Rockwell Automation Allen-Bradley Micro850, Оригинальное руководство пользователя

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Rockwell Automation Publication 2080-UM002L-EN-E - November 2021 279
Appendix F PID Function Blocks
During autotune, the controller will automatically set the process value to zero.
To autotune, perform the following steps:
1. Set the Initialize input to TRUE.
2. Set the AutoTune input to TRUE.
3. Wait for the Process input to stabilize or reach a steady state.
4. Note the temperature fluctuation of the process value.
5. Calculate deviation value with reference to the fluctuation. For example,
if the temperature stabilizes around 22 °C (72 °F) with a fluctuation of
21.7…22.5 °C (71…72.5 °F), the value of ‘ATParams.Deviation’ is:
6. Set the deviation value, if you have not set it yet.
7. Change the initialize input to FALSE.
8. Wait until the ‘AT_Warning’ shows 2. The autotune process is successful.
9. Get the tuned value from the ‘OutGains’.
How Autotune Works
The auto tune process begins when the ‘Initialize’ is set to FALSE (Step 7.) At
this moment, the control output increases by the amount of ‘Step’ and the
process waits for the process value to reach or exceeds ‘first peak’.
First peak is defined as:
For Direct Operation: First peak = PV1 - (12 x Deviation)
For Reverse Operation: First peak = PV1 + (12 x Deviation)
Where PV1 is the process value when Initialize is set to FALSE.
Once the process value reaches first peak, the control output reduces by the
amount of Step and waits for the process value to drop to the second peak.
Second peak is defined as:
For Direct Operation: Second peak = PV1 - (3 x Deviation)
For Reverse Operation: Second peak = PV1 + (3 x Deviation)
Once the process value reaches or falls below second peak, calculations
commence and a set of gain will be generated to parameter OutGains.
Step
Step value should be between 3
*
Deviation and ½ load. The step provides an offset for the
load during autotuning. It should be set to a value high enough to create a significant change
in process value.
ATDynamSet
Set this value to a reasonably long time for the autotune process. Every system is different,
so allow more time to a system with a process value that takes longer to react to change.
ATReset
Set this parameter to TRUE to reset the output to zero after the autotune process completes.
Set this parameter to FALSE to leave the output at load value after the autotune process
completes.
Table 65 - AT_Parameter Values (Continued)
AT Parameter Recommendation
For °C:
22.5...21.7
2
= 0.4 For °F:
72.5...71
2
= 0.75