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For step response method: Before doing auto tune, the system should be under the non-control
steady state. Take the temperature for example: the measured temperature should be the same
to the environment temperature.
For critical oscillation method: user needs to set the sampling time at the beginning of the
auto tune process. For slow response system, 1000ms. For fast response system, 10-100ms.
For critical oscillation method: the system can start the auto tune at any state. For object
temperature, the current temperature doesn’t need to be same to ambient temperature.
Two different methods and PID control diagram:
(1)
Step response method
Make sure current temperature is equal to ambient temperature
output
D0
+DIFF
D0
Setting value
D0
-DIFF
(2)
Critical oscillation method
The auto tune start temperature can be any value.
t
Output
D0
+DIFF
D0
Setting value
D0
-DIFF
To enter the auto tune mode, please set bit7 of (
S3+ 2)
to be 1 and turn on PID working
condition. If bit8 of (
S3+ 2)
turn to 1, it means the auto tune is successful.
PID auto tune period value [S3+12]
Set this value in S3+12 during auto tune. This value decides the auto tune performance, in a
general way, set this value to be AD result corresponding to one standard tested unit. The
default value is 10. The suggested setting range: fall-scale AD result×0.3~1%.