Page 331 - The ROV Manual - A User Guide for Remotely Operated Vehicles 2nd edition

deformation of the transducer and (considering that a voltage is applied to the transducer element) the resistance measurement directly correlates to the load applied. The sensor element can be any of a series of sensor types including a “bending beam,” column-type load cell, or shear-web. All have their strengths and weaknesses depending upon the particular application.
12.2.8 Humidity
Humidity is the measure of water vapor in air or other gases and is measured as a ratio of the tem- perature/dew point spread or relative humidity (ratio of moisture content to the saturation point considering a constant pressure/temperature combination—abbreviated “RH”).
As with other sensors described above, RH sensors can make use of several technologies includ- ing capacitive RH sensors, thermoset polymer-based capacity RH sensors, and resistive humidity sensors.
Humidity sensors are sometimes used in subsea vehicles as moisture sensors inside air-filled electronics bottles to sense for water intrusion.
12.2.9 Optical and radiation
The sensing of optical and near-infrared radiation is useful for many applications using light detec- tion sensors. Light comes in discrete particles called “photons” that have an energy and wavelength—the determination of which yields some peculiar characteristics useful in the subsea industry.
Light detectors can be characterized as either quantum detectors (converting radiation directly into electrical signals in semiconducting materials) or thermal detectors (absorbing thermal energy for indirect measurement of radiated energy).
Optical sensors do not see widespread use in the subsea industry other than through light- sensing devices tied to artificial lighting.
12.2.10 Other sensors
Other sensors that find limited use in the subsea industry include radiation sensors such as the so- called Geiger Counter. The Geiger
Mu¨ller tube (commonly referred to as “GM tube”) detects alpha, beta, or gamma rays through ionization produced in a low-pressure gas. These instruments detect the presence of radiation (quantity but not magnitude/energy) by sensing the ionization of the gas. The gas becomes momentarily conductive when ionized through the “Townsend ava- lanche effect,” thus conducting a current through the gas—the event of conduction is then counted per unit time (or cumulative) by electronic circuits. This is useful with primary and secondary cool- ing tank inspections within nuclear power plants (which are often inspected via ROV). Gamma radiation detectors of various types have been developed for ROV use.
There is a wide array of additional sensors available for use in the subsea industry. The require- ments for use of these sensors are simply to provide power for the sensor’s electronics and a communications channel for transmission of the data to the surface for dissemination and discrimination.
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