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Application Note

3m Level Sensor for Offshore Wave-Height Measurement

3M Long water level sensor designed for offshore wave-height measurement

At Gill we have the ability to produce custom capacitive liquid level sensors for most applications. Sensors are typically designed for applications ranging from 30mm to 1500mm long, however when a customer recently approached us requesting a three metre long level sensor for an offshore salt-water application, our engineers set to work to overcome the design challenges.

The application in question was a wave energy device, with the sensor required to monitor wave height around the base of a wind turbine on an offshore wind farm. With rough seas, corrosive salt-water and exposure to the elements, in addition to the challenges of designing and manufacturing a capacitive sensor at such a long length, this was no straightforward task.

Mounting and installation arrangement

With such a long probe, we decided to use the standard SAE 5-bolt flange mount, which offers a stable mounting platform to support the sensor. The sensor flange was heavily strengthened in order to withstand the extreme operating conditions experienced offshore, with the joint between the underside of the flange and the outer tube of the sensor welded together to increase strength.


It was important to select a material that would not suffer from corrosion in the harsh salt-water environment. For this application, 316 stainless steel was selected due to its excellent resistance to corrosion.

Rapid Response

Gill capacitive liquid level sensors monitor the level of fluid between the inner and outer tubes of the sensor. In most applications, the sensors are mechanically damped to prevent tank ‘slosh’ effects on the output. In this application, however, the opposite effect was required. Due to the speed and direction of the rise and fall of the wave, it was important to produce a sensor that would correctly represent the rise and fall in real-time. In order to achieve this, the whole length of the outer tube was drilled at one-inch intervals to allow water to enter and leave the sensor rapidly.

Interesting calibration

As with all Gill liquid level sensors, each sensor is factory calibrated prior to dispatch. This usually takes place in our laboratories, however this was just not possible with such a large sensor. In the end a team of our engineers headed down to the local harbour to perform the calibration. The team received some very odd looks, but the calibration was successful.

Rapid turnaround time

The time taken from design to delivery was just eight weeks. Packaging and shipping such a large product was, however, another challenge.

salt water level sensor
salt water level sensor