The UTV measures non-invasively from above through the tank lid—without moving parts in the medium. This makes it the ideal solution for wastewater and blackwater tanks. However, it has three peculiarities that should be known before drilling.
How it measures
The sensor sits in the tank lid and sends an ultrasonic pulse downwards. It calculates the distance from the time taken for the pulse to travel to the liquid surface and back—and from that, the fill level. A voltage signal of 0.5–2.5 V is output, which can be connected to common tank monitors.
Since nothing is immersed in the liquid, nothing can become contaminated or mechanically damaged. This is precisely why it is recommended for wastewater and blackwater—where float sensors regularly fail.
The first measurement is available after approximately five seconds of power-on time. The averaging time is 50 seconds—meaning the value reacts deliberately slowly and thus smooths out short-term movements of the surface.
The Dead Zone: 2.5 Centimetres
Directly below the sensor is an area of 2.5 cm where no measurement can be taken. The reason is inherent to the principle: at this distance, the transmitted pulse and the returning echo can no longer be separated in time. If the liquid is in this area, there is no usable measurement value—not an inaccurate one, but none at all.
In practice, this means: a tank filled to the brim will report nothing useful in the last 2.5 cm. This is precisely why the UTS 25 spacer ring exists. It is 25 mm high—exactly the dead zone—and raises the sensor by this amount. This places the dead zone above the maximum fill level, making the full tank measurable again.
Where it doesn't belong
For fuel and water tanks, the manufacturer recommends other sensors. The reason lies in the measurement principle: in the event of heeling, rough seas, or a completely full tank, ultrasonic measurement in the upper dead zone area does not provide reliable results—and for these media, the full state is precisely what matters.
For water and diesel, a hydrostatic submersible probe is therefore the more robust choice: it measures independently of the tank shape and has no dead zone at the upper end.
The Bore Hole
A bore hole of at least 36 mm is required. If a sound guide tube is also installed—which should be the case in most situations—it will be 40 mm.
This decision is made before drilling, not after. Enlarging a 36-mm bore hole to 40 mm on an installed tank is difficult to impossible—and the shavings will fall into the tank.
NoteBefore drilling, check that the sensor is vertical at the intended location and has a clear view downwards. A stiffener, baffle, or slanted tank top in the sound path will generate echoes that the sensor mistakes for the surface.
Why the sound guide tube is almost always included
The UFT sound guide tube is formally an accessory and practically a prerequisite for usable values in motion. It does three things:
- It guides the sound. In case of倾斜 (heeling) and swell, the measuring path remains defined instead of being deflected by an angled surface.
- It protects against foam. Foam on the surface is a poor reflection surface for ultrasound and leads to fluctuating values.
- It protects against contamination of the sensor area.
In a stationary tank that never moves, it can be omitted. In anything that moves or floats, omitting it is the most common cause of fluctuating values.
Choosing the right length
The UTV is available in ten installation lengths from 20 to 80 cm. The crucial factor is the height of the tank, not its volume—measured from the inside of the tank lid to the bottom.
If you are between two lengths, you should check the installation situation: a sensor that is too long will sit too deep, and one that is too short will not detect the lower area. Both can only be corrected afterwards with a new order. If a spacer ring is used, its height must be included in the same calculation.
Connection and operation
The input voltage is 10–30 V, and the current consumption is 50 mA. The temperature range extends from −40 to +85 °C, thus practically never being the limiting element.
The output signal of 0.5–2.5 V goes to common tank monitors. In a P-Bus system, the sensor is integrated via the tank interface, which recognizes this voltage signal as a sensor type.
Typical Errors
- Used in water or fuel tanks. Measurements become unreliable when heeling, in rough seas, or with a full tank.
- Installed without a sound guide tube. Works when stationary, but fluctuates when in motion.
- Drilled 36 mm and then wanted the tube. This requires 40 mm—the decision must be made before drilling.
- Obstruction in the sound path. Stiffeners and baffles create false echoes.
- Full tank not displayed. The level is in the 2.5 cm dead zone—the UTS 25 spacer ring is available for this.
