If you want 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 a so called level probe. The characteristic submersed application implicates a maximum contact with the encompassing, 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 length of the cable. Furthermore, 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. That is true not merely during operation, but a lot 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 into the cable ends of the submersible pressure transmitter can occur early and irreversibly with insufficient protection measures, and, in virtually all cases, lead to premature failure of the instrument.
The ingress of moisture in to the cable outlet and from there on downwards in to the electronics of the 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, which 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 is logical that there surely is a constant threat of a moisture-related failure because of moisture ingress (both via the ventilation tube and through the specific 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 particular level probe, through the cable and out of your level probe by the end of the cable. Because of capillary action within the ventialation tube useful for ambient pressure compensation, moisture can even be transported from the surrounding ambience right down to the sensor.
Thus not merely air, but additionally moisture penetrates into the tube, hence the sensor in 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 particular level probe. To avoid 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
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 down to the submersible pressure transmitter. As a leading 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 lifetime 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) which 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 as a way 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, it is possible to order a connection box having an integrated air-permeable, water-impermeable membrane.
Ultimately, moisture ingress can happen not only through the exposed end of the cable, but additionally through mechanical harm to the cable sheath or because of liquid diffusion because of improper chemical resistance of the cable material. In this article ? ร้านซ่อมเครื่องวัดความดันโลหิต 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 your application, please use our contact form.
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