21
2.8 Auto-tune
Note. Auto-tune is not available for Auto/Manual Station or Indicator templates, or when
boundless or heat/cool control types are selected.
Information.
• Auto-tune optimizes process control by manipulating the COMMANDER 350 output and then
monitoring the process response.
• At the end of an auto-tune, the control parameters are updated automatically.
• Before starting auto-tune, the process variable must be stable.
• The COMMANDER 350 monitors the noise level of the process variable for 30 seconds and if
it is greater than 2% of the engineering range the auto-tune is aborted.
• The COMMANDER 350 selects either 'start-up' or 'at set point' tuning automatically, depending
upon the level of the process variable relative to the control set point.
2.8.1 Start-up Auto-tune
If the process variable is more than ±10% from the set point, 'start-up' tuning is carried out.
• 'Start-up' tuning – steps the output to drive the process towards the set point. The process
response to this step change is monitored and PID parameters are calculated.
• The output step applied = % deviation from the set point x 1.5.
• If no errors exist, the COMMANDER 350 enters auto mode and begins to control the process
using the new PID parameters.
• If an error occurs during the auto-tune, the COMMANDER 350 reverts to manual mode with the
control output set to the default output value. An error message is displayed in the operator
level – see Table 2.1.
2 OPERATOR LEVEL…
+2%
– 2%
t
A – Stable process before auto-tune
SPT
PV
B – Process response during auto-tune
t
PV
1
/
4
wave
damping
Controlling to Set Point
Auto-tune complete
SPT
>10% span
rorrEnoitpircseDrorrEnoitpircseD
1enut-otuagniruddeliafVP7
tuodetaluclacsaweulavDroI,PtnatluserA
egnarfo
2
enut-otuanagnirudtuodemitsahenut-otuA
pets
8)enut-otua'putratS'(dedeecxetimilVP
3enut-otuaotysionootssecorP9edomnoitarugifnocotnituprellortnoC
4enut-otuaottsafootssecorP01resuybdetanimretenut-otuA
5
sruoh21xam(enut-otuaotwolsootssecorP
.)selcyc-flahneewteb
11
gnirudnoitceridgnorwehtnignignahcsiVP
tsetpets
6
.gne%52>ybtnioptesmorfdetaivedVP
tsetesnopserycneuqerfgnirudnaps
Fig 2.7a Typical 'Start-up' Auto-tune Cycles
Table 2.1 Auto-tune Error Codes
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