Abstract
In conventional instruments high reliability is achieved by using a sound physical principle and ensuring that the system is well engineered with high quality components: the user's confidence in the ability of the instrument to perform correctly then has to be supported by frequent functional checks. Where such instruments are used to detect an infrequent condition, eg, the presence of unwanted water in parts of a steam turbine plant, checks must be made at even more frequent intervals to reveal any inability to operate correctly and this is costly and disadvantageous because of consequent hazards to the main plant. Furthermore, instrument malfunctions can inhibit wanted operation and can also give rise to false operations which may shut down a large plant unnecessarily.
The patented philosophy used in the systems described results in greater availability and eliminates all need for routine testing. The paper outlines a range of water presence detectors (Hydratect) in which any instrument defect is made self-proclaiming thus eliminating the need for testing. This ‘multi-headed’ sytem permits false operations to be discounted and under rare conditions of a failure of one instrument path the system calls for maintenance but still continues to provide useful service.
Although it is at present applied and is being increasingly used for the vital detection of unwanted water in steam turbine plant, the basic method is applicable to both binary and analogue transducers where exceptionally high reliability and availability are necessary. Examples arise wherever a hazard exists due to the possible malfunctioning of conventional instruments.
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