Smart Sensors: Hot Stuff
Fire watches, or vigils, have existed since Ancient Rome. Today, instead of people, the latest generation of sensors do all the work much more reliably – and a lot cheaper. The fire detectors work together in a network and sound the alarm via the cloud and Smart Sensors.
Healthy sales volumes and highly integrated chips mean it has never been so cheap and easy to buy reliable protection against fire damage. For as little as €42, you can get an Internet-enabled IoT device with minimal energy consumption that will last ten years without maintenance.
Smoke detectors
Smart-home smoke detectors can do even more than sniff the air. In the event of a fire, all the detectors in the house will sound the alarm and absent residents will be notified by SMS or email. These systems can also light escape routes or raise blinds and shutters to facilitate rapid evacuation. Some manufacturers even populate and integrate their detector hubs with their intrusion detection systems. Monitoring is done via an app or web interface and calls for help from the emergency services can be made from anywhere at the push of a button. A fire causes minute specks of soot to be released into the air and a modern fire detector contains a scattered-light sensing chamber to monitor for these particles. In this air trap, a light-emitting diode (LED) shines light of a single color through the air in the sensor and a photodiode registers any light scatter caused by soot particles. More expensive systems use two colors, which enables the size of the soot particles to be determined. The detectors may also test for other fire indicators by measuring the ambient temperature, as well as checking he concentration of carbon monoxide in the air.
Bosch Smart Home System
Watching out for intruders as well as fire
The Bosch Smart Home system is a multi sensor infrastructure which integrates fire detection, home security, and heating controls. The Bosch Smoke Detector not only guards against fires and gas leaks but also has a motion detector which can be linked to other intrusion detectors (door or window contacts and surveillance cameras) to offer complete security. The Smart Home system uses the Zigbee wireless protocol to communicate between the numerous detectors. A Bosch Smart Home Controller gateway connects the Zigbee network to the Internet via a router, which allows alerts to be sent directly to a smartphone.
Honeywell Faast XM System
Sucking up smoke
Suction systems are the specialist units among smoke detectors. They draw in the air via a pipe system (aspiration tubes) which can be up to 320 meters long, making them ideal for use in listed buildings or rooms with suspended ceilings. In addition, larger particles in the airflow are filtered out, making suction systems suitable for use in dusty environments, such as production environments or animal enclosures. The detection chambers usually use expensive IR laser diodes (as used in DVD players) as their light source instead of the usual LEDs. This increases sensitivity and “noise” immunity enormously. The picture shows the Honeywell Faast XM system which has two scattered-light detection chambers supporting up to four aspiration tubes. Each unit can be connected directly to a local bus network and onwards to the Internet via Ethernet and TCP/IP.
Honeywell Smart4 IRX-751CTEM-W
No more false alarms
The Honeywell Smart4 IRX-751CTEM-W combines four sensor types: carbon monoxide, IR, smoke, and heat. The Smart4’s microprocessor dynamically adjusts the unit’s detection profile as it monitors the inputs from the sensors. In this way, transient “noise” can be detected and ignored to offer immunity from false alarms and improved fire detection. Aspirating smoke detectors (ASDs) use suction systems