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Analog Input & Output Range

Created by: nic_c at: 9/24/2008 8:55 AM (10 Replies)

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9/24/2008 8:55 AM	Rate (0)
nic_c Posts: 19 Rating: (0)	Dear Experts here, I plan to use S7-200 for the application below, The input range for both AI is 0 - 2000 ug/kg (corresponds to 4-20mA). I want to retransmit the output signal with a modification on its signal. The transmitted output range shall become, 0 - 200 ug/kg (corresponds to 4-12mA) and; 200 - 2000 ug/kg (corresponds to 12-20mA). This is applicable for both AI. Can S7-200 do this application? Hope to get your opinion soon.... Regrads, nic
nic_c Posts: 19 Rating: (0)
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9/24/2008 9:43 AM	Rate (1)
Khaled_Ezzat Silver Member Joined: 9/7/2007 Last visit: 10/9/2024 Posts: 550 Rating: (62)	Hi nic_c It seems that you want the analog output signal to be scaled onto two steps first one: 0-200 ug/ kg that corresponds to 4-12 mA and the other step is: 200-2000 ug/kg corresponds to 12-20mA. That can be easily done in S7-200. The problem is that the analog input channels in S7-200 series do not support 4-20 mAmp only support 0-20 mAmp.
	Best Regards
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9/24/2008 11:34 AM	Rate (2)
AMAZINGAHMED Gold Member Joined: 8/27/2006 Last visit: 10/22/2024 Posts: 719 Rating: (88)	I think it's not a problem that the 200 PLC doesn't support 4-20mA, because you can solve it using math For example, you need a 0-2000 ug/Kg range for 4-20mA range which also corresponds to some digits range 0mA->0 digits (unipolar) 20mA->32000 digits Therefore, you'll consider your zero = 4mA which corresponds to 6400 digits (offset) and keep the 20mA at the 32000 digits. Now you have a linear equation Y=mX+C. We get the slope (m) of the line by using the formula: (y2-y1)/(x2-x1) which will be (2000-0)/(20-4)=125, and by substituting in the linear equation we get C=-500 Therefore Y=125X-500 *****and that's your equation for the full range You can use the same linear equation technique to divide it to 2 ranges.
	Last edited by: AMAZINGAHMED at: 9/24/2008 11:41 AM Last edited by: AMAZINGAHMED at: 9/24/2008 11:35 AM The more you know, The more you know that you don't know
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9/24/2008 1:18 PM	Rate (0)
marcsinclair Posts: 49 Rating: (5)	Khaled_Ezzat Hi nic_c The problem is that the analog input channels in S7-200 series do not support 4-20 mA only support 0-20 mA. But 0-20 covers 4-20. Sensing the full range allows you to detect open circuit or faulty sensors. Some sensors will use a level of less than 4mA to signal a problem, like out of range, or signal loss. The method of reading 4-20mA sensor is simple Check if the input is less than 6400 (4mA) if so, then set a fault flag (I use a slightly lower figure, to be sure) Subtract 6400 from the input value then divide by 256 (use DIV or SHIFT to give you 0-100% (you can use another factor here to scale into engineering units if you wish) I've attached a program that contains the subroutine to do this. (program is in IEC and uses FBD) Attachment level.mwp.zip (330 Downloads)
marcsinclair Posts: 49 Rating: (5)
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9/24/2008 2:10 PM	Rate (0)
JMJ Posts: 487 Rating: (45)	Also here is some info on how to use 4-20mA signal with S7-200. http://support.automation.siemens.com/WW/view/en/22149157
JMJ Posts: 487 Rating: (45)
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9/24/2008 2:42 PM	Rate (0)
Ayman Elotaify Platinum Expert Joined: 5/28/2008 Last visit: 11/6/2024 Posts: 4516 Rating: (839)	Hello nic, You can do it easily using scaling library. For our example here, you will use scaling function as follows: Inpus: real quantaty representing the phisical quantaty 0-200 & 200 - 2000 ug/kg. Outputs will be the analog digits 0 - 32000. NB: As you want to make two linear scaling, so you will call the scalling function twice. Once for input range 0 -200.0 & output 6400 - 19200 (4-12 mA) The second: input range 200.0 to 2000.0 & output: 19200 - 32000 (i.e. 12 - 20 mA) If you do not have the scalling function, give me your e-mail and I will send it to you as its size is more than 2 MB. Regards,
	Last edited by: Ayman Elotaify at: 9/24/2008 2:42 PM Last edited by: Ayman Elotaify at: 9/24/2008 2:42 PM Ayman Elotaify
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9/24/2008 6:24 PM	Rate (0)
Denilson Pegaia Platinum Member Joined: 9/23/2005 Last visit: 11/14/2024 Posts: 4352 Rating: (1452)	Hi, taka a look the post in forum: /tf/WW/en/Posts/13551#top
	Denilson Pegaia Siemens Industry Sector Technical Support
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9/25/2008 12:03 AM	Rate (0)
CS Moderator Moderator Joined: 9/1/2005 Last visit: 11/18/2024 Posts: 4113 Rating: (195)	Hello Ayman Elotaify, at the moment an upload up to 4 MB is possible. Best regards CS Moderator
	My Forum is the place to personalize your profile, track your topics, and maintain content that interests you. Best regards CS Moderator
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9/25/2008 7:34 PM	Rate (0)
nic_c Posts: 19 Rating: (0)	Ayman, you can send to [snip]... Thanks
nic_c Posts: 19 Rating: (0)	Last edited by: CS Moderator at: 10/4/2011 11:43 AM contact data deleted
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10/1/2011 1:38 PM	Rate (0)
shanmugam Posts: 25 Rating: (0)	please send me scaling manual ..this my mail id : [snip] ...
shanmugam Posts: 25 Rating: (0)	Last edited by: CS Moderator at: 10/4/2011 11:44 AM contact data deleted
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