30
5
Firing Rate Controller (optional)
I >
→
faster approximation to the setpoint
danger of overshooting!
•
D term
The derivative term is calculated from the variation of the actual values. It has acceleration
and respectively slowing effects.
In practice the adjustment of the PID-controller is specified to each controlled system. With
the characteristics of the controlled system you try to deduce acceptable data, i.e. the values
are defined experimentally
•
P term, I term, D term are added together and act as adjustment on the firing rate default
for the ratio control. The value is added up, starting from the instantaneous internal firing
rate.
•
As long as the actual value is below the setpoint, P term and I term are positive, that is to
say both these term will increase the firing rate default.
•
Only the D term is negative in such a case (assuming that the boiler temperature is rising).
Use the D factor sparingly because it leads to a higher burden of the actuators.
•
In order to avoid excessive overshoot during burner start-up, the parameters should be
adjusted to achieve a suitably large D-term.
•
If, despite a large setpoint deviation, the burner is not running at full firing rate or base firing
rate, the P term should be increased.
•
The longer the adjustment time, the quieter the group. However, this also increases the
actual value's deviation from the setpoint value and leads to slower adjustment.
Values must be adjusted according to the controlled system.
* Default value
Fig. 5-5 Controller operation with P-term too high
Hot Water Installations
Steam Boiler Installations
P term
120*
600
I term
60*
300
D term
20*
25
Adjustment time
15*
20
Characteristic
Control Process
Control Mode
Start-up Procedure
P term higher
decrease of
attenuation
stronger reaction with
overshoot
faster start-up with
overshoot
P term smaller
increase of
attenuation
less reaction, less ten-
dency to oscillate
slower startup
Characteristic
Control Process
Control Mode
Start-up Procedure
I term higher
decrease of atten-
uation
stronger reaction with
tendency to oscillate
faster start-up with ten-
dency to oscillate
Summary of Contents for VMS 4
Page 2: ......
Page 119: ...118 10 Appendix...
Page 129: ...128 10 Appendix Fig 10 9 Ger t 4 Ger t 5 with output regulator...
Page 141: ...140 10 Appendix 10 14 Declaration of Conformity...
Page 142: ...141 10 Appendix...
Page 143: ...142 10 Appendix 10 15 Protocol Example...
Page 144: ...143 10 Appendix 10 16 O2 Setpoint Curves...
Page 145: ...144 10 Appendix...
