Types of smart building sensor and how they work
The world of smart building sensors can be a confusing one. There are lots of different options out there and there’s a whole lot of information too – ranging from the very basic to the impossibly technical.
We’ve put this list together to introduce the various types of sensor available and explain the main benefits of each.
Types of smart building sensor:
Simply put, temperature sensors measure heat to detect changes in temperature. They’ve been used for years to control things like heating and air conditioning but, thanks to the emergence of the Internet of Things, have found many more uses.
For example, many machines used in manufacturing and computing are sensitive to temperature and have to be protected from overheating. With smart temperature sensors, businesses can automate heating, ventilation and air conditioning controls to maintain ideal conditions and automatically detect failure or faults as they happen.
Not only is the right temperature vital to people’s comfort, it can also prove dangerous. Anyone in control or a business premises or renting out a property has a responsibility to reduce the risk of exposure to legionella. The bacteria can spread in hot and cold water systems and can thrive if water in any part of the system is between 20 and 45°C.
There are four types of temperature sensor:
- Semiconductor-based sensors: Placed on an integrated circuit, these identical diodes use temperature sensitive voltage compared with current conditions, allowing them to record changes in temperature.
- Thermocouple: As the name suggests, this consists of two wires – these are made from different metals and placed a different points, with the change in voltage between the two points showing change in temperature.
- Resistance Temperature Detector: A film or wire is wrapped around a ceramic or glass core, with temperature measured from the resistance between the element with temperature. These tend to be the most accurate type of sensor, but can also be the most expensive.
- Negative Temperature Coefficient Thermistor: Providing high resistance at low temperatures, as temperature increases resistance quickly drops – reflecting changes quickly and accurately.
Humidity, also known as relative humidity, is defined as the amount of water vapour in the atmosphere. Just as many machines don’t tolerate certain temperatures, humid conditions also present difficulties. Too much moisture in the air causes condensation, which can cause some machinery to corrode.
Humidity sensors let you maintain ideal conditions and take action straight away if there’s a change. In homes and businesses they’re used to control heating, ventilating, and air conditioning systems. They’re used in manufacturing plants, hospitals, museums, greenhouses and weather stations – any environment that’s sensitive to moisture.
There are three common types of humidity sensor:
- Capacitive: With a porous dielectric substance at the centre, surrounded by two electrodes, the sensor uses water vapour to monitor humidity – when the vapour reaches the electrodes it creates a voltage change.
- Resistive: Less sensitive than capacitive, they operate on a similar basis, using electrical change to measure relative humidity. However, they use ions in salts to measure this change to resistance on the electrodes.
- Thermal: Two matched thermal sensors conduct electricity based on humidity of the air surrounding them. One is coated in dry nitrogen, the other measures ambient air – with the difference between them measuring the humidity reading.
Motion / occupancy sensors
Motion sensors pick up on physical movement – whether that’s a person, animal or object – in a given area and transform that information into an electric signal. Motion detection has been used in the security industry for years to alert businesses to intruders. They’re found in appliances we use every day, like automatic doors, toilet flushes and hand dryers. And they can also be used to automate building controls like heating and lighting depending on whether or not a space is occupied – helping to reduce both energy consumption and running costs.
Lately though, they’ve found a further use: helping businesses understand how rooms and spaces are used. By detecting the presence of people or objects in real time, occupancy sensors allow organisations to understand which spaces get the most use, or know which desks or meeting rooms are available at any one time. In a large organisation, being able to use space more efficiently can lead huge cost savings, not to mention increased productivity.
Motion or occupancy sensors work by detecting infrared energy or by sending out ultrasonic waves or radio waves and measuring their reflection off a moving object. We currently supply under-desk passive infrared (PIR) motion sensors. This small, wireless device two slots made of a material that’s sensitive to infrared light. When the sensor is idle, both slots detect the same amount of ambient infrared radiation. When a person enters the sensor’s field of view, the movement reaches one half of the sensor before the other. It’s this change between the radiation detected by the two slots that tells the sensor someone is present.
