Douglas E Carr

US Patent:

46690409, May 26, 1987

Filed:

Sep 19, 1984

Appl. No.:

6/652181

Inventors:

John W. Pettit - Derwood MD
Douglas M. Carr - Sterling VA

Assignee:

Eurotherm Corporation - Reston VA

International Classification:

G05B 1300

US Classification:

364162

Abstract:

Method and apparatus for self-tuning a Proportional Integral-Derivative controller for controlling at least one load characteristic to a predetermined setpoint from calculated values of Proportional Band (PB), Integral Time Constant (ITC) and Derivative Time Constant (DTC) by application of power to the load, establishing a cut-off point to remove power to the load, determining the slope of a measured value of the at least one load characteristic and starting an integral time counter upon detection of the power cut-off point, determining at least one value X. sub. min at which the value of the measured value decreases by a fixed percentage, determining the maximum value X. sub. max of the at least one load characteristic, calculating the values of the PB, ITC and DTC by determining the rise X. sub. r =X. sub. max -X. sub. min and determining PB and ITC from a stored table relating X. sub. r to PB and the value incremented in the integral counter, determining the DTC value from the value incremented in the integral counter, storing the values of PB, ITC and DTC in a non-volatile storage and controlling the load with the aforementioned calculated values of PB, ITC and DTC.