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| 12/17/2010 12:54 PM | |
Joined: 10/7/2005 Last visit: 11/18/2024 Posts: 3027 Rating:
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Hello hellf I somewhat disagree with Chilly_Garfield's above advise. The TEMP variables of an OB are read only, you can use OB35_EXC_FREQ to find out what the call rate of the OB is, but can NOT use it to change its call rate. To do so, you must go into HWconfig - CPU propoerties and then change it in the Cyclic Interrupt tab (see attached pic). Note that a HWconfig download is required afterwards (which requires CPU Stop-restart) to activate the new call interval time. Note further that you need to be mindful about how short you make this time and make sure that the the logic that you execute from withing OB35 has a runtime that is shorter than thecall intervaltime of OB35 (asOB35 will otherwise try to interupt itself which will get you into trouble). I hope this helps |
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| 12/18/2010 12:37 PM | |
Joined: 1/28/2009 Last visit: 10/26/2024 Posts: 6852 Rating:
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Dear Hellf Sampling time of 100ms is enough for handling vast variety of process variables.Temprature is really sluggish in variation, flow or level have also normal variation in steady states.First of all observe the type of physical or internal parameter of PLC in term of variations and then execute you program to calculate integral in 100ms and another sampling rate less than 100ms.If the error is negligble so 100ms is ok. For your information, you can also use a integrator function provided in modular PID control function section 2.1.8.Attachment contain the extracted information from manual and also check the examples provided by SIEMENS. Best regards hdhosseini AttachmentINTEGRATOR.pdf (517 Downloads) |
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