodulation circuit in a preferred embodiment of the present invention; Figure 3 This is a schematic diagram of a laser photoelectric sensor suitable for marine environments in a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0018] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0019] The laser photoelectric sensor suitable for marine environment of the present invention comprises: a transmitter and a receiver; the transmitter comprises: a voltage stabilizing module, a control unit MCU module, a driving module, an optical signal amplitude modulation module and an optical signal transmitting module, the optical signal transmitting module comprises a high-power 532nm laser light source, the driving module comprises an LED laser light source driving circuit, the optical signal amplitude modulation module is used to load the luminous signal into the carrier of different frequency components, when propagating in the water body, only the light wave emitted by itself or the echo reflected by the detected object can keep the modulation information, and the echo reflected by the water body at different distances will be superimposed on each other and lose the modulation information; the receiver comprises: a photosensitive component for receiving the optical signal and a signal amplifying circuit connected to the photosensitive component, an optical signal modulation and demodulation module and an output circuit.

[0020] The optical signal modulation and demodulation module can restore the original light signal when demodulating the light signal emitted by itself or the light signal reflected by the detected object, thereby effectively removing the interference of the refraction of the seawater on the light signal.

[0021] The output circuit can change the output mode of the sensor according to the initialization setting of the sensor and the comparison result between the demodulated signal and the signal before transmission modulation.

[0022] The optical signal amplitude modulation module can obtain the required modulation signal by simulating the multiplication of the original signal to be modulated A1 and the carrier signal f1, and adding a DC component Bias. The modulation depth of the amplitude modulation can be changed by controlling the amplitude of the original signal to be modulated A1. The frequency of the carrier signal f1 is the frequency of the modulation signal. The DC component Bias is used to control the emission intensity of the above-mentioned optical signal transmitting module.

[0023] The optical signal amplitude modulation module includes a control unit MCU, a high-frequency sine wave generator, an integrated analog multiplier and a peripheral voltage regulator circuit; the peripheral voltage regulator circuit provides a positive power supply VDD and a negative power supply VSS to the optical signal amplitude modulation module, and the circuit reference provided by the peripheral voltage regulator circuit can obtain the proportional parameter SF and the DC component Bias required by the optical signal amplitude modulation module through voltage division; the control unit MCU outputs the original modulated signal A1 through the built-in DAC digital-to-analog converter; the high-frequency sine wave generator is used to configure the output carrier signal f1, and the signal expression function is ; Where f is the frequency of the sine wave signal, t1 and are respectively the time and phase of the carrier signal; the output function of the integrated analog multiplier is: , where X1 and X2, Y1 and Y2 represent the input quantities of the two differential multiplier input ports of the analog multiplier, respectively, and Z1 and Z2 represent the input quantities of the differential bias input ports of the analog multiplier, the same below. By configuring the peripheral circuit of the integrated analog multiplier, the output function of the analog integrated multiplier can be changed to achieve the required function, and its target output function is: , and then provide the original modulated signal A1 and the carrier signal f1 to the integrated analog multiplier, and the output is the required amplitude modulation signal.

[0024] The optical signal amplitude modulation module modulates any original signal to be modulated A1 and any frequency carrier signal f1 into an amplitude modulation signal AM1 with adjustable amplitude and offset. The mathematical expression is: .

[0025] The optical signal modulation and demodulation module multiplies the demodulated signal obtained after the optical signal amplification circuit is processed by the carrier signal f1 used by the optical signal amplitude modulation module. Since the optical signal amplitude modulation module and the carrier signal f1 used by the optical signal modulation and demodulation module have the same frequency and phase, the multiplied signal can be restored to the original undistorted modulated signal A1 through low-pass filtering. The optical signal modulation and demodulation module includes a high-frequency sine generator, a high-pass filter, an integrated analog multiplier and a low-pass filter.

