A customer developing a bespoke tide monitoring system required a robust and reliable level sensing solution for permanent installation in a remote coastal location. The primary challenges for this application involved ensuring long-term survivability in corrosive seawater, maintaining accuracy by compensating for atmospheric pressure fluctuations, and adhering to a strict low-power budget dictated by the off-grid solar and wind power supply. Furthermore, the new sensor needed to be exceptionally reliable to replace an aging tide gauge system where maintenance involved hazardous access procedures on the open sea, making a “fit and forget” solution highly desirable.
- Continuous and permanent submersion in seawater to a depth of approximately 10 metres.
- Suitability for a remote, off-grid installation powered by solar and wind generators, demanding minimal power consumption.
- A method to automatically compensate for barometric pressure changes to ensure true tidal level readings.
- A high-level 0-5Vdc signal output for interfacing with a custom wireless telemetry and data logging system.
The proposed solution was the SWL series submersible level transmitter, specifically configured to meet the unique demands of this remote tide gauging application. For long-term use in corrosive seawater, a standard stainless steel housing was deemed insufficient. Instead, the SWL was selected with a housing machined from Marine Bronze (CA104), a material known for its excellent durability in saline environments. This was paired with a special TPE (thermoplastic elastomer) cable sheath, also chosen for its compatibility with permanent seawater immersion, and Viton seals to complete the protective enclosure.
Internally, the SWL features a piezo-resistive ceramic sensing diaphragm , which offers outstanding corrosion resistance and is ideal for installations even in stagnant or warm seawater. To address the need for barometric pressure compensation, an absolute pressure range was replaced with a 10 mWG (metres water gauge) vented gauge pressure range. This design incorporates a vent tube within the protective cable sheath, allowing the back of the sensor diaphragm to reference the surface atmospheric pressure. This automatically cancels out any effects from changing weather patterns on the level reading, simplifying the customer’s software and improving measurement integrity.
To meet the low-power and signal requirements, the transmitter was configured with a 3-wire, 0-5Vdc output. This high-level voltage signal is easily integrated with modern data loggers while maintaining a low typical current consumption suitable for battery and renewable energy sources. Finally, the inherent reliability of the SWL design, which utilises a microprocessor-based amplifier with no mechanical adjustment pots, ensures high stability against shock and vibration, delivering a dependable, low-maintenance solution perfect for replacing the aging, difficult-to-service equipment at the remote site.
SWL Submersible Seawater Tide Depth Sensor
- Part No: SWL-G1000-6A4-BAV015-000
- Pressure Range: 10 mH2O g
- Output Signal: 0-5Vdc (3 wire)
- Cable Type: TPE
- Length of Cable (metres): 15 meters
- Seals exposed to media: Viton (standard)
- Accuracy (BSL): 0.25% FS (standard)
- Thermal Zero Shift: 0.04% FS/degC (standard)