Runaway Processes
A classic “textbook” example of a runaway process is an inverted pendulum: a vertical stick balanced on its end by moving the bottom side-to-side. Inverted pendula are typically constructed in…
Gas Flow Formulas
Gas Flow Units MMSCFD - Million standard cubic feet of gas per day - a common volume of gas measure (unit abbreviation MMscf) SCFD - Standard cubic feet per day (gas) SCFM - Standard cubic feet…
RS485 Serial Communication
RS232, RS422, RS423 and RS485 are serial communication methods for computers and devices. RS232 is without doubt the best known interface, because this serial interface is implemented on almost all…
Flow Meter K-factor and Calculations
What is Flow Meter K-factor ? The K-Factor expressed in pulses per unit volume, used to calculate the volumetric flow rate from flow meter.
Integrating Processes – Liquid Level Control
A good example of an integrating process is liquid level control, where either the flow rate of liquid into or out of a vessel is constant and the other flow…
Modbus : History, Structure, Modes, Addressing, Functions
Modbus primary purpose was, of course, to exchange data between PLCs and other devices in the industrial plants.
Self-regulating Processes – Liquid Flow Control
If a liquid flow-control valve is opened in a step-change fashion, flow through the pipe tends to self-stabilize at a new rate very quickly. The following illustration shows a typical…
Process Dynamics and PID Controller Tuning
To tune a feedback control system means to adjust parameters in the controller to achieve robust control over the process. “Robust” in this context is usually defined as stability of…
PID Controller Functions
For any PID controller to be practical, it must be able to do more than just implement the PID equation. This article explains some of the basic features found on…
Fieldbus Control
The DCS revolution started in the mid-1970’s was fundamentally a moving of control system “intelligence” from a centralized location to distributed locations. Rather than have a single computer (or a…
