Siemens SIPART DR22 Manual page 67

Manual
In the ratio controller the standardized nominal ratio wv and the standardized actual ratio xv are
displayed on the digital w and x displays respectively. Via d*I a physical display is possible. The
controlled variable x1 and the evaluated commanding procesan be switched to the external
nominal ratio (display level II) (display level I must be set, display level II is automatically set
the same). Signaling of the display levels, see S1 = 3, fos variable w are displayed on the ana-
log x and w displays respectively so that a direct control difference monitoring is possible at all
times.
With the Shift key (12) the digital w-display cllow-up controller. The digital x-display shows the
actual ratio xv in both display levels.
The actual ratio is gained by back calculating the ratio formula with the current process
variables x1, x2:
x1--c5
v =
is
x2
= xv (vE -- vA) + vA gives for xv =
v
ist
xv is displayed and is required for x-tracking mode. For the xv-display, x1 and x2 are limited to
+0,5 % so that the display does not become too restless for small x1 and x2 or flip from positive
to negative in the case of negative x2. The linearizers can be used for linearization of the com-
manding process variable x2 (via FE2 in the freely connectable input range) and the following
process variable x1 (via FE1 also in permanently connected input range).
The linearization then acts on the analog displays and the ratio formation and therefore indi-
rectly on the digital displays for nominal and actual ratio. The ratio controller has no nominal
ratio limiting because the ratio factor range already marks the limit. The commanding process
variable x2 can be limited by the freely connectable range (S4 = 1) if necessary.
The ratio controller behaves like slave controller S1 = 3 in switching of the setpoint ratio wv so
that the information and tables there apply accordingly. The variables wi and w
replaced by wvi and wv
ratio (manually adjustable) or with commanded ratio factor.
A fixed ratio factor is used for example in simple combustion rules, (see example in figure 1-33)
where the ratio factor is reset manually if necessary for varying fuels. If it is possible to measure
the effects of the ratio factor (combustion quality, pollutants in the flue gas) a commanded ratio
controller is used. Here a master controller adjusts the ratio factor (ratio cascade) with the com-
bustion quality as a control variable.
Another application for ratio cascades are concentration controls, e.g. pH-value controls. The
pH-value is the controlled variable of the master controller, the flow of alkali and acid the com-
manded process variable and the following (controlled) process variable of the ratio controller.
SIPART DR22 6DR2210
C79000-G7476-C154-03
v --vA
is
vE--vA
. This controller type can also be used as a ratio controller with fixed
E
1.5 Functional description of the structure switches
1.5.4 Controller types (S1, S49 to S53)
x1--c5
- vA
x2
or xv =
vE--vA
1 Technical Description
must be
E
65