This technical description look at the installation of a weighing system for craft under construction or under repairing arranged on various support systems (wood block and similar). Usually, during this period, craft is supported by a series of supports whose quantity and consistency is due to the
This technical description look at the installation of a weighing system for craft under construction or under repairing arranged on various support systems (wood block and similar).
Usually, during this period, craft is supported by a series of supports whose quantity and consistency is due to the logistic requirement of the shipyard and to the main craft characteristics such as:
· Main dimensions;
· Hull shape;
· Structural frame arrangement.
The standard support configuration where the weighing system can be installed consists of a maximum of 21 elements located according to the customer’s requirements.
Having to share out the whole craft weight on a series of maximum 21 supports and supposing of concentrate the 60/70 % of weight on the stern supports is possible to obtain the average value of the weight on each support easily. This value allow to establish that a system composed by N load
cells (each cell to be installed on the support under the hull) can satisfies the customer demand.
Very important is also the correct sizing of the load cell respect to possible over charge of the system: in this context is necessary to obtain a good matching between the maximum load that each cell can support and its precision. The storage of the measurement of each load cell will set up the main input of a calculation program able to provide total weight and centre of gravity position of the craft.
Figure 3 shows the complete measuring system. The peripheral unit of the system is composed by the load cell together with an analogical/digital converter that allow the signal transmission too. The peripheral unit will be carried out in the same way for all the measurement point. For this reason the strain gauge bridge of the load cell will be exempt from inaccuracy cause by the load cell wiring. Inside wiring system linking the peripheral unit with the PC interface will be present digital signal only. For this reason measure quantitiesmanagement results very easy.
Forces measured by the N load cell, after the PC acquisition, will be joined in a.txt format file easy to
handle by the customer.
The core unit of the load cell is shown in Fig. 2 an in Fig. 3. In order that this element can be correctly inserted between ship and support, it is necessary the insertion of appropriate accessories able to make the cell more suitable for this measurements. The easy way is to insert the appropriate mounting accessory provide by the load cell maker that consists of two not deformable stainless steel plates placed in the upper side and in the lower side of the cell. Shipyard will take care of the correct positioning of the plates by spirit level during the installation under its liability. Shipyard will take care of the load cell insertion too.
Peripheral units TD RS-485 are connected to load cell by a sheathed cable (it can vary between 5m and 30m) complete with watertight connectors on the electric cabinet. All the TD RS-485 units are liked by a communication bus an supplied by a DC voltage. The complete wiring is provided by the writer.
Software can manage the whole sensor web (max. 21) and the calculation procedure to determine craft’s weight and center of gravity position of the craft. Software can also produce ascii files that customer can import by excel for further processing.
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