Even if you don’t always notice it, sensors are part of our everyday life. It’s them who tell you to make a stop at the filling station, it’s them who open the doors at the grocery stores and take a guess, who warns you when you’re out of coffee beans in the coffee machine?…attaboy, it’s them again. So, in this article, we’ll dive a bit deeper and discuss what a sensor is, what it can do and find out its various industrial applications.
What is a sensor?
I am probably not revealing any secret by telling you that a sensor is a device meant to sense something…crazy, right? But scientifically speaking, a sensor can be defined as a device that detects changes in electrical, physical or chemical states of the environment and reacts with an electrical output.
It is alleged that humans have at least 6 senses, and sensors aren’t that far behind. Of course, there are no devices with intuitive or supernatural powers but, nowadays, we have sensors that can hear, see, smell and even taste.
Technological types
Sensors can be classified by type, size, accuracy, or even color if you want, but let’s focus only on a few aspects.
Based on the nature of the detected properties they can be tagged as temperature, pressure, position, level, speed and many other sensors. Here are some examples:
Temperature:
- Thermocouple – based on the Seebeck effect, a pair of dissimilar metals in contact with each creates a small voltage potential at temperature changes.
- Resistance Temperature Detector (RTD) – based on the variable electrical resistance of a conductor at different temperatures.
- Thermistor – semiconductor element whose potential drop depends on ambient temperature.
Applications:
- Industrial temperature monitoring
- Electrical motors and turbines
- Pharmaceuticals
- Fire alarms
Pressure:
- Gauge strain – being properly aligned and glued onto a surface, the resistance changes when external forces are applied. The same principle is used for weight, load, vibration and other measurements.
- Solid state – built with a hermetic all stainless steel diaphragm which is subjected to external pressure.
- Capacitive – detects changes in electrical capacitance caused by the movement of a diaphragm.
Applications:
- Oil and gas industry
- Food processing
- Precise scientific measurements
- Automotive engine applications
Vibration:
- Piezoelectric – a piece of quartz crystal put under stress releases a stream of electrically charged particles that can be measured.
- Strain gauge – same principle as for pressure measurement.
- Eddy Current – measures the position of a conductive component based on magnetic fields.
Applications:
- Radial and axial vibrations in shaft alignments
- Aerospace
- Electronics
- Transportation
Position:
- Inductive/Capacitive – detect the position of an object by changes in the characteristics of the magnetic field.
- Hall Effect-based – based on the unequal distribution of electrical charges placed in a magnetic field.
- Optical – consists of an emitter and receiver which analyses the parameters of the light beam (wavelength, intensity).
- Ultrasonic – same as the optical one but uses high-frequency sound waves instead.
Applications:
- Alarm systems
- Smoke detectors
- Automatic door openers
- Conveying and assembly lines
- Robotics
Functional types
From the perspective of the operating principle, a sensor can be either Active or Passive. The only difference between them is that a passive sensor requires an external power supply while the active one generates the signal based on internal physical processes.
Examples:
- Thermocouple
- Piezoelectric
- RTD
- Strain gauge
Reading a sensor
It’s all fun and games until you get to read the measured values. The main problem is that most sensors provide very weak measuring signals, for instance, a thermocouple’s voltage will vary only 10mV over a 200℃ temperature deviation (see proofs below).
You might say “Hey, that thing barely measures any temperature!”, and you would be absolutely right but that’s not a problem for an industrial controller. Moreover, in control systems a wide range of analog values are acquired based on a 4-20 mA current range, that’s 10 times less than what a light bulb consumes (you should be impressed). Now the only thing left is to scale the electrical value according to the datasheet kindly provided by the manufacturer and you’re good to go, thanks mister controller – you’re the best!
Summary
Okay, let’s sum up now…
- There is a mind-blowing range of sensors and even more applications for them.
- This technology and automation in general are constantly evolving, so the rise of the machine might be not so hypothetical, think about it.
- I didn’t use any formulas whatsoever not to annoy you or cause any school physics flashbacks, you are welcome.
That’s all folks! It was supposed to be fun, so don’t disappoint me 😀