If you intend to measure the degree of a liquid easily and reliably, a lot of people will 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 just limited to the wetted parts of the pressure sensor housing, but additionally to the complete immersed amount of the cable. In addition, outside the directly immersed level probe parts, the cable, and in particular the cable end, are often exposed to moisture due to 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 necessary. Irrespective of the mark 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 almost 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 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, which 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 surely is a constant risk of a moisture-related failure because of moisture ingress (both via the ventilation tube and through the specific cable itself) if there are no adequate precautionary measures. To pay the ambient pressure ?resting? on the media, a ventilation tube runs from the sensor element within the level probe, through the cable and out of your level probe by 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 surrounding ambience down to the sensor.
Thus not only air, but also moisture penetrates in to the tube, hence the sensor in the probe and the electronics around it really is irreparably damaged. This can lead to measurement errors and, in the worst case, even to failure of the particular level probe. To avoid any premature failure, the ingress of moisture into the ventilation tube must be completely prevented. Horror against moisture penetration through the ventilation tube is supplied by fitting an air-permeable, but water-impermeable filter element at the end of the vent tube.
bare wires
Not to be ignored can be the transport of the liquid through high-humidity loads across the only limitedly protected internals of the cable, e.g. across the wires, completely down to the submersible pressure transmitter. As a leading manufacturer, WIKA uses appropriate structural design to avoid fluid transport, as far as possible, into the electronics of the submersible pressure transmitter. Fulfill to molecular diffusion and capillary effects, a guaranteed one-hundred percent protection on the full duration of the submersible pressure transmitter, however, is never achievable.
Hence, it is 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 exposed to weather and varying temperature conditions, additionally it is recommended to pay focus on a controlled pressure equalisation in order to avoid the formation of condensation or perspiration water and pumping effects. To address this technical requirement, as an accessory to a submersible pressure transmitter, you’ll be able to order a link box with an integrated air-permeable, water-impermeable membrane.
Ultimately, moisture ingress can occur not merely through the exposed end of the cable, but also through mechanical harm to the cable sheath or because 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 Cheerful in selecting the submersible pressure transmitter the most suitable for your application, please use our contact form.
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