U.S. Geological Survey Open-File Report 2009-1101
The Partition Intervalometer: A Programmable Underwater Timer for Marking Accumulated Sediment Profiles Collected in Anderson Sediment Traps: Development, Operation, Testing Procedures, and Field Results
After the newly designed instruments were fabricated and assembled, extensive laboratory trials and operational protocols were developed. Additionally, the instruments were tested in pressure chambers to ensure the proper operation of the firmware, mechanical and electronic components, and watertightness of the pressure cases.
Each Intervalometer was filled with 20 sequentially numbered discs. The instrument was programmed for a selected time interval, mounted on a stand, and allowed to execute the firmware by dispensing the full complement of discs. During these trial periods, the overall operation of each unit was evaluated, mechanical or electronic problems were identified, and suggested improvements were employed and documented.
The most consistent malfunction observed during testing was the wedging (jamming) of discs between the rotor and the manifold. During the instrument’s programmed operation in the laboratory and in the course of pressure testing (as described in the next section), one or more discs would randomly jam between the moving rotor and the magazine release borehole or become wedged between the rotor and the manifold body of the Intervalometer as the disc traveled to the drop hole. On many occasions, the friction produced excessive binding of the rotor and motor strain that frequently caused a failure of the DC motor by shearing the internal gear teeth. These failures typically required the installation of a replacement motor.
The jamming failure has been greatly reduced by refabricating the discs, stacking of the discs concave upward in the supply magazine, reorienting the position of the rotor relative to the drop hole on the end cap, and redesigning the rotor.
The discs have been slightly refabricated from the original design. They now have chamfered and radially scored edges and a small-diameter-hole (0.24 cm, 3/32 inch) at its center to facilitate stacking, reduced cohesion between the discs in the manifold, and a reduced probability of dropping onto the rotor and becoming jammed.
The rotor and its opening (the cutout portion that captures a disc) have also been redesigned and constructed of thicker material with an improved tolerance to match more closely the diameter and thickness of the discs. This modification restricts the movement of a single disc as it is captured by the rotor from the manifold chamber and transported to the drop hole of the end cap.
The starting point of the rotor has also been repositioned to an area where the opening is slightly counterclockwise and above the drop hole on the end cap. The rotor captures a single disc from the manifold after approximately 90° of counterclockwise rotation and then releases the disc through the drop hole of the end cap. The rotor continues its rotation past the drop hole where it comes to rest at its original starting position.These developments have significantly reduced the frequency of jamming and improved the mechanical reliability of the disc capture and release process.
In order to duplicate the operational environment of Intervalometers at depth in the open ocean, the integrity of the sealed pressure case was initially tested up to 4,500 pounds per square inch (psi), the pressure at a water depth of approximately 3,200 m (10,500 ft). The operation of the electronics and associated mechanical parts housed within the pressure case was successively tested to 1,500 psi, the pressure at a water depth of 1,000 m (3,280 ft).
The Intervalometers were loaded with a full complement of 20 discs and programmed for a 10-minute test-mode deployment interval. The units were suspended in a wire mesh basket and placed in a sealed water-filled pressure chamber. The pressure was slowly increased from ambient to approximately 1,500 psi over a period of a few minutes and allowed to remain at that point until the entire deployment period had elapsed.
During testing, water leaked into the electronics chambers of several instruments. Additional pressure tests revealed that several units also failed as a result of disc(s) lodged between the rotor and end cap.
Water leaks were resolved by modifications to the nylon rotor shaft and emplacement of a different dynamic O-ring seal on the shaft.
Motors failed on several of the Intervalometers because discs became jammed between the rotor and manifold housing.
After repairs and modifications were completed, programmed intervals were longer in tests under similar pressure conditions.