• The LSU broadband Lambda sensor is a planar ZrO₂ two-cell limit current sensor with integral heater.
• It is suitable for measuring the oxygen content and the λ value of exhaust gases in vehicle engines.
• A constant characteristic curve in the range from λ = 0.65 to air makes it suitable for universal use for λ =1 and for other λ ranges.
• Signal evaluation for Bosch broadband Lambda sensor 4.x: Signal evaluation module: 1267379259

Application

Engine management

• Gas engines
• Block-type thermal power stations
• Diesel engines
• Gasoline engines
• Lean combustion engine

Industrial processes

• Tempering furnaces
• Chemical industry
• Packaging equipment
• Process engineering
• Drying plants
• Metallurgy

Measurement and analysis processes

• Flue gas measurement
• Gas analysis
• Determination of Wobbe indexIncineration plants
• Wood
• Biomass

Design and operation

The LSU broadband Lambda sensor is a planar ZrO₂ two-cell limit current sensor with integral heater. It is suitable for measuring the oxygen content and the λ value of exhaust gases in vehicle engines (gasoline and diesel). A constant characteristic curve in the range from λ = 0.65 to air makes it suitable for universal use for λ =1 and for other λ ranges. The connector module includes a trimming resistor, which determines the characteristics of the sensor and is necessary for the sensor to function. To function, the LSU requires special operating electronics (e.g. AWS. LA4 or IC CJ125 evaluation circuit) and may only be operated in conjunction with these.

The Lambda sensor consists of two cells. It is made up of a Nernst type potentiometric oxygen concentration cell and an amperometric oxygen pump cell. Nernst cells have the property that oxygen ions diffuse through their ceramic at high temperatures, as soon as there are differences in the partial oxygen pressure at both ends of the ceramic. The transport of ions results in an electrical voltage between them, which is measured using electrodes.

The components of the exhaust gas diffuse through the diffusion duct to the electrodes for the pump and Nernst cell, where they are brought to thermodynamic equilibrium. Control electronics record the Nernst voltage U_N in the concentration cell and supply the pump cell with a variable pump voltage U_P. If U_N takes on a value of less than 450 mV, the exhaust gas is lean and the pump cell is supplied with a current that causes oxygen to be pumped out of the duct. By contrast, if the exhaust gas is rich, U_N> 450 mV and the flow direction is reversed, causing the cell to pump oxygen into the duct.

An integrated module (CJ125) can be used for signal evaluation. As well as the controller for the pump flow and the controller that keeps the Nernst cell at 450 mV, this module includes an amplifier.

The sensor element is manufactured using thick-film techniques, which results in production distribution. This means that the characteristic curves for different sensors will vary. At an oxygen concentration of 0%, the output voltage is a uniform 0 V, as when using the evaluation circuit. However, at air the voltage scatters between approx. 6 and 8 V. This means that each sensor has to be individually calibrated so that a clear relationship between the measured oxygen concentration and the output voltage can be created. Calibration can be carried out on air in which the oxygen content is 20.9%. Calibration is recommended at each maintenance.

Explanation of characteristic quantities

Installation instructions

• Installation in exhaust pipes at a location where the exhaust gas composition is representative whilst complying with the specified temperature limits.
  The sensor ceramic is rapidly heated when the sensor heating is switched on. After heating of the ceramic, any incidence of condensation water that could damage the hot sensor ceramic is to be ruled out.
• The selected angular installation position should be as close to vertically upwards as possible, but at least 10 from the horizontal. This prevents liquid from accumulating between the sensor housing and the sensor element. An inclination of 90 to the exhaust gas flow is ideal, but the maximum is 90 + 15 between the gas inlet hole and the exhaust gas flow) or 90 - 30. Other angular positions are to be evaluated separately where required.
• Installation with special grease on screw-in thread (e.g. Bosch no. 1 987 123 020 for the 120 g can)
• Tightening torque: 40 – 60 Nm, material properties and strength of the thread must be designed accordingly.