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PID Compact - OB vs FB cycle time?

Created by: mdudas at: 2/6/2012 4:45 PM (1 Replies)

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2/6/2012 4:45 PM	Rate (0)
mdudas Posts: 2 Rating: (0)	During my work with PID, I've come across a problem. In general, there are two places where I can define the sampling time for the PID: the sampling time input of PID_Compact, as well as the sampling time of OB that contains the PID instance. According to the manual, the sampling time is evaluated independently, basing on the PID_Compact execution time. Thus, it should be eventually equal to the sampling time of the cyclic OB. My question is: what is the purpose of sampling time input of the PID_Compact? As far as I'm concerned, it has no influence on its operation, as the only time that matters is the OB cycle time. What if I would set eg. 100 ms as the sampling time for the PID_Compact input and 200 ms for the cycle time of the OB? And vice versa? Would that cause an error?
mdudas Posts: 2 Rating: (0)	Last edited by: mdudas at: 2/6/2012 4:46 PM
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2/6/2012 7:23 PM	Rate (0)
umencho Grandmaster Joined: 3/21/2006 Last visit: 1/10/2026 Posts: 10247 Rating: (1183)	How do you estimate the sampling interval CYCLE and the largest possible number of controllers in a S7 CPU? How do you restart a PID controller that has been stopped because of a scan time error or switch off the scan time monitoring?

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