Development Of A Multi-Channel Data Logger For Detection Of Marine Chemical Parameters

This thesis describes the development of a. multi-channel data logger in the deep sea for real-time in-situ monitoring. The data logger can process the signals of both ion-selective electrodes (ISEs) and current type sensor simultaneously with the characteristics of high input impedance, online communication, low power consumption, compact size and high reliability. It can connect various types of chemical sensors, including pH electrode, Ca2+electrode, H2S sensor, etc. The data logger consists of a preamplifier circuit for processing signals from the sensors, a micro controller unit (MCU) for circuit control, a flash memory for data storage, a RS-485communication interface and a power module. The thesis designs these sub-modules separately and integrates them to a whole system.The thesis takes MSP430F149of the Texas Instruments as the MCU. MSP430F149has characteristics of abundant on-chip peripheral modules, ultra-low power consumption and low supply voltage. So it is suitable for system miniaturization and low power consumption design. According to calculation, the data logger can operate for283days continuously with2Hz sampling frequency. The signal acquisition channels of ISEs utilize the operational amplifier which has high input impedance to follow the voltages, which ensures the data logger measure the signals of ISEs accurately. The signal acquisition channel of current type sensor utilizes the three-electrode system. The signal acquisition channel of temperature sensor utilizes three-wire circuits which could eliminate the wire resistance and improve the accuracy of measurement. The power module consists of a low dropout linear regulator and two lithium batteries. The storage module is a1GB flash memory. The communication module utilizes RS-485protocol. Then the thesis continues data format definition, communication protocol development and state machine setting which are the software parts of the system.The thesis shows the tests of data acquisition, data storage and communication function of the data logger, especially the tests of the signal acquisition channels of ISEs, current type sensor and temperature sensor. The results show the data logger achieves the expected goals and all the modules of the data logger work well. The thesis also shows the experiments of data logger with pH electrodes and dissolved oxygen sensor. The results prove that the data logger could acquire the signals of the sensors very well.