[0026] The high-frequency sine generator is a high-frequency sine generator used in the optical signal amplitude modulation module, and the signal function generated by it is: ; The mathematical expression of the demodulated signal AM2 after amplification by the optical signal amplifier circuit is: ; Wherein, A1 is the original signal to be modulated, a is the amplitude coefficient of the received light signal after being amplified by the optical signal amplifying circuit, and Z is the DC offset coefficient of the received light signal after being amplified by the amplifying circuit. The DC offset coefficient can be removed by high-pass filtering the signal AM2 to obtain the received light amplified signal AM3 with the DC offset removed. The mathematical expression is: ; The output function of the integrated analog multiplier is: , by configuring the peripheral circuit of the integrated analog multiplier, changing the function to obtain the desired output function The input of the integrated analog multiplier is the light-receiving amplified signal AM3 with the DC offset removed and the carrier signal f1. AM3 is multiplied by the carrier signal f1 through the analog multiplier. Since the cosine component of AM3 and the cosine component of the carrier signal have the same frequency and phase, the output signal can be obtained after multiplication: , the signal is the original signal to be modulated A1 and the high frequency component The signal is filtered through a low-pass filter to remove the high-frequency component, and the original modulated signal A1 can be restored.

[0027] The interior of the laser photoelectric sensor adopts a vacuum glue filling process to provide waterproof and pressure-resistant protection for electronic components, and the external structure of the laser photoelectric sensor adopts a high-temperature vulcanized rubber process to provide waterproof and corrosion-resistant protection.

[0028] Reference Figure 1 As shown in: 1 is an integrated analog multiplier, which is used to synthesize the modulation wave mentioned above; 2 is an adjustable proportional parameter module, which provides an adjustable amplification factor for the modulation wave ; 3 is a waveform input module to be modulated, which provides the original modulated signal A1 generated by the control unit MCU module of the ocean laser sensor for the modulated wave AM1; 4 is a carrier input module, which provides a high-frequency cosine carrier signal f1 for the modulation wave AM1; 5 is an adjustable DC bias module, which is used to provide an adjustable DC component Z2 for the modulation wave AM1; 6 is an output high-pass filter module, which filters out the low-frequency component in the output waveform of the integrated analog multiplier; 7 is a modulation wave AM1 output module. This modulation wave is output to the LED drive circuit and is the emission signal of the laser transmitter.

