Setpoint Processing, Closed-Loop Control - Siemens SIMATIC S5 Manual

Description of the Firmware

1.1.4 Setpoint Processing, Closed-Loop Control

For each controller, two setpoints and two positive and two negative tolerances can be set. If these
values are violated, an error bit is set.
Zone upper limits or lower limits can be preset for each individual controller. The control operates
within these zones (zone control).
It is also possible to specify a response threshold for the output manipulated variable. If, for
example, a response threshold of 10% is specified, the calculated values will only be output in the
range from 10 to 90%; under 10% the output is disabled, above 90% it is always enabled.
To smooth sudden setpoint changes, a ramp can be planned with a slope in C/h. Fig. 1.1.4/1 shows
an example of the curve of the actual setpoint value (setpoint ramping).
The ramp begins at the current actual value and continues until the required setpoint is reached.
If the setpoint is changed before the old value is reached (as at t
restarted with a negative slope.
The output for the setpoint ramping is indicated in message 21. If no setpoint ramping is used, the
setpoint you have selected is indicated in message 21. This does not apply to cascaded control.
Fig. 1.1.4/1 Actual curve of the setpoint with setpoint ramping
Temperature setpoints and actual values can be input or output in degrees Celsius or degrees
Fahrenheit. Degrees Celsius are converted to degrees Fahrenheit by the following formula:
T [ F] = (T [ C] x1.8 + 32);
The parameters are written to the transfer RAM of the module by the CPU at system start up using
function block FB 162.
4–10
in Fig. 1.1.4/1) the ramp is
4
IP244
C79000–B8576–C860–02