<Dd> T i (\ displaystyle T_ (i)) is the integral time </Dd> <Dd> T d (\ displaystyle T_ (d)) is the derivative time </Dd> <P> The negative feedback amplifier was invented by Harold Stephen Black at Bell Laboratories in 1927, and granted a patent in 1937 (US Patent 2,102,671 "a continuation of application Serial No. 298,155, filed August 8, 1928 ..."). </P> <Dl> <Dd> "The patent is 52 pages long plus 35 pages of figures . The first 43 pages amount to a small treatise on feedback amplifiers!" </Dd> </Dl>

Describe homeostasis and give an example of both a negative and positive feedback mechanism