[0029] Reference Figure 2 As shown in: 10 is a signal input module to be demodulated, and this signal is an electrical signal after the signal received by the photosensitive element is conditioned by the signal amplification circuit; 20 is an input high-pass filter module, which removes the DC component and stray low-frequency noise in the signal to be demodulated; 30 is an integrated analog multiplier input module, which inputs a high-frequency AC demodulated signal AM3 to the integrated analog multiplier; 40 is a demodulation carrier input module, which inputs the carrier f1 with the same frequency and phase as that in the aforementioned signal modulation module into the integrated analog multiplier to restore the original signal; 50 is an adjustable output DC bias module, which changes the DC offset output by the demodulation circuit so that the output signal can be read by the control unit MCU; 60 is an integrated analog multiplier, which is configured to multiply the demodulated signal AM2 with the carrier signal f1 and output the original signal before modulation; 70 is an adjustable proportional parameter module, which is used to provide an adjustable amplification factor for the output signal ; 80 is an output low-pass filter module, which can filter out the high-frequency components in the output signal of 60 to obtain the original signal to be modulated A1; 90 is a demodulated signal output module, which inputs the signal into the control unit MCU of the laser photoelectric sensor and compares it with the original signal to be modulated A1 generated by the control unit MCU, so as to determine whether the signal received by the photoelectric sensor is a reflected echo of the transmitted signal. Reference Figure 3 As shown in: 100 is a power input port module, which is used to provide over-current, over-voltage, under-voltage and EMC protection for the internal voltage stabilization circuit; 200 is a voltage stabilizing circuit module, which is responsible for providing a stable working voltage level to the internal electronic appliances; 300 is a driving circuit module, which can drive the LED transmitting tube at high frequency and high efficiency; 400 is a 532nm laser light source module, whose transmitting unit is the special wavelength emitting LED mentioned above. The emitted laser signal has the characteristics of strong seawater penetration and is not easily interfered with. 500 is a photosensitive element module, the sensitive wavelength of which is the emission wavelength of the special wavelength light-emitting LED mentioned above, and can convert the light signal emitted by 400 into an electrical signal; 600 is a signal amplification circuit module, which is used to perform signal conditioning processing such as filtering and amplification on the electrical signal converted by 500, in preparation for subsequent signal processing; 700 is an amplitude modulation circuit module, which is used to convert the low-frequency signal to be modulated sent by the control unit MCU into a high-frequency modulation signal to be finally transmitted; 800 is a carrier generation circuit module, which has the ability to stably generate a high-frequency carrier under various working conditions. The high-frequency carrier is used to modulate and demodulate the signal; 900 is a modulation and demodulation circuit module, which performs signal synthesis processing on the output signal of 600 and the carrier signal output by 800, and outputs a demodulated signal of the light signal received by the photosensitive element to the control unit MCU; 1010 is a control unit MCU module, which is the central control system of the laser photoelectric sensor. Its main functions are: providing the emission signal to be modulated to 700, controlling the frequency and phase of the carrier generated by 800, receiving and identifying the demodulated received signal output by 900 and comparing it with the emission signal, judging whether the received light is the reflected light of the emission light, and issuing an output control signal according to the judgment result; 1011 is an output circuit module, which can change the output state of the laser photoelectric sensor according to the output control signal sent by 1010.

[0030] Obviously, the above embodiments are merely examples for clear explanation and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the protection scope of the invention.

Claims

1. A laser photoelectric sensor suitable for marine environment, characterized in that: include: Transmitters and receivers; The transmitter includes: a voltage stabilizing module, a control unit MCU module, a driving module, an optical signal amplitude modulation module and an optical signal transmitting module, wherein the optical signal transmitting module includes a high-power 532nm laser light source, the driving module includes an LED laser light source driving circuit, and the optical signal amplitude modulation module is used to load the light emitting signal into carriers of different frequency components. When propagating in the water body, only the light waves emitted by itself or the echoes reflected by the detected object can maintain the modulation information, and the echoes reflected by the water bodies at different distances will be superimposed on each other and lose the modulation information; The receiver comprises: a photosensitive component for receiving a light signal, a signal amplifying circuit connected to the photosensitive component, a light signal modulation and demodulation module and an output circuit.

2. The laser photoelectric sensor suitable for marine environment according to claim 1, characterized in that: The optical signal modulation and demodulation module can restore the original light signal when demodulating the light signal emitted by itself or the light signal reflected by the detected object, thereby effectively removing the interference of the refraction of the seawater on the light signal.

3. The laser photoelectric sensor suitable for marine environment according to claim 1, characterized in that: The output circuit can change the output mode of the sensor according to the initialization setting of the sensor and the comparison result between the demodulated signal and the signal before transmission modulation.

4. The laser photoelectric sensor suitable for marine environment according to claim 1, characterized in that: The optical signal amplitude modulation module can obtain the required modulation signal by simulating the multiplication of the original signal to be modulated A1 and the carrier signal f1, and adding a DC component Bias. The modulation depth of the amplitude modulation can be changed by controlling the amplitude of the original signal to be modulated A1. The frequency of the carrier signal f1 is the frequency of the modulation signal. The DC component Bias is used to control the emission intensity of the above-mentioned optical signal transmission module.

