PID Control 3.2

An ActiveX control that does Proportional-Integral-Derivative output just like real industrial controllers. 16-bit VBX, DLL, and 32-bit ActiveX versions available.

An essential software component for building industrial process control applications.

There are many books available on process control theory. You can find them at any good technical library. Process control is a complex field of study - far too broad to cover in detail in this document. The following covers some of the basics to get you started. A lot can be learned just by "playing" with the PID control. It is possible to connect your PC to laboratory equipment through a special analog adapter and perform real process control, using the PID control in Visual Basic or Visual C++ to perform the control calculations and output.

Process control is divided into two broad categories; "Open Loop" and "Closed Loop". Open loop controllers send an output signal (air pressure or electrical) to a pneumatic valve or electronic solenoid. The level of the output signal is adjusted with no knowledge of conditions at the point of control. For example, a steam valve could be set to 50% of its travel. The kettle of water being heated is at some unknown temperature and heats up as steam is fed to it. The temperature of the water rises continuously to some point of equilibrium. No change occurs to the steam valve setting unless the operator manually adjusts the output to the valve.This type of control is manual.

Closed loop control is a technique for automatically adjusting valve or other component settings based on the measured value of the material being controlled. For example, placing a thermocouple in the kettle of water and feeding the measured temperature back to the controller allows the controller to determine a new setting for the steam valve.