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Integral Control Summary
Example of Proportional Plus Reset Control

Instrumentation and Control 2 of 2
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Process Controls PROPORTIONAL PLUS RESET CONTROL SYSTEMS PROPORTIONAL PLUS RESET CONTROL SYSTEMS Proportional plus reset control is a combination of the proportional and integral control modes. EO 1.4 DESCRIBE the characteristics of the following types of automatic control systems: d. Proportional plus reset control system Proportional Plus Reset This   type   control   is   actually   a Figure 22   Response of Proportional Plus Reset Control combination    of    two    previously discussed control modes, proportional and integral. Combining  the  two  modes  results in   gaining   the   advantages   and c o m p e n s a t i n g f o r t h e disadvantages of the two individual modes. The     main     advantage     of     the proportional  control  mode  is  that an  immediate  proportional  output is  produced  as  soon  as  an  error signal  exists  at  the  controller  as shown    in    Figure    22. The proportional controller is considered   a   fast-acting   device. This    immediate    output    change enables the proportional controller to    reposition    the    final    control element  within  a  relatively  short period  of  time  in  response  to  the error. The  main  disadvantage  of  the  proportional  control  mode  is  that  a  residual  offset  error  exists between the measured variable and the setpoint for all but one set of system conditions. The  main  advantage  of  the  integral  control  mode  is  that  the  controller  output  continues  to reposition  the  final  control  element  until  the  error  is  reduced  to  zero.    This  results  in  the elimination of the residual offset error allowed by the proportional mode. Rev. 0 Page 33 IC-07







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