Coping with communications delays and different time scales when applying central automatic control

A problem that we encountered during the implementation of a central automatic control system for a sewer system was the variable delay in data and command transmission. Another problem was the discrepancy between safe run times for pumps. Pumps with a large local buffer can be left running longer. In general even the pumps with small local storage can run several minutes on dry weather flow. However, the latter type may necessitate checks on the validity of the current pump settings before the next regular call to the controller, especially when there are variable delays in communication. We describe how these problems affected the final controller design.