s7-300 pid

I want to controlling of heating room using electrical heaters.Therefore I did not decide which is used control blocks of S7-300 Pid .(0-450 celcius thermocouples )
and another question.How can I tunning correctly?

if using step7, there is section "Libraries/ Standart Library/ PID Control Blocks" in LAD/STL/FBD block editor :: FB41 and FB42 are the PIDs, one is with analog output, second with binaries ... but i guess that for electric heating you'll use the second one (FB42)

- those FB are called cyclically in OB35 and you have to set timing for it. etc.
- if you simply place FB42 (or FB41) into ladder, click on it and then press F1, it will show you nice help
- both of them need to have own assigned data block (created automatically then try to choose block)
- both can be monitored via PID control parameter assignement program, and set using it too (offline in simulator or directly online)
- analog unit values always returns temperature in particular engineering units
- pid blocks are using input values in REAL data format, so you may have to convert these values into real

what do you mean by "tunning"?

marius said:

if using step7, there is section "Libraries/ Standart Library/ PID Control Blocks" in LAD/STL/FBD block editor :: FB41 and FB42 are the PIDs, one is with analog output, second with binaries ... but i guess that for electric heating you'll use the second one (FB42)

- those FB are called cyclically in OB35 and you have to set timing for it. etc.
- if you simply place FB42 (or FB41) into ladder, click on it and then press F1, it will show you nice help
- both of them need to have own assigned data block (created automatically then try to choose block)
- both can be monitored via PID control parameter assignement program, and set using it too (offline in simulator or directly online)
- analog unit values always returns temperature in particular engineering units
- pid blocks are using input values in REAL data format, so you may have to convert these values into real

what do you mean by "tunning"?

Click to expand...

Hi,I have got a heating control project.There is the continuous conveyor bant at the line and there are 6 heating chambers on the same line.There are 2 electrical heaters per chamber (ranging between 0-450 celcius). At the input of this process giving plactic rubber and after passing 6 chambers ( 6 pid loops) this materials (plastic rubbers) cutting and boxing.I want to make controlling of this heating chambers by PID loops.Which can I use pid blocks (FB41,42,43,58,59) ?
I will use s7-300 cpu313 C,SM331 TC Module,OP270 and last question; How is adjusting pid parameters? thanks....

so, we are talking about 6 independently regulated zones, each with two heaters ... and they both (in one chamber) regulated together ok? - mean one termocouple for two heaters)(6 pid loops)?

well... can you tell more about outputs? will be heater controlled by contactor or something else? because this really matters for selecting of suitable PID

you can monitor & set some parameters using program called "PID Control" available through menu start "SIEMENS -> STEP7 -> Simatic", here's the screenshot >> http://www.alteruter.net/temp/plcs.net/pid_pidcontrol.gif

marius said:

so, we are talking about 6 independently regulated zones, each with two heaters ... and they both (in one chamber) regulated together ok? - mean one termocouple for two heaters)(6 pid loops)?

well... can you tell more about outputs? will be heater controlled by contactor or something else? because this really matters for selecting of suitable PID

you can monitor & set some parameters using program called "PID Control" available through menu start "SIEMENS -> STEP7 -> Simatic", here's the screenshot >> http://www.alteruter.net/temp/plcs.net/pid_pidcontrol.gif

Click to expand...

Thanks for your reply.I will be use contactor output for controlling of heaters.

... then you will regulate just by switching contactor on/off ... this work can be done by using FB42 or FB59 (but i used FB42 myself only for pressure control) ... it's step control, that mean the input is real (current value/ desired value) and output binary ('more' and 'less')

FB42 is universal
FB59 is according to manual designed for temperature controls

the interesting job is in tranforming of these two binary signals into one (which will represent contactor) because its designed for use with 3-states of valve open/nothing/close

20.0 QLMNUP OUTPUT BOOL FALSE MANIPULATED SIGNAL UPIf the "manipulated signal up" output is set, the valve will be opened.
20.1 QLMNDN OUTPUT BOOL FALSE MANIPULATED SIGNAL DOWNIf the "manipulated signal down" output is set, the valve will be closed.

probably easiest is just to enable output (contactor on) then QLMNUP is set and QLMNDN is not set, otherwise disable it

btw... if interested (but this may be more difficult)... you should be able to use analog regulator as well for it with few changes ... return value (for example) will be in range of 0% .. 100% ... then you will desire that
0 - 10 mean ... disable heating
90 - 100 mean ... enable heating
and range in the middle will be calculated like partially
enabled/disabled ... (for example 20sec cycle - as you may know relay and contactor have limited switching cycles per minute or hour) so 20% will mean 2sec on &18 sec off
and 80% 18sec on & 2 sec off

(in real world you have to define smallest enable/disable-idle too)
(this could be effective for particular technology)

i can post here some example for converting input for use with regulator if interested ...

what is the difference between FB42 and FB43?.According to I understand what did you say,FB 42 is conformable for this process.

... i never used it, so i'm not really sure, but it seems that FB43 can convert output of analog PID (FB41) to one binary output ... it should provide similar logic, like i've mentioned before ... here's picture from manual ::

http://www.alteruter.net/temp/plcs.net/pid_pulsegen.gif

(CONT_C is FB41 and PULSEGEN is FB43)

thanks my collage,I decided to use FB42,. I mentioned before there was 6 PID loop.Will it ( FB42)call 6 times in OB35 ( 100 ms)?and How can adjust PID parameters very simply?Must I use only PI in this process?

well... i think your question about FB43 was really good one, maybe fb41 + fb43 is suitable too (maybe even better, if you have some time it's worthy of test, imho) ...

but, to question of parameters

... important arguments of FB42 are
proportional gain
reset time
minimum pulse time
minimum break time
motor actuating time
dead band with
! and you have to enable "automatic operation" too ... if don't, block will not work atomatically after cpu unit start
! you have to set reset (COM_RST) input too, if it's equal FALSE, pid is stopped (this is usable for error handling etc.)
! time value must be equal to OB35 cycle timing, for default it is 100ms ... but if you want it more precise you can set both for 10ms or something else (note ... more calls in second, more CPU time eaten as well)

! the SP_INT and PV_INT are your temperature coeficient values
! QLMNUP and QLMNDWN are binary outputs of block

... for fb41 you will decide which component (P - I - D) will be major/minor or even unused and you can set important parameters using the program i've mentioned ... for FB42 is quiet simplier (as above) ... this PID CONTROL PA is also good for online monitoring, it will show you current/ desired value and operation interfere as well graphically, so you can decide what is neccessary to change ... because all input/ouputs and parameters are saved as datablock, you can edit simply datablock itself ... here's how it looks for FB42 : http://www.alteruter.net/temp/plcs.net/pid_datablock.gif

(datablock can be physically opened in "db param editor" or in "LAD/STL/FBD program block editor" - it seems to perform same work to me, step will ask you which one then you try to open any)

anyway ... don't forget to 'upload' changed values back to your pc if working with PLC online ... and be sure that there is some restart time of FB then you perform changes of 'some' values (changes must not appear immediately) .... sometimes is even better to stop&run unit again...

- for the timing of 6 independent pid block, i think you don't have to worry much, it will just require six networks and in 100ms, cpu will handle it nicely, they will be called during interrupt just in order of creation ...