West Control Solutions KS98-1 - Manual (Page 267)

Ratio = Type 2 W
X N
X X SFact
=
+
+ ×
1 0
1 2 ( )
In this example, water (x1) must be batched as a percentage of
the total (paste; x1+x2). As the paste quantity is not available
directly as a measurement signal, the total is calculated inter-
nally from x1 and x2. N0 = 0 must also be adjusted in this case.
Ratio = Type 3 W
X X N
X SFact
=
- +
×
2 1 0
2
Unlike the previous examples, yoghurt (x2) and the final product
(x1) are measured in this case.
Three-element control
With three-element control, process value calculation is accor-
ding to equation
x X a X X
eff
= + × 1 2 3 ( \ ) whereby term ( \ ) X X 2 3 is
the difference between the steam and water flow rates. Factor
b for flow range matching used so far is omitted, because the
mA signals are converted directly into physical units during in-
put value conditioning (x0, x100). The calculated process value
is displayed on the process value display.
For selecting a three-element controller, ‘ CFunc =
3-elem.‘ must be entered in the configuration.
Correcting variable processing
The following considerations related to
correcting variable processing are appli-
cable to continuous controllers,
two-point, three-point and three-point
stepping controllers with position feed-
back. The diagram opposite shows the
functions and interactions of correcting
variable processing.
9499-040-82711
Process value calculation III-267
Flour
X1
X2
x1
x2
Water
w = (x1+N0) / (x1+x2) SFac w
Dough
Fig. 87
x1-x2
x2
w = (x2 - x1) / (x2 SFac) w
Fat
Yoghurt
x2
x1
X2
X2
Fig. 88
Setpoint w
Water
Steam
Fd
Level L
Fw
+ Process valuex = x1 +a (x2 - x3)
y + dFd/dt
_
X3
X1
X2
Fig. 89
x
w
Ypid
Ymax Ymin
Y2
Y0
+
OVC
a/m
y/y2
Y
Fig.: 90 Steps of the output signal processing