Page 166 - The ROV Manual - A User Guide for Remotely Operated Vehicles 2nd edition

154 CHAPTER 7 Power and Telemetry
properly control the vehicle. With the cost of broadband fiber-optic transmission equipment drop- ping into the range of most small ROV equipment manufacturers’ budgets, more applications and sensors should soon become available to the ROV marketplace. The ROV is simply a delivery plat- form for transporting the sensor and tooling packages to the work location. The only limitation to full sensor feedback to the operator will remain one of lack of funding and imagination. The human
robot interaction (the intuitive interaction protocol between the human operator and the robotic vehicle) is still in its infancy; however, sensors are still outstretching the human’s ability to interpret this data fast enough to react to the feedback in a timely fashion. This subject is probably the most exciting field of development for the future of robotics and will be of considerable interest to the next generation of ROV pilots.
7.1.7.1.3 Data transmission and protocol
Most small ROV manufacturers simply provide a spare shielded twisted pair (STP) of conductors for hard-wire communication of sensors from the vehicle to the surface, while on larger vehicles the sensor output is routed through the vehicle’s telemetry system or with a separate break-out fiber. The strength of the break-out method is that the sensor vendor does not need engineering sup- port from the ROV manufacturer in order to design these sensor interfaces. The weakness is that unless the sensor manufacturers collude to form a set of transmission standards, each sensor con- nected to the system “hogs” the data transmission line to the detriment of other sensors needed for the task. A specific example of this problem is the need for concurrent use of an imaging sonar sys- tem and an acoustic positioning system. Unless the manufacturers of each sensor package agree upon a transmission protocol to share the single STP data line, only one instrument may use the line at a time. A few manufacturers have adapted industry standard protocols for such transmis- sions, including TCP/IP, RS-485, and other standard protocols. The most common protocol, RS-232, while useful and seemingly ubiquitous in the computer industry, is distance limited through conductors, thus causing transmission problems over longer lengths of tether. On larger ROV systems, a common (albeit expensive) technique is to place a multiplexer into a separate cir- cuit for gathering sensor data feed into a central point and then transmitting through a separate copper or fiber line. More on this technique in Chapter 17.
7.1.7.1.4 Underwater connectors
The underwater connector is said to be the bane of the ROV business. Salt water is highly conductive, causing any exposed electrical component submerged in salt water to “leak” to ground. The result is the “ubiquitous ground fault” as discussed in Section 7.1.4. The purpose of an underwater connector is to conduct needed electrical currents through the connector while at the same time squeezing the water path and sealing the connection to lower the risk of electrical leakage to ground.
The underwater connector is lined with metal or synthetic rubber that blocks the ingress path of water while allowing a positive electrical connection. Connectors sometimes experience cathodic delamination, causing rubber peeling and flaking from the connector walls.
Even when the contacts are right and the connector has good design features, the connector must be appropriate for the intended use and environment. The connector materials must be able to withstand the environmental conditions without degradation. For example, extended exposure to sunlight (ultraviolet energy) will cause damage to neoprene, and many steels will corrode in seawa- ter. Check that the connector will fully withstand the environment.