Level Sensors for AdBlue/Diesel Exhaust Fluid


Manufacturers of modern Diesel engine driven Off-highway vehicles employ the Selective Catalytic Reduction (SCR) using AdBlue to comply with increasingly stringent emissions legislation. To ensure the emissions criteria for NOx will always be fulfilled, AdBlue level sensors like the popular SST Optomax level switches can be employed to monitor that there is always enough of the Diesel Exhaust Fluid (DEF) in the AdBlue tank.

The introduction of selective catalytic reduction (SCR) and diesel particulate filter (DPF) technology in engines is responsible for the improvements. A typical SCR system includes a diesel exhaust fluid (DEF) storage tank, the SCR chamber with catalyst, an injector, sensors, NOx analyzer, cable connections and a control unit.

In operation, after filtering through the particulate filter, the exhaust gas flows into the SCR chamber, where a dose of DEF is injected. A reaction takes place that converts NOx into harmless nitrogen and water.

AdBlue, which is composed of 32.5% high-quality urea and 67.5% distilled water, is the most popular diesel exhaust fluid on the market today. More significantly, vehicle manufacturers have designed their engines to limit power when the AdBlue tank is empty. This is to prevent users from driving against regulations and emitting NOx and particulates.

SCR systems have created a paradigm shift for vehicle operation. Simply put, just as vehicles cannot function when their fuel tanks are empty, they cannot function when their Adblue tanks are empty.

The ability to detect the presence or absence of AdBlue in the storage tank is therefore critical to SCR system performance and compliance.

AdBlue level sensors take the guesswork out of the equation. These sensors detect the level of fluid in the tank and relay the information to the ECU. Depending on the input, the ECU can:

  • allows the vehicle to operate normally
  • .
  • issues a warning message to the driver in the form of a visual (display) or audible alarm, or
  • limits the vehicle's performance, stalling operation or reducing productivity, until the AdBlue tank is refilled.
  • Since AdBlue consumption in heavy-duty vehicles accounts for about 3-5% of total fuel consumption, it's a simple guideline that users fill their AdBlue tank whenever the diesel tank is full. And where there are no AdBlue filling stations, it is recommended that users carry a refill container.