There are four types of motion detector sensors, which can be used in different ways:
Motion sensors or passive infra-red (PIR)
These sensors work by detecting heat emitted by people. When a person enters a sensor’s field of view, the sensor detects motion and tells you someone is present within that space. The sensor continues to monitor the space and can send you regular occupancy updates. These types of sensor are GDPR and privacy-compliant solutions as no images or personal information is stored or transmitted. Our PIR sensors come in varying forms, some as units which stick to your walls or ceiling, others which are placed under desks. They are unobtrusive, easy to install, low maintenance and a great cost-effective option.
- Desk occupancy sensors: These simply stick to the underside of a desk. The PIR sensor has a hood covering half of the sensor, so only detects motion within a 180-degree radius. Coupled with a narrow-angle lens, this makes it highly accurate, detecting just a person under a desk, and not people walking behind or to the side of it.
- Table occupancy sensors: Similar to desk sensors, these stick to the underside of a table and use a narrow-angle lens. However, the PIR sensor detects motion within a 360-degree radius, so can detect people sitting around a table. Based on average table height, the detection range is 0.5m.
- Room occupancy sensors: These stick to the ceiling and have a 360-degree field of view and use a wide-angle lens to detect people within a wider field of view. Based on a typical 2.5m ceiling height and 64-degree detection angle the estimated detection range is 5m.
- Cubicle occupancy sensors: As with desk sensors, these detect a 180-degree view, so can be placed on a wall or ceiling of a cubicle to detect people within that space and avoid those walking past. These are great for toilets or meeting cubicles.
Emit an infrared light beam that reflects off a person and returns back to the sensor, the time taken to return gives an accurate distance calculation. The sensor uses these measurements to determine if the person is moving towards or away from the sensor, making it an effective entry/exit sensor.
- People-flow sensors: Detecting people and the direction of movement, these can be used to monitor real-time people flow in and out of any single-occupant doorway. Bi-directional, they detect people as they walk towards or away from the sensor, so you can determine the number of people in a space. These only detect movement, not faces, and they are not cameras, making them privacy and GDPR compliant.
Infrared array sensors
These sensors allow you to detect moving or motionless objects, temperature distribution, thermal image, and moving direction by measuring the temperature as a person or object moves nearer or further away from the sensor. As the distance from the sensor increases, the field of view expands but angular size appears smaller. As the proximity to the sensor narrows, the sensor can detect accurate temperature and shape.
- People counter and movement sensors (coming soon at Pressac): Detect the number of people within a space, exactly where they are within that space, and how they move around. Only detecting people movement, these sensors are privacy and GDPR compliant.
Contact sensors are also known as position or status sensors, or building monitoring sensors. Contact sensors are a simple way to tell whether a door, window or other similar mechanism is open or closed.
The sensors come in two pieces – one that’s fixed to the door or window and another that’s fixed to the frame. The two parts use magnetic fields to detect when they’re touching (meaning the door or window is closed) and when they’re moved apart (as the door or window is opened).
For a range of reasons, including safety, security and energy efficiency, it’s useful to know what’s going on around your building at any one time. Building monitoring using contact sensors lets you see the live status of doors and windows around your building, including doors on cupboards, cabinets and fridges. You can automatically detect unlocked doors or cabinets, open or broken windows or a presence in a room, and automate building controls based on live occupancy.
Gas / air-quality sensors
Gas sensors are used to monitor changes to air quality and detect the presence of various gases. They’re used to monitor air quality, detect toxic or combustible gases, and monitor hazardous gases in manufacturing, pharmaceutical, petrochemical and mining industries. Depending on use, you could monitor carbon dioxide, carbon monoxide, hydrogen, nitrogen oxide, oxygen, air pollution or gas.
