Pressure sensor vs ultrasonic sensor:
Which one to choose for your tank?

compress 1. How hydrostatic pressure sensors work

The pressure sensor, also called a hydrostatic sensor, measures the pressure exerted by the column of liquid above it. Placed at the bottom of the tank, it uses the physical principle P = ρgh (pressure = density × gravity × height).

Specifically, the higher the liquid above the sensor, the higher the pressure. By measuring this pressure with an accuracy of ±2 litres, the sensor accurately deduces the volume remaining in the tank, regardless of its shape.

Benefits of the pressure sensor

• Exceptional accuracy: direct measurement, independent of liquid surface.
• Insensitive to vapours: perfect for volatile liquids.
• No moving parts: no float or mechanism that could jam.
• Works in total darkness: Unlike some optical technologies.

Hydrostatic measurement is the technology recommended by tank manufacturers for its long-term robustness and reliability.

graphic_eq 2. How ultrasonic sensors work

The ultrasonic sensor works on the principle of echolocation. Placed above the liquid (usually attached to the manhole of the tank), it emits an ultrasonic wave that reflects on the surface of the liquid. The wave's return time is used to calculate the distance to the surface and therefore the liquid level.

This technology is widely used in industry for Water tanks and unpressurized tanks. It offers the advantage of not being in contact with the liquid.

Limitations of ultrasonic sensors

• Foam sensitive: surface foam distorts measurement.
• Affected by vapours: certain types of vapours may weaken or deflect the ultrasonic signal.
• Reduced accuracy: Generally ±5% against ±2L for a pressure sensor.
• Measurement angle: requires a clear detection cone, problematic in tanks of complex shape.
• Condensation: Condensation on the sensor can result in false readings.

table 3. Detailed technical comparison

straighten 4. Accuracy: ±2L vs ±5%

The accuracy is probably the most important criterion. With a tankio pressure sensor, the accuracy is ±2 litres, whatever the amount of liquid in the tank. An ultrasonic sensor typically specifies an accuracy of ±5% of the measured height.

For a 3000-litre tank, this means that the ultrasonic sensor uncertainty is ±150 litres. In other words, your tank could be empty while the sensor still indicates 150 litres remaining. The consequences can be serious.

Why the pressure sensor is more accurate

Hydrostatic pressure directly measures the weight of the liquid column. It does not depend on external factors such as temperature, humidity or the presence of vapour. The ultrasonic measurement is affected by the speed of sound that varies with the temperature and composition of the gas above the liquid.

build 5. Installation: above or inside

The installation differs significantly between the two technologies. The ultrasonic sensor is fixed above the tank, usually on the manhole. It must have a clear line of sight to the surface of the liquid, which can be problematic if the tank contains obstacles (reinforcements, pipes).

The Tankio pressure sensor is installed through the inspection hatch and descends to the bottom of the tank. It is held by a cable or rod and does not require any particular alignment. The installation is simple and fast, without special tools.

For tanks buried or not easily accessible from above, the pressure sensor is often the only viable option. The ultrasonic sensor requires access to the top of the tank to be installed and maintained.

verified 6. Reliability and maintenance

The long-term reliability is a determining criterion, especially for a tank that remains in service for many years. The Tankio pressure sensor contains no moving parts. No float to jam, no membrane to puncture, and no spring to lose tension.

The ultrasonic sensor, although waterproof, is exposed to vapours which can form a film on the emitting surface, gradually reducing the accuracy of the measurements. Periodic cleaning is necessary, which means reopening the tank.

In real conditions, users of ultrasonic sensors report Measurement deviations up to 15-20% after a few months of use in a tank, due to the accumulation of residues on the sensor.

"I tested both technologies. The ultrasonic sensor gave inconsistent measurements after a few months. The tankio pressure sensor has been working perfectly for 18 months without any maintenance." — Marc, tankio user in Liège.

euro 7. Cost and value for money

At first glance, ultrasonic sensors may seem cheaper to buy (between €80 and €150). But this price does not reflect the total cost of ownership. Frequent replacements, maintenance and the risk of failure due to inaccurate measurements increase the actual cost.

The Tankio pressure sensor is designed to operate for more than three years without routine maintenance. Its precise readings help manage the water reserve, identify anomalies and prevent the pump from running dry.

checklist 8. Which sensor is right for your application?

The choice depends on your application. Our recommendations include:

For a rainwater or wastewater tank

Tankio pressure sensor, without hesitation. Surface foam, impurities and temperature variations make the ultrasonic sensor unreliable over the long term. Accuracy of the pressure sensor is essential for reliable monitoring. Discover our connected solution for water tanks.

For a rainwater tank

Both technologies work. The ultrasonic sensor may be suitable if the tank is accessible from above and the water is clear. But the pressure sensor remains more reliable over the long term, especially if water contains impurities. Consult our connected gauge for rainwater tanks.