Page 322 - The ROV Manual - A User Guide for Remotely Operated Vehicles 2nd edition

314 CHAPTER 12 Sensor Theory
Sensor
Electrical output
FIGURE 12.13
Binary data
Signal (time varying)
Reception (time varying)
Binary data
Interface
Transmitter
Receiver
Interface
Output device
Sensor information
Simplified model of a sensor system.
is the requirement for a fiber-optic multiplexer on both the vehicle and the surface for transmit and receive (TX/RX) functions on the spare fiber as well as the requirement for another pass on the fiber- optic rotary joint (FORJ or “slip ring”).
12.1.7 Installation
The final consideration for sensor system integration is the placement of the sensor on the vehicle necessary to achieve the desired outcome. As previously discussed, the sensor may be fully func- tional and still output erroneous and/or nonusable information. The sensor must be placed in a loca- tion that allows for sensing the environment. It must be free from the parasitic influences of the vehicle and be allowed to assess the local conditions with the full dynamic range of the sensor’s capabilities.
12.2 Sensor categories
It would be difficult to include all possible ROV-deployed sensors within this section; however, the basic categories of subsea sensors typically used in the subsea environment will be examined. Sensors break down into categories based upon the type of physical phenomena being sensed.
12.2.1 Acceleration/shock/vibration
This sensor measures acceleration and outputs the measurement into various formats depending upon the sensor’s application. The output of this category of sensor is typically used for vehicle control, position, orientation, or other motion-based parameters.
The most common sensor technology in this category is the piezoelectric accelerometer due to the sensor’s wide linear amplitude, range, and rugged durability (Figure 12.14). The piezoelectric properties of the sensor allow for a proportional electrical output signal due to the stress applied to the materials. Using this general sensing method upon which all accelerometers are based, accelera- tion acts upon a known mass that is restrained by a spring or suspended on a cantilever beam and converts a physical force into an electrical signal. Before the acceleration can be converted into an electrical quantity, it must first be converted into either a force or displacement.