INFICON 2020ppbPRO Portable Photoionization Detector - Manual (Page 64)

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5. Use the up, down and right arrows soft keys to enter the desired number.
6. Highlight the  and press the DONE soft key.
7. Press the DONE soft key to return to the main display or press the SELECT
soft key to edit another value.
8. To return to the Main Menu, press SELECT then DONE.
To select a pre-programmed compound stored in the 2020ppbPRO ’s Preset RF
library:
1. Press the MENU key.
2. Choose “Memory Slots”, then press the SELECT key.
3. Press the EDIT key.
4. Press the PRESET key.
5. Use the DOWN ARROW key to choose the alpha range of the compound of
interest, then press the SELECT key.
6. Choose the compound of interest using the DOWN ARROW key and press
the SELECT key.
7. Press the SELECT key to accept the choice or press EDIT to modify the
preset values for STEL, TWA and PEAK alarm as shown above.
Calibration Technical Description
Periodic calibration is required to compensate for the 2020ppbPRO output changes
due to inlet filter restriction, ionization chamber contamination, lamp cleanliness,
pump wear and other factors.
During calibration, the 2020ppbPRO is first exposed to zero air. A small (zero) signal
is generated. This zero signal is stored by the microprocessor.
The 2020ppbPRO is next exposed to span gas. This span gas signal is stored by
the microprocessor. The microprocessor subtracts the zero signal from the span gas
signal and divides the difference by the user-entered span gas concentration. The
resulting sensitivity is stored in the selected Memory Slots with the zero signal and
the alarm levels. This number is then multiplied by the response factor and
displayed.
The 2020ppbPRO readings are always relative to the calibration gas. After
calibration with isobutylene, the 2020ppbPRO will respond directly in units
equivalent to isobutylene. Most volatile organic compounds will be detected by the
2020ppbPRO. It cannot distinguish between isobutylene and other ionizable
compounds. A reading of 10 ppm indicates all ionizable compounds that are present
have generated an ion current proportional to 10 ppm of isobutylene. The reading is
actually 10 ppm isobutylene equivalent units. The 2020ppbPRO readings give an
indication of the total ionizables present and their concentration relative to the
calibration gas.