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CPU313C + rotary encoder + interrupts

Created by: Cheeky at: 8/21/2007 12:16 PM (6 Replies)

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8/21/2007 12:16 PM	Rate (0)
Cheeky Posts: 6 Rating: (0)	Hi! I'm fairly new to Step7 programming so please have patience. :) I'm making a simple force measuring device. Currently I'm using CPU313C, one turn encoder (4096), sm338 encoder input card and fast analog card SM 331, to which I have connected strain sensor with amplifier (0-10V). My program takes samples from analog card every 5° (from 90°to 270°) and then saves data into DB, which at the end of one turn I send to HMI (TP270) and display it as a chart. My problem is, that all samples are taken only when encoder turns really slow, otherwise samples are left out. That is because of cyclic execution of the program, which has faily long response time (large program). Could I use interrupts to sample data a little faster? The rest of the program is not time critical, just this part. At maximum machine speed I would like to take a sample from analog card every 25ms (or more - depending on how fast encoder is turning). Is that possible? What could I do best with this CPU? I'm only developing program on this CPU to see how it works. Final application will run on CPU319.
Cheeky Posts: 6 Rating: (0)
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8/22/2007 8:41 AM	Rate (0)
jacek d Platinum Member Joined: 9/23/2005 Last visit: 10/3/2023 Posts: 4280 Rating: (670)	Hi, you can use timed interrupt (OB35) and call your sampling routine at constant intervals. What is the scan time now ? Are you sure that it's matter of the scan time lenght, not theprogram itself ?
	Last edited by: jacek d at: 22.08.2007 08:41 Regards, Jacek What is confusing you is the fact that you never see a number but always its digit representation. So you end up thinking that the number is the representation. - Andrej Bauer Any claims against me - based on whatever legal reason - resulting from the use of any code and/or ideas presented on this forum shall be excluded. #StayWithUkraine
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8/23/2007 7:00 AM	Rate (0)
Cheeky Posts: 6 Rating: (0)	The problem is that sampling every 25ms is only when machine is running at full speed, but it can run with lower speed - so the time between samples must increase. That is why I would like to trigger an interrupt, when encoder turns for 5°, but I think that isn't possible with CPU I'm using. PS: Where in Step7 can I see how long is the program cycle time?
Cheeky Posts: 6 Rating: (0)
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8/23/2007 8:41 AM	Rate (0)
jacek d Platinum Member Joined: 9/23/2005 Last visit: 10/3/2023 Posts: 4280 Rating: (670)	Cheeky Where in Step7 can I see how long is the program cycle time? When connected to a PLC, in Simatic Manager press Ctrl+D. Cheeky The problem is that sampling every 25ms is only when machine is running at full speed, but it can run with lower speed - so the time between samples must increase. That is why I would like to trigger an interrupt, when encoder turns for 5°, but I think that isn't possible with CPU I'm using. First of all. If you want interrupts based od the encoder position, the you need the FM352 module. On the other hand, if I got it right, speed of the machine at full speed is 5°/25ms, which is 5ms/1°. So having timed intterupt at 5ms will do. Other story is if the analogue input card you use is fast enough. Tell which hw do you use.
	Regards, Jacek What is confusing you is the fact that you never see a number but always its digit representation. So you end up thinking that the number is the representation. - Andrej Bauer Any claims against me - based on whatever legal reason - resulting from the use of any code and/or ideas presented on this forum shall be excluded. #StayWithUkraine
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8/23/2007 3:00 PM	Rate (0)
Cheeky Posts: 6 Rating: (0)	First of all thanks for all the info so far. You are correct. Max. machine speed is 1°/5ms. Hardware is as follows: CPU 313C-2DP (later CPU319) SM338 Pos. module SM331 Fast analog card (6ES7 331-7HF01-0AB0) Other non-Siemens hardware -TR electronic SSI one turn (4096) encoder, HELM PTM-1 strain I/O module and HELM HT400 strain gain sensor. I think the analog card is fast enough (conversion time 52us per channel) and I'm reading max. 2 inpust consecutively. I'll try what I can do with 5ms cyclic interrupts.
Cheeky Posts: 6 Rating: (0)
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8/23/2007 3:36 PM	Rate (0)
jacek d Platinum Member Joined: 9/23/2005 Last visit: 10/3/2023 Posts: 4280 Rating: (670)	Siemens hw seems to be choosen OK. Other hw I don't know so I can't tell. If you need help with configuring/programming interrupts, drop a line.
	Last edited by: jacek d at: 23.08.2007 15:36 Regards, Jacek What is confusing you is the fact that you never see a number but always its digit representation. So you end up thinking that the number is the representation. - Andrej Bauer Any claims against me - based on whatever legal reason - resulting from the use of any code and/or ideas presented on this forum shall be excluded. #StayWithUkraine
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4/3/2017 4:57 PM	Rate (0)
Min_Moderator Platinum Member Joined: 9/3/2014 Last visit: 3/13/2019 Posts: 4792 Rating: (123)	New question published by bussyasbee is split to a separate thread with the subject Interrupt program. Best regards Min_Moderator

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