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Comparator function

Created by: alexandrebr at: 9/21/2021 8:01 PM (5 Replies)

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9/21/2021 8:01 PM	Rate (0)
alexandrebr Posts: 13 Rating: (0)	Hey good afternoon is there any block or function in step 7 for this application: compare 2 values and when there is a difference of 2%, turn on a bit?
alexandrebr Posts: 13 Rating: (0)	Last edited by: Jen_Moderator at: 09/22/2021 08:57:48 Edited text for better reading.
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9/21/2021 9:10 PM	Rate (0)
dchartier Grandmaster-Expert Joined: 9/27/2006 Last visit: 1/14/2026 Posts: 12481 Rating: (2722)	Hello alexandre; This looks like an easy enough function to program yourself. Something like this pseud-code: [ IF (x_value - y_value)/100 = 0.02 THEN DB10.DB0.0 ] What S7 PLC family are you working with, and what progamming language are you familiar with? What data type would you use for the x_value and y_vaiue, would they be of type INT, DINT, REAL? Hope this helps, Daniel Chartier
	Last edited by: dchartier at: 09/21/2021 21:12:48
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9/21/2021 9:21 PM	Rate (0)
alexandrebr Posts: 13 Rating: (0)	I use the s7-300 I'm more familiar with FBD function block and the data type is the real type
alexandrebr Posts: 13 Rating: (0)	Last edited by: Jen_Moderator at: 09/22/2021 08:58:30 Edited text for better reading.
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9/21/2021 9:43 PM	Rate (0)
alexandrebr Posts: 13 Rating: (0)	and if to turn a bit there is a difference of 2% up or down, to show that the signal has a discrepancy
alexandrebr Posts: 13 Rating: (0)
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9/21/2021 10:51 PM	Rate (0)
dchartier Grandmaster-Expert Joined: 9/27/2006 Last visit: 1/14/2026 Posts: 12481 Rating: (2722)	Hello alexandre; I have prepared one possible FBD function that could rsolve your issue. If the difference between the 2 REAL inputs x_value and y_value is greater than 2%, bit DB10.DBX0.3 will turn ON. Please feel free to modify it as you need. If this is a single call program it as you see. If you need to do this test recurrently, program it inside an FC, which you can call with different parameters x_value and y_value. Here is a link to the S7-300 FBD programming language, it may prove useful. https://support.industry.siemens.com/cs/ww/en/view/109751819 Hope this helps, Daniel Chartier Attachment FBD function example.jpg (403 Downloads)

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9/22/2021 9:08 AM	Rate (0)
mopS04 Posts: 5521 Rating: (1058)	hi alexandredr, have a look to the Library of general functions. The block "LGF_CompareLRealByPrecision" does exactly what you want. Have a look into the documentation chapter 3.3.3. hope this helps, regards,
mopS04 Posts: 5521 Rating: (1058)
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This contribution was helpful to 1 thankful Users dchartier

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