In-depth | DIGITAL TECHNOLOGY


Made to measure: intelligent sensors are de rigueur for the smart owner


As elsewhere in life the move to digital technology is evident in many aspects of ship operation today, but one area that has been slow to take the step forward is tank gauging and data acquisition systems.


and bunker tanks is still the hydrostatic head or pressure principle. Te most basic of this technology is the direct “bubbler” or air reactive gauge but since it is essential on most modern vessels it is essential that data is in electronic format the direct electronic sensor with a 4-20mA analogue signal is probably the most cost effective and certainly the most flexible to install. The past argument that a directly


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installed sensor could be less reliable is certainly not true today. Mechanically, many quality marine sensors have been specifically developed to withstand the rigours and corrosive aspects of these applications. Electrically, too, correct design considerations ensure their performance and reliability is not compromised by thermal and other adverse affects imparted by the duty. Meeting all the above criteria and


ensuring compliance with Intrinsic Safety parameters has in the past only been practical using analogue electronic circuits and clearly millions of such sensors have been installed onboard ships of all types. Tat all sounds well and good, but that


is where the development has remained for many years now and as with most things in life and at sea there is an increasing downside to this technology. In a conventional arrangement each


transmitter requires its own cabling which runs from the point of measurement to the point of display. Some systems have adopted marshalling arrangements where sensor cabling is routed to one or more instrument cabinets which convert the 4-20mA signal to a digital format for onward transmission, but these provide only a half-way solution and conversion errors compromise on the accuracy of the overall measurement. Te downside is that although the cost of


The Naval Architect November 2009


rom a cost perspective the predominant technology employed for level measurement of ballast, service,


A digital transmitter sharing three different mounting options.


sensors has gradually reduced as demand increases, there is a greatly increased cost of cable and skilled labour to install and commission these systems. In many larger systems the cost of installation can exceed the cost of the system components. Aſter more than two years of shipboard


trials of both Royal Navy platforms and commercial ships PSM Instrumentation is releasing its Intelligent Ceramic Transmitter (iCT) and associated system products. Te iCT is type approved and ATEX certified and for the first time enables the full implementation of a digital tank gauging system. It is arguably the most advanced sensor system available for the duty and when one reviews its advantages and features it is clear that there should be significant benefits derived by the shipyard, system installer and the operator. In the first instance PSM calculates


that over 70% of the cost of cable and installation components including cable trays, trunking, junction boxes, penetrators etc can be saved on an average system. In detail, the iCT measures tank level


hydrostatically using an ultra stable ceramic capacitance cell that contains an embedded microprocessor that processes the level measurement locally to provide a direct


A typical screenshot of a tank level monitoring system that would be located in the cargo control or bridge.


digital output. Te output format employs industry standard MODBUS protocol for universal compatibility transmitting onto a robust and proven RS485 standard. Compared to a conventional analogue


signal which just represents the pressure measured, the data output may be scaled directly within the iCT sensor for tank sounding tables, sensor offsets, and product specific gravity, greatly simplifying the processing needed at the display end. In addition iCT incorporates a temperature sensor as a standard feature so that tank temperature is also available. All parameters are held in non-volatile


memory and remotely accessible / editable from a standard laptop. In practice this new technology gives


clear benefits to both the shipyard when installing and commissioning the system, and to the owner when the equipment is in service.


Installation &


Commissioning Benefits Being addressable over RS485 and with each transmitter having its own unique identification number enables a multi-drop connection arrangement where, all


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