# Block reduction technique

< Mentor Note -- thread moved to HH from the technical forums, so no HH Template is shown >

Hi!

I've been working on reducing a controller with block reduction in order to understand it and I have trouble to continue since I've stumbled across something that I haven't seen before. My goal is to find a transfer function basically. The block that I reduced looks like this one : https://postimg.org/image/qqfa54ltf/

My attempt now was to reduce the outer integrator, 1/s, by dividing it into two parallell blocks (a rule that I've followed) and continue with the block reduction. Here is what I got after doing this step.
https://postimg.org/image/fkdmoqzpv/

And it is now that I'm lost. I know that I need to reduce the outer loop but I don't know how to do it when we have two summations in row. Anyone that can help?

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berkeman
Mentor
Hi!

I've been working on reducing a controller with block reduction in order to understand it and I have trouble to continue since I've stumbled across something that I haven't seen before. My goal is to find a transfer function basically. The block that I reduced looks like this one : https://postimg.org/image/qqfa54ltf/

My attempt now was to reduce the outer integrator, 1/s, by dividing it into two parallell blocks (a rule that I've followed) and continue with the block reduction. Here is what I got after doing this step.
https://postimg.org/image/fkdmoqzpv/

And it is now that I'm lost. I know that I need to reduce the outer loop but I don't know how to do it when we have two summations in row. Anyone that can help?
Are these block reduction threads of yours for schoolwork problems? If so, they need to be posted in the Homework Help forum, using the HH Template that you are provided there.

Are these block reduction threads of yours for schoolwork problems? If so, they need to be posted in the Homework Help forum, using the HH Template that you are provided there.
Yes.

Oh, okay. Did not think of that.

berkeman
Mentor
No worries, I'll move them...

At first, there is no need to use the block reduction method because you have already a single-loop system.
Of course, you can combine (multiply) the transfer functions of two succeeding blocks into one single block - but this is not necessary because you must multiply both functions anyway.
Secondly, what is the purpose of the first summing junction? It has only one single input. Did you forget something?
Otherwise you can forget it.
You can find the wanted transfer function simply by applying Black`s famous formula for negative feedback.