PID Control With S7

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May I thank everyone that has posted on this forum with regards to PID control using FB41 blocks.

I plucked up the courage last week to try one of these PID controls and ended up doing six.

All the information that I used had come from this forum.

I successfully carried out PID control loops for speed control of 3 pumps which to achieve set flowrates and to control modulating valves for process heating one cooling and two heating applications.

The blocks proved to be stable on a wide set point range.


I did get a little stuck on the cooling application which required a negative proportional band.

Has anyone tried the other Temperature PID Control FB58 (I think?) Are they any different to FB41 blocks.

Again Thanks to everybody,

New to Siemens
 
Hello;

Always glad if we helped you out a little.

The Temperature PID Control are very similar to the FB41; the main difference is in the output, which generates a PWM pulse train to trigger a bank of SCRs controlling heaters. Basically, once you are familiar with the basic PID blocks from Siemens, it is very easy to move on to the next.

When you say you need a negative proportionnal band, do you mean an inverting control (Error increases, output must decrease)? Have a look at this: (Entry ID # 8718842 from Siemens support website)
fb41_rev.jpg


Hope this helps,
Daniel Chartier
 
I've always seen control action expressed as "reverse" or "direct", as opposed to negative or positive gain. Is negative gain for direct action a typical European expression?

Dan
 

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