29
5
Firing Rate Controller (optional)
5.2.3
Control Range
The control range lies around the setpoint. The content of the "Burner on" parameter is sub-
tracted from the setpoint value to form the switch-on value. The value of the "Upper control
range" parameter (P 803) is added to the setpoint value to form the upper limit of the control
range. The control range may therefore lie asymmetrically around the setpoint.The shut-off
range is upwardly limited by the "Burner off" parameter (P 804). The parameter is added to
the setpoint value. If this value is exceeded, the burner is shut off.
The range between "Upper control range" and "Burner off" forms the shut-off range. If the ac-
tual value reaches this range, the to cancel firing rate controller, press key "Manual" again runs
at base firing rate.
It also follows from this that the value in "Burner Off", is generally higher than that in "Upper
control range". Otherwise there is no shut-off range and the burner is shut off on immediately
reaching the limit.
The burner 'ON' switching point also can be located above the setpoint. In this case the pa-
rameter 802 has to be set negative (<0).
5.3
Control Mode
The firing rate controller tries to bring the actual value into line with the setpoint value. In doing
so, a direct correlation is assumed between internal firing- ate and boiler temperature, e.g. the
greater the internal firing rate, the faster the boiler temperature rises. Should the curves be
programmed differently, the firing rate controller will not function.
Four parameters determine the control action.
•
Adjustment time
The adjustment time determines at what intervals the deviation is checked and the new
adjustment is determined.
•
P term
The proportional term acts directly on the deviation, that is the difference between setpoint
value and actual value.
P >
→
higher step response
•
I term
The integral term is calculated from the instantaneous deviation and the previous devia-
tion from the setpoint value.
Fig. 5-4 Control range
*(1) = P 804
*(2) = P 803
*(3) = P 802
*(4) = P 796 - P799
Summary of Contents for VMS 4
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