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Analog Inputs

Created by: camcor at: 11/20/2012 9:20 AM (3 Replies)

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11/20/2012 9:20 AM	Rate (0)
camcor Posts: 2 Rating: (0)	I have a 331-7KF02-0AB0 analog input card (8 x 12bit) set up on a test bench communicating to a PLC over profibus witha ET 200M module (IM153-1). I have one channel set up fora 4-20mA signal. From the manual I expect 0 plc units for a 4mA signal up to 27648 for a 20mA signal. However I get a reading of 64 when I apply a 4 mA signalto the card and 27712 when I apply a 20mA. As I go through the range in between I get a lot of readings that are 64 units greater than the theoretical. See attached for reference. Has anyone come across a similar issue. Thanks Attachment C:\Documents and Settings\bmcnam01\Desktop\AIcard.pdf (173 Downloads)
camcor Posts: 2 Rating: (0)
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11/20/2012 7:34 PM	Rate (0)
SteveA Posts: 297 Rating: (41)	It sounds like you have set the interference frequency in the hardware properties for the analog input card to 400 Hz. This provides the fastest conversion rate, but the lowest resolution, of 9 bits instead of 12 (or 14, if you select 10 Hz). With 9 bit resolution, the smallest resolvable difference in current will be 64 counts. If you want the best resolution, set the interference frequency to 10 Hz. HTH, SteveA
SteveA Posts: 297 Rating: (41)
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11/21/2012 1:33 AM	Rate (0)
Ayman Elotaify Platinum Expert Joined: 5/28/2008 Last visit: 1/2/2025 Posts: 4518 Rating: (841)	Hello, Here it is the related FAQ which supports SteveA answer: How can you set or change the resolution of the analog module SM331 (6ES7331-7K..)?
	Ayman Elotaify
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11/22/2012 9:11 AM	Rate (0)
camcor Posts: 2 Rating: (0)	Thanks a lot guys, I set it up with 16.6ms integration which is fast enough for my application and got a much better response. The readings are still sometimes significantly different from the theoretical but I was looking for a technical justification for scaling my input for a report as much as I was looking for accuracy, so again, many thanks for your help.
camcor Posts: 2 Rating: (0)
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