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How to measure energy consumption from pulse meter

Created by: Martil at: 1/15/2013 1:19 AM (34 Replies)

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1/15/2013 1:19 AM	Rate (0)
Martil Posts: 15 Rating: (0)	Hello experts. Im new here and i need your help. I have to solve problem with surplus of solar energy. I need to create program that will compare energy consumption on 2 different electrical phases and in case of defined difference (for ex. at least 100W and more) switch on something (heater, etc.) Also I need to log actual and periodic consumption and use it on webserver (time graphs, etc.). I have energy meters with pulse output - 2000 imp/kWh. So at first i need toto create short program for measure energy on each phase. At this time I have short program, that can measure time between two pulses and then it calculate immediate consumption in Wh (TONR). The problem is, that TONR cannot keep highest value of measured value but it measure continuously from 0 til end of pulse so i cannot read MAXIMUM duration of pulse. Meanwhile i have to reset TONR akumulator for next measurement so measured duration of first pulses is lost and TONR measure next pulses... So my BIG question is: How to akumulate measured time or how to make some "pause" on TONR to keep highest value (duration between pulses). Thank you very much bosses. I'm searching for a few weeks and found nothing so i please you
Martil Posts: 15 Rating: (0)	Last edited by: Martil at: 1/15/2013 1:22 AM
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1/15/2013 10:36 AM	Rate (0)
Denilson Pegaia Platinum Expert Joined: 9/23/2005 Last visit: 11/19/2024 Posts: 4353 Rating: (1454)	Hi, forthe case of long time sums ("integrations"), I suggest adapt the sample program that stay on: How is numerical integration for the S7-1200 programmed in STEP 7 (TIA Portal) V11? http://support.automation.siemens.com/BR/view/en/42469594
	Denilson Pegaia Siemens Industry Sector Technical Support
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1/15/2013 11:35 AM	Rate (0)
Martil Posts: 15 Rating: (0)	Pegaia Hi, forthe case of long time sums ("integrations"), I suggest adapt the sample program that stay on: How is numerical integration for the S7-1200 programmed in STEP 7 (TIA Portal) V11? http://support.automation.siemens.com/BR/view/en/42469594 Thanks for answer, version of TIA is V11 SP2. As i Said, at this time i already have FB that calculate final power consumption but at the end of pulse the TONR timer is reseted and the final value is also reseted. So i need some function that hold the value or exactly before the end of pulse read final value just before reseting the TONR (to count next pulses). As time between pulses grows in miliseconds, the consumption at the and of calculator decreases. And just while next pulse comes, the final value is reseted. I thought to use some MOVE instruction to move the value to other memory adress and then use it (to use for webserver, etc.). But how to say to MOVE instruction when it has to read the value... I look at your link but i though i am too close to solve it :). I have not project here, later i attach the project to have a look.
Martil Posts: 15 Rating: (0)
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1/16/2013 10:19 AM	Rate (0)
Denilson Pegaia Platinum Expert Joined: 9/23/2005 Last visit: 11/19/2024 Posts: 4353 Rating: (1454)	Hi, I don't understood what you means with " As time between pulses grows in miliseconds, the consumption at the and of calculator decreases. And just while next pulse comes, the final value is reseted. " It seems that each pulse represents a increment in the count value. It is ok? It seems also that at some "event" you should save this value someware (maybe a data log) and reset the counter. Is it right too? To use the integrator, move 0 or a constant to integrator input, depending if the pulse comes: pulse->p triger -> move constant, else move 0. There is a reset that could be set by a user logic too.
	Denilson Pegaia Siemens Industry Sector Technical Support
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1/16/2013 6:06 PM	Rate (0)
Martil Posts: 15 Rating: (0)	Thank you very much for your time spent to me. Pegaia As time between pulses grows in miliseconds, the consumption at the and of calculator decreases. And just while next pulse comes, the final value is reseted. You would understand immediately what I mean if you should see my project, but i cannot attach any zip atachment (zip comprimed by milion variants) - forum writes still same error: "data provider error" :( So i can attach only no-comprimed files - jpg. Look at JPG file and you will see what I mean. For you as expert it would be little toy :) Just need to know HOW TO READ AND STORE into any place value of consumption from calculator and this value overwrite by new value after each pulse and so on and so on. Maybe im looser, but if you help me, i will be very happy and gonna solve most of new projects :D Attachment screen.jpg (1034 Downloads)
Martil Posts: 15 Rating: (0)
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1/17/2013 12:05 PM	Rate (0)
Marko Bursic Platinum Member Joined: 9/8/2009 Last visit: 7/17/2023 Posts: 1410 Rating: (153)	I have done similar project many years ago with different plc, I will explain the basics. I suggest to get some book or teory based on measurment of frequency and period. You will find that it is suitable to measure period for lower frequencies and measure the frequency at higher frequencies. When the sistematic error of one method is greater then other you shall switch the method in your program. I would use a hardware interrupt on pulse input and one cyclic interrupt for internal counter. At hw intr. you can measure the time elapsed between two pulses using RTC clock, while evaluating the number of pulses generated of cyclic intr..At that point you have information to calculate the period/frequency of pulses for a minimal sistematic error.

