Technical defects alarms
REPORT ON THE TREATMENT OF TECHNICAL DEFECTS
To lose or damage livestock in an aquaculture site at the end of the 20th century, because of a technical problem due to logistics, is not acceptable.
We are always meeting fish farmers who have lost their stock, or worse, their whole farm due to a lack of water, a cut in electricity, a heating problem, an oxygen flow which is too low, etc...
There are technical means which are at our disposal today which can guarantee a 99.99 % reliability of an installation.
For an installation to be reliable means respecting three main criteria:
According to the old and very true aquaculture proverb "Prevention is better than DEATH" it is therefore essential to know there is an abnormality right from its origin.
But an aquaculture installation does not have to be be a succession of alarms signalling transient changes of state. The installation must be designed so that faulse alarms disappear and so that only true defects remain to be taken into account. The efficiency of an alarm system is largely dependent on the study of the various circuits.
From a simple contact with an alarm, to an expert system controlling computerized processes, there are many ways for the prescriber and the installer to control an installation in general. For aquaculture installations the choice is more restricted. The reaction time and the self-monitoring of the system itself are the determining factors.
The definition of a network
The definition of an alarm is its action of conveying a signal generated by an abnormal situation from a point A to a point B. Point A can be a simple circuit or a junction of a circuit of a site called divisional centralization.
Point B has the equipment making it possible to centralize and to deal with the alarm.
The processing may be local, using one or more sound or luminous warning devices, or transferred over a distance by a cable radio relay system or Telecom network (Eurosignal, Alphapage, Telephone). A review can be kept on paper or in a remote electronic memory.
It should be noted that the sound and luminous warning devices need to be perceived at all points on the site, taking into account buildings, and the noise of water and the machines.
The pyramid type network, called "in cascade" maintains an effective hierarchy in conveying the alarm signal.
A fault on a checking device will give a visible alert at the place where the Fault Signal 'FS' is generated, a signal will then be sent to a Divisional Centralization "DC" corresponding to a zone or a room, then the faulkt is signalled to a Treatment Centralization "TC".
It is possible to insert between the level of the Fault Signal "FD" and the point of Treatment Centralization "TC" several successive stages of divisional centralization "DC".
All the centralization equipment and signal transport must be of the "positive safety" type, wich basically means that this equipment has a self-monitoring mechanism and gives an alarm at the level of its own fault.
An alarm signal can never be voluntarily or involuntarily cut off by the user.
In the event of failure of the "normal" power supply, (Circuit supplied by electricity company), a 'Relief' batteryl takes over with a working reserve of several hours.
An alarm network according to E.E.I.A. (a French company), must:
A yellow light LED indicates a good power supply to the centralisation equipment. A green light LED indicates that a manual discharge has occured. A red light LED identifies the alarm and remains lit until the fault has been dealt with.
Despite all these restrictions, which are essential for maximum reliability, the cost must be tolerable for the investment budget of the aquaculture project.
Standardising the centralization unit gives a very reasonable selling price, around the 500 FF per divisional centralization alarm, and around 1000 FF per centralization treatment alarm for an average installation.
The use of identical units at all levels means a very low maintenance amounting only to the installation of a centralization unit.
In conclusion, experience shows that the quality of an alarm network is more a problem of awareness of the necessity than of the budget.
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