INFICON 2020ppbPRO Portable Photoionization Detector - Manual (Page 54)

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VIEW selects datalogger review.
TAG selects “No Label”, “Background”, or “Sample”.
MENU selects the 2020ppbPRO ’s internal menu for the 2020ppbPRO setup by the
user.
Interval Mode
Interval displays the instantaneous readings as well as STEL, TWA, and PEAK
readings. Interval mode is identified by the letters “INT” in the upper right-hand
corner of the 2020ppbPRO display. Interval automatically calculates and updates
STEL, TWA, and PEAK readings. Interval mode also automatically stores these
readings in the 2020ppbPRO
’s memory at a preset interval selected by the user. In
Interval mode, the soft keys are VIEW, CLEAR and MENU.
VIEW selects datalogger review.
CLEAR selects clearing the values for “TWA”, “PEAK”, “ALL”.
MENU selects the2020ppbPRO ’s internal menu for the 2020ppbPRO setup
by the user.
Short-Term Exposure Limit (STEL) Mode
The Short-Term Exposure Limit (STEL) mode displays the concentration as a 15-
minute moving average. The 2020ppbPRO maintains 15 samples, each
representing a one-minute averaging interval.
Once every minute, the oldest of the 15 samples is replaced with a new one-minute
average. This moving average provides a 15-minute average of the last 15 minutes
with a one-minute update rate. Since the average is calculated using 15 one-minute
averages, the meter display will only update once every minute.
STEL is set to zero each time the instrument is turned on. Since STEL is a 15-
minute moving average, there is no need to clear or reset the STEL.
STEL calculations are always being performed by the 2020ppbPRO. You can
display the results of the calculations by selecting Interval Mode.
Time-Weighted Average (TWA) Mode
The TWA accumulator sums concentrations every second until 8 hours of data have
been combined. If this value exceeds the TWA alarm setting, a TWA alarm is
generated. The TWA is not calculated using a moving average. Once 8 hours of
data have been summed, the accumulation stops. In order to reset the TWA
accumulator, press the “Clear” key, then select “TWA” using the “Down Arrow” key,
then press “Clear”.
This sum will only be complete after 8 hours, so the meter displays the current sum
divided by 8 hours.
TWA calculations are always being performed by the 2020ppbPRO. You can display
the results of the calculations by selecting Interval mode.