Monitoring fluid levels in sub-surface wells containing mixtures of water and aviation fuel requires robust sensing and efficient data transmission. This application story explores the integration of high-accuracy hydrostatic sensors with wireless telemetry systems using digital communication protocols to streamline monitoring in low-I/O environments.
- Hydrostatic level monitoring in fuel-contaminated wells.
- SDI-12 digital interface for multi-sensor wireless nodes.
- 316L stainless steel and Viton construction for hydrocarbon resistance.
- Integrated temperature and pressure measurement from a single device.
The requirement involves the continuous monitoring of fluid levels within underground wells located approximately 50 to 100 centimetres below ground level. These wells are situated in a closed, permanently wet environment where temperature fluctuations remain relatively stable between 0 and 30 degrees Celsius. The primary technical challenge stems from the media composition, which consists of a mixture of water and JetFuel A1 (kerosene), with hydrocarbon contamination levels reaching up to 10%. The monitoring system is designed to integrate with a wireless telemetry interface using a long-range, low-power wide-area network. However, a specific constraint was identified regarding the limited input/output capacity of the wireless nodes, necessitating a digital solution where multiple sensors could be connected to a single interface.
To address the limited I/O availability, the S12S hydrostatic level sensor which utilises the SDI-12 communications protocol provided the solution. This multi-drop bus interface allows for the connection of several sensors to the same data line, with each device assigned a unique address from 0 to 9. By moving away from traditional 4-20mA or voltage signals—which would require dedicated analog-to-digital converter channels for every sensor—the digital output enables the integration of multiple hydrostatic transmitters into a single wireless gateway. This significantly reduces the hardware footprint and power requirements, as the digital sensors are designed for high-efficiency operation, consuming less than 250µA while idle and under 4mA during active measurement cycles.
Material compatibility is critical when dealing with aviation fuels like kerosene. While initial considerations might lean toward specialised alloys, 316L stainless steel was selected for the housing and diaphragm due to its proven resistance to JetFuel A1. The internal sensing element is a highly stable piezo-resistive silicon sensor, which provides superior resolution and stability for low-pressure ranges, such as the 0 to 1 mH2O required for shallow well monitoring. To ensure long-term integrity in the presence of hydrocarbons, Viton was chosen for the media-exposed seals.
The sensor electronics incorporate a microcontroller-based circuit that eliminates the need for manual adjustment potentiometers, ensuring long-term signal stability and a total error band of less than ±0.1% across a wide temperature range. A significant advantage for environmental research and process monitoring is the dual-output capability of the device, which provides both hydrostatic level and media temperature data through the digital interface. This removes the need for separate temperature probes, further simplifying the installation within the narrow confines of the well. The process connection features a removable nose cone that protects the sensitive 316L diaphragm from sediment or physical damage while allowing the hydrostatic pressure of the liquid column to be accurately measured.
The resulting system provides a high-resolution, low-drift monitoring solution that effectively manages the complexities of the application requirements. By leveraging the addressable nature of the digital protocol, the design achieves high data density without the need for complex, multi-channel wiring. This approach is particularly effective for large-scale environmental monitoring projects where dozens of wells may need to be networked back to a central data management system using minimal power and infrastructure.
S12S SDI-12 Coms IP68 Hydrostatic Level Sensor
- Pressure Range: 0 to 1 mH2O
- Range Type: Gauge / Vented (atm to +P)
- Output Signal: SDI12 communications protocol interface
- Housing & Diaphragm Material: Stainless steel 316L
- Media Exposed Seals: Viton
- Cable Type: PUR
- Cable Length: 3
- Cable Length Units: Metres (m)
- Process Connection: G1/4 male DIN3852 with removable nose cone