Development Of Seawater Salinometer Based On Photoelectric Sensing Technology

Detection of seawater salinity has a very important practical significance for oceanographic research, marine environmental monitoring, seasonal climate prediction, marine fisheries and so on. However, at present the sensors mostly used at home and abroad are based on the traditional conductivity method to achieve its long-term continuous detection, which has an error coming from non-synchronized detection of three parameters. Therefore, this paper is committed to the development of a novel seawater salinity meter, to overcome the shortcomings of the traditional conductivity CTD instrument.Based on sufficient investigation of salinity detection techniques at home and abroad, this paper systematically proposes a seawater salinity measurement scheme based on a novel approach, establishes a mathematical model, designed the sensing probe structure and produces a prototype. In this paper, the applied core theory is the refractive index differential measurement principle and semiconductor optical absorption principle. The primary works in this paper are resting on the achievements of past generations as well as our own and making the corresponding improvement to these achievements, in detail includes the following aspects:1. Propose a salinity detection method based on the refractive index of seawater and with PSD as the core component, and design the corresponding sensor model. In the sensor model, the introduction of a reference fluid design idea, forms a differential measurement, effectively eliminating the temperature effect on the measurement results.2. On the basis of theoretical derivation and simulation analysis, design and produce a salinity sensor. The prototype has advantages of simple structure, low cost, high practicality, being convenient for remote measurement and easy to be realized and so on.3. Improve the laser light source and PSD used in the old prototype, use a modular light source and higher-resolution PSD, significantly improving the system accuracy and stability.4. Improve the sink structure of the old prototype, in which previously two water tanks are extended to five tanks, and further amplify the location offset of the light emitted, improve the system resolution.5. Improve the light emission and signal conditioning circuitry of the old prototype, increase the light source modulation and enhance software filtering algorithm, effectively reduce impact on the measurement from background light, dark current and external disturbance.Finally, on the basis of repeated experiments, measure the salinity calibration curves, and the stability and influencing factors of the system are also measured. Salinity detection resolution reaches 0.0198‰, with resolution about two orders of magnitude higher than the old prototype. The stability is better than±0.034‰. The error cause by temperature and disturbance is 0.027%o/℃and±0.0913‰respectively. Experimental results validate the rationality of the system scheme and structural design, and the effectiveness of improvement measures of the new prototype. Detection of seawater salinity has a very important practical significance for oceanographic research, marine environmental monitoring, seasonal climate prediction, marine fisheries and so on. However, at present the sensors mostly used at home and abroad are based on the traditional conductivity method to achieve its long-term continuous detection, which has an error coming from non-synchronized detection of three parameters. Therefore, this paper is committed to the development of a novel seawater salinity meter, to overcome the shortcomings of the traditional conductivity CTD instrument.Based on sufficient investigation of salinity detection techniques at home and abroad, this paper systematically proposes a seawater salinity measurement scheme based on a novel approach, establishes a mathematical model, designed the sensing probe structure and produces a prototype. In this paper, the applied core theory is the refractive index differential measurement principle and semiconductor optical absorption principle. The primary works in this paper are resting on the achievements of past generations as well as our own and making the corresponding improvement to these achievements, in detail includes the following aspects:1. Propose a salinity detection method based on the refractive index of seawater and with PSD as the core component, and design the corresponding sensor model. In the sensor model, the introduction of a reference fluid design idea, forms a differential measurement, effectively eliminating the temperature effect on the measurement results.2. On the basis of theoretical derivation and simulation analysis, design and produce a salinity sensor. The prototype has advantages of simple structure, low cost, high practicality, being convenient for remote measurement and easy to be realized and so on.3. Improve the laser light source and PSD used in the old prototype, use a modular light source and higher-resolution PSD, significantly improving the system accuracy and stability.4. Improve the sink structure of the old prototype, in which previously two water tanks are extended to five tanks, and further amplify the location offset of the light emitted, improve the system resolution.5. Improve the light emission and signal conditioning circuitry of the old prototype, increase the light source modulation and enhance software filtering algorithm, effectively reduce impact on the measurement from background light, dark current and external disturbance.Finally, on the basis of repeated experiments, measure the salinity calibration curves, and the stability and influencing factors of the system are also measured. Salinity detection resolution reaches 0.0198‰, with resolution about two orders of magnitude higher than the old prototype. The stability is better than±0.034‰. The error cause by temperature and disturbance is 0.027%o/℃and±0.0913‰respectively. Experimental results validate the rationality of the system scheme and structural design, and the effectiveness of improvement measures of the new prototype.