48
6 Commissioning
6.6.2 Control Strategy
6.6.2.1 With Pre-setting For Firing Rate Changes
O
2
trim by means of a comparison between target and actual values is only performed if no
output change (firing rate change) takes place (’internal firing rate’ static). After a preceding
firing rate change, an target/actual value comparison is performed and an actuation step trig-
gered only after expiry of the set lag time (parameters 898 and 900).
If the O
2
actual value corresponds to its target value, the current correction value, referenced
to the firing rate vale and the firing rate direction, is stored in a table. The updated value is
output at the next firing rate change.
A pre-update is already carried out as from the 2
nd
target/actual value comparison, after a fir-
ing rate change. As soon as the actual value gets close to the target value, the correction value
is updated.
When the firing rate changes, control is terminated immediately after target/actual value com-
parison and the neutral value, or if relevant the correction value obtained (updated) for this
firing rate point,is output pre-setting!
Control after a target/actual value comparison is only performed again if the firing rate is sta-
tionary and on expiry of the lag time.
In this type of control, the overshoot is automatically deactivated in the VMS. The actuators'
hysteresis is compensated for by the firing rate direction-dependent updating of the correction
value.
Control strategy with pre-setting for firing rate changes
1 Pre-purge/ignition
The correction is switched off; i.e. the neutral correction value is output.
2O
2
trim on standby the "Correction value with deactivated controller” specified in parame-
ter 901/902 is output.
3 Controller takes over the neutral correction value,or the updated correction value is output.
4 On expiry of the set lag time, the residual deviation between target and actual value is cor-
rected.
5 firing rate change
O
2
trim is suspended and pre-setting carried out - neutral correction value, or the updated
correction value is output.
6 Control is deactivated, e.g. by a fault
The correction value for deactivated controller specified in parameter 901/902, or the one
specified in parameter 917/918 for ’Air shortage’, is output.
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