The Thermo Scientific™ Model 42i NO-NO2-NOx Analyzer utilizes chemiluminescence technology to measure the amount of nitrogen oxides in the air from sub-ppb levels up to 100ppm. In the event you are unable to calibrate your Model 42i NO-NO2-NOx analyzer with zero air or nitrogen and receive a background “above or below limit” error, this month’s Fast5 tip can help.
You need to isolate and determine where the elevated background/zero is coming from as it could be external contamination in your zero air or your sample line/umbilical. The elevated background could also be electronic noise from the PMT (Photomultiplier Tube) or your input board may require calibration. See the Model 42i NO-NO2-NOx Analyzer
Troubleshooting High/Low background errors technical bulletin.