siemens FB41 Level control

sirhiss2

Member
Join Date
Oct 2003
Posts
109
I'm Still trying to setup a basic level control using this FB41 Block. bawling I have had help from some of you guys before so I will field these questions to see if anyone can answer them. I have been talking to siemens and it seems to me that they don't want to give me all the Info I need to finish this little project of mine. They keep refering me to documents that don't answer my questions! :(
Am I the only one having this problem? :unsure:
Here is a copy of the last email I sent to them.

#1. If I put FB41 block into OB35 (set at 100ms) do I have to do anything with Com_RST?

#2. On SP_INT It says (-100.0...100) if I wanted a value of 50%, do I enter 0 (which is half way between -100 and 100) or do I just enter 50?

#3.On Gain in DB1 (of FB41). Is there a way that I can have this value change (call integer value from another address) so that I don't have to go into DB1 and manually type the value in? Note: I wish to be able to change gain value from HMI. What address would I use to do this?

#4. According to the Info I have, If I took the word address (PIW 448) and entered it in FB41 on the block @ PV_PER, it should scale my analog input for me. Yes? How do you setup what scaling takes place?
Or do it matter? What would I have to do with CRP_IN & CRP_OUT?

#5. Can I use a word address PQW 464 at the FB41 block LMN_PER output to give me a 4-20 mA signal on my analog output card that I can use with my I to P to control a valve? What will I have to do to manipulate the output of LMN_PER to give me a 4-20 mA signal at my analog output card?

I want to thank all you guys for the help.
:site:
 
#1. If I put FB41 block into OB35 (set at 100ms) do I have to do anything with Com_RST?

Answer++ No- but I typically call the block (FB41) in OB100 and put a closed contact in front of it so that the PID block is reset before it is called from OB35.

#2. On SP_INT It says (-100.0...100) if I wanted a value of 50%, do I enter 0 (which is half way between -100 and 100) or do I just enter 50?
Answer++ Just put in a 50, the PID is going to try and get to the SP however it can. It you are using a 4-20ma output (which is 0-27648) then use 0-100.



#3.On Gain in DB1 (of FB41). Is there a way that I can have this value change (call integer value from another address) so that I don't have to go into DB1 and manually type the value in? Note: I wish to be able to change gain value from HMI. What address would I use to do this?

Answer++ Your HMI can write directly to the data block, or you can put a value in front of the call for FB41 (in the GAIN input)



#4. According to the Info I have, If I took the word address (PIW 448) and entered it in FB41 on the block @ PV_PER, it should scale my analog input for me. Yes? How do you setup what scaling takes place?
Or do it matter? What would I have to do with CRP_IN & CRP_OUT?

Answer++ The scaling takes place (by default) that the input (when using PV_PER) will be 0-27648.

#5. Can I use a word address PQW 464 at the FB41 block LMN_PER output to give me a 4-20 mA signal on my analog output card that I can use with my I to P to control a valve? What will I have to do to manipulate the output of LMN_PER to give me a 4-20 mA signal at my
analog output card?


Answer++ Just assign the LMN_PER to your PQW464- The output to the valve will be 4-20ma (provided you set it up this way in the hardware config.)


Anyway- Enclosed is a sample- It should be just what you are looking for.


Jay
 
Thanks JRW. Thats Helpful Info. (y)
Bye the way I did get more Info. from Siemens After.
I can send you a copy of the email if you want?
It's basicly the same answers you gave me but without an example that I could look at.
Thanks for the help. beerchug
 
I looked over the material that you sent me. Good stuff!
You set NC contact infront of COM_RST in OB100 to M0.1.
and COM_RST in OB35 to M0.1. This is so that FB41 Resets all info before OB35 calls for it again? I'm still having trouble understanding why you did this. If COM_RST has to be 0 in OB35, why set it to a value of M0.1? also, in OB100 why don't you just put a connecting line to COM_RST without NC Contact(M0.1)? The rest of the programming I understand.
 
It was just a quick way of turning on the COM_RST in OB100 and turning it off in OB35. Do it anyway that works for you.

Jay
 
Hi I am struggling with this logic.

have tried the supplied code in the simulator but my output does not change from 0.

COM_RST = 0
MAN_ON = 0
PVPER_ON=1
CYCLE=T#100MS
SP_INT=40
PV_PER=0
MAN=20
GAIN=10

If I change MAN_ON = 1 the output still stays at 0

Please advise
 
I have one question regarding the FB41 block also.

I've was able to set up my PID regulation with no problems. Everything works fine(if the process variable rises above the entered setpoint the manipulated output value starts decreasing and vice versa.
But now I have to set it up so that it will work the other way around. If the proces value will rise above the setpoint, the manipulated output value will raise. Like so.

Is this even possible with this block???

Any info would be great.

Thanks & regards
Ales
 
Thanks Dennis.

I've been reading the help file for this FB and came across this variable: PV_FAC - PROCESS VARIABLE FACTOR
The "process variable factor" input is
multiplied by the process variable. The
input is used to adapt the process variable
range.
Would I get the same result if I would set this input to -1 ???

Regards
Ales
 
i need solved examples to fb41 to be able to know which i/p s and o/p s must i use be cause when i monitored the Sp_int,pv_in and lmn on the flexible there is no o/p displayed on the trend
 
to doing closed loop control to the pressure on the flow system and i input the Sp as analog input to the fb41.
is this correct or i must bring real plant to try on it
 
icon5.gif
I didn't catch the problem.

Is i/p = input and o/p = output?

And which trend?

What about a screenshot?

Kalle
 

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