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Measure time between pulses

Created by: flop at: 3/27/2017 9:11 PM (10 Replies)

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3/27/2017 9:11 PM	Rate (0)
flop Posts: 9 Rating: (1)	Can a experienced user tell me if it is posible to measure time between pulses from different -high speed- inputs in a S7 1200? The application has a couple of sensor in a roller conveyor that are placed about 20mm in the direction of movement. When a box slides down the conveyor this application has to measure time between impulses and calculate speed as accurate as possible. This speed will be used in further calculations to feed other devices downstream. Thank you.
flop Posts: 9 Rating: (1)
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3/28/2017 12:51 AM	Rate (0)
Jeff Casagrande Posts: 1529 Rating: (202)	May ways to do this. One suggestion - On first input, set hardware interrupt and start a timer in the interrupt routine - On second input, go to hardware interrupt, read timer and reset it.
Jeff Casagrande Posts: 1529 Rating: (202)
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This contribution was helpful to 1 thankful Users mindware

3/28/2017 8:54 AM	Rate (0)
jacek d Platinum Member Joined: 9/23/2005 Last visit: 11/15/2024 Posts: 4793 Rating: (733)	Another one. Use RD_SYS_T to get a "time stamp" of the interrupt. Then with T_DIFF you can calculate the time passed.
	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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This contribution was helpful to 3 thankful Users Jeff Casagrande mindware C-3PO

3/28/2017 9:59 AM	Rate (0)
#dP Posts: 2826 Rating: (686)	Hello. Gravity feed or driven? If gravity: What is the acceleration the box experience on the downward slope? What about the influence of friction? If driven: Fixed speed or variable speed? Consider also the cross interference of two light beam sensors when mounted 20mm apart. Bye. Dan
#dP Posts: 2826 Rating: (686)
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3/28/2017 10:22 AM	Rate (0)
enof Silver Member Joined: 2/10/2012 Last visit: 10/30/2024 Posts: 314 Rating: (59)	Is RD_SYS_T affected by adjusting the cpu system clock? Either manually or auto by means of ntp? It seems not but I don't understand how it works nor can't find any doc.

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3/28/2017 1:33 PM	Rate (0)
flop Posts: 9 Rating: (1)	Jeff Casagrande May ways to do this. One suggestion - On first input, set hardware interrupt and start a timer in the interrupt routine - On second input, go to hardware interrupt, read timer and reset it. Jeff, Looks like best timer resolution is 1ms (correct me if I'm wrong). If boxes come at 1m/s and sensors are 20mm apart, then it would take 20ms between pulses. So measured speed error would be at least 1ms in 20ms (5%), probably a bit more. I would be happy with a 1% error, but I don't know if I can achieve this figure with timers.
flop Posts: 9 Rating: (1)	Last edited by: flop at: 3/28/2017 1:34:37 PM
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3/28/2017 1:36 PM	Rate (0)
flop Posts: 9 Rating: (1)	#dP Hello. Gravity feed or driven? If gravity: What is the acceleration the box experience on the downward slope? What about the influence of friction? If driven: Fixed speed or variable speed? Consider also the cross interference of two light beam sensors when mounted 20mm apart. Bye. Dan Assume boxes reach terminal speed.
flop Posts: 9 Rating: (1)
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3/28/2017 1:42 PM	Rate (0)
Jeff Casagrande Posts: 1529 Rating: (202)	Probably 10ms s the best resolution you can achieve. If you need more, I would put and encoder on the belt and measure speed directly
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3/28/2017 1:50 PM	Rate (0)
flop Posts: 9 Rating: (1)	jacek d Another one. Use RD_SYS_T to get a "time stamp" of the interrupt. Then with T_DIFF you can calculate the time passed. Jacek, T_DIFF output time resolution is 1 ms? It's a pitty RD_SYS_T has nanoseconds and information is lost when time difference is calculated. I need at least 1% error, if boxes come at 1m/s and sensors are 20mm apart, with 1ms resolution error is at least 1ms in 20ms (5%). Is there a way to calculate RD_SYS_T difference using full nanosecond resolution?
flop Posts: 9 Rating: (1)
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3/28/2017 1:52 PM	Rate (0)
flop Posts: 9 Rating: (1)	Jeff Casagrande Probably 10ms s the best resolution you can achieve. If you need more, I would put and encoder on the belt and measure speed directly I see, but there's no belt, is a roller conveyor. https://www.sjf.com/conveyor/bushman_gravity_roller.jpg
flop Posts: 9 Rating: (1)
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This contribution was helpful to 1 thankful Users diamondphoenix

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