West Control Solutions KS98-1 - Manual (Page 266)

For optimum combustion, the fuel-air ratio must be controlled. With stoichiometric combustion, the ratio is selected so
that there are no inflammable residues in the waste gas. In this case, the relative rather than the physical ratio is dis -
played as process value and adjusted as setpoint.
If the transmitters used by the controller are designed with a stoichiometric ratio,
l = 1 is met exactly with restless
combustion.
With a process value display of 1,05, the instantaneous air excess is clearly 5%. The amount of air required for atomi -
zing is taken into account by constant ‘
N0‘. For selecting a ratio controller, CType = Ratio must be selected.
Moreover, configuration word ‘ Ratio‘ must be taken into account.
a
With ratio controller,
note that parameters
Xn0 and Xn100 must be set to the input range of connector X1.
Example of standard ratio control:
Standard ratio control at the example of stoichio-
metric combustion. Analog input INP1 is configured
to 4...20 mA with physical unit m
3 /h (air). Values 0
and 100 are allocated to input variables 4 mA ( x0)
and 20 mA ( x100).
Atomizing air N0 is added to this input.
E.g. INP5 is selected as second ratio input. This in-
put is also configured for 4...20 mA and m
3 /h
(gas). x0 and x100 values 0 and 100 are allocated
to the input variables.
Weff effective as relative ratio is multiplied by
stoichiometric factor SFac (e.g. SFac = 10), i.e. a
„stoichiometric“ flow ratio can be used for calcula-
tion of the control deviation. The instantaneous
(controlled) process value is calculated from the physical ratio, multiplied by 1/SFac and displayed as relative value.
Material batching and mixing
The following examples are intended to show that various control possibilities can be used. This is necessary, since
the materials to be mixed (e.g. paste) are not always directly measurable due to their consistency. Other cases may re -
quire a component to be controlled in relation to a total rather than to another component.
Ratio = Type 1 W
X N
X SFact
=
+
×
1 0
2
The first case is obvious. Almost everybody knows what hap-
pens during brewing.
Yeast (x1) must be batched in relation to
the original wort (x2). The is adjusted
in ‘%yeast’, e.g. W= 3%. The ratio inputs are scaled in equal
units. The control deviation is
multiplied by ‘
SFac = 0,01’ and calculated
according to equation xw = (x1 + N0) - 0,03 w x2, so that exact-
ly 3% of yeast are batched with xw = 0. Process value display
is also in %. Constant
N0 is without importance (N0 = 0)
9499-040-82711
III-266 Process value calculation
X1
X2
w= (X1+N0) / (X2 SFac) w
Air
Fuel
x1
x2
Burner
atomized air
N0
Fig. 85
x1
x2
original wort
Yeast
X2
X1
w = (x1+N0) / (x2 SFac) w
Fig. 86