Sensors and Sensibility

Sensors and Sensibility

In machine and process automation, we use sensors. Sensors are eyes and ears of equipment and machines. Though they are there from years working mostly hidden behind the facade, because of IIOT they have come to the forefront.

Sensors are of different types. Some are contact types; some are non-contact types. Normally, limit switches are by design, contact types to provide positive hard stops.

Other than limit switches there are several non-contact type sensors. Most commonly used are proximity sensors which we call proxy, in short.  They can be of different types e.g., capacitive, inductive, or photoelectric- based on the source they are using. Photoelectric sensors may use infrared, Ultraviolet or fibreoptic as sources. Proxies are mainly used to detect a presence (or absence) of an object. Sometimes they are used to measure the distance.

In process equipment, there are height or level sensors. They are also of various types: from very basic mechanical or float type to incrementally sophisticated like vibratory fork, capacitive or ultrasonic level sensors.

Other applications will need specific sensors like temperature (thermocouple), pressure, piezoelectric, motion, vacuum, weight (strain gauges, load cells), camera vision sensors, etc.

Sensors can be analog or digital based on measuring and output signals.

Apart from them there are special sensors.

We, as industrial engineers know and use all the above sensors. However, many a time these sensors come pre-installed on the process equipment or packaging machinery from the Original Equipment Manufacturers (OEMs). Thus, we don’t have to look into gaining knowledge at the time of their installation.

But, after the warranty period is over, if something goes wrong in the machine or equipment- our shopfloor persons start to struggle. Instead of finding the root cause, they call the OEM technicians. Most of the time, they take a few minutes or an hour to set the thing right. However, the time of getting the technician and the hassle associated with it cause us heartburn.

Based on experience, it has been proven that most machine problems happen because of malfunctioning of the sensors. However, in all these cases sensors, per se are not to blame. Sensors are mass manufactured and rugged enough. So, seldom do they become defective. However, we as human beings are prone to first blame the machine quality and then the sensors.

Most of the time, the actual culprit is the environment. It can be extra dust, machine vibration, mounting bracket, cable break, excessive heat, humidity, chemical corrosion, product deposit, calibration shift, etc. are the root causes.

In the next series of posts, I will cover different aspects of sensors and their sensing-with particular emphasis on process equipment and packaging automation. Makes sense?

Soumik Nath

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