AREVA > AREVA Diagnostics > Leakage Monitoring System > Technical Description 1

FLÜS - Technical Description 1

 




doppelpfeil 

The FLÜS Measuring Principle on Different Components.

For a closer look please click on the graphic or here. 

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doppelpfeilDiffusion principle
 

The FLÜS measuring principle is based on a FLÜS “sensor tube”, into which humidity from the ambient air can diffuse through closely spaced porous sinter metal tablets (“humidity sensing elements”). In this way, the local distribution of ambient humidity along the sensor tube is mapped onto the – initially dry – air column within the sensor tube in a matter of minutes. The increase in local humidity is particularly prominent in the immediate proximity of a leak, i.e. within the component insulation. For component monitoring, the FLÜS sensor tube should therefore be preferentially installed within the insulation so that an optimum detection sensitivity is achieved.

doppelpfeilPeriodic measuring cycles
 

In order to record this diffusion-induced distribution of concentration, periodic measuring cycles are automatically performed at adjustable intervals. During a measuring cycle, the air column of the tube line (so-called “monitoring line”) is moved through a central humidity sensor, which determines the absolute humidity in relation to the transport time (see illustration below). At the same time, the FLÜS tube is purged with dry air for the next diffusion phase.

doppelpfeilAbsolute humidity profile
 

The spatial position of each humidity data sample along the tube line is derived from the flow sensor signal of the measured air. In this way, a so-called absolute humidity profile is calculated for each measuring cycle, which provides the distribution of the outside humidity along the tube line. This profile is continuously compared with that of a reference measurement and adjusted with respect to the spatial positions, e.g. in order to compensate for fluctuations in the temperature distribution along the tube line.

doppelpfeilLeakage detection and localization
 If the measured humidity value exceeds the preset threshold (see pt. 1 resp. 2 of the graphic), a leak alarm is triggered by the FLÜS system. The leak position can be pinpointed within a few meters by determining the relative position of the leakage peak within a monitored section.

doppelpfeilAutomatic selftesting of the system
 

In each measuring cycle, an integral functional check of all FLÜS components is performed via a pattern matching with the background humidity profile of the reference measurement. Any significant deviations will trigger an automatic system alarm. Not least because of this integral selftest, an availability rate of more than 99 % (as per MIL standard) has been certified.