The information needed to successfully select and install instruments is spread out in articles, books, handbooks, papers, and vendor catalogs and in knowledgeable individuals who do not have the time or incentive to publish.
Articles and papers tend to focus on success stories, with few details. The articles are designed more to sell than to help implement the automation system component. Even if the article or paper lists a user as the author or coauthor, it was probably written by a marketing or sales engineer of the supplier. This is not to say the article or paper does not provide valuable technical content or is misleading. These people know how to present information in a readable and understandable manner.
Books and handbooks tend to give the principle of operation or theory, which is great, but you need to move on to all of the practical considerations for a successful application. Information and guidance for instrument and equipment selection, configuration, and installation is often missing in the literature. I tried to provide guidance in my book The Essentials of Modern Measurements and Final Elements. However, the reader has hundreds of pages to read. Also, despite the author’s best efforts, some things may be missing because they were not known to be important at the time.
I decided something better needed to be done. I concluded what would be helpful would be succinct insights, rules of thumb, and checklists. In the future, all of my books will have these features. With this in mind, I have included all of my checklists to date in Appendix C of the book 101 Tips for a Successful Automation Career. The checklists ask questions to make sure you are covering all the bases. You can pose these questions to your suppliers of automation products and services or use them in searches of online publications. In the long run, you can start to realize better how to address all aspects in the selection, installation, and use of automation system components.
I personally believe the best way to present essential information in our profession involves checklists in addition to concise statements of concepts, details, watch-outs, exceptions, insights, rules of thumb, and resources exemplified in this book. For presentations, the statements should be bullet points.
Concept: The information needed to take advantage of the best technology and to address all of the considerations of an application is often difficult to find. Engineers don’t have time to dig through dozens of sources and hundreds of pages for each automation system component. Search techniques don’t help much if you don’t even know what questions to ask. Suppliers may not know your application well enough to help you make the best choice. Checklists can succinctly list the right questions to ask.
Click this link to download all checklists from Appendix C to “zero in” on what you need to know about control valves, differential pressure and pressure transmitters, inline flowmeters, temperature sensors and transmitters, pH electrodes and transmitters, PID controllers, radar level devices, trend charts, and variable speed drives.
Details: Use the key questions for control valves to avoid specifying a valve with excessive deadband, poor resolution and threshold sensitivity, and insufficient rangeability. Use the key questions for inline flowmeters to minimize drift and noise and extend rangeability.
Use the key questions for temperature sensors to minimize drift and conduction error and improve precision. Use the key questions for pH electrodes and transmitters to minimize drift and improve response and life expectancy. Use the key questions for PID controllers as to external-reset feedback, setpoint filter, setpoint rate limits, and wireless enhancement to achieve process objectives.
Use the key questions for radar level to minimize erratic signals from swirling, turbulence, and low dielectric constant. Use the key questions on trend chart compression, variables to plot, and time scale to help analyze loop and process performance. Use the key questions on variable speed drives to minimize loss of rangeability from overheating, slip, and high static heads.
Watch-outs: The checklists cannot cover all possible scenarios and the effects of harsh process conditions. For example, high temperatures can degrade sensor performance and cause premature sensor failure even though the temperature is below the supplier’s specified high limit. This deterioration is particularly significant for a resistance temperature detector (RTD) and a pH electrode. High temperatures may require remote mounting of the transmitter. Wetted materials of construction including gaskets and O-rings must meet the worst-case corrosion conditions including abnormal operations.
Exceptions: There are exceptions to every rule and every checklist. Plant practices and procedures important for a safe and reliable installation and operation are not included in the checklists. Except for pH, maintenance considerations are not covered.
Insight: Checklists can provide the questions to ask yourself and your resources.
Rule of Thumb: Make sure each question on the checklist is answered or is determined to be inapplicable.