Page 326 - The ROV Manual - A User Guide for Remotely Operated Vehicles 2nd edition

318 CHAPTER 12 Sensor Theory
FIGURE 12.17
Benzene infrared spectrum
0.8 0.6 0.4 0.2 0.0
3000 2000 1000 Wavenumber (cm–1)
Benzene infrared spectrum.
simply emits light at one frequency and senses fluorescence at the second resonant frequency to posi- tively identify the compound.
Other methods of sensing chemical compounds in water are through electrochemical detection tech- niques such as particle diffusion, gas chromatography as well as many other technologies. Chemical testing has a much broader capability for sampling in air, but water (being the universal solvent) allows trace elements to be suspended in solution for sensing at low chemical concentrations. Consult a basic text on chemical sensing for further information on this topic (such as Wilson, 2005).
12.2.4 Capacitive/inductive sensors
Capacitive/inductive sensors measure conductive potential between two conductors that are sepa- rated by nonconductive materials. The advantages of this noncontact technique include higher dynamic response to moving targets, higher sensor resolution, more rugged sensor design, and min- imal hysteresis.
Both capacitive and inductive sensors consist of a probe as well as a driver. The probe generates the sensing field while the driver drives the probe’s electronics. These types of sensors are used extensively in applications whereby the sensor is needed to measure proximity to certain conductive materials (e.g., paint coating thickness) or for measurement of metal integrity (e.g., eddy current measurement).
Capacitance probes are reactive to three parameters:
1. The relative surface sizes of the probe/target combination 2. The size of the gap between the probe and target
3. The makeup of the material within the gap
(From NIST webbook.)
Transmittance