4-20mA Graphical Calculations
An illustration sometimes find helpful in understanding analog signal ranges is to consider the signal range as a length expressed on a number line. 4-20mA Graphical Calculations For example, the common…
Field Instruments Scaling and Unit Conversions
The Instrumentation and Controls is all about managing information. Today, process information must be prepackaged, timely, and accurate, so we in the controls profession must be adept at managing information, from…
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…
