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High speed application of S7 1200

Created by: Ras Sharif at: 1/9/2012 5:56 AM (9 Replies)

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1/9/2012 5:56 AM	Rate (0)
Ras Sharif Posts: 69 Rating: (0)	Hi everybody I have just started the PLC with S7 1200. My project is to ON a switch at a moment on 50 Hz voltage frequency. That is to detect the instantaneous amplitude coresponded to the special angle through analog input and ON the switch through digital output. Is it true that I can configure the I/O addresses of channels to none cyclic ( means immedate read/write ) and My project is possible? Thanks a lot for the help
Ras Sharif Posts: 69 Rating: (0)
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1/9/2012 9:06 AM	Rate (0)
Marko Bursic Platinum Member Joined: 9/8/2009 Last visit: 7/17/2023 Posts: 1410 Rating: (153)	I think that no PLC is capable of what is your intention.

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1/9/2012 12:09 PM	Rate (0)
Ras Sharif Posts: 69 Rating: (0)	Dear all I see "immediate read/write" in the S7 1200 manual which described to direct access to I/O points rather than cyclic image process. What it means? Regards
Ras Sharif Posts: 69 Rating: (0)
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1/9/2012 2:43 PM	Rate (0)
Steven-81 Posts: 7 Rating: (2)	Even if you couldperform immediate read and write, the analog input is too slow to detect phase angle of line frequency power.
Steven-81 Posts: 7 Rating: (2)
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1/9/2012 2:48 PM	Rate (0)
0_Einstein Diamond Expert Joined: 7/7/2010 Last visit: 11/6/2024 Posts: 15385 Rating: (2443)	R. Sharifi Dear all I see "immediate read/write" in the S7 1200 manual which described to direct access to I/O points rather than cyclic image process. What it means? Regards Since my PLC applications for the S7-1214C's has scan times around 10ms (100Hz processing capabilities for cyclic OBs), I think a standard cyclic OB would work. However, with a timed interrupt of 10 ms to look directly at the input and force the output directly using the Ix.x:P and Qx.x:P direct access you can get what you want. You could probably reduce the 10ms considerably if there is little code in it.
	science guy
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1/9/2012 8:27 PM	Rate (0)
Ras Sharif Posts: 69 Rating: (0)	Dear everybody The analog module is 4 ch. and the conversion time is 625 us totally. I think that i can read the Analog ch. immediatly ( no cyclic ) in a loop. Once the amplitude reached, to write the digital output immediatly. Is it possible? Regards
Ras Sharif Posts: 69 Rating: (0)
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1/9/2012 9:33 PM	Rate (0)
0_Einstein Diamond Expert Joined: 7/7/2010 Last visit: 11/6/2024 Posts: 15385 Rating: (2443)	That would only work if you could disable the watchdog timer functionality of the PLC as a constant loop would simply fault the PLC on watchdog timeout.
	science guy
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1/10/2012 10:19 AM	Rate (1)
Marko Bursic Platinum Member Joined: 9/8/2009 Last visit: 7/17/2023 Posts: 1410 Rating: (153)	There are also already built electronic modules to control phase angle like SSR with analog input if you want to control a SSR. Its not only to fire a SSR at determined angle since you may have current and voltage with phase difference a SSR wont fire all the time at desired angle and if it miss you need to re-trigger. Phase angle circuit is some more advanced than only compare analog input and set an output. If you really insist I would think about different strategy. Instead using analog input go for digital input, you will need a power resistor and azenner diode, you will have on dig. input quadratic pulse (or you mght use two dig. inputs in complementary) and you set up an interrupt on transition from 0 to 1. It could be better than using analog input. Or you can use capacitor circuit instead a big resistor, you add an optocoupler and on interrupt set output immediately. If you want to reachpeak, then this is way to go - capacitor will add 90 deg lag and withdiode resistance it will be less than 90,let say80 degress, if the plc procedure and output lags are more than 10deg then you can add resistance in series to capacitor to get more lag and so you can adjust your circuit tobe fired exactly on peak.
	Last edited by: Marko Bursic at: 1/10/2012 10:52 AM
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This contribution was helpful to 1 thankful Users Ras Sharif

1/13/2012 12:13 PM	Rate (0)
Ras Sharif Posts: 69 Rating: (0)	Dear all, Marko Bursic! Thank you for the suggestion. I am trying to use the methods such as capacitor phase shifting. Regards,
Ras Sharif Posts: 69 Rating: (0)
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1/14/2012 10:44 AM	Rate (0)
Marko Bursic Platinum Member Joined: 9/8/2009 Last visit: 7/17/2023 Posts: 1410 Rating: (153)	http://www.edn.com/article/472167-Improved_optocoupler_circuits_reduce_current_draw_resist_LED_aging.php maybe just for info

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