Author: John Mulindi
-
How to Minimize Water Vapor in Instrument Air/Pneumatic Systems
Water is one of the most common contaminants in instrument air systems, causing corrosion of metal components and as a result clogging of orifices. Special devices referred to as air dryers installed in instrument air systems use solid materials called desiccants to absorb water entrained in the compressed air. The desiccant material is “regenerated” by…
-
Key Requirements for Industrial Control Computers
A computer is often used as part of a control system. The input data is typically from the operator’s commands and signals from the plant (flows, pressure, temperatures, limit switches, etc.). The output data comes in form of control actions to the plant and status displays to the operator. The instructions fed into the computer…
-
A Basic Introduction to Ladder Diagrams for PLC Programming
The ladder diagram which is a special type of wiring diagram consists of two power rails, which are placed vertically on each side of the diagram, and rungs, which are placed horizontally between the power rails. The power rails are the source of power in the circuit (ac or dc), where the left rail is…
-
What are Control and Instrumentation Cables?
While power cables are what we can refer to the “arteries” of industry, control and instrumentation cables are its “nerves” and are used for the control of equipment and data collection. They range from switch-core cables utilized in the wiring of control panels and switchgear, to the complex control and instrumentation cables employed in power…
-
The Goals of Robust Control Techniques
Robust control is normally used to handle systems with uncertainties & disturbances and with high performances. The objective of robust control is to be able to design controllers that achieve a desired level of performance and also, be able to handle a collection of uncertainty structures specified by the designer. A typical approach is to…
-
Basic Elements of an Electronic Instrument
An electronic instrument is made up of the following key elements: Transducer This is the first sensing element and is needed only when measuring a non-electrical quantity such as pressure or temperature. Its task is to convert the non-electrical physical quantity into an electrical signal. An example of a transducer is a thermocouple for sensing…
-
Key Causes of Uncertainty in Control Systems
One of the objectives of a control system is to achieve good plant performance in the face of uncertainty. The major sources of uncertainty in control are: Unmeasurable Perturbations Unmeasurable perturbations produce output deviations. With a controller in place, the achieved deviations must be below a user-defined bound. Modelling Errors Modelling errors can be classified…
-
How Synchros are used as Position Transducers
Let’s consider the transformer in Figure 1.0 whose secondary winding can be rotated with the respect to the primary winding. At an angle ϴ, the output voltage will be given by: Vo = KVicosϴ where K is a constant The output amplitude is dependent on the angle, and the signal can be in phase or…
-
Centralised vs. Decentralised Control Systems
Centralised control is usually carried out via computer software, having as inputs all the available sensors and producing signals for all the available actuators in the system. This control strategy is the most powerful, at least in theory, capable of extracting “optimal” performance. However, in practice, it requires non-standard apparatus (industrial computer data acquisition cards,…
-
Actuators as Automation Components
An actuator is normally controlled by the controller. The actuator, in turn, changes the output of an automated process. The actuator in an automated process may in actual fact be several actuators, each of which provides an output that drives another in the series of actuators. Let’s consider the hydraulic actuator that controls the position…