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Water
Ingress Alarm Monitoring System
A Step guide to the PSM System |
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| System overview |
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The
individual elements and components that comprise the PSM system are as
follows. The quantity of individual components may be selected to suit
the actual vessel. To assist in cost preparation a component breakdown
sheet is attached from which, a full system cost can be readily
calculated. A questionnaire form is available for use by specifiers and customers. Simply fill in the requested data and return
to our Sales Engineering dept. for an instant quotation. Also for quick
reference purposes, a brief guide to the regulation indicates the
designation of various holds and spaces. However, this is a guide only
and is not the definitive regulation. Purchasers should refer to the
relevant Standards and Bodies to satisfy themselves of compliance.
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| Water Detecting Sensor options. |
Hydrostatic Sensors
The
Series 260 sensor body is all 316 stainless steel with a sensing
diaphragm in Hastelloy C276 for corrosion resistance. The sensor was
designed from the outset for arduous shipboard application and features
unrivalled tolerance to shock, overload, and extremes of application
conditions. All active electronics are housed remotely in the amplifier
module which is itself contained within the deck mounted termination
enclosure. The Deck enclosure also contains a simple test mechanism for
the sensor. A small hand operated pump is used to temporarily simulate
an applied pressure and cause the sensors output to rise to alarm
levels. There are no additional pressure lines required for this
function as this is carried within the sensor cable, there is no
possibility of damaging the sensor by over pressuring and the sensor
will automatically reset a few seconds after the pump is operated. The
Hydrostatic sensor outputs a 4-20mA signal in relation to actual liquid
level, this means that only one sensor is needed to detect both Pre and
Main alarm conditions. PSM system does not need expensive washdown and blow down systems to test operation, as is necessary with other solutions.
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| Siting of the sensors. | In
accordance with the regulations two alarm points are required per cargo
hold, one at a low level typically at 0.5metres representing a
pre-alarm, and one typically at 2 metres elevation for main alarm
detection. A single sensor should be mounted as close as possible to the
cargo hold floor. Other dry spaces are also required to be monitored by
the regulations, for
example forepeak tank, bosuns store, etc, these also only one sensor which should be mounted as low as possible
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| Principle of operation |
When the Hold (or dry space) is empty the sensor outputs a continuous signal of 4mA. Upon loading the output increases to a value representative of the actual cargo product. For example, Wet coal, metallic ores etc. will provide a different characteristic of dielectric value to dry products such as powders. When all holds are loaded the operator runs an “initialisation” routine by pressing a dedicated button on the central monitor. The central monitor logs the actual mA value from all sensors which then represents a “normal” condition. In the event of water ingress the sensor immediately detects this and initiates a step change in output to 20mA. The central monitor detects this output change and triggers an alarm. A variable time delay can be set to prevent spurious alarm.
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| Central Monitor/Alarm Station. |
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| Diagnostic “comms” and MODBUS |
In addition to the 4-20mA signal, each sensor incorporates Modbus communications. In operation the sensor continually runs an internal diagnostic routine to confirm its operational health. This Modbus link is connected to the central monitor, which interrogates the sensor approximately every 5 seconds to confirm correct operation. In the event of a fault this is immediately signalled on the central monitor via both a dedicated system fault lamp and a specific description on the LCD display. In addition to this monitoring function, the Modbus link can be used for test & diagnostic purposes. Simple to follow menu routines on the central monitor allow an operator to simulate either an hold empty or water alarm condition by instructing a particular sensor to change its signal output. This can be done irrespective of the actual content of the hold, and thus provides an alternative to entering the tank which may be required for testing of alternative sensor types.
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| Mounting considerations for Central Monitor | Typically,
the central monitor should be located in a continuously manned area
(e.g. Navigation bridge) where this is not possible or additional
displays are required, an optional repeater panel may be provided. These
repeater panel(s) communicate with the central monitor via a single
screened twisted pair cable using an RS485 link and multiple repeaters
can be daisy chained. The repeaters can be for display only, or may be
enabled for alarm acknowledgement.
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| For use in Hazardous Zones |
Where the cargo hold or deck is classified a Hazardous Zone, Zener barriers are incorporated into the central monitor to provide an Intrinsically Safe installation.
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| Holds used for seawater ballast purposes. | Where
a hold / tank is to be used for Ballast on a specific voyage the sensors
can be temporarily disabled via a simple menu command. When the hold or
tank is emptied of Ballast water the system automatically re-enables the
alarm as per the requirements of the regulation.
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| Factory Configured – simple installation |
The
system is factory configured in accordance with a questionnaire which should be completed by the user for each installation.
Installation and commissioning of the system is straightforward an
requires no specialist knowledge and may be undertaken by Shipyard
personnel or Riding squads whilst the Ship is underway.
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| Full support – Future proof | Full
support documentation is included, and should the system change or
expansion be required additional sensors can be readily added or
substituted.
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| PSM Engineers can assist | If
preferred PSM can supply qualified engineers to oversee the systems
commissioning or offer a complete installation. Either way, PSM
technical support and network of agents is available to help you with
any queries.
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| Installation considerations |
Sensors
are designed to provide complete simplicity and flexibility on retrofit
and new builds. Adaptors are provided so they may be clamped in the
holds, secured onto pole or pipe ends, or inserted into a “Still”
tube enabling later removal without entering the hold, tank or void
space. If a still pipe is used then a separate (PSM supplied) filter
assembly may also be employed. Whereas the filter is not necessary for
operation it is recommended as it will significantly reduce the need for
any routine cleaning of the sensors, as the cargo has no way of coming
directly into contact with them. The filter itself is designed for
simple cleaning / flushing, either from within the hold or by
back-flushing via the still pipe. Typically, the central monitor should be located in a continuously manned area (e.g. Navigation bridge) |
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| Bulkhead & deck Penetration | PSM
offers purpose designed deck penetrations to greatly simplify the
installation cabling procedure. A bonus feature of the PSM tank stool
arrangement when used with the still pipe arrangement as detailed above
is to enable instant removal of sensors from the deck even with
loaded holds.
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| Cabling |
Each
sensor is pre-fitted with a specified length of cable to allow
termination in the Deck enclosure. The 4-20mA signal from each sensor requires a 2 core cable which is run back from each deck enclosure to the central monitor. For the RF sensor solution a single 4-core (two twisted pair) cable may be used to carry both 4-20mA sensor signals from each hold Optionally,
a marshalling enclosure may be provided which enables all cabling from
the deck to be combined in a single multi-core that runs to the Main
display on the Bridge. This marshalling enclosure will normally be
located in the accommodation block.
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| What Next? | Simple. Contact PSM or click a copy of our questionnaire form. We will send a no obligation quotation and data by return | ||
