7.2. Sensors
Ship Sensors
A sensor is a device that collects real-life data and transfers it to the control system to monitor or control the system under control: either it is engineering system (ballast, fuel, cooling, etc.) or the unmanned autonomous vessel, proceeding without the crew.
An engineering sensor controls engineering systems: fuel supply, steam or fuel pressure, tank level, presence of light, smoke, etc. Navigation sensors can assist in autonomous ship navigation, cargo sensors can be useful in prevention of parametric rolling, explosions, self-ignition of cargo, liquefaction, affecting safe navigation. Crew member and passenger sensors include such functions as the identification of visual cards, CCTV cameras observation, eye scanning and fingerprint technologies, space occupancy detection, accident (slip and fall) detection as well as Man Overboard detection.
All sensors can be classified as analogous or digital.
Analogue signal is the “original “signal, that is expressed in m/s for speed, volts for voltage, etc. Analogous sensors measure the parameter continuously, while digital sensors measure the parameter in frequent intervals of time, each time receiving the value of the parameter in zeros and ones. Analogous signals are converted into digital ones for the processing with microcomputers.
Engineering sensors are the most typical ones.
According to the parameters they measure the following: pressure; temperature; humidity; position; rotation; speed; velocity; distance; acceleration; angle; direction; force; strain; torque; vibration; voltage; current; resistance; capacitance; impedance; power; frequency; count; fluid level; fluid capacity; viscosity; heave/pitch/roll; air flow; motion; noxious gas; time/date; error, other.
For example, one class of sensors measures fluid and bulk level of different liquid tanks (potable, ballast water, black sewage, hydraulic fluid, fuel, lubricant oil, waste oil or liquefied gases).
This can be done by a resistive element, attached to a float or lever; depending on the movement of it, the resistance changes and indicates the level of liquid.
Hydrostatic sensors measure hydrostatic pressure of liquid column.
Capacitance sensors send radiofrequency signals that vary due to dielectric changes in the rise and fall of liquid level.
Radar and ultrasound sensors emit signals (microwaves or sound signals) that are sent from tank top to the tank bottom, they reflect from the liquid surface and the amount of ullage is detected. Thus the remaining liquid in the tank can be ascertained.
Also gas sensors for the detection of atmosphere composition, oxygen, carbon monoxide (CO) hydrogen sulfide (H2S) and Lower Explosive Limit (LEL) of such gases as methane or natural gas are useful for detecting hazardous conditions in enclosed spaces.
Microphones can be considered as sensors for the Public Addressing (PA) system.
Video Cameras can also be regarded as sensors for video images. In engineering, cameras with infrared spectrums can assist in detecting machinery that is running hot.
Reference:
Wright, R. G. (2024) Ship sensors: conventional, unmanned and autonomous. First ed. Routledge, N.Y.