Problem
An oceanographer asked us do design a small, lightweight and inexpensive data logger to record water temperature and pressure. The researcher also desired a simple method to attach the device to a cable.
Solution
We decided to encapsulate the circuit in urethane to produce a light, inexpensive waterproof pressure case. The circuit contained a processor, data storage memory, high resolution temperature and pressure sensors. It included an inductive serial communications interface to allow the device to be programmed and data to be retrieved.
The typical way similar instruments were attached to cables was to cut the cable and attach shackles to the ends. The cable was prepared before the ship went to sea, and when the instruments were being deployed the cable was stopped, the shackles opened, and the unit was attached to both ends of the cable. This procedure was time consuming and required the lower end of the cable to be secured to the ship before the shackles were parted. This also required the instrument to have a heavy enclosure that was strong enough to support the weight of the anchor, cable, and any other instruments in the chain.
The 9311 was designed in two sections. One side was the data logging instrument and the other was the battery. The two sections fit together on a hinge pin, allowing the unit to swing open. Two tabs projected from each half of the case. The tabs on the battery pack had channels to allow the unit to fit around a mooring cable. The wires connecting the battery to the circuit were enclosed in a pocket between the two halves.
Prior to deployment the mooring cable was prepared by crimping a sleeve around the wire at each data logger position. When the units were deployed the cable was stopped with a sleeve at the deck edge. A technician then simply clamped the 9311 around the cable with the sleeve between the tabs and then fastened the case around the cable with plastic cable ties. Retrieving the instrument was a simple matter of clipping the cable ties as the units were raised to deck level.
Results
The 9311s were used in several projects. Two versions were built, one with both temperature and pressure sensors and a lower cost unit with a temperature sensor only.