If you would like 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 just limited by the wetted elements of the pressure sensor housing, but additionally to the entire immersed amount of the cable. Furthermore, beyond your directly immersed level probe parts, the cable, and in particular the cable end, tend to be exposed to moisture as a result of splash water, rain and condensation. That is true not merely during operation, but even 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 may appear early and irreversibly with insufficient protection measures, and, in almost all cases, lead to 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 the user. To gauge the level with highest accuracy, the varying ambient pressure above the liquid media, that is also ?resting? on the liquid, should be compensated against the hydrostatic pressure acting on the pressure sensor (see article: hydrostatic level measurement).
Ventilation tube
Thus, it really is logical that there is a constant threat of a moisture-related failure because of moisture ingress (both via the ventilation tube and through the actual cable itself) if you can find no adequate protective 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 the level probe at the end of the cable. Due to capillary action within the ventialation tube used for ambient pressure compensation, moisture can be transported from the encompassing ambience right 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 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
Not to be ignored can be the transport of the liquid through high-humidity loads along the only limitedly protected internals of the cable, e.g. along the wires, all the way down to the submersible pressure transmitter. As a respected manufacturer, WIKA uses appropriate structural design to avoid fluid transport, as far as possible, in to the electronics of the submersible pressure transmitter. Due 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.
It is therefore 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 prevent the formation of condensation or perspiration water and pumping effects. To handle Billion , as an accessory to a submersible pressure transmitter, you’ll be able to order a connection box with an integrated air-permeable, water-impermeable membrane.
Ultimately, moisture ingress can occur not only through the exposed end of the cable, but also through mechanical damage to the cable sheath or because of liquid diffusion due to improper chemical resistance of the cable material. In the 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 the hydrostatic-pressure level measurement. For further assistance in selecting the submersible pressure transmitter most suitable for your application, please use our contact form.
Please find further information on this topic on our information platform ?Hydrostatic level measurement?