Flow Totalizer S7-300??

Viggen

Member
Join Date
Nov 2007
Location
Oslo
Posts
2
Hi there!


I have used the search button for help to find some solution`s
to make a totalizer for flow.
I did see many solution`s but all the answers are in STL.
Because i allways have been using LAD for programming the STL is greek for me.

Is it anybody that wants to make an example for totalizer in ladder??

input is 4-20mA
Flow rate 25000kg/h

ps. Sorry for my bad english


regards
Eivind
 
Here's a very simple and sometimes accurate enough way:

0 - 25000kg/h = 0 - 6.944kg/second

So: scale 4-20mA input to floating point value of 0 - 6.94kg/sec
Then: use 1 second timer to snapshot "sample" 0 - 6.94kg/sec floating point value and move/add it to another floating point register "Total."

Every second the total will grow based on the flow rate at that 1 second snapshot.

This is primative but works and CAN be optimized with the usage of scan time considerations and time slices but that's more complicated and PLC specific.
 
This is my implementation.

I like using cyclic interruption blocks such as OB35 which is executed every 100 ms (default)
You have input 4-20 mA = 0-25000 kg/h
25000kg/h = 6.9444 kg/s = 0.69444 kg/(100ms)

So, first scale your input (in S7-300/400 it is integer range 0-27648) to 0 - 0.6944 with standard FC105

Second, just summarize current input value to current totalizer and that's it.

I'd like others to express their opinions about this solution.
 

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