L24er qbfc1b io

Holmux

Lifetime Supporting Member
Join Date
Oct 2013
Location
Aalborg
Posts
279
Hi All

I am setting up some internal analog IO setup in the L24ER, I like all the options for the IO's but finds the input value info limited (or havne't found the right manual :) )

I am setting up a 4-20 ma input in Raw/Proportional, the manual says I will get a value from -32767 to 32767 full range (3,2 to 21 ma) well it would have been super nice to add the values for 4 - 20 ma in the manual at well, just for kicks :)

My calculation tells me i will get the value -29822 at 4 ma and 29085 at 20 ma, I just wanted to hear if anyone came up with the same numbers.

Thanks
/Holmux
 
First, when I setup Studio 5000 with the processor you have, I do show a setting for 4 to 20mA. I’m not sure why you don’t but I’d look again.
Next, I suck at math, so I let Excel to the work. First if took 65534 and divided it by 21 and got 3120.66. 65534 represents a 32-bit word which the analog input uses. The only difference is it starts at -32767 rather than 0. 21 represents the number of points in 0 to 21mA. I then created a spread sheet and entered 0 thru 21 in a column and then in the next column, on the next row down, I created the formula “=sum(G6+3120.66) and expanded it to go from 1 to 21 (G6 is the cell that the lowest value will be). I copied it to the next column over and set the cells to be “numbers” with the decimal point at “0” (this will round the numbers to whole numbers. I did this because the PLC can’t display anything other than whole numbers in a DINT). In the row that is for 0mA, in the first column I entered “0” and in the next column I entered -32767. I believe that should give the values the raw input will see for a given mA input. The reason I believe it works is when you get down to the row for 21mA, the first column shows 65534 and the next one shows 32767. With that, 4mA shows a value of -20284 and 20mA shows 29646.
The spread sheet is attached so you can see how I put it together and try different values.
 
Last edited:
Hi Firejo

The option for a 4-20 ma is in the module, that is exactly the one i picked.

The problem is the value it spits out when you set it up to Raw, then you get for the full spectra = 3.2 - 21 ma = -32767 - 32767 and you have to do your own calculations to get to the 4 - 20 ma values.

What i did was to calculate the output if the value dropend to 3 ma, just in theory, I got to -33503 then it was easier to calculate the line from 3 to 21 ma

I am fairly sure my calculations are correct, just wanted to double check if anyone else was getting the same result :)

I have attached my calculation in Excel, on sheet 2

Thanks again
/Holmux
 

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