This invention relates to instrumented cables and more particularly to condition sensing cables such as are used to determine physical conditions in the ocean or other medium.
Condition sensing cables having a linear array of electrical instruments incorporated on or in the cable have been used in collecting data on, or monitoring of, conditions of temperature, pressure or the like, in large bodies of water. Similarly, temperature sensing cables have been used to maintain surveillance of temperatures at various levels in large masses of particulate material, for example grain in a storage elevator.
Measurements of ocean temperature gradients are obtained by suspending a cable through the zone of measurement, which cable is provided with a plurality of temperature sensors, usually thermistors, spaced therealong. Each thermistor usually requires a pair of wires and accordingly the cable usually comprises a bundle of insulated wire pairs, equal in number to the number of thermistors.
A variety of prior art temperature sensing cables have been known. However, they have generally included heavy strength members in an effort to prevent strecthing and breakage of wires and molded plastic or rubber sheaths in the interest of protection against a hostile environment and also against damage during shipboard handling and deploying. Because the measurement zones of interest have been expanded to require sensing cables of 1000 meters or more in length that can be towed from a ship or suspended for extended periods from a buoy or float, the prior art cables of the just mentioned constructions have proven to be too heavy, stiff and unwieldy to be practical. In addition, they have generally been unable to withstand the jerking motions imposed by wave actions on the buoys.
A considerable measure of improvement has been achieved in the construction of thermistor array cables which are more flexible and light in weight by providing a bundle of wire pairs bound together by a suitable frapping, fishing a wire pair from the bundle at each sensing station, connecting the leads of a thermistor to the wires, coating the thermistor and its connections with a potting compound in a bulge at the side of the bundle, and then running the bundle through as rope braiding machine to weave a tightly braided cover of nylon, aramid fiber, or other plastic material over the bundle and thermister bulges to provide a finished thermistor array or cable.
Experience has shown, however, that although such a cable is superior to its predecessors, some of the thermistors will be damaged or connections broken either in passage through the braiding machine or due to flexing and jerking in use.