The temperature and salinity of seawater are essential physical parameters for marine science. The measurement of conductivity is an important means of salinity measurement. In this article, seven electrodes are used to design a temperature and salinity sensor. The sensor detects voltage signal and current signal in strong marine noise environments using lock-in amplifier technology to improve the measurement accuracy of seawater conductivity. A seven-electrode temperature and salinity sensor and a Seabird SBE37-SI temperature and salinity sensor are used for laboratory comparison, the temperature measurement error and the conductivity measurement error are within ±0.005°C and ±0.0003s/m. The temperature and salinity sensor is installed on an ocean buoy, and offshore testing is carried out. The test data shows that the sensor's measurement data is accurate and reliable, and can be used to measure the temperature, conductivity, and salinity of seawater.
In the observation of CO2 flux, high-speed and high-precision measurement of CO2 concentration is an urgent problem to be solved, and the collection frequency of CO2 concentration must be greater than 10Hz. The Tunable Diode Laser Absorption Spectroscopy (TDLAS) technology is widely used in various gas monitoring fields with high requirements for sensitivity, response time, and no background gas interference. In this paper, interband cascade laser at 4.26 micron is used as the system light source, and the second harmonic peak-peak value and the Root Mean Square (RMS) of sinusoidal are used to measure the CO2 concentration. When the laser CO2 analyzer was developed, comparative experiments were conducted using LI-7500DS and self-developed equipment. The CO2 concentration values measured by the laser gas analyzer and the LI-7500DS gas analyzer are synchronously collected using a sampling frequency of 10 Hz. The experimental results show that the trend of CO2 concentration measured by the two devices is consistent, and deviation of CO2 concentration is within ±2%, which can meet the needs of carbon dioxide flux measurement.
Seawater salinity is one of the basic elements of marine hydrological observation, and seawater conductivity measurement is an important means of salinity measurement. In order to improve the measurement accuracy of seawater conductivity sensor, a seven-electrode conductivity sensor is developed by using lock-in amplifier technology, which can measure the seawater conductivity by detecting the voltage and current signals in the strong noise environment. The comparison experiment was carried out by using seven-electrode conductivity sensor and seabird CTD sensor SBE 37-SI, the indication error of conductivity measurement is within ±0.0003s/m, which can meet the needs of high-precision measurement of seawater conductivity.
The linearity and the stain resistance of existing humidity sensor is poor, which exists the problems such as low resolution at low temperatures, low faded wet in high humidity environment, large measurement error and long response time. Tunable diode laser absorption spectroscopy technology is studied to measure the environmental humidity, and digital quadrature lock-in amplifiers are used to extract the first harmonic signal and the second harmonic signal, which can eliminate the influence of the phase delay angle and can improve the detection accuracy of the system. Comparative experiment between TDLAS humidity sensor and R.M.YOUNG humidity sensor was completed in the lab, experimental results show that the consistency of the humidity data is very good, which can proves the validity of the TDLAS humidity measurement technology.
Humidity is an important environmental parameter, which is difficult to be measured accurately and quickly using traditional measurement methods. Under the environment of low temperature or high humidity, traditional humidity and temperature sensor has shortages in humidity measurement accuracy, corresponding time and wet fade speed. To solve these problems, this paper proposes a method to measure the environmental humidity with wavelength modulation technology and harmonic detection technology based on tunable diode laser absorption spectroscopy. H2O molecular absorption line near 1392 nm is selected as the characteristic spectra. The effects of temperature, pressure and water concentration on the absorption spectrum width, the wavelength modulation coefficient and the amplitude of the harmonic signal are analyzed. Humidity and temperature sensor is modified using temperature and pressure compensation model, and the influence of the water concentration variation is eliminated by the iterative algorithm. The new humidity and temperature sensor prototype is developed, and the structure of the optical system is simple, which is easy to be adjusted. The response frequency of the humidity detection is 40 Hz. The experiment was carried out for 3 months at Qingdao national basic weather station. Experimental results show that the consistency of the humidity and temperature data is very good, which can proves the validity of the humidity measurement technology.
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