Hach Ultra MET ONE 237AB, User Manual, Page: 24 / 57

21
Operation
To sample the room in the automatic mode:
1. Carry the MET ONE 237 particle counter to the center of the first area of the large
room to be tested.
2. Place or hold the counter about 4 feet off the floor.
3. Make sure that the opening of the isokinetic probe faces directly into the laminar flow.
4. Press
RUN/STOP
to initiate counting. The display shows three 1-minute samples
being taken, separated by a 10-second hold time.
5. The printer will print the results after each count period. When all three cycles are
complete, the counter will print an additional record showing the average of all the
three samples.
6. Move to the next location to be tested and program the Location Number as
described above.
When the sampling is complete, the count results can be downloaded to a computer and
analyzed to verify the condition of the room. Refer to
Appendix B on page 43 for
download procedures and data string descriptions.
5.3.3 Concentration mode
The concentration mode in the MET ONE 237 particle counter is useful for taking a quick
snapshot of airborne particulate contamination levels.
Note: The Concentration mode is not a substitute for full sampling.
The concentration mode is appropriate for areas where the particulate levels are
unknown and may exceed the operating limits of the counter. The concentration counting
mode does not store/write the data records in the memory buffer. The concentration
mode gives a continuously updated approximation of the number of particles per cubic
foot or per liter. The approximation is based on a user-selectable sample period of one to
ten seconds.
In concentration mode, the counter begins sampling and estimates the counts per cubic
foot or per liter based on a programmable period of time. The MET ONE 237 particle
counter updates the calculation results on the display at 1-second intervals. The
programmable period sets the size of a moving calculation ‘window’ which is moved each
second to incorporate a new second of sample data and discard the oldest second of
sample data in the ‘window’ of calculations.
The MET ONE particle counter uses a
3-second period to calculate the concentration based on a 3-second window (refer to
Figure 9 ).
The counter calculates the concentration based on a 10-second window that moves
every second (refer to
Figure 10 ). A 10-second period provides a good representation of
actual concentration because it covers a longer period.
Note: Longer periods also allow high particulate levels to contaminate the sensor. Use a shorter
period to calculate the Concentration for unknown environments