Negative feedback amplifier with disturbance. Similar to <a rel="nofollow" class="external text" href="https://books.google.com/books?id=d8EJP8qQQcwC&amp;pg=PA308&amp;dq=%22Classical+single+input,+single+output+control+loop%22&amp;hl=en&amp;sa=X&amp;ei=3r9XVLKfApO5ogTjsILoDA&amp;ved=0CB8Q6AEwAA#v=onepage&amp;q=%22Classical%20single%20input%2C%20single%20output%20control%20loop%22&amp;f=false">Marc Thompson's figure</a>
<a href="//commons.wikimedia.org/wiki/User:Brews_ohare" title="User:Brews ohare">Brews ohare</a>
<span class="int-own-work" lang="en">Own work</span>