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PULSE DURATION MEASUREMENT

Created by: kate at: 8/23/2007 7:54 AM (4 Replies)

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8/23/2007 7:54 AM	Rate (0)
kate Regular Member Joined: 3/28/2007 Last visit: 9/19/2007 Posts: 15 Rating: (0)	Dear ALL, I am struck in one problem.where in it is a customer requirement. I want to measurea pulse duration from the positive and negative edge of the pulse i.e, i want to measure ontime of pulsewith resolution of 1ms . I have tried withtimer but minimum is 10msprovided in simatic manager.and it showing only elapsed time.I am using CPU 314 So i kindly request you to give me solution for this. with regards kate

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8/23/2007 6:06 PM	Rate (0)
Denilson Pegaia Platinum Member Joined: 9/23/2005 Last visit: 9/26/2023 Posts: 4237 Rating: (1366)	Hi, I'm not sure if it for your case, but the new firmware for CPU 314 make possible to read the clock with resolution of 1ms. http://support.automation.siemens.com/BR/view/en/16749674 However, pay attention on the scan cycle of your program.
	Denilson Pegaia Siemens Industry Sector Technical Support
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8/27/2007 6:33 AM	Rate (0)
Aret Posts: 2348 Rating: (262)	Dear kate, there are 2 things to mention. One of them Pegaia already mentioned - your scancycletimewouldbemore,than1ms. YoucanuseOB35with1msforexample-butcodeinthatOBmustbereallytiny. 2nd problem - which module do you use? Each input module has it's conversion time - so if it's around 20ms there is no sense to measure with 1ms accuracy.
Aret Posts: 2348 Rating: (262)
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8/27/2007 1:36 PM	Rate (0)
Thijs Posts: 121 Rating: (16)	The code off the program in OB35 will not be the only problem. A standard input card is about 1.2/4.8ms. You might want to use a 314C. This one as 24 high speed inputs. Frome these inputs you can configure a interrupt (OB40) on each P and/or N edge detection. Or you can use a 6ES7 321-1BH10-0AA0 card. This is a 16 input 24VDC card with a delay off 24/75us. with this card you need constant polling (1ms with OB35) to catch the edge Another option is to use a 6ES7 7BH01-0AB0 card. This one can generate a interrupt. with this option you won't need a constant polling off the inputs. You can use a HW interrupt and program OB40. this could save a huge amount op CPU time. Please now that this info is from the top off my head. Haven't done this before
Thijs Posts: 121 Rating: (16)
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8/28/2007 6:52 AM	Rate (0)
Aret Posts: 2348 Rating: (262)	Thijs is absolutely right about OB40. But take care about it's priority, as if it would bee too low you can lose your signal's time.
Aret Posts: 2348 Rating: (262)
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