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Principles of Feedback Control

Instrumentation is the science of automated measurement and control. Applications of this science abound in modern research, industry, and everyday living. From automobile engine control systems to home thermostats to aircraft autopilots to the manufacture of pharmaceutical drugs, automation surrounds us. This chapter explains some of the fundamental principles of automatic process control.


Basic feedback control principles

On/off control

Proportional-only control

Proportional-only offset

Integral (reset) control

Derivative (rate) control

Summary of PID control terms

Proportional control mode (P)

Integral control mode (I)

Derivative control mode (D)


P, I, and D responses graphed

Responses to a single step-change

Responses to a momentary step-and-return

Responses to two momentary steps-and-returns

Responses to a ramp-and-hold

Responses to an up-and-down ramp

Responses to a sine wavelet

Note to students regarding quantitative graphing


Different PID equations

Pneumatic PID controllers

Automatic and manual modes

Derivative and integral actions

Fisher MultiTrol

Foxboro model 43AP

Foxboro model 130

External reset (integral) feedback


Analog electronic PID controllers 

Circuit design

Single-loop analog controllers

Multi-loop analog control systems


Digital PID controllers

Stand-alone digital controllers

Direct digital control (DDC)

SCADA and telemetry systems

Distributed Control Systems (DCS)

Fieldbus control

Practical PID controller features

Manual and automatic modes

Output and setpoint tracking

Alarm capabilities

Output and setpoint limiting



Note to students

Proportional-only control action

Integral-only control action

Proportional plus integral control action

Proportional plus derivative control action

Full PID control action




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Lavigne, John R., Instrumentation Applications for the Pulp and Paper Industry, The Foxboro Company, Foxboro, MA, 1979.

Lipt´ak, B´ela G., Instrument Engineers’ Handbook – Process Control Volume II, Third Edition, CRC Press, Boca Raton, FL, 1999.

Mollenkamp, Robert A., Introduction to Automatic Process Control, Instrument Society of America, Research Triangle Park, NC, 1984.

“Moore 353 Process Automation Controller User’s Manual”, document UM353-1, Revision 11, Siemens Energy and Automation, 2003.

Shinskey, Francis G., Energy Conservation through Control, Academic Press, New York, NY, 1978.

Shinskey, Francis G., Process-Control Systems – Application / Design / Adjustment, Second Edition, McGraw-Hill Book Company, New York, NY, 1979.

“SPEC 200 Systems”, technical information document TI 200-100, Foxboro, 1980.

“SPEC 200 System Configuration”, technical information document TI 200-105, Foxboro, January 1975.

“SPEC 200 System Wiring”, technical information document TI 200-260, Foxboro, 1972.

Ziegler, J. G., and Nichols, N. B., Optimum Settings for Automatic Controllers, Transactions of the American Society of Mechanical Engineers (ASME), Volume 64, pages 759-768, Rochester, NY, November 1942.

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