| Capable of collecting water samples from chosen locations and discrete depths is essential for charactering the vertical and horizontal distribution of the physicochemical and biological elements of most types of water column. Sampling could be defined as a process of selecting a portion of material small enough in volume in selected location to be transported conveniently, handled and latterly analyzed in the laboratory. In some circumstances, it is demanded to sample in columned water at distinct depths to obtain vertical distribution information. Various qualified devices or samplers have been developed and come into wide use in recent decades.In most circumstances, either a conventional CTD rosette sampler equipped with Niskin (or Go-Flo) bottles or a shipboard pumping system whch are employed for accurate water sampling still have disadvantages in the application. It is essential to design a new kind of sampling device which is suitable for different size of ships.I describe here a new type of Auto-Returned WAter sampling Device (ARWAD) which is designed primarily for collection of column water in shallow systems (gulf, lakes or estuaries), with operations conducted even from a small boat. Pre-set each bottle's sampling depth on the deck, the ARWAD is launched carrying 4 or more 1.5-liter Niskin bottles. Attached with adjustable weight, ARWAD falls deep in the water under its own gravity with no oceanographic wire attached to. Trapping each bottle water sample at determined depth is done during the retrieve process, after casting away the weight attachment.(1) The mechanical design and the seal method are presented in the paper. The mechanical system for ARWAD consists ofâ‘ weight attachment loading and unloading system, andâ‘¡bottle firing mechanical system.(2) The control system for the ARWAD is designed based on the utilization of a single-chip microcomputer SST89C54. The hardware circuit and software method design are presented. The ARWAD interfaces with high performance pressure transmitter to provide accurate sampling capability, depending on user requirements. The MCU program is to control the weight attachment loading and unloading process and bottle firing system; the PC program is to pre-set weight attachment unloading depth and each bottle firing depth.(3) Mechanical components are designed, and their mechanical strength is verified both in analytic method and FEM (Finite Element Method).(4) For controlling its rising speed of the ARWAD (with no more than 2.0m/s) to make sure the depth accuracy, FEM method is utilized to calculate the sampler's resistance coefficient and its maximum rising speed.(5) The ARWAD sampling device has been tested in natural body (in Jiaozhou Bay) in April, 2008 by collecting column samples for suspended solids materials analysis later in laboratory. For comparison purposes, a LISST was used to obtain vertical profiler data of particle size distribution (PSD) at the same site after the ARWAD sampling is done. The sample results (ARWAD laboratory measurements) and LISST data have good correlation, which means ARWAD works quite well.There is no hydrowire attached to the ARWAD, so the depth recording error brought by vane and hydrowire is eliminated to minimal. A present commonly used CTD rosette is often fixed to the end of an electromechanical cable, and the water sampling bottles are closed when desired by electrical command from on deck. Unlike a CTD rosette, the ARWAD is free to fall vertically, which eliminates the need for motion compensated winch systems and performs its duty to trap column water by command directly from control system in the pressure case. Larger volumes of water may be obtained by using larger water sample bottles. ARWAD could be used as a complement of traditional CTD sampler or pump with its benefits including small size, low cost to construct and operation, and ease of deployment in a small boat. |
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