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

If you want to measure the degree of a liquid easily and reliably, most people can do this using hydrostatic pressure measurement, e.g. with a submersible pressure transmitter or a so called level probe. The characteristic submersed application implicates a maximum contact with 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 complete 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 even 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 in to the cable ends of the submersible pressure transmitter can occur early and irreversibly with insufficient protection measures, and, in virtually all cases, result in premature failure of the instrument.
The ingress of moisture into the cable outlet and from there on downwards in to the electronics of the particular level probe should 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 contrary to the hydrostatic pressure acting on the pressure sensor (see article: hydrostatic level measurement).
Ventilation tube
Thus, it 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 specific cable itself) if you can find no adequate protective measures. To compensate เกจวัดแรงดัน ?resting? 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. Due to capillary action within the ventialation tube useful for ambient pressure compensation, moisture may also be transported from the encompassing ambience down to the sensor.
Thus not merely air, but additionally moisture penetrates into the tube, hence the sensor inside the probe and the electronics around it might be 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 into the ventilation tube must 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
Not 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. across the wires, all the way right down to the submersible pressure transmitter. As a respected manufacturer, WIKA uses appropriate structural design to prevent 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 lifetime of the submersible pressure transmitter, however, is never achievable.
It is therefore recommended that the cable is definitely terminated in a waterproof junction box with the appropriate 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, it is also recommended to pay attention to a controlled pressure equalisation so that you can 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 having an integrated air-permeable, water-impermeable membrane.
Ultimately, moisture ingress can occur not only through the exposed end of the cable, but additionally through mechanical damage to the cable sheath or due to liquid diffusion due to improper chemical resistance of the cable material. In the article ?Selection criteria for preventing moisture-related failures of submersible pressure transmitters or level probes? this failure mode is described in detail.
WIKA offers comprehensive solutions for the hydrostatic-pressure level measurement. For further assistance in selecting the submersible pressure transmitter most suitable for the application, please use our contact page.
Please find more info on this topic on our information platform ?Hydrostatic level measurement?