TROLL 9500 Operator's Manual - Geotech Environmental Equipment

Section 13: Dissolved Oxygen—Polarographic16. Click Next to continue. A screen like this will be displayed:• Current temperature and barometric pressure are shown; thesevalues are used to calculate the stimulus.TIP: If the calibration stimulus was entered from a look-uptable at step 15 and the temperature is not as expected, youmay select Stop, then Back to retrieve the Setup page andre-enter the User Set stimulus.1718. When readings have stabilized (or you click to Accept the Nominalresult), the calibration will advance automatically.If doing a 1-point calibration, go to step 20.For a 2-point calibration, the Wizard displays a screen similar tothe one shown below and waits for you to situate the sensor inoxygen-depleted medium—either the Cal Cup filled with sodiumsulfite solution, or a nitrogen-saturated water bath.This time, theD.O. sensor membrane should be completely immersed in solution,as well as the temperature sensor.17. Select Run to begin stabilization for the first calibration point.The display will continuously update as readings are taken andcompared against the stabilization criteria.• Status indicators:NOT TESTED is displayed until you begin the calibration byselecting Run.UNSTABLE indicates the sensor response does not meet thecriteria for a valid calibration point.NOMINAL indicates the sensor deviation meets early stabilizationcriteria.The Accept button becomes available when nominal stability isachieved. You may accept the early value, or wait for completestability. If you accept the early value, the status will bedesignated “USER SET” in the calibration report. (For more oncalibration reports, see “Calibration History” in Section 10.)STABLE is displayed when the readings have stabilized sufficientlyto take a valid calibration point. The calibration proceedsautomatically to the next screen.• Sensor Reading: The current sensor response in nanoAmps.• Sensor Deviation: Change in response between the last 2 readings.This enables you to follow the progress of the stabilization,but the deviation from the previous reading is not necessarily thebest indicator of stability as the software is looking at longer-termtrends.19Allow about 15 minutes for the sensor to stabilize in the medium.19. Select Run to begin the stabilization for the 0% calibration point.Controls and status indicators are the same as for the first calibrationpoint (step 17).In true 0% conditions, the sensor reading will be 10 nA orless. If the sensor needs maintenance or there is oxygen inthe medium, readings will be higher than 10 nA andcomplete stability will never be reached. If an accurate 0% calibrationis important to your application, do not accept Nominal. Cancel thecalibration, perform sensor maintenance and/or check the conditions,and repeat the calibration.TROLL 9500 Operator’s Manual 840095110 rev. 007 01/09