Introduction Instrumentation and Process Control

Sensors to measure process conditions and valves to influence process operations are essential for all aspects of engineering practice.  Engineers want to design and operate processes that remain in safe conditions, produce the desired amounts of high quality products and are profitable.  Therefore, engineers must provide measuring devices for key variables and valves (or other devices, such as variable speed electric motors) to influence of “steer” the process.  This site provides educational material on sensors and valves for use in the process industries. 

While sensors and valves are important in all aspects of engineering, they assume greatest importance in the study of automatic control, which is termed process control when applied in the process industries.  Process control deals with the regulation of processes by applying the feedback principle using various computing devices, principally digital computation.  Process control requires sensors for measuring variables and valves for implementing decisions.  Therefore, the presentation of this material is designed to complement other learning topics in process control. 

Since successful process control requires appropriate instrumentation, engineers should understand the principles of common instruments introduced in this section.  The descriptions in this section cover the basic principles and information on the performance for standard, commercially available instruments.  Thus, selection and sizing of standard equipment is emphasized, not designing equipment “from scratch”.

Perhaps the best advice for engineering students is that “instruments are always incorrect”.  This surprising statement is not intended to undermine reasonable confidence in applications of sensors and valves.  However, new engineers sometimes tend to accept instruments as exactly correct without evaluating the likely errors associated with their use.  Depending on the instrument, the process operating conditions and the application, the instrument errors can be small enough to be insignificant or can be large enough to seriously degrade control performance.  The engineer must evaluate each application during the process design and select an appropriate instrument.

Lets remember that chemical engineers work in a wide range of industries: chemicals, pulp and paper, microelectronis, mineral processing, metals production, polymer processing, power generation, and more. Perhaps, many of the details on sensors and valves might not be applicable to every industry. However, the principles used to select the appropriate sessors and final elements can be applied to essentially all industries. Therefore,

The Material in this document is gathered from a large array of public-domain sources, and it provides a good introduction to the principles of common instrumentations and a summary of they key features important for control application. However, many important sensors are not addressed here, and new equipment is becoming available. Therefore, readers should gather information used to specify, procure, install, and maintain industrial equipment from reliable and up-to-date sources, such as testing laboratories, engineering handbooks, professional and industrial organizations, and equipment suppliers

The following topics are addressed at this site.

2.         Sensors
3.         Valves
4.         Signal transmission for process control
5.         Instrumentation safety
6.         Control equipment cost
7.         Process Drawings
8.         Solved examples
9.         Terminology
10.        Conclusions
11.        References 

Each section contains valuable introductory material and links to excellent resources on the WWW for further study and solving open-ended problems in university courses and industrial practice.