Every day, more and more objects are being made ‘smart’ and connected to the ever-expanding Internet of Things (IoT). In order to collect the data that is the lifeblood of the IoT, these objects are fitted with various sensors depending on their function.
This article looks at eight types of sensor, what they are being used for and how they work.
1. UV sensors
UV sensors can be used for a variety of purposes from detecting the dim blue light of oil burners to warning sunbathers of harmful UV-B radiation levels (which is associated with the development of skin cancers).
There is a lot of interest in incorporating incident UV detectors into wearable technology such as smart watches. Ultraviolet light is electromagnetic energy which is of too short a wavelength (less than 400 nanometers) for most humans to see. In terms of the visible spectrum it is just above the wavelength of violet colored light, hence its name.
UV sensors make use of special types of photodiodes with PN junctions that react only to ultraviolet light. Filters are used to more accurately calibrate the diode to the specific wavelengths required.
2. Current Measuring Devices
There are two common variations of current sensing devices. One uses Ohm’s Law and the other Faraday’s Law of Induction. Ohm’s Law states that the voltage drop across a resistor is proportional to the current passing through it. Precision resistors known as shunt resistors are used to measure both AC and DC current and are relatively cheap.
Sensors based on Faraday’s Law (which relates the electromotive force in a closed circuit to magnetic flux linking the circuit) sometimes make use of a simple coil of wire known as a Rogowski coil to measure current.
Current measuring devices can be used for monitoring power consumption or as circuit breakers for safety purposes.
3. Proximity sensors
Proximity sensors detect whenever something comes close or touches them (or moves away from them). They have many uses from touchscreen technology and parking aids to rollercoasters, fluid level detectors and conveyor systems.
Two common types of proximity sensor include induction and capacitive sensors.
Induction proximity sensors include an oscillator and coil which together generate a magnetic field near the sensing device. When a metal target (actuator) comes into range of the device, the amplitude of the oscillation is dampened. A threshold circuit detects this change and alters the detector’s output signal.
What if you want to detect a non-metallic object, for example a finger on a touchscreen? In this case, you would need to use a capacitive proximity sensor. These trigger oscillations when registering a difference in capacitance between the two plates of a capacitor.
An open capacitor can be created by coating just one surface of a substrate and applying a voltage to it (creating an electrostatic field). Any substance with a dielectric different from air (a liquid, gas or even a solid like a human finger) will create a difference in capacitance.
4. Magnetic field (Hall Effect) sensors
Magnetic field sensors are used in automotive technology to measure wheel speed and determine the position of crankshafts and other components. They can also be used as a form of proximity sensor and for switches.
Most magnetic field sensors make use of the Hall Effect. This is the voltage difference created at the edges of a conductor due to the Lorentz Effect – the bending of an electrical current in response to the presence of a magnet. When a magnet approaches the sensor, the Hall Effect creates a small current which is then amplified and detected.
Another version of the sensor includes its own magnetic field which is disrupted when a metal object comes into proximity.
5. Barcode (pattern) sensors
Barcodes have been with us since the 1950s. Barcode sensors are now used for everything from applying discounts to goods and stocktaking to tracking parcels. They can be used to read both standard linear barcodes and the more recent QR codes which originated from Japan.
Barcode and QR scanners and readers all work by sensing differences in the pattern of reflected light coming from the barcode or QR code. Whereas some devices create the light themselves, others just read the ambient light.
The light is converted into a binary signal via a photodiode and this is then processed appropriately by the mobile device or connected computer.
6. Temperature sensors
Temperature sensors are important in all kinds of domestic and commercial environments from measuring room temperature in an HVAC system to keeping your oven at the correct temperature to cook your food efficiently.
Contact temperature sensors include thermocouples and thermistors. Thermocouples work on the principle that different metals have a different conductivity. Two metals are joined together and the voltage difference measured at the junction. As the thermocouple heats up the voltage changes and is converted to a temperature reading.
A thermistor is made of a semiconductor material with a resistance that is sensitive to temperature. As the thermistor heats up, its resistance decreases in a predictable (and hence measurable) way.
Non-contact temperature sensors include infra-red sensors which detect the radiation coming from objects. These are often used where temperatures would be too high for a contact sensor.
7. NIR sensors
The electromagnetic waves just below the frequency of visible light have just the right properties to make them ideal for medical diagnosis and other organic fingerprinting. This band of the spectrum is known as the near infra-red (NIR) and can be detected using low cost silicon CCD or CMOS technology. Sensors can be ‘tuned in’ to specific bands of the NIR spectrum using filters.
8. Multispectral light (color) sensors
Remote multispectral light sensors are used by drones, planes and satellites to produce detailed images containing useful geographical information. They are also used for investigating paintings and ancient writings where full spectrum light obscures important details. As with UV and NIR sensors, multispectral sensors use special materials and/or filters to restrict response to specific wavelength bands (usually three to ten).
Brent Whitfield is the CEO of Los Angeles IT Support and advice specialists DCG Technical Solutions Inc. Brent has been featured in Fast Company, CNBC, Network Computing, Reuters, and Yahoo Business. https://www.dcgla.com was recognized among the Top 10 Fastest Growing MSPs in North America by MSP mentor. Twitter: @DCGCloud