21.
TAI Engineering - Automation, Systems Integration and Controls Engineering
(www.taiengineering.com)
22.
Lessons in Industrial Instrumentation - Great overview of the field
(ibiblio.org)
23.
Putt's Law
(en.wikipedia.org)
24.
AB Circuit Protection Methods - Whitepaper
(literature.rockwellautomation.com)
25.
Maxwell's Equations Explained Intuitively
(www.maxwells-equations.com)