Pneumatic control: Testbed for Ziegler-Nichols tuning

By Dick Johnson, CONTROL ENGINEERING July 1, 1999

Up until 1940, controller tuning was an art conducted by seat-of-the-pants methods. At the Taylor Instrument Co. (then Rochester, N.Y.), engineers John G. Ziegler and Nathaniel B. Nichols were working with then state-of-the-art controllers to develop the now famous ‘Ziegler-Nichols’ method of controller tuning. However, this now time-tested tuning technique was not developed on an analog controller as many control engineers may suspect.

The culmination of control advances during the ‘golden age of control’ from 1935 to 1940 resulted in Mr. Ziegler and Mr. Nichols setting out to design the Model 100 Fulscope, in order to incorporate automatic reset action provided by the double response unit. The 100 Series device was pneumatic and used parallelogram linkages to change the mechanical feedback of proportional response sensitivity. Also included in the design were reproducible needle valves for setting reset rate and pre-act time.

The upshot of the development work and simulator tests on the Fulscope 100 by Mr. Ziegler and related mathematical analysis and simplification by Mr. Nichols was the paper, ‘Optimum Settings for Automatic Controllers,’ which was presented to the annual meeting to the American Society of Mechanical Engineers in New York City in December of 1941. PID tuning was born. The full story of this ground-breaking development is covered in ‘Modern Control Started with Ziegler-Nichols Tuning’ ( CE , Oct.’90, 2nded., pp. 11-17)