Understanding Sensors

The desire to know about the truth from afar had been our endeavor from long ago. Dhritarashtra, in Mahabharata, had Sanjaya to relay to him all the information about the battlefield. More recently, in the last century, a lot of efforts and resources were devoted just for this purpose: ability to monitor remote locations. Earlier, paper traversed across continents on ships but now, we have every second of a cricket match in any city of the world, along with all data about the play, flashing on all connected screens which happen to be available with us at that moment.

Sensors play an important role in sports. DRS with the real-time Snickometer has claimed many batters. Cameras are now very inexpensive and available with anyone who has $10 to spare. Motion sensors control lights in offices and homes. A $30 smartwatch has an accelerometer, a gyroscope, a heart rate monitor, a GPS, and a barometer! A decade back, these were expensive and would certainly not sit on your wrist while you swim.

All these are not possible without inexpensive sensors coupled with wireless technology and IoT. While we may not realize it, there wouldn't be a day when a sensor had not made our lives better.

But when did we first encounter a sensor?

The Thermocouple - World's first sensor

The world got its first sensor when, much to the excitement of the scientific community back in 1821, Dr Seeback discovered the thermoelectric effect. Today's appliances like the egg boiler, the rice cooker, the electric geyser, etc. in our homes use a simple bimetallic strip switch based on this 200 year old technology, which has made our lives very convenient.

Our senses fail us in the modern world!

By 1885, the industry, like the cement industry, measured temperature using a more accurate platinum based thermocouple. It's made of two different metal wires that form a junction, and when the junction is heated or cooled, a small proportionate voltage is generated in the thermocouple's electrical circuit. This voltage can be calibrated to give an accurate reading of the temperature of the process.

The need for accurate measurement of temperature arose as we wanted to sense beyond what our senses could - process temperatures could be a few hundred degree Celsius or more. The output cement quality depended on our ability to sense the temperature accurately and take appropriate action.

With the onset of the industrial revolution, it was clear that:

• We need to sense beyond our senses (high temperatures, x-rays, current, pathogens, chemicals, etc.)
• We need to be accurately report the values of things being sensed (current, chemicals, temperature, etc.)
• We need to interpret the meaning of several sensors (numbers, kinds) and the relationship between them
• We need to take timely action based on them: generate alerts, notifications and / or take action
• All this we may need to do automatically and periodically - perhaps several hundred times a day!
• And the brains will need to reside on the cloud, like a virtual conductor of an orchestra, which plays every note with precision, accuracy and timing!

How to choose the sensor for your IoT project

Today, sensors are purpose built for applications where they are used. Price should not be the key outlook. An expensive sensor may not be the right one - perhaps a very low cost alternative is a better choice. For example, if deployment is not very difficult, a thermistor based sensor serves the purpose in several cases and it costs just a few cents. But for some other applications, while a thermistor can serve the purpose, but deployment and the environment may not be very conducive for using just a thermistor. We may need to complement it with wireless modules or we may need a Optical Fiber based of sensor (say, to measure pipeline temperature for several kms) which are more costly, but makes the project viable.

Based on my experience, one should keep the following in mind while buying sensors:

• Deployment ease: The utility of a sensor increases manifold when the location is not easily accessible. It could be in a motor which is underground or a pipeline going through a forest. Hence deployment ease is a key consideration.
• Durability: Not all application need a durable sensor - some are also the inexpensive kind. All sensors in my car are durable one certified for automotive use. The cars environment and my safety concerns dictate this and there are regulations to be complied with. However, the sensors in my child's toy car need not be.
• Maintainability: I would not like to be bothered with sending an engineer to difficult locations (remote factory, inaccessible areas), hence I would use a sensor device which is remotely maintainable. I would not penny pinch in such cases.
• Accuracy: Some processes may need a 0.1% accuracy class sensor and another might be fine with a 5% accuracy. I choose my sensor accordingly. Why would I use a 0.1% accuracy sensor where I do not need it? I would not like to waste money on such an accurate sensor.

I believe we are getting a hang of sensors and how to go about selecting one. Have you ever come across someone who has deployed a wrongly chosen sensor? What was the use case and why was the selection incorrect? Let us know!

In the next edition, we will go a little deeper in this topic of sensor appropriateness and the impact it can make from a commercial and utility standpoint.

Do leave behind your comments and suggestions.