Hydrostatic measurements

November 14, 2022  321  321   

It is a fact that most drinking water comes from groundwater. No longer confined to the Global South, general water scarcity is now an ever-present issue in technologically developed countries as well. Climate change, forest fires, glacier melting and the resulting rise in world sea levels are all arguments in favour of the proper, well-thought-through management of groundwater resources. 

Furthermore, monitoring the fill level in tanks or sealed containers of oil or similar liquids is very important, especially on cost grounds, and can also double as theft protection. Determining the exact fill level right down to the centimetre can therefore save users a fair amount. Using an additional radio module, a purchase order can be triggered automatically in various applications as soon as the fill level falls below a certain threshold. 

The most common form of electronic fill level measurement is hydrostatic pressure measurement.

Hydrostatic pressure

Hydrostatic pressure is the pressure that forms within a liquid or gas at rest due to the influence of the force of gravity. The fluid at rest exerts a dead weight on the layers below as a result of its mass. Neither the type of medium nor whether or not the fluid is in motion plays a role here. Dynamic pressure due to flow is not recorded.

Hydrostatic pressure can be measured in either an open or freely accessible, container or body of water as well as in a sealed tank with positive or negative pressure. In all cases, the actual fill level is determined in consideration of the ambient pressure. The pressure of the gas trapped above the liquid must also be factored in if the container is sealed. This is done by taking another pressure measurement on a second transmitter, which is usually screwed into the side of the tank.

Hydrostatic pressure factoring in ambient pressure

This formula can be used to calculate the hydrostatic pressure while factoring in ambient pressure:

p(h, p0) = ρ * g * h + p0

And can be applied to open bodies of water and fluids at rest (static) in containers. A differential pressure measurement to factor in p0 (lid pressure) is used for sealed containers. To factor ambient pressure into open scenarios, measurements are taken using relative pressure probes or AA (absolute-absolute) technology.

Remote transmission via the Internet

When monitoring groundwater/fill levels in open bodies of water or outdoors, the measuring points may be relatively far away and difficult to reach. For these applications, KELLER Pressure has solutions involving level loggers via short-range radio interfaces as well as level loggers with a remote data transmission unit via GSM or the Internet.

Kolibri Cloud / Desktop is used to process and analyse/prepare the collected data.

Product overview for hydrostatic measurements

• LEVEL PROBES  Submersible probes for level and fill measurement. With a special design and cable and housing materials that have been chosen for compatibility with their surroundings, these probes can be used in a wide range of liquids.
• DATA LOGGERS  A variety of data logger designs for recording pressure and temperature profiles. Depending on the system, the data is read out via a plug connection or remote transfer.
• MULTI-PARAMETER DATA LOGGERS  The Keller DCX-22-CTD  measures conductivity and temperature as well as pressure, along with the depth of bodies of water. The integrated Pt1000 achieves an accuracy of ±0,1 °C, and the conductivity can be measured at ± 2,5% of the selected range (0,2 / 2 / 20 / 200 mS/cm). Thanks to their long-life battery, they can keep recording measurement results for years (up to 10 years at a rate of one measurement per hour). The logger can be configured using the supplied software (measurement interval, incident management, delayed measurement start etc.) and data that has been read can be displayed in a graph or chart, corrected using air pressure values, converted into fill levels or other units, and exported.
• KOLIBRI CLOUD  Web app for collecting and displaying measured values that are recorded by KELLER IoT devices and transmitted via mobile radio or LoRaWAN. KOLIBRI Cloud offers a wide variety of options for device configuration and displays current measured values and logger recordings in graph form. Thanks to the search and filter options, saved measurement data can be organised with ease and can also be exported as an image, as an Excel or Word report, or in additional formats. Existing software solutions can be used to access data in KOLIBRI Cloud via JSON API. All products in the KOLIBRI suite are inter-compatible and can exchange data with one another. The functions are continually being further expanded and optimised.