If you want to measure the level 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 is not only limited by the wetted parts of the pressure sensor housing, but additionally to the entire immersed amount of the cable. In addition, outside the directly immersed level probe parts, the cable, and specifically the cable end, are often exposed to moisture because of splash water, rain and condensation. This 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 should be actively eliminated by preventive actions by the user. To measure the level 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 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 because of moisture ingress (both via the ventilation tube and through the actual cable itself) if you can find no adequate protective measures. To compensate 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 from the level probe by the end of the cable. Because of capillary action within the ventialation tube useful for ambient pressure compensation, moisture may also be transported from the surrounding ambience right down to the sensor.
Thus not merely air, but additionally moisture penetrates in to the tube, hence the sensor inside the probe and the electronics around it could be irreparably damaged. This can result in measurement errors and, in the worst case, even to failure of the level probe. To avoid 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 provided 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, completely right down to the submersible pressure transmitter. As a leading manufacturer, WIKA uses appropriate structural design to prevent fluid transport, so 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 lifetime 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 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, it is also recommended to pay attention to a controlled pressure equalisation to be able 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 link box with an integrated air-permeable, water-impermeable membrane.
Ultimately, เกจวัดแรงดันอาร์กอน 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 because of 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 the most suitable for the application, please use our contact page.
Please find further information on this topic on our information platform ?Hydrostatic level measurement?