5 | Operation FISCHER Mess- und Regeltechnik GmbH
74 BA_EN_DE90
In order to be able to determine the degree of contamination by means of differ-
ential pressure measurement, it is therefore necessary to carry out the meas-
urement at maximum volume flow. This measurement is carried out at regular
intervals.
This is not necessary for dynamic filter monitoring. An approximation of the filter
characteristic curve is calculated by determining some system-specific paramet-
ers. With this approximated characteristic curve, the degree of contamination of
the filter can now be determined at any time without changing the fan speed.
Parameterisation
NOTICE!The filter characteristic curves shown serve to illustrate the rela-
tionships and can only be transferred to a real characteristic curve to a
limited extent.
The pressure difference in the filter increases due to the storage of dust. Ap-
proximately, this increase is quadratic for large dust filters and linear for particu-
late air filters. The approximation formula to be used therefore depends on the
plant. This is determined by the parameter Approximation . Experience
shows, however, that the linear approximation is sufficient in most cases.
The two input channels are assigned with the parameters Channel ∆p (dif-
ferential pressure measurement) and Channel Q (volume flow measure-
ment). Please make sure that you do not assign the same channel twice and
that the input channels have been parameterized according to the measure-
ment task (see Measurement C1 [}47]).
In general, the filter characteristic curve looks as follows:
50
Δp
Q
1
100
150
200
250
300
2 3 4 5 6 7 8 9 10
[1000 m
3
/h]
[Pa]
Q
max
Q
min
clean Filter
soiled Filter
operating zone
Δp
max (soiled)
Δp
max (clean)
0
0
Fig.105: filter characteristic curve
Explanation of the Quantities used:
Flowrate Q =
dV
dt
The flow rate states how much volume of a gas flows
through a defined cross-section in a certain time.
The flow rate is stated in m³/h.
Q
max
Maximum volume flow of the fan.
Q
min
Minimum volume flow of the fan.
formula symbol parameter description
Max. volume flow
Min. volume flow
Differential pressure above the soiled filter
at the maximum flow rate.
Current differential pressure above the filter.
Differential pressure above the clean filter
at a maximum flow rate.
Formelzeichen Parameter Beschreibung
∆p clean
∆p verschmutzt
Δp
max (soiled)
Δp
max (clean)
Δp
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