Short note: Feedback control system

A feedback control system is a closed-loop system in which the output (actual performance) is measured and fed back to be compared with the desired standard (plan). If there is a difference (error), corrective action is taken to bring the output back to the standard. The aim is self-regulation.

Elements

1. Standard / plan (set point): the target for time, cost and quality.
2. Process: the project work.
3. Sensor / measurement: records the actual progress, cost and quality.
4. Comparator: compares actual with standard and finds the variance.
5. Decision and corrective action (effector): the manager adjusts the inputs (resources, method) to remove the variance.

            Plan / Standard (set point)
                    |
                    v
Input --> [ Process: project work ] --> Output
               ^                          |
               |                          v
        [ Corrective              [ Sensor: measure
          action ]                    actual ]
               ^                          |
               |                          v
               +------ [ Comparator: ] <--+
                         actual vs plan

Example: the budgeted cost of a building at 50 % progress is Rs 40 lakh, but the actual cost is Rs 46 lakh. The report (feedback) shows an overrun of Rs 6 lakh. The manager reduces wastage, renegotiates rates and re-plans the remaining work to bring the cost back within the budget.

Features: it is continuous, automatic or semi-automatic, and corrects only after a deviation has occurred (so there is some time lag); it works best with timely information.