S7-200 and EM231 : weighing amount of water

melon52 · Oct 6, 2013

Hello everyone,
I want to weigh a certain amount of water (in kg). For this I use an S7-200 (CPU226) and EM231 analog module. I did the program in question, but I do not know if correct or not. Thank you for any help or advice. (I am a beginner in this field).

balash · Oct 6, 2013

melon, it's hard to read it withou comments. could you explain how stuff should work or what is what.
as for scaling, it's siemens library as i noticed and as that it should be ok. also you didn't mention if it's voltage or current measurment on voltage (or current) input card.

melon52 · Oct 6, 2013

AIW0 corresponds to the voltage (0-10V) provided by the weight indicator. I open the valve (Q0.0) for weighing the water on a balance and closes the valve when the desired weight is reached.

balash · Oct 6, 2013

first as you have 0-10V input the scale is 0-32000 not 6400-32000.
ok, what's flying weight?

EDIT:
when calculating weight, try call once S_ITR and save the result in memory rather than call the subroutine more times.

melon52 · Oct 6, 2013

flying_weight is the weight of the amount of water (estimated) located after the closing of the valve and which is not yet occurred in the balance.

Code:

when calculating weight, try call once S_ITR and save the result in memory rather than call the subroutine more times.

? How should I proceed? thank you

balash · Oct 7, 2013

ok, i'll try to rewrite it.
first remarks for your future work:

don't use multiple coil for same output like you do with Q0.0 - coil can only have one of two states and doing that will result that output will follow the last one coil (as outputs are set at end of program cycle) and disregard previous, in your case output Q0.0 will follow only the coil in network 3.
settling time - i guess you wanted to prevent oscillation of AIW around target weight. AIW will rarely be same even when valve is closed, so you either use hysteresis (tolerance can act like that) or you use TOF (Off delay) with (weight < target) as IN that will keep the valve opened for additional minimum period that IN has to be false to start closing.
use less SR instruction. set/reset can cause undesirable effect if you forget one action somewhere or if stuck in the middle. try combine condition and if SR is unavoidable use it at minimum.

balash · Oct 7, 2013

okey here is what i wrote, first version, need to test...

S7-200 and EM231 : weighing amount of water

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