UltraRAE 3000 User’s Guide3. Zero calibration starts a 30-second countdown and displaysthis message:Zeroing...During the zeroing process, the instrument performs the Zerocalibration automatically and does not require any action on your part.Note: To abort the zeroing process at any time and proceed to Spancalibration, press [N/-] at any time while zeroing is being performed.You will see a confirmation message that says “Zero aborted!” andthen the Span calibration menu appears.When Zero calibration is complete, you see this message:Zeroing is done!Reading = 0.0 ppmThe instrument will then show the Calibration menu on its display,with Span Calib highlighted.19.3 Span CalibrationThis procedure determines the second point of the sensor calibrationcurve for the sensor. A cylinder of standard reference gas (span gas)fitted with a 500 cc/min. flow-limiting regulator or a flow-matchingregulator is the simplest way to perform this procedure. Choose the500 cc/min. regulator only if the flow rate matches or slightly exceedsthe flow rate of the instrument pump. Alternatively, the span gas canfirst be filled into a Tedlar bag or delivered through a demand-flowregulator. Connect the calibration adapter to the inlet port of theinstrument, and connect the tubing to the regulator or Tedlar bag.Another alternative is to use a regulator with >500 cc/min flow butallow the excess flow to escape through a T or an open tube. In thelatter method, the span gas flows out through an open tube slightlywider than the probe, and the probe is inserted into the calibrationtube.52
