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 When dust passes between
the transmitter and receiver, the momentary blockage of light by the particles causes the receiver
to see a modulating signal from the transmitter (see picture above). The amplitude of the signal modulation increases
with increasing dust concentration.
The receiver senses the signal modulation and converts it to a dust concentration with the microprocessor.
Therefore, signal modulation is proportional to dust concentration. The CPM responds only to particulate
moving through ductwork or the stack.
Because it measures signal variations resulting from moving particles
rather than from a diminishing intensity of the light beam, the CPM is
relatively unaffected by particulate accumulation on the windows of the
transmitter heads, optical misalignment, or aging of the transmitter and
receiver.
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