Effect of Delay on Control

Delay of a signal for a period of time is called distance-velocity lag . For example, plug flow of a solution through a pipe may have negligible mixing or dispersion, thus an element of fluid may be assumed to traverse the pipe unchanged. This assumption is quite good for the oil pipelines that traverse the country, and it is possible to move different grades of oil or gasoline in segments and to cut sharply at the receiving end. For flow of solutions through pipes, a graph of the inlet concentration can be exactly the same as a graph of the outlet concentration except for a displacement in time. Here is an example:


¬Select delay here.
This is over simplified. Real systems have more elements.
When the distance-velocity lag is small, control can be excellent.
When it is large, control can be terrible.

Computer coding for distance-velocity lag
This page last updated by Henry Bungay bungah@rpi.edu in June 2017