Basic Process Control System
Consider a typical process control system. For a particular example let us look at an open tank, which supplies a process, say, a pump, at its output. The tank will require a…
ON-OFF Controller Principle
On-Off control is the simplest form of feedback control. An on-off controller simply drives the manipulated variable from fully closed to fully open depending on the position of the controlled…
Comparison of Transistor Configurations
There are three leads in a transistor viz., emitter, base and collector terminals. Â However, when a transistor is to be connected in a circuit, we require four terminals; two for…
DP Level Measurement Problems
The DP level measurement techniques use inferred (indirect method) processes and not direct measurements. Namely, the indication of fluid level is based on the pressure exerted on a differential pressure (DP)…
DP Level Transmitters Compensation Techniques
It would be idealistic to say that the DP Level Transmitters can always be located at the exact the bottom of the vessel where we are measuring fluid level in. Hence, the measuring…
Proportional Controller Principle
If the outflow (Qo) increases then the level in the tank will fall. The pressure sensed by the level transmitter, which is representative of the level in the tank, will also fall…
Infrared Open Path Gas Detectors Working Principle
An alternative method of measuring gas concentration is based on absorption of infrared (IR) radiation at certain wavelengths as it passes through a volume of gas. Devices using this technology have a…
Integral Controller Principle
Reset of Integral Action Most of the processes we will be controlling will have a clearly defined setpoint. If we wish to restore the process to the setpoint after a disturbance then…
Derivative Controller Principle
RATE OR DERIVATIVE ACTION Consider a control system subjected to a disturbance, which causes the error to increase in a ramped manner. Proportional control would respond to this ramped error with a…
Thermocouple and its Principle
A thermocouple consists of two pieces of dissimilar metals with their ends joined together (by twisting, soldering or welding). When heat is applied to the junction, a voltage, in the range of…
