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Sample program: PID Lean PWM generator for standard IO

Created by: Denilson Pegaia at: 4/28/2010 5:57 PM (5 Replies)

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Thanks 23

6 Entries

4/28/2010 5:57 PM	Rate (7)
Denilson Pegaia Platinum Expert Joined: 9/23/2005 Last visit: 3/21/2025 Posts: 4406 Rating: (1475)	Hi, Follow there is a sample program that emulate a PWM generator in a normal user program timing (i.e. without the help of the special digital output of the CPU). Attachment PWM.zip (4821 Downloads)
	Last edited by: Pegaia at: 10/19/2010 11:45 AM change subject only Last edited by: Pegaia at: 4/29/2010 12:16 PM subject correction Denilson Pegaia Siemens Industry Sector Technical Support
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This contribution was helpful to 18 thankful Users umencho Gerdoo Yu-wen Tang Tanle Dilli Tranhieu0983 Nelliyan randy lee_dong25 111111 mva-78 1990 Alpha Tech rouzbeh y calvin_huy ht_group86 EddyDosSantos AutoGen_747279 Jens Petersen

3/14/2012 7:26 PM	Rate (1)
Erik Sparre Posts: 10 Rating: (3)	I found a serious bug in my code. Apologies to anyone who is trying to use it. I have therefore deleted the original attachment. I'll get back once I have fixed and tested it properly. Original posting: I wanted a simple software PWM like then one above. I try to write all my code in SCL and I noted that I couldn't create "multi-instances" of the supplied PWM since it is not coded in SCL. It seems one cannot create instances of FBD inside SCL function blocks. So I decided to write my own software version of PWM in SCL. It has been developed and tested on a S7-1200 system, but I think you can get it to work on S7-300/400 systems too. If you need many instances of this PWM, consider moving the calculation of "dt" (delta-time) outside of the FB to speed up processing. I.e. do it once for all PWMs in the same OB cycle. Enjoy! An please reply to this post with bug reports and improvements. /Erik
Erik Sparre Posts: 10 Rating: (3)	Last edited by: Erik Sparre at: 7/14/2013 6:35 PM
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This contribution was helpful to 3 thankful Users umencho Tranhieu0983 lee_dong25

6/18/2012 6:31 PM	Rate (0)
Gerdoo Posts: 23 Rating: (2)	Hi Guys, What is the maximum frequency we can get to with these soft PWMs? I assume it should be the cycle time of intrrupt OB that FB is called in x 2. Is that correct?
Gerdoo Posts: 23 Rating: (2)
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6/19/2012 12:16 PM	Rate (1)
Denilson Pegaia Platinum Expert Joined: 9/23/2005 Last visit: 3/21/2025 Posts: 4406 Rating: (1475)	Hi, you have two things that you should pay attention: 1 -The total cicle time (Total cicle time = Time on + time off = constant) 2 -Time errorof desired output (Time error [absolut] = +/-1 scan time of CPU;Time error [%] = +/-1 scan time of CPU / Total cicle time ) The point is: despite you could have Total cicle time of 2x CPU scan time, the limit will stay on your the desired precision/error. For example: Total cicle time = Time on + time off = 2 x CPU scan time => error[%] = 1/1+1 = 50% (!) error[%] = 10% => Total cicle time >= 10 x CPU scan time error[%] = 1% => Total cicle time >= 100 x CPU scan time etc...
	Denilson Pegaia Siemens Industry Sector Technical Support
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This contribution was helpful to 2 thankful Users calvin_huy sazan

4/4/2016 2:56 PM	Rate (0)
Min_Moderator Platinum Member Joined: 9/3/2014 Last visit: 3/13/2019 Posts: 4766 Rating: (122)	New question published by DKLEIGH is split to a separate thread with the subject How to power a RC servo motor using the PWM on the PLC?. Best regards Min_Moderator

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1/20/2017 1:08 PM	Rate (0)
Min_Moderator Platinum Member Joined: 9/3/2014 Last visit: 3/13/2019 Posts: 4766 Rating: (122)	New question published by ss7479 is split to a separate thread with the subject PWM, generate train of pulses having frequency of 50Hz,100Hz, 200Hz, 500Hz, 1Khz. Best regards Min_Moderator

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