While many applications are concerned with safety, the effects of poor air quality aren’t always severe, or even that easy to spot. In today’s well-insulated buildings, rising carbon dioxide levels can lead to stale, stuffy air and complaints like tiredness and headaches. It can affect people’s comfort and wellbeing as well as productivity. And seeing as employers have a responsibility to provide a healthy working environment, it’s not surprising more businesses are using environmental monitoring to maintain temperature and air quality.
There are three common types of air quality sensor:
- Oxygen: This electrochemical sensor can detect any gas which can be oxidized or reduced electrochemically.
- Carbon Monoxide: This is also an electrochemical sensor which operates in a similar way to the oxygen sensor.
- Carbon Dioxide: An infrared detection sensor, this transmits an infrared beam through a light tube, detecting how much of the beam’s energy is left and converting to carbon dioxide levels.
Electrical current monitoring sensors
Electrical current (CT) sensors measure real-time energy consumption at a circuit, zone or machine level. Knowing how much energy is being used has two main uses. Firstly, you can identify where you use and waste the most energy, allowing you to make savings. You can also automatically switch off assets when they’re not in use.
Secondly, if you can recognise normal operating conditions you can also see when machinery isn’t functioning as well as it should. For example, a higher-than-average operating current could tell you that a motor has been overloaded. This insight means you can schedule maintenance when it’s actually needed rather than pay for routine inspections. You can also fix potential problems straight away and keep unplanned downtime to a minimum.
Types of CT sensors:
- Split core: These can be opened and fitted around a conductor, so are ideal for existing configurations.
- Hall Effect /DC: These sensors use what’s known as the Hall Effect to measure both AC and DC current, measuring the changing voltage when a device is placed in a magnetic field. They can be be either open or closed loop. Open loop are compact, low cost and accurate, closed loop offer fast response and low temperature drift.
- Rogowski coils: Flexible current transformers, these are easy to install. A thin coil threads around the conductor and is snapped closed.
- Solid core: Best for new installations, these sensors are complete loops with no way of opening. They are renowned for their high levels of accuracy.
Other types of sensor
While we don’t currently offer these sensor types as off-the-shelf products, we can work with you to develop bespoke solutions – read up on our design and manufacturing capabilities to find out more or use our contact form to get in touch.
- Optical sensors measures electromagnetic energy including electricity and light. They’re used in industries such as healthcare, energy and communications to monitor variables including light, radiation, electric and magnetic field and temperature.
- Proximity sensors, much like motion sensors, detect the presence of an object and measure how close it is. One of the most familiar uses is reverse parking sensors in cars.
- Pressure sensors detect pressure and alert the system administrator of any deviation from the standard pressure range – similar to machine monitoring. This is useful in manufacturing as well as in water and heating systems.
- Water-quality sensors are used in environmental management to measure chemicals, ions, organic elements, suspended solids and pH levels in water.
- Chemical sensors detect the presence of chemicals in water or air. They’re used to track air and water quality in cities, to monitor industrial processes and to detect harmful chemicals, explosives and radioactive materials.
- Smoke sensors detect levels of airborne particulates and gases. While they’ve been around for a while, the development of IoT means they’re now able to notify users of problems immediately.
- Level sensors determine the level of fluids, liquids or other substances in an open or closed system. They’re mainly used to measure fuel levels, but are also used to measure sea and reservoir levels and in medical equipment, compressors and hydraulics.
- Image sensors can be found in digital cameras, medical imaging and night vision equipment and biometric devices. They’re also used in the car industry and play an important role in the development of driverless cars.
- Accelerometer sensors detect vibration, tilting and acceleration in an object. Uses include anti-theft devices, vehicle fleet monitoring, aircraft and aviation industries and consumer electronics, including smartphones and pedometers.
- Gyroscope sensors are used together with accelerometers and measure angular velocity, defined as a measurement of speed of rotation around an axis. Their main applications include car navigation systems, game controllers, robotics and consumer electronics.
Editor’s note: This post was originally published in 2019 and has been updated for comprehensiveness. Originally published Mar 4 2019, updated October 13 2020.