A quick recap....

Today, we will not discuss any new basics of industrial instrumentation, but will catch up with what has been discussed in our previous articles so far and what we have coming in the next few articles.

The first article was about what is automation in general and why it is used in the industry. So once the basic concept of industrial automation is cleared we could move forward to see, how the system SEE various process variables and then control, indicate, record or accumulate the data for the certain process variable. In this context, we have seen different industrial process variables most common like flow,, pressure, temperature and level, though there is a wide range of variables which are monitored, and controlled in process industry as well.

Our first target was to evaluate different industrial flow measuring techniques which are more commonly used to measure flow of a fluid. Unfortunately, the first article in the series got missing. which discussed the basic differential pressure measurement using an orifice plate and venturi tubes. (it will soon be republished). As we went through the series of articles, variable area flow meters and velocity meters (2nd article in the series), positive displacement type meters, then magnetic and ultrasonic flow measuring methods, target meters, Coriolis flow, optical flow measurement and in the final article thermal mass flow and multiphase flow meters which are the latest but not the last inclusion were discussed.

Then before we moved to the next common industrial process variable, some doubts raised by our readers were addressed when we discussed the instrumentation evolution through time in industry. Process instrumentation, Safety instrumented Systems, Analytical and fire and gas plus building management systems were discussed. These areas overlap in many cases and hence a precise definition cannot be concluded.

In the next articles we saw how the field instruments are classified as local and remote based on the sensing device used and how signals generally got transmitted from the field to the main control room. This topic is detailed in our recent article series where we talk about basics of industrial instrumentation signals.

The pressure measurement in industry has a very crucial part. Its proper measurement, indication and control is important for plant and personal safety. Uncontrolled over pressure can cause big damages, as can under pressure or creation of vacuum, which can collapse a process. Hence we saw many local and remote basic measurement type of instruments for pressure which include manometers, barometers, pressure gauges and the criteria for material selection for these instruments. Also we have discussed electronic means like strain gauges, LVDT and capacitive probes for pressure detection. The different pressure types also have been our topic of discussion in the fourth article of this series.

Temperature an other important parameter being measured in industry is also discussed where we have seen the basic methods of measuring it locally and remotely using mechanical (thermo-bulbs, bi-metallic elements & thermometers) and (thermocouples, RTD, thermister etc. ). Optical and radiation type pyrometers are also discussed in this series in addition to the types, and methods of thermocouples, two three and four wires RTD configuration and their different types as well.

Last but not the least, level measurement series comprising of eight articles discussed variety of industrial level measurement techniques from simple ball and floats to more common displacers and differential pressure measurements, to radioactive and radar based level measurement devices in the industry.

As each application has its own pros and cons, so in industry when measuring weather level, temperature, pressure or flow due consideration must be given to the process and fluid or material being measured, to select appropriate measuring instrument suitable for the particular case.

Finally we have seen the way these signals are transmitted in the earlier industrial revolution (Industry 1) to modern era (Industry 4) which in future may utilize newer techniques as the technology advances at a very fast pace . All these articles have touched the basic concepts so far, and as we go into details in future things will be elaborated more.

Now what next?

In our upcoming articles first we will be discussing basics of final control elements which most commonly are control valves, but are also variable frequency drives, speed controlled conveyors and many more. Any finally after that the brain of the control system which is a controller, receiving a measured value from field, and controlling it according to a set parameter or set point by sending an output signal to the final control element which will be manipulating the variable to achieve a desired process condition. This is also the ultimate target of any control system strategy to control process parameters automatically with minimal human intervention. The DSC or distributed control systems or PLC based system all break down to single loops control when we are talking about process control systems. Then we will be discussing a variety of complex loops like cascade, ratio or three element control just to name a few.

In this article as we recapture the basics, we have now concluded what we have learned so far and what is next in the pipeline. If someone has missed any part, one can refer back to the relevant article for reference and understanding. Instrumentation is now such a vast field that just covering basics might take up a long time. However we will be delivering the concepts each week for the professionals of our field (seniors) to jog their memories, and to fresher for clearing their concepts if there are any doubts.

Newsletter INSTRUMENT REVISITED is about providing general information about the industrial instrumentation aspects. Feel free to share it if you like it. Also suggestions, comments and feedback will help to improve the articles.

(Please note that though the accuracy of the information provided here is based not only on reliable sources, but also based on personal experiences, but it is for providing a general picture and the author is not liable for any loss or damages arising from the use of this information in any instance)