Up to now, we have dealt solely with applied single-axis mechanical force and applied torque only. That leaves only bending moment and shear force, which we will discuss in a future articles, and pressure, which is the subject of this article.
Depth and level measurement in liquids is a vital requirement in a number of process and utility sectors where industry-standard fieldbus outputs are required for integration of depth measurement into process control. This can include wells, boreholes, waste water, lakes, reservoirs, rivers, water and sewage treatment plant as well as other liquids in bulk such as chemicals, fuel and diesel oil.
These days, it is possible to get a very wide range of depth sensor products that are very rugged and are capable of achieving ±0.1% accuracy and can be fully integrated into process plant or into hazardous areas by virtue of their ATEX certification. What is more, they normally are designed and rated to resist the electomagnetic surges caused by nearby lightning strikes. At first this appears to be a strange requirement given that they are normally at earth potential in say the ocean. However, the transducer’s leads go into the areas that are not so protected.
Applied Measurement's ATEX Depth Sensor pi99ex
Depth transducer equipment that are commercially available, nearly all use ceramic (Aluminium Oxide) piezoresistive sensors as the barometric pressure sensing element for depths exceeding 10mWG and these have sealed (or closed) bodies. For depths less than 10m, a vented stainless steel sensor is normally employed for greater accuracy at low barometric pressures. The vent passes to the open atmosphere via the combined cable tube.
The casings are very rugged and are normally stainless steel turnings although I have seen titanium (Tn) bodies where mechanical strength in extreme conditions is specified.
Some models, instead of having a nose cone with an open end to the liquid being monitored, have a modified nose with a tapping to ½” BSPP male for insertion into a submerged pipeline. Neat!