What does a negative span check error mean?
Negative span check errors mean that the measured span in scattering between filtered air and filtered CO2 is not as large as the computer expects. This could be because either the filtered air measurement shows higher scattering than expected, the filtered CO2 measurement shows lower scattering than expected, or both. Large negative errors on the order of 60% typically mean that CO2 either is not getting into the nephelometer or is being sucked out of it by the vacuum system through a faulty solenoid bypass system. Check to make sure CO2 is getting into the neph during a span check.
