XDT User’s Manual

DEWPOINT legends will also appear. Use the UP and DOWN buttons to modify this dew- point to match the dewpoint of the reference gas.

•Press the MODE button, the display will alternately show 720 / HRS / INTR, indicating that the calibrations are scheduled at 720 hours interval. Use the UP and DOWN buttons to change the interval time to whatever is determined to be most effective for your application, consult with your representative if you are in doubt. An interval of 0 Hrs (appears as a blank on the display), disables any further scheduled unattended calibrations, however the instrument will continue to make use of calibration values acquired previously or manually in the future. Pressing the Pressure Correct button will cause the instrument to momentarily display 150 / HRS / LEFT, indicating that there are 150 hours left until the next scheduled calibration is per- formed. This is a useful indication in cases where it is not known when the next calibration will be performed.

•Press the MODE button, the display will show BEG/S.C., prompting to begin the Self Calibra- tion.

-If the MODE button is pressed the calibration procedure will be canceled and instrument will go to the Serial Number mode. All setup will still be in effect, e.i. newly entered reference dewpoints, the scheduled interval time etc. will still be used by the system.

-If the DOWN button is pressed the Self Calibration corrections will be disabled; any Self Calibrations performed previously will not be used in correcting the computed dewpoint of the instrument. However newly entered reference dewpoints and the scheduled interval time will still be in effect; thus when the time elapses a Self Calibration will be performed and its values will be used in correcting the computed dewpoint from that time on.

•Press the UP button to initiate the Self Calibration. the display will show CNF/SC?, prompting for a confirmation that the Self Calibration should be performed.

If the DOWN or Pressure Correct buttons are pressed the Self Calibration will be aborted, however everything set until now will remain in effect.

•Press the UP button to confirm the Self Calibration. The display will show SLF/CAL/-41.5indicating that self calibration has started and it is measuring a dewpoint of -41.5°C, (this is also the entry place into the procedure when the scheduled time elapses). Now the instrument will “freeze” the analog output and the alarm relays so that they are not influenced by the ref- erence gas dewpoint. Then the instrument will activate the electrically actuated switchover valve and thus introduce the reference gas to the sensor, and initiate a 15 minute time out allowing the system to reach equilibrium. (Since the program will perform the above when the scheduled interval elapses, this step may be occurring in an unattended mode, thus the refer- ence gas bottle and regulator must be left in the open positions, the switchover valve will keep them from being exhausted.)

•After the 15 minute stabilization time out, the display will show alternately S.C./STB /-41.5, indicating that Self Cal Stabilization is being checked and currently the instrument is measur- ing -41.5°C. When the measured dewpoint is stable within 0.5°C for 3 minutes the instrument will record the new single point self calibration values. Note that the program will spend at least 3 minutes on this stage of the calibration.

•The electrically actuated switchover valve will be deactivated thus introducing the sample gas to the sensor, and the dewpoint will be monitored for stability. The display will show S.C./ FIN/-42indicating that self calibration has finished and it is measuring a dewpoint of -42°C. When the measured dewpoint is stable within 0.5°C for 3 minutes the instrument will “unfreeze” the analog output and relays and go to the display dewpoint mode.