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1/17/2013 3:49 PM	Rate (0)
0_Einstein Diamond Expert Joined: 7/7/2010 Last visit: 11/27/2024 Posts: 15441 Rating: (2452)	Marko Bursic I have done similar project many years ago with different plc, I will explain the basics. I suggest to get some book or teory based on measurment of frequency and period. You will find that it is suitable to measure period for lower frequencies and measure the frequency at higher frequencies. When the sistematic error of one method is greater then other you shall switch the method in your program. I would use a hardware interrupt on pulse input and one cyclic interrupt for internal counter. At hw intr. you can measure the time elapsed between two pulses using RTC clock, while evaluating the number of pulses generated of cyclic intr..At that point you have information to calculate the period/frequency of pulses for a minimal sistematic error. Thanks for your post. I am working on a simple solution to capture duty cycle and frequency for an automobile PWM valve control signal for a data acquisition system. Another solution might involve a couple of high speed counters with a low preset to capture the frequency as well. If you are simply looking for a way to shift load by varying the phase slightly, can you just look at the voltage difference between the two signals? When equal, no load sharing, when one leads, the voltage > 0 and the higher voltage is pulling more load. You can also put a current transformer on the wire from the meter and measure it that way. Less accurate perhaps. There are also similar solutions on things like hack-a-day where they count the revolutions of the meter dial to arrive at the power consumption with smaller purpose-built hardware systems.
	science guy
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1/18/2013 2:14 PM	Rate (0)
Martil Posts: 15 Rating: (0)	Hello Marko, thank you for post and maybe youre right, but you are too general for me :). Could you please make some sketch of your proposal or something very simple for me to understand how do you think that? I found very similar project here: /tf/WW/en/Posts/85546#top But its for LOGO, not for S7-1200 :( I would like to ask anyone of you experts to write down very simple sketch how it should be and ill try to program it or link to any similar solution would help me. To Huggy: I want to measure right with energy-meter pulses because it's the most accurate.
Martil Posts: 15 Rating: (0)
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1/18/2013 5:40 PM	Rate (0)
Marko Bursic Platinum Member Joined: 9/8/2009 Last visit: 7/17/2023 Posts: 1410 Rating: (153)	I made this applicatin nearly 15yrs ago, sorry only remainds. Maybe a look how bench instruments work will help you, I have found one link: http://www.leapsecond.com/pdf/an200.pdf From what I understand error is defined: (1/N)100%, N is number of pulses that can be pulses of your signal that came in a period of measuring or number of pulses of internal source gerator (RTC timer) in a time beetwen two pulses of your source. Now this let me to one fast conclusion: If measured signal has 1Hz we get: 1. mesuring time from one pulse to other with rtc timer we get 1000 pulses (if rtc resloution is 1ms), error is (1/1000)100%=0.1% 2. measuring number of pulses within a period of 10s (cyclic interrupt) gives 10 counts -> error =(1/10)100%=10% If we measure inputsignal of 10Hz we get: 1. method1 : (1/100)100%=1% 2 method2: (1/100)*100%=1% All higher frequencies will give better accuracy using method 2, all frequencies below 10Hz will give better result with method 1. You can improve measuring with syncronizing time base with end signal like described in link of instrument. I do not have a plug&play solution for you, so sorry.

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1/19/2013 9:20 PM	Rate (0)
Martil Posts: 15 Rating: (0)	Marko, at this time I dont need to know nothing about errors. Now i dont even have any theory or concept of this solution, its of course simple but i am new user of S7-1200 so I need help, the best from Pegaia or anyone like him (expert). I atach my concept again. The question is still one and still simple: "HOW TO READ AND STORE into memory the value from Calculate (consumption in Wh) just when the pulse stops (right before next pulse comes on)." The problem for me is that time between pulses is different after each pulse so I dont know how to catch the value at the end of calculator (Wh), because that value just reset when counter is reseted. Maybe i should use any interrupted OB to stop final value and store it into memory and then cycleOB again for next pulse and again, again. Please, look anyone (who knows TIA V11 SP2) on attached picture and kick my ass please :) Attachment screen.jpg (698 Downloads)
Martil Posts: 15 Rating: (0)
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