INFICON 2020ComboPRO Portable Photoionization Detector - Manual (Page 58)

ISP-074-575-P1D 51 51
these readings in the 2020ComboPRO’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 the2020ComboPRO’s internal menu for the
2020ComboPRO 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 2020ComboPRO 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 2020ComboPRO. 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 2020ComboPRO. You can
display the results of the calculations by selecting Interval mode.
PEAK Mode
The PEAK mode displays the current detected concentration. The reading is updated
once a second. In the background, the 2020ComboPRO datalogger is sampling the
concentration and measuring minimum, maximum, and average concentrations for
the selected averaging interval. At the end of every interval, one entry is placed in
the datalogger until the datalogger is full.
In order to reset the PEAK reading, press the “Clear” key then select “PEAK” using
the “Down Arrow” key then press “Clear”