Broadband lambda sensor

NTK Broadband lambda sensors are used as regulating sensors for petrol engines and are being used more and more frequently for diesel vehicles.
Broadband lambda sensor

With the requirement to reduce consumption and emissions, it has also because necessary to operate engines outside of the stoichiometric operating point. For this purpose, so-called broadband sensors were developed.

These linear lambda sensors are capable of issuing a signal proportional to the residual oxygen content of the exhaust air. This signal is available over a broad air-fuel ratio.

The output signal corresponds to the pump current which is necessary to set a constant oxygen content (lambda = 1 corresponds to
450 mV) in a measuring cell. The greater the deviation of the exhaust air from this value, the greater the pump current and thus the output signal of the sensor.

The broadband lambda sensor offers the following advantages:

  • Fast operational readiness
  • Monolithic element with embedded heater
  • Hermetically-sealed structure means self-generated oxygen reference
  • Temperature resistance
  • High level of reliability

These sensors are used as regulating sensors for petrol engines and are being used more and more frequently for diesel vehicles.

The planar element of an NTK broadband lambda sensor is comprised of multiple layers. Along with a pump cell and a measurement cell, it also has an integrated heater.
Spatial representation of the element of a broadband sensor

Method of operation of the broadband lambda sensor

Broadband sensors have two cells - a measuring cell and a pump cell. Using the measuring cell, the oxygen content of the exhaust air in the detection chamber is measured and compared with a target value of
450 mV.

If this value deviates, then - by switching a pump flow to the pump cell - as many oxygen ions are pumped into or out of the detection chamber as necessary for the voltage value of the measurement cell to once again correspond to 450mV.

Cross-section through the planar element of a broadband lambda sensor

This pump current is the measurement which describes the precise lambda value of the mixture almost linearly. For stoichiometric mixtures, it is zero, as the oxygen partial pressure in the detection chamber corresponds to the target value indicated above.

Cable assignment

NTK broadband lambda sensors have five cable connections. The heating element is supplied with voltage through yellow and blue. The signal of the pump flow (Ip+) flows through the white cable; the signal of the measurement cell (Vs+) flows through the grey cable. The black cable represents the earth connection for pump and measurement cells.

NTK broadband lambda sensor cable assignment