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Calculation of the PM
Concentration with
Digital Filter and Fixed
Time Constant
Thermo Fisher Scientific
Calculation Mode:
2.5
From the accumulated particulate mass (Σm), a discrete mass value (m) is
calculated every four (4) seconds. The discrete mass is then passed through
a digital filter with the time constant (τ
smoothes the discrete mass fluctuations, resulting in a smoothed discrete
mass value (m
RM
calculated (dm
RM
(Q) from the last 4-seconds, resulting in a raw concentration (C
storage cycle time is four (4) seconds, thereby recognizing rapid
concentration gradients. However, C
level through this short period of time and therefore a second digital filter is
applied with a second time constant (
concentration for reporting (C
The above description provides the basis for the beta attenuation derived
mass concentration. Simultaneously, the nephelometer concentration is
measured as a 1-minute running average (N
C
are passed through a digital filter with a dynamic time constant (
RM
ranging from 20-480 minutes, whereby the time constant used is a
function of the coefficient of variation of the nephelometer signal:
No matter what the constant, both N
resulting in synchronized long-tern averages N
). The mass differentiation with respect to time in then
/dt). Thus, dm
/dt is divided by the average air flow rate
RM
does exhibit an unacceptable noise
e
τ
2
).
RM
dm
RM
dt
=
C
;
Ce
e
Q
τ
ν
∝
f
(
v
N
f
_ n
1
f_1n
Model 5030 SHARP Monitor Instruction Manual
Calculation of Particulate Mass on Filter Tape
) of 20 minutes. The filter
1
) of 20 minutes to offer a final
τ
⎯
⎯→
2
C
RM
). Thereafter, both N
f_1n
)
and C
are passed through
RM
τv
τv
and C14
f_
f_
Introduction
). The
e
and
f_1n
τ
)
v
τ
v
, respectively.
1-5
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