A multi-channel data logger of in-situ chemical sensors for cabled seafloor observatories

This paper describes the development of a multi-channel data logger for real-time in-situ monitoring. The data logger can connect various types of chemical sensors, including pH electrode, Ca²⁺ electrode, H₂S sensor, etc. It can process the signals of these chemical sensors with high input impedance, online communication, low power consumption, compact size and high reliability. The data logger consists of a preamplifier circuit for processing signals from the sensors, a micro controller unit (MCU), a flash memory, a RS-485 communication interface and a power module. A cylindrical pressure vessel ensures the security and reliability of the data logger when used under deep sea. The data logger with a novel pH sensor which consists of the all-solid-state reference and pH electrode based on poly(3,4-ethylenedioxythiophene) (PEDOT) doped with poly(styrenesulfonate) (PSS) (PEDOT(PSS)) and plasticized polyvinyl chloride (PVC) membrane was tested to measure five tris(hydroxymethyl)aminomethane-HCl (Tris-HCl) buffer solutions at different pH values. And the results prove that the data logger works well and meets the requirements of cabled seafloor observatories.