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Shift in time train of pulses

Created by: drgry at: 6/10/2014 9:09 AM (14 Replies)

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6/10/2014 9:09 AM	Rate (0)
drgry Posts: 13 Rating: (3)	Hello, I need some help in solving problem of shifting pulses sequence in time. The problem is following: Sequence of pulses of constant/variable length is coming to PLC in regular (to some degree) intervals, for example pulses of 50ms (+/-) in intervals of 1 second. I need to delay these impulses for 200ms preferably keeping their length or shaping them all to some constant length. To all this is related, as a problem to me, measuring time duration of impulses. I need to implement this in TIA portal. Any help is appreciated. Best regards
drgry Posts: 13 Rating: (3)
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6/10/2014 11:20 AM	Rate (0)
Jens_app Gold Member Joined: 1/5/2011 Last visit: 11/29/2024 Posts: 815 Rating: (123)	drgry Hello, I need some help in solving problem of shifting pulses sequence in time. The problem is following: Sequence of pulses of constant/variable length is coming to PLC in regular (to some degree) intervals, for example pulses of 50ms (+/-) in intervals of 1 second. I need to delay these impulses for 200ms preferably keeping their length or shaping them all to some constant length. To all this is related, as a problem to me, measuring time duration of impulses. I need to implement this in TIA portal. Any help is appreciated. Best regards Hi drgry, What about using the memory clock bit of the plc to create the delay? & The rising and falling edge of the input signalcombined with the memory clock bit of your plc to count the time the pulse is set? Could that work for you? Kind regards, Jens
	Keep it simple and on-topic. A simple straight-to-the-point answer is often of more quality than a complicated one.
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6/10/2014 11:29 AM	Rate (0)
William_B Posts: 5225 Rating: (1198)	Hi there. Is it a action that you wish to delay using an encoder as your "timer"? w
William_B Posts: 5225 Rating: (1198)
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6/10/2014 12:15 PM	Rate (0)
drgry Posts: 13 Rating: (3)	Hello, Thank you for fast replies. Maybe I put problem in "little" general form, but the basic problem is this: I am reading proximity switch on one of digital inputs on my S7-1200. Pulses come in period of 1 sec (from conveyor belt) and have duration of approximately 50 ms. Nothing special. These pulses generate some actions machine. What I need is same these pulses (in same form 1sec period/50ms duration) shifted in time for time between 0 - 1s to trigger some other actions on machine. From this problem came more general question I raised: if I have pulses on machine with some period and duration, not necessarily fixed, but with some period/duration uncertainty (because they come from physical source) - how can I shift it for certain delay in boundaries of period and reproduce them as they came. I came up with partial solution (example for 1sec period/50ms pulse/200ms delay: 1. Input -> TP with 250ms duration -> TON with 200ms delay -> now input is shifted for 200ms and has 50ms duration But his is not what I would call optimal solution. More like quick and dirty. So any help would be appreciated.
drgry Posts: 13 Rating: (3)
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6/10/2014 12:30 PM	Rate (0)
Jens_app Gold Member Joined: 1/5/2011 Last visit: 11/29/2024 Posts: 815 Rating: (123)	drgry Hello, Thank you for fast replies. Maybe I put problem in "little" general form, but the basic problem is this: I am reading proximity switch on one of digital inputs on my S7-1200. Pulses come in period of 1 sec (from conveyor belt) and have duration of approximately 50 ms. Nothing special. These pulses generate some actions machine. What I need is same these pulses (in same form 1sec period/50ms duration) shifted in time for time between 0 - 1s to trigger some other actions on machine. From this problem came more general question I raised: if I have pulses on machine with some period and duration, not necessarily fixed, but with some period/duration uncertainty (because they come from physical source) - how can I shift it for certain delay in boundaries of period and reproduce them as they came. I came up with partial solution (example for 1sec period/50ms pulse/200ms delay: 1. Input -> TP with 250ms duration -> TON with 200ms delay -> now input is shifted for 200ms and has 50ms duration But his is not what I would call optimal solution. More like quick and dirty. So any help would be appreciated. Hello drgry, I advice you to make a function based on the suggestion I did before. If this solution would work for you I'd be glad to help you further. Kind regards, Jens
	Keep it simple and on-topic. A simple straight-to-the-point answer is often of more quality than a complicated one.
