Working Principle
The measuring principle of the piezoelectric balance-type dust counter is completely different
from that of the previous light random type. This measurement calculates the concentration of dust
in air by directly measuring the weight of dust in air per unit volume. As a result, both stability
and precision are greater than by light random mode.
The dust particle in the air is spread in a diameter ranging from subparticle to tens of
micrometer. The instrument is graded by use of an impacter and specially measures the
concentration of dust particles that affect the human body, namely, the dust concentration in the
range of subparticle to tens of micrometers. The graded suspended particle has nothing to do with
the diameter of particle. Dust is colleted onto the piezoelectric element (crystal) at an approximate
rate of 95% by electrostatic collection method. Depending upon the dust mass collected, the
inherent frequency of the piezoelectric element will change correspondingly, proportional to the
dust mass collected. The instrument calculates the concentration value finally in terms of the
change in frequency of the piezoelectric element after a certain quantity of air absorbed in a given
time and dust particles are collected onto the piezoelectric element. The calculation formula:
C=
α
×
f
C ---- Concentration value
f
---- Frequency difference measured for the crystal
α
---- calculation factor
，
α
=1/EStQ, E=charged efficiency, S=crystal sensitivity, t=test time,
Q=flow.
Besides, in this instrument, two piezoelectric elements are used to correct the temperature
error, thereby improving the precision and stability of measurement greatly. The sampling air is
absorbed by a subminiature rotary pump and its air flow has nothing to do with the change in
power voltage. The use of electronic governor ensures the stability of the instrument to absorb air
in a given time. As these gears are adopted, the measurement precision is improved remarkably
with guaranteed stability.
Processing of data measured: the instrument adopts MCU for control, which features great
speed, few errors and menu set-up. It can store 500 data records and can communicate with the
computer or print out data directly, thereby making it more intelligent.
Besides, the dust deposited on the elements should be removed by manual cleaner.
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