If you wish to measure the degree of a liquid easily and reliably, most 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 contact with the surrounding, mainly water-based medium, respectively to ?moisture?.
Exposure isn’t only limited by the wetted elements of the pressure sensor housing, but additionally to the entire immersed amount of the cable. Furthermore, outside the 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. That is true not only during operation, but a lot more during installation and commissioning, or when maintenance or retrofitting is necessary. Irrespective of the target application, whether in water and wastewater treatment or in tank monitoring, moisture ingress into 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 into the electronics of the particular level probe should be actively eliminated by preventive actions by an individual. To เพรสเชอร์เกจ with highest accuracy, the varying ambient pressure above the liquid media, that is also ?resting? on the liquid, should 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 there are no adequate protective measures. To pay the ambient pressure ?resting? on the media, a ventilation tube runs from the sensor element within the particular level probe, through the cable and out of the level probe by the end of the cable. Because of capillary action within the ventialation tube used for ambient pressure compensation, moisture can be transported from the surrounding ambience down to the sensor.
Thus not only air, but additionally moisture penetrates into the tube, hence the sensor inside the probe and the electronics around it might be irreparably damaged. This can 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 provided by fitting an air-permeable, but water-impermeable filter element at 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 definitely 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 attention to a controlled pressure equalisation in order to avoid the formation of condensation or perspiration water and pumping effects. To address this technical requirement, being an accessory to a submersible pressure transmitter, it is possible to order a connection box having an integrated air-permeable, water-impermeable membrane.
Ultimately, moisture ingress can happen not merely through the exposed end of the cable, but additionally through mechanical harm to the cable sheath or because of 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 the most suitable for your application, please use our contact page.
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