Some info regarding oxygen sensors, from AEM's PEMS bulletin board, posted by an AEM technician.
Originally posted by JR
UEGO is Universal Exhaust Gas Oxygen
Typical production car O2 sensors rely on “nernst cell” technology, commonly called “Narrow Band”, “2 wire”, “4 wire” and sometimes erroneously described as “Wide Band”. This is a very cost effective method that outputs a voltage based on the oxygen content of the gas being sampled. It is accurate in the region surrounding stoichiometric operation and leaner. Unfortunately, in the rich region where high performance engines usually operate, their accuracy and repeatability is virtually non-existent.
Wide Band generally refers to a temperature compensated narrow band sensor. The rich region output of a common O2 sensor is very temperature dependant which renders it useless if an accuracy greater than 1.5:1 AFR is desired. This is immediately obvious given the fact that a single output voltage actually represents wildly different AFR’s depending on the sensor temperature. These sensors were only designed for operating closed loop around the stoichiometric AFR (14.64 for gasoline). Accurately measuring and controlling the tip temperature of these types of sensors extends thier usability range somewhat.
UEGO sensors work on a different principle than the normal oxygen sensor you would find in your car. They use a “current pump” within the sensor itself to determine the actual oxygen concentration within the sensing element or, lacking any O2, it determines the amount of oxygen required to regain stoichiometric operation. The output is in the form of a very small current which varies depending on the air-fuel ratio. This is completely different from a normal oxygen sensor (1, 2 and 4 wire types) which directly output a voltage. The UEGO design allows measurement of the exact air fuel ratio over the entire operating range.
Each UEGO sensor (both Bosch and NTK) is individually calibrated and a resistor integral to the connector body set with the calibration value.
JR
http://forum.aempower.com/bbs/viewtopic.php?t=3690