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Trouble using SCALE (FC105) (SOLVED)

Created by: noddster at: 5/18/2009 1:03 PM (8 Replies)

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5/18/2009 1:03 PM	Rate (0)
noddster Posts: 10 Rating: (0)	Hi! I'm trying to read an analog signal and convert it to engineering units with the SCALE function FC105. I'd like to read the 0-10V signal from a potentiometertransmitter and scale it to 0-120. See the attached picture for information. I've set 120 (1.2e002) as high limit, 0 as low limit, 0 for unipolar and the output to MD0 ("analog_input") The problem is that when the input is below 7376 the output is somewhere between 8.000-8.00019 and when the input is over 7376 (or close to that number) the output is 32.0000-32.00019 What have I done wrong? Thanks for any help! -Steffen- Attachment FC105.JPG (423 Downloads)
noddster Posts: 10 Rating: (0)	Last edited by: noddster at: 5/19/2009 10:13 AM
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5/18/2009 1:41 PM	Rate (0)
SINAMICS_TO Bronze Member Joined: 4/24/2008 Last visit: 5/19/2023 Posts: 144 Rating: (15)	I see no error in the picture. 0V =0; 10V= 27648 0V =0; 10V=120 0=0; 120=27648 7376 = 32 = 2,67V the FC works like you have parametrise it. Maybe this FAQ http://support.automation.siemens.com/WW/view/en/1765297will help you to understand the function.

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5/18/2009 1:55 PM	Rate (0)
noddster Posts: 10 Rating: (0)	Yes, but for every value above 7360 the output is 32. Input: 0-450 (or somewhere around there) gives output 0.500000-0.500019 Input: 450-1840 (or somewhere around there) gives output 2.0000-2.00019 Input: 1840-7360 (or close to those values) gives output 8.0000-8.000019 Input: 7360-27648 (or close to those values) gives output 32.000-32.00019 So it seems the output jumps in steps of 4x at around 450, 1840 and then again at 7360ish. Attachment FC105-2.JPG (191 Downloads)
noddster Posts: 10 Rating: (0)
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5/18/2009 4:45 PM	Rate (0)
Sydney Gold Member Joined: 1/4/2008 Last visit: 3/8/2023 Posts: 703 Rating: (96)	Hello, when I try to call the SCALE with theshown values, the output is 18.89 which seems to be ok, maybe there is some strange behaviour in monitoring or the values are written somewhere else... Regards Sydney
	Last edited by: Sydney at: 5/18/2009 5:06 PM
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5/18/2009 10:02 PM	Rate (0)
noddster Posts: 10 Rating: (0)	Thanks for your help! :) I wrote my own scale function, and itscales like it should. However, whenI inserta function that is reading analog input (both my own and FC105) it seems to mess up something. I am suddenlyunable to set and reset some of the memorybits I'm using in my program. None of these memorybits are used anywhere in the analog input block. The program works like it should without without the analog input, but when I read inputvalues and scale them I get some strange behaviour. As you'll se in the jpg attached from a function called in OB1: "Deactivating" =1 & "Home_Limit"= 0 will reset certain variables. One of them is the memorybit M1.5 ("Deactivating"). You'll see that it is reset, and that should lead to RLO of the & function is 0 on the next cycle, but it isn't. This network did as intended before I read the analog value in OB1, but once I added FC105 or my own function (that doesn't include any thing more than math operations to scale the input) it wont reset memorybits properly. I'm baffled! Attachment Unable_to_reset_bit.JPG (150 Downloads)
noddster Posts: 10 Rating: (0)
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5/18/2009 10:09 PM	Rate (0)
noddster Posts: 10 Rating: (0)	As a reference I've added a jpg of the same function as previous post, with only one difference in the program; I've deleted the reading and scaling of analog input. Attachment Without_analog_function.JPG (135 Downloads)
noddster Posts: 10 Rating: (0)
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5/18/2009 10:14 PM	Rate (0)
noddster Posts: 10 Rating: (0)	Sorry for the spam, but I'd like to attach my scale FC too. The inputs to the FC are real values (Min_in = 0, max_in=27648, Min_out = 0, Max_out =120, analoginput = PIW752 and output is MD0 (Analog_input)) I don't see how this could affect setting and resetting of memorybits. Thanks for any input :) Attachment FC3.pdf (152 Downloads)
noddster Posts: 10 Rating: (0)
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5/19/2009 10:14 AM	Rate (0)
noddster Posts: 10 Rating: (0)	Hehe, now I feel somewhat like an ***.. Seems I stored my analog inputvalue as Real in MD0. I forgot that M1.0 ++ is a part of MD0. ;) Does anybody have a nice illustration of the memory areas so I can streamline my use of them somewhat? Thanks! :)
noddster Posts: 10 Rating: (0)
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5/19/2009 11:25 AM	Rate (0)
Sydney Gold Member Joined: 1/4/2008 Last visit: 3/8/2023 Posts: 703 Rating: (96)	Hello, you don't need any ilustration of memory areas. Only you have to put in mind is that the S7 PLC is byte oriented and the number in address isn't serial number of data types but always the address of the first byte in corresponding memory area! So if you use address from 0 then used memory area depends on access method, when you use byte access then you use just byte0, whenword access then it's byte0+byte1 and so on. For better imagination you can use the DB, in which declare some variables of a different data types, system assigns the addresses automatically. There is also another rule that the variables with more then one byte lengthalways starts on the even byte address. Regards Sydney
	Last edited by: Sydney at: 5/19/2009 11:32 AM
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