Q: What does a wideband unit do?
A: A 2Y unit's major function is to measure the lambda/AFR of exhaust gas, which is usually coming from an internal combustion engine. To do that, the unit is connected to a sensor, which is placed in the exhaust gas stream. Engine tuners adjust the amount of fuel fed to an engine so that the engine runs well, is economical and does not emit excessive pollution. AFR means "Air Fuel Ratio", the ratio of the mass of air divided by the mass of fuel. Lambda is a parameter which has a value of 1 when there has been complete combustion, with no oxygen or fuel left over. Oxygen is 20.9% of air. The AFR at which lambda is 1 is known as the "stoichiometric ratio", or "stoich" for short. AFR is lambda times stoich. Stoich is 14.7 for unleaded fuel. Free air corresponds to a lambda of infinity.
The sensor is sensitive to lambda, it is a Lambda Sensor Unit (LSU). Then AFR is calculated by multiplying by stoich. Stoich varies for different fuels, depending on the calorific value. Lean means there is excessive air for the amount of fuel, then lambda is greater than 1. Rich means there is excessive fuel for the amount of air, then lambda is less than 1. Lambda is 1 at stoich. Most engines run best at or near stoich. So engine tuners want to know if the engine is running rich or lean. So they want to measure lambda. To do that they need a wideband unit and some means of recording what happened under various circumstances (accelerating, cruising, high speed, low speed, etc.). That is what the 2Y unit is for.
The 2Y unit measures lambda, using the sensor. It can measure other parameters, such as engine RPM (Revolutions Per Minute), throttle position or temperature. A TPS (Throttle Position Sensor) is basically just a potentiometer, mechanically attached to the throttle, fed with 5V from the 2Y unit and giving an output which goes to the unit. Temperature measurement can be done with a standard Type K thermocouple, which is then connected to the unit.
All these parameters get bundled up into a logging frame which is sent out through the unit's RS232 port. During normal operation the unit emits a continuous series of logging frames. That is what a wideband unit does — it takes in analog data from sensors and sends out logging frames.
Those frames then can go to a Tech Edge display to show the user AFR, or lambda, or RPM or whatever the user cares to measure. The frames can also go to an attached PC (Personal Computer, such as a laptop). The PC can display the data in the frames in real time. The PC can also record the frames for later display and analysis.
The primary input is the sensor. The primary output is the logging frames. The other analog inputs are secondary. There are also secondary analog outputs, namely WBlin, SVout and NBsim. WBlin is the most important. It varies linearly with lambda, from 0 to 5 Volts. It is generated by the 2Y unit with an accuracy of 12 bits, by an internal 12-bit DAC (Digital to Analog Converter). Lambda = 1 is at 2.85 Volts, as standard. WBlin can be read by an external voltmeter or fed to an analog logger or anything else the user may care to do with an analog voltage. One way of using the unit is to connect it to power, a sensor and a voltmeter to indicate lambda. The wideband unit owner can then use that information to do engine tuning.
However, using WBlin is not particularly satisfactory. Analog voltmeters often have an annoyingly slow response. They read in volts, not lambda or AFR, so the user has to convert somehow. A Tech Edge display or a PC, reading the logging frames, is a much better option. Since the logging frame is all digital (being characters on an RS232 connection) there is no loss of accuracy. Tech Edge displays are designed to give the user fast response in the bargraph part of the display and accuracy in the digital display. As standard, a display has four views; the user can switch between seeing AFR, lambda, RPM and an analog parameter. That is more convenient for the user.