There are a lots of control sytems like cascade control ,feedback control,feedforward control,split controls etc used in the process industries in this session we are gonna discuss about 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 to hold the process variable at the setpoint value determined by the operator. The next step in complexity after simple automatic control is to automate the adjustment of the setpoint for a process controller. A common implementation of this concept is the automatic cycling of setpoint values according to a timed schedule. An example of this is a temperature controller for a heat-treatment furnace used to temper metal samples:
Here, a computer “monitors” the temperature of the oven by communicating reference point values to the controller that indicates the temperature (TIC) through a digital network interface such as Ethernet. From the perspective of the temperature controller, this is a remote set point signal, unlike a local reference point value that would be set by a human operator on the controller’s faceplate. Since the heat treatment of metals requires particular temperature ranges and rates of change over time, this control system relieves the human operator of having to manually adjust the reference point values over and over during the heat treatment cycles. Instead, the computer programs different reference point values at different times (including reference point values that change constantly at a certain rate over a period of time) according to the needs of the type of metal and type of treatment in particular. Such a control scheme is quite common for thermal treatment processes
Process controllers configured for supervisory setpoint control typically have three operating
• Manual mode: Controller takes no automatic action. Output value set by human operator.
• Automatic mode with local SP: Controller automatically adjusts its output to try to keep PV = SP. Setpoint value set “locally” by human operator.
• Automatic mode with remote SP: Controller automatically adjusts its output to try to keep PV = SP. Setpoint value set “remotely” by supervising computer.
Supervisory setpoint control is also used in the chemical processing industries to optimize production efficiencies by having a powerful computer provide setpoint adjustments to regulatory controls based on mathematical models of the process and optimization constraints. In simple terms, this means having a computer make setpoint adjustments to the normal PID loop controllers instead (or in addition to) human operators making setpoint changes. This forms a two-layer process control system: the “base” or “regulatory” layer of control (PID loop controllers) and the “high” or “supervisory” level of control (the powerful computer with the mathematical process models). Such “optimizing” control systems are usually built over a digital network for reasons of convenience. A single network cable not only is able to communicate the frequent setpoint changes from the supervisory computer to the multitude of process loop controllers, but it may also carry process variable information from those controllers back to the supervisory computer so it has data for its optimization algorithms to operate on: