Preventing the ingress of moisture through the cable of submersible pressure transmitters and level probes?

If you intend to measure the level of a liquid easily and reliably, most people can do this using hydrostatic pressure measurement, e.g. with a submersible pressure transmitter or perhaps a so called level probe. The characteristic submersed application implicates a maximum exposure to the surrounding, mainly water-based medium, respectively to ?moisture?.
Exposure isn’t only limited by the wetted parts of the pressure sensor housing, but also to the entire immersed length of the cable. Furthermore, beyond your directly immersed level probe parts, the cable, and specifically the cable end, tend to be exposed to moisture as a result of splash water, rain and condensation. This is true not only during operation, but a lot more during installation and commissioning, or when maintenance or retrofitting is required. Irrespective of the prospective application, whether in water and wastewater treatment or in tank monitoring, moisture ingress into the cable ends of the submersible pressure transmitter may appear early and irreversibly with insufficient protection measures, and, in almost all cases, result in premature failure of the instrument.
The ingress of moisture in to the cable outlet and from there on downwards into the electronics of the level probe must be actively eliminated by preventive actions by an individual. To gauge the level with highest accuracy, the varying ambient pressure above the liquid media, that is also ?resting? on the liquid, must be compensated against the hydrostatic pressure functioning on the pressure sensor (see article: hydrostatic level measurement).
Ventilation tube
Thus, it really is logical that there is a constant risk of a moisture-related failure due to moisture ingress (both via the ventilation tube and through the actual cable itself) if you can find no adequate precautionary measures. To pay the ambient pressure ? เพรสเชอร์เกจไฮดรอลิค ? on the media, a ventilation tube runs from the sensor element within the level probe, through the cable and from the level probe at the end of the cable. Because of capillary action within the ventialation tube used for ambient pressure compensation, moisture may also be transported from the encompassing ambience down to the sensor.
Thus not merely air, but also moisture penetrates in to the tube, hence the sensor inside the probe and the electronics around it usually is irreparably damaged. This may result in measurement errors and, in the worst case, even to failure of the level probe. To prevent any premature failure, the ingress of moisture in to the ventilation tube should be completely prevented. Additional protection against moisture penetration through the ventilation tube is supplied by fitting an air-permeable, but water-impermeable filter element by the end of the vent tube.
bare wires
Never to be ignored is also the transport of the liquid through high-humidity loads across the only limitedly protected internals of the cable, e.g. along the wires, completely down to the submersible pressure transmitter. As a leading manufacturer, WIKA uses appropriate structural design to avoid fluid transport, so far as possible, into the electronics of the submersible pressure transmitter. Because of molecular diffusion and capillary effects, a guaranteed one-hundred percent protection over the full duration of the submersible pressure transmitter, however, is never achievable.
Hence, it is recommended that the cable is always terminated in a waterproof junction box with the correct IP protection (e.g. IP65) that is matched to the installation location. If this cable junction box is subjected to weather and varying temperature conditions, additionally it is recommended to pay focus on a controlled pressure equalisation so as to avoid the formation of condensation or perspiration water and pumping effects. To handle this technical requirement, being an accessory to a submersible pressure transmitter, it is possible to order a link box with an integrated air-permeable, water-impermeable membrane.
Ultimately, moisture ingress can happen not only through the exposed end of the cable, but additionally through mechanical harm to the cable sheath or as a result of liquid diffusion due to improper chemical resistance of the cable material. In this article ?Selection criteria for the prevention of moisture-related failures of submersible pressure transmitters or level probes? this failure mode is described at length.
WIKA offers comprehensive solutions for your hydrostatic-pressure level measurement. For further assistance in selecting the submersible pressure transmitter most suitable for your application, please use our contact page.
Please find further information with this topic on our information platform ?Hydrostatic level measurement?

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