PEDAL AS 3648725 - Caterpillar

Illustration 1 g00783563
Relationship between the concentration of oxygen and the duty cycle of the oxygen buffer (Y) Percent of oxygen (X) Duty cycle of the oxygen buffer (1) Relationship after calibration of the oxygen sensor in the atmosphere (2) Relationship after calibration of the oxygen sensor in the exhaust stack at full loadThe second calibration of the oxygen sensor is performed when the engine is running at full load. This calibration adjusts the linear relationship between the percent of oxygen that is measured and the duty cycle of the oxygen buffer. For engine operation at full load with exhaust emissions at 1 g/bhp h of NOx, the exhaust oxygen will be approximately 9 percent. As a result, the value of the control's target for the oxygen level will also be approximately 9 percent.The first calibration in the ambient air establishes the "z" and "a" values for 0 percent and 20.9 percent of oxygen. However, the engine is not intended to operate with these levels of exhaust oxygen.Calibration of the oxygen sensor at full load enables the "z" and "a" values to be adjusted in order to match the control's reading with the reading of an emissions analyzer. Usually, the "a" value is adjusted at full load.Consider the calibration curve of line (1) in Illustration 1. If the engine is then run at full load and the duty cycle from the oxygen buffer is 43.8 percent, the control will display a 9 percent reading for exhaust oxygen. However, if an accurate emissions analyzer reads an exhaust oxygen level of 9.3 percent, the control's "a" value must be adjusted until the control displays an exhaust oxygen level of 9.3.Calibration of the oxygen sensor at full load adjusts the percentage of the duty cycle that is associated with oxygen of 20.9 percent. Line (2) in Illustration 1 shows that the curve has shifted. The duty cycle that is associated with oxygen of 20.9 percent has increased.