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Problem with an increment

Created by: Ayzetina at: 7/31/2013 10:12 PM (3 Replies)

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7/31/2013 10:12 PM	Rate (0)
Ayzetina Posts: 14 Rating: (0)	tHi dear experts, right now I have a problem with a math function, I need to increase a variable by a reason of 1. Let me explain better: I have a variable db100.dbd170, and i want to increase it in a value of 1, everytime that i get a signal from a normally opened contact, and also want to save the output in the db100.dbd170 register, so that i have an acumulated of this variable. i tried with the add function and INC function, but everytime that I put the PLC to RUN mode, it starts to do something very weird, it increases the value of this variable randomnly, not by 1 as I want,. how can i make this to work??? Thanks
Ayzetina Posts: 14 Rating: (0)
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7/31/2013 10:28 PM	Rate (1)
0_Einstein Diamond Expert Joined: 7/7/2010 Last visit: 12/11/2023 Posts: 13998 Rating: (2284)	Ayzetina tHi dear experts, right now I have a problem with a math function, I need to increase a variable by a reason of 1. Let me explain better: I have a variable db100.dbd170, and i want to increase it in a value of 1, everytime that i get a signal from a normally opened contact, and also want to save the output in the db100.dbd170 register, so that i have an acumulated of this variable. i tried with the add function and INC function, but everytime that I put the PLC to RUN mode, it starts to do something very weird, it increases the value of this variable randomnly, not by 1 as I want,. how can i make this to work??? Thanks You may want to add an edge detector for your NO contact so you only add ONCE per event rather than for every single scan the plc sees your NO contact is on. I tend to use P_TRIG to make it obvious to anyone looking that I am intentionally only looking for the first occurrence of that event.
	science guy
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7/31/2013 10:48 PM	Rate (0)
Ayman Elotaify Platinum Member Joined: 5/28/2008 Last visit: 12/9/2023 Posts: 4486 Rating: (834)	Hello, As huggy adviced, add an edge will solve the problem. I want to explain something here, the value does not increase randomly that as you said. It is normal because when the DI is being high for several scan cycles. Each cycle, the value in your data block increment by one. Normally scan cycle duration is not fixed and normally it's few milli-seconds. So, if the DI is being high for only 1 second, it will increment the value in data block by [No. of scan cycles that have been executed during this second]. Even if each time you enrgize this DI for exacltly sec., it may increment this value in DB by different values. Thus because the number of executed scan cycles is different. What I wanted to say, nothing is random, the CPU is just execute what you already wrote. Hope I could explain it for you.
	Ayman Elotaify
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This contribution was helpful to 3 thankful Users 0_Einstein peterplavec Ayzetina

8/2/2013 10:10 AM	Rate (0)
O_Moderator Diamond Member Joined: 4/24/2009 Last visit: 11/23/2023 Posts: 2683 Rating: (135)	New question was splitted to use a variable as index for a Modbus programm Best regards O_Moderator
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