How does an electronic gauge work
in a tank?

schema 1. General principle of an electronic gauge

An electronic gauge is an instrument that measures the level of a liquid in a tank using a sensor. Unlike a mechanical gauge (float, graduated ruler), it converts a physical quantity into an electrical signal, which is then processed by a microcontroller.

The process consists of 3 steps:

1. Measurement: The sensor (pressure, ultrasound, capacitive) measures a physical quantity related to the liquid level.
2. Conversion: A microcontroller converts this measurement to a level value (cm, litres, percentage).
3. Transmission: The value is displayed locally or transmitted to a smartphone via LoRa, WiFi or Bluetooth.

Each measuring technology has its advantages and disadvantages. The three main ones are the hydrostatic pressure sensor, the ultrasonic sensor and the capacitive sensor.

water_pump 2. Hydrostatic pressure sensor

The hydrostatic pressure sensor is the technology used by tankio. Its principle is simple: the pressure exerted by a liquid at the bottom of a tank is directly proportional to its height.

How does it work in practice?

Imagine you're diving into a pool. The lower you go, the higher the pressure on your eardrums. This is exactly what the sensor uses. Placed at the bottom of the tank, it measures the pressure exerted by the column of liquid above it.

Sensor components

• A membrane: thin layer that deforms under liquid pressure.
• A Wheatstone Bridge: electrical circuit (strain gauges) which measures the deformation of the membrane.
• Analogue-to-digital converter: turns the electrical signal into a digital value.
• A microcontroller: calculates the volume according to the shape and dimensions of the tank.

Benefits

• Exceptional accuracy (±2 litres regardless of quantity).
• Insensitive to vapours, foam and condensation.
• The Tankio implementation is designed for water tanks and other compatible water reserves.
• No moving parts, so no mechanical wear.

graphic_eq 3. Ultrasonic sensor

The ultrasonic sensor works like sonar. It emits a high frequency sound wave (inaudible to the human ear) that reflects on the surface of the liquid. By measuring the time the wave takes to return, we calculate the distance and thus the level.

It is placed above the liquid, attached to the manhole of the tank. It is not in contact with the liquid, which may seem an advantage but it also has significant limitations.

Limitations of ultrasonic sensors

• Accuracy: ±5% of the measured height, i.e. ±150L on a 3000L tank.
• Vapour sensitivity: vapours reduce the ultrasonic signal, reducing accuracy.
• Foam: Surface foam absorbs ultrasound, distorting measurement.
• Blind zone: requires a clear area above the liquid, which is not always the case in complex-shaped tanks.

For a detailed comparison, see our article pressure sensor vs ultrasonic sensor.

capacitor 4. Capacitive sensor

The capacitive sensor measures the level by detecting the variation in electrical capacitance between two electrodes. Since the liquid and air do not have the same dielectric constant, the measured capacitance varies with the level.

In concrete terms, an electrode is placed vertically in the tank. The capacitance between this electrode and ground (or a second electrode) changes depending on whether the space is filled with liquid or air. By measuring this capacitance, we deduce the level.

Where do we find capacitive sensors?

This technology is common in the industry for specific applications (conductive liquids, pressurized liquids), but it is not suitable for tanks private individuals. Temperature variations, insulating nature and the formation of deposits on the electrode make measurement less reliable.

In addition, the capacitive sensor requires accurate calibration for each type of liquid and each tank, which makes it less convenient for a domestic installation.

star 5. Why tankio chose the pressure sensor

At tankio, we tested the three technologies before selecting the hydrostatic pressure sensor for our connected probes. This is why:

Reliability above all

A pressure sensor provides stable measurements under normal water-tank conditions, including surface foam, condensation and temperature changes. Reliability is the main criterion for an installation expected to remain in service for many years.

Accuracy for savings

A precise measurement helps track the reserve, identify unusual consumption and prevent the pump from running dry. With a wider tolerance, it is harder to know how much water is actually available.

Compatible water reserves

The same hydrostatic-pressure sensor is suitable for rainwater tanks and other compatible water reservoirs. Configuration takes each tank’s shape and dimensions into account.

We designed our sensor to be as reliable as possible in the real conditions of a Belgian cellar. No compromise on quality.

science 6. Science behind measurement: P = ρgh

For the curious, here is the scientific explanation behind the tankio pressure sensor. Don't worry, you don't need to understand this equation to use our product, but it's always interesting to know how it works.

Concrete example

For a water tank filled to a height of 1.5 metres, the pressure at the bottom is:

P = 1,000 × 9.81 × 1.5 = 14,715 Pa (approximately 0.147 bar)

The sensor measures this pressure with an accuracy of ±0.01% of the measurement range, which makes it possible to detect variations in the level on the order of a millimetre. The tank’s shape and dimensions are then used to convert the measured height into a volume in litres.

The tankio application does all these calculations automatically. Just fill in the type and dimensions of your tank during the initial configuration, and the system will handle the rest.