Category Archives: Control System

Ratio control

Most people  have likely had the experience of adjusting water temperature as they took a shower with dual valves: one valve controlling the flow of hot water and another valve controlling the flow of cold water. In order to adjust water temperature, the proportion of one valve opening to the other must be changed. Increasing or decreasing total… Read More »

Supervisory control

In a manually-controlled process, a human operator directly actuates some form of final control element (usually a valve) to influence a process variable. Simple automatic (“regulatory”) control relieves human operators of the need to continually adjust final control elements by hand, replacing this task with the occasional adjustment of setpoint values. The controller then manipulates the final control element… Read More »

Ziegler-Nichols Tuning method

Ziegler-Nichols open-loop tuning procedure :- The first process tuned in simulation was a “generic” process, unspecific in its nature or application. Performing an open-loop test (two 10% output step-changes made in manual mode, both increasing) on this process resulted in the following behavior: From the trend, we can see that this process is self-regulating, with multiple lags… Read More »

On-Off control sytem

Once while working as an instrument technician in a large manufacturing facility, a mechanic asked me what it was that I did. I began to explain my job, which was essentially to calibrate, maintain, troubleshoot, document, and modify (as needed) all automatic control systems in the facility. The mechanic seemed puzzled as I explained the task of “tuning”… Read More »

Closed loop control system

If liquid flow-control valve is opened in a step-change fashion, flow through the pipe tends to selfstabilize at a new rate very quickly. The following illustration shows a typical liquid flow control installation, with a process trend showing the flow response following a manual step-change in valve position:   The defining characteristic of a self-regulating process is its… Read More »