5. The laser photoelectric sensor suitable for marine environment according to claim 4, characterized in that: The optical signal amplitude modulation module includes a control unit MCU, a high-frequency sine wave generator, an integrated analog multiplier and a peripheral voltage stabilization circuit; The peripheral voltage stabilizing circuit provides a positive power supply VDD and a negative power supply VSS to the optical signal amplitude modulation module. The circuit reference provided by the peripheral voltage stabilizing circuit can be used to obtain the proportional parameter SF and the DC component Bias required by the optical signal amplitude modulation module through voltage division; The control unit MCU outputs the original signal A1 to be modulated through the built-in DAC digital-to-analog converter; The high-frequency sine wave generator is used to configure the output carrier signal f1, and the signal expression function is: ; Where f is the frequency of the sine wave signal, t1 and are the time and phase of the carrier signal respectively; The output function of the integrated analog multiplier is: , where X1 and X2, Y1 and Y2 represent the input quantities of the two differential multiplier input ports of the analog multiplier, respectively, and Z1 and Z2 represent the input quantities of the differential bias input ports of the analog multiplier, the same below. By configuring the peripheral circuit of the integrated analog multiplier, the output function of the analog integrated multiplier can be changed to achieve the required function, and its target output function is: , and then provide the original modulated signal A1 and the carrier signal f1 to the integrated analog multiplier, and the output is the required amplitude modulation signal.

6. The laser photoelectric sensor suitable for marine environment according to claim 5, characterized in that: The optical signal amplitude modulation module modulates any original signal to be modulated A1 and any frequency carrier signal f1 into an amplitude modulation signal AM1 with adjustable amplitude and offset. The mathematical expression is: .

7. The laser photoelectric sensor suitable for marine environment according to claim 1, characterized in that: The optical signal modulation and demodulation module multiplies the demodulated signal obtained after processing by the optical signal amplification circuit with the carrier signal f1 used by the optical signal amplitude modulation module. Since the frequency and phase of the carrier signal f1 used by the optical signal amplitude modulation module and the optical signal modulation and demodulation module are the same, the multiplied signal can be restored to the original undistorted modulated signal A1 by low-pass filtering.

8. The laser photoelectric sensor suitable for marine environment according to claim 7, characterized in that: The optical signal modulation and demodulation module comprises a high-frequency sine generator, a high-pass filter, an integrated analog multiplier and a low-pass filter.

9. The laser photoelectric sensor suitable for marine environment according to claim 8, characterized in that: The high-frequency sine generator is the high-frequency sine generator used in the optical signal amplitude modulation module, and the signal function generated by it is: ; The mathematical expression of the demodulated signal AM2 after amplification by the optical signal amplifier circuit is: ; Wherein, A1 is the original signal to be modulated, a is the amplitude coefficient of the received light signal after being amplified by the optical signal amplifying circuit, and Z is the DC offset coefficient of the received light signal after being amplified by the amplifying circuit. The DC offset coefficient can be removed by high-pass filtering the signal AM2 to obtain the received light amplified signal AM3 with the DC offset removed. The mathematical expression is: ; The output function of the integrated analog multiplier is: , by configuring the peripheral circuit of the integrated analog multiplier, changing the function to obtain the desired output function The input of the integrated analog multiplier is the light-receiving amplified signal AM3 with the DC offset removed and the carrier signal f1. AM3 is multiplied by the carrier signal f1 through the analog multiplier. Since the cosine component of AM3 and the cosine component of the carrier signal have the same frequency and phase, the output signal can be obtained after multiplication: , the signal is the original signal to be modulated A1 and the high frequency component The signal is filtered through a low-pass filter to remove the high-frequency component, and the original modulated signal A1 can be restored.

10. The laser photoelectric sensor suitable for marine environment according to claim 1, characterized in that: The interior of the laser photoelectric sensor adopts a vacuum glue-filling process to provide waterproof and pressure-resistant protection for electronic components, and the external structure of the laser photoelectric sensor adopts a high-temperature vulcanized rubber process to provide waterproof and corrosion-resistant protection.

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