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General Information
2.3 Theory of operation
The MET ONE 237A/B particle counter is a compact, fully featured particle counter that
includes sensor, pump, electronics and the printer. Both the variants use the same
sensor, pump, CPU and display electronics. The MET ONE 237A particle counter is
calibrated with channel one sensitivity of 0.5 µm and the MET ONE 237B particle counter
is calibrated with a channel one sensitivity of 0.3 µm. Both operate at a flow rate of 0.1
cfm.
The sample passes through a laser beam in the sensor. The particles in the sample
scatter the laser light. The sample then passes through the pump and a filter to trap
particles in the counter. The flashes of scattered light are converted to electronic pulses
directly proportional to the amount of scatter to make a correlation to particle size. The
electronic pulses are counted and stored in channel bins in a data record which includes
the date and time from the CPU clock. If the RH/T probe is attached, snapshots of
environmental conditions are also included (refer to Figure 2 below).
Figure 2 Theory of operation
1
Sample inlet
6
Sample outlet
2
Sensor
7
Serial data out
3
Flow monitor
8
Printer
4
Pump
9
Control electronics
5
Filter
10 Display
8