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Step 7 S7-300 PLC - ADD_R Block Issue

Created by: smangan at: 6/16/2011 6:50 PM (6 Replies)

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6/16/2011 6:50 PM	Rate (0)
smangan Posts: 1 Rating: (0)	I have a problem with an Add_R Block that I have incrementing a value to itself via a pulse every second. I am adding the value 0.00041667 to a Real Value Datablock Address. The Real Value has reached the figure “8192” and has stopped incrementing. The pulse is continuing to work so this is not an issue. Also if I change the figure of “8192” to anything less than this, say “8190”, the incrementing begins again no problem. The problem may be to do with the decimal place of the figure being added. For example, if I change “0.00041667” to “0.0041667” then the incrementing seems to work again fine. Would you know anything about this issue?
smangan Posts: 1 Rating: (0)
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6/16/2011 7:02 PM	Rate (0)
IBN-Service Posts: 8946 Rating: (1000)	That is a problem / restrictionof Floatingpoint, because the mantissa is only 24 bit... You can not use it for your kind of calculation.
IBN-Service Posts: 8946 Rating: (1000)	Last edited by: IBN-Service at: 6/16/2011 7:03 PM Last edited by: IBN-Service at: 6/16/2011 7:03 PM
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This contribution was helpful to 1 thankful Users Ton Verra

6/16/2011 10:11 PM	Rate (0)
Ton Verra Gold Member Joined: 4/20/2007 Last visit: 1/2/2026 Posts: 731 Rating: (43)	seems I learned something today to... Just curious here.. So when he comes over the 8000 something value, the place for storing the value is getting to large? What if he makes sure the value got less decimals? That would solve a bit of the problem?

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6/17/2011 7:24 AM	Rate (0)
fritz Diamond Expert Joined: 10/7/2005 Last visit: 1/12/2026 Posts: 3054 Rating: (1062)	Have a look at the FAQ below guys, it will (should) answer all your questions: How accurately can I calculate with REAL numbers that are used in extensive formulas?
	Cheers fritz The advice and opinion given in this thread is that of the author and does not necessarily reflect the views of I S Systems Pty Limited. To find out how I S Systems can help you with your automation needs please visit www.issystems.com.au.
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This contribution was helpful to 1 thankful Users Ton Verra

6/17/2011 6:53 PM	Rate (0)
IBN-Service Posts: 8946 Rating: (1000)	Ton Verra ...So when he comes over the 8000 something value, the place for storing the value is getting to large? No, not 8000 but8 digits.
IBN-Service Posts: 8946 Rating: (1000)
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This contribution was helpful to 1 thankful Users Ton Verra

6/17/2011 7:33 PM	Rate (0)
Ton Verra Gold Member Joined: 4/20/2007 Last visit: 1/2/2026 Posts: 731 Rating: (43)	I just meant the value he mentioned 8192

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6/17/2011 8:27 PM	Rate (0)
IBN-Service Posts: 8946 Rating: (1000)	Here is a very easy example to show the problems with real - resolution. Attachment Gleitpun.zip (279 Downloads)
IBN-Service Posts: 8946 Rating: (1000)
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