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6/10/2014 12:47 PM	Rate (0)
William_B Posts: 5225 Rating: (1198)	@Jens: I think I know what the problem is.. so please bare with me. @drgry: I am going to explain a scenario for you. If this will work for you.. please let us know. The example scenario.. A constantly running conveyor has a sensor and a kick-off mechanism. Another sensor monitors the rotation of the converyor's motor with pulses.. let us call it an "encoder". The product passes the sensor. The sensor trigger the position and length of the product. The kick-off is several meters away. The kick-off is activated for the whole length of the product as soon as it arrives. There can be several products between the sensor and the kick-off. The conveyor speed is not always the same. ---- Now the question.. if you knew the solution for this scenario, would this also help you to solve your application? My applologies for taking this long route.. I need to understand what you need and I am not sure yet what you need. w
William_B Posts: 5225 Rating: (1198)	Last edited by: William B. at: 6/10/2014 12:48 PM mention of conveyor speed
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6/10/2014 12:51 PM	Rate (0)
drgry Posts: 13 Rating: (3)	Jens_app Hello drgry, I advice you to make a function based on the suggestion I did before. If this solution would work for you I'd be glad to help you further. Kind regards, Jens Problem I see is that signals from input and clock memory are not synchronized. I need to shift signal from rising edge of input signal for some delay. This signal can come in any time asynchronously form clock memory and can have variable period (conveyor accelerating/decelerating). Also clock memory is offering only some predefined periods. I need to tune delay to be able to perform some actions in correct moment to synchronize these actions on machine. Or I do not understand your solution correctly.
drgry Posts: 13 Rating: (3)
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6/10/2014 1:10 PM	Rate (0)
drgry Posts: 13 Rating: (3)	@William B. Same, same but different - as good friend of mine would say. Your example is exactly that I want to do. There are two functions: 1. Marks (pushers) on conveyor are passing before sensor. On each pusher I need to trigger some action but delayed for some time, so I do not need to measure pulse duration. I can reconstruct pushers with pulses with fixed duration some time later (delayed). 2. As you put it, on some other place i need to measure product passing time, and then shift if and reconstruct exactly some time later. If delay is less then product passing time this can be done with TON - TOF pair. But if delay is greater than passing time I need to measure time and then reconstruct it after delay. Problem I proposed is generalization of these two scenarios so I can use one function throughout program. I apologize if something is "lost in translation" as English is not my native language. I hope I can explain problem in enough detail so we can came to good solution. So general problem would be: If I have repetitive pulses of variable duration and fixed period (or to be precise period of which I know minimal time), how I can shift this pulses for time which is constant and known in advance. This delay is fraction of (minimal) period - I do not need to remember more than one time in some buffer, as this is only needed if delay is greater than period. I need pulses to be the same as they come, only delayed. Simple as that
drgry Posts: 13 Rating: (3)	Last edited by: drgry at: 6/10/2014 1:27 PM
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6/10/2014 1:46 PM	Rate (0)
Jens_app Gold Member Joined: 1/5/2011 Last visit: 11/29/2024 Posts: 815 Rating: (123)	drgry Jens_app Hello drgry, I advice you to make a function based on the suggestion I did before. If this solution would work for you I'd be glad to help you further. Kind regards, Jens Problem I see is that signals from input and clock memory are not synchronized. I need to shift signal from rising edge of input signal for some delay. This signal can come in any time asynchronously form clock memory and can have variable period (conveyor accelerating/decelerating). Also clock memory is offering only some predefined periods. I need to tune delay to be able to perform some actions in correct moment to synchronize these actions on machine. Or I do not understand your solution correctly. Hello drgry, Correct, both aren't "synchronized". But do know there isalways a difference in time between your actualinput signal state and the inputstate read by the plc. As you know, your inputs aren't monitored constantly by the plc. The plc will executefollowing activities cyclically;update the process input image -> execute the main program (ob1) -> communicate with programming device and other stations -> transfer process output image -> and again... So you will have a difference in time between actual input and input read by plc. And also between input and output. So the question is, can you live with the frequency the clock memory provides? Concluded out of your previous posts I'd say no. So you can ignore my suggestions. Maybe if the accuracy is that great of a deal, you might want to look at fast counter function modules. But since that's not my field of experience I'll let William do the talking now. Sorry I couldn't be of more help (yet). Kind regards, Jens
	Keep it simple and on-topic. A simple straight-to-the-point answer is often of more quality than a complicated one.
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6/10/2014 2:05 PM	Rate (0)
William_B Posts: 5225 Rating: (1198)	@Jens.. I am giving my alternative a try. If this is not what is required then we (forum) will have to see how to get a syncronise solution or at least get the sampling rate high enough. Think about the problem as if it is a music recording.. you need to up the sampling rate and write into a bit buffer. The issue is that the normal commands does not allow such huge bit shifting. You will have to employ a rotating bit array buffer. But let's try something else first. @drgry.. You do not need reproduce the pulses in time space. Have the pulsing sensor trigger a counter (HSC). The counter can run continuously. Every pulse represents a distance. --non industrial example-- Think of the counter as if a meter-wheel. Every click of the wheel is a meter. On the meter-wheel is a counter. When the meter-wheel reads 100m and you need to walk 3m you will walk until the meter-wheel says 103m. --back to our problem-- When the product is at the "registration" sensor you can record the product position by looking the (HSC) counter value. The action that needs to take place is a set fixed distance from the registration sensor. Add the distance - in counter units - to the count value that was recorded. Write the new value in an array of DINT values. The action takes place when the counter (HSC) reaches the value you calculated earlier. Now you decide how long the action takes place by timer or use the counter's distance. Many detail points are not mentioned. Especially the handling of the array. But the technique works very well. Will this work for you? Greetngs. w
William_B Posts: 5225 Rating: (1198)
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