Industrial instrumentation

We have covered the basics of industrial instrumentation in my last article on this newsletter. Here we will see how these instruments are used in the industry to control, monitor, indicate or record the process variables like flow, level, temperature, pressure, pH, conductivity, weight, mass, volume etc.

An industrial instrument can be used for direct measurement of a process variable like level or temperature. For example an industrial thermometer can measure temperature at a certain point while a level gauge indicates the level in a tank or vessel etc. These are locally mounted instruments which require people to come to the location where these are installed to check out the value or process variable physically. But this is not always a convenient method though it is used as a reference for other measuring instruments.

Some process variable needs remote monitoring or control. Here we use sensors, which will sense a variable and transmit it to a local or remote location for indication, recording or control. The sensors also are categorized as direct sensing elements like thermocouple or piezo-electric sensors or transducers which convert the signals into an equivalent electrical or pneumatic signal which is then transmitted to a remote location. Though sensors and transducers are sometimes referred as synonyms but in definition these differ because of the way these work. A sensor usually transmits its signal directly as is the case of a thermocouple, RTD or Piezo electric sensor, whereas a transducer amplifies, replicate or transforms a signal to make it "transmittable" to a location remote or local.

Transmission of a signal is done from a transducer or transmitter (as is used commonly) through many different mediums including electrical (voltage or current), pneumatic or hydraulic mediums. Each one has its own advantages and disadvantages which will be discussed separately. Now with the evolving technology, smart sensors and transmitters are replacing conventional field instruments which use HART protocol or fieldbus communications, reducing need of individual field wirings to a great extent. Wireless transmission is another option and with IIoT it is even more simplified (in terms of communication) while some other disadvantages exists which we can not cover here in this post.

Whatever the case, these inputs are integrated in PLC or DCS systems to have a centralized control. Though in some cases individual control loops also exist for each process variable.

Our main aim is to provide the information for those who are new to this field and also for the seasoned ones to jog their memories. Just subscribe to this newsletter INSTRUMENTATION REVISITED and receive updated version every week. Please feel free to share it if you like it. Comments, suggestions, feedback are always welcomed.

(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)