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8 Options
value. In all other cases there is no shut-off range and burner is immediately shut-off when
reaching limit.
The burner 'ON' switching point can also be located above setpoint. In this case P0054 has to
be set negative (< 0).
8.1.9 Checking the Safety Limiter
For testing purposes of the safety limiter change the setpoint. This also causes a change in
shut-off range as well. The safety limiter can therefore be overrun in manual mode.
8.1.10 Control Mode
The firing rate controller is attempting to adjust actual value to setpoint value. A direct corre-
lation is assumed between internal firing rate and boiler temperature, i.e. the higher the inter-
nal firing rate, the faster boiler the rise of temperature. If curves are programmed in a different
way the firing rate controller will not operate.
Four parameters define the control characteristics:
• Adjustment time
Adjustment time defines the intervals of deviation is checked and a new adjustment is de-
termined.
• P term
The proportional term affects directly on deviation defined as difference between setpoint
value and actual value.
P > → higher step response
• I term
The integral term is calculated from present deviation and previous deviation to setpoint
value.
I > → faster approximation to setpoint → danger of overshooting!
• D term
The difference term is calculated from variation of actual values. This may result in accel-
erating, respectively retarding effects.
In practice adjustments of PID-controller is orientated by given controlled system. Out of char-
acteristics of the controlled system data can be deduced, i.e. by experimental determination.
Fig. 8-5 Control range
*(1) = P 0056
*(2) = P 0055
*(3) = P 0054
*(4) = P 0048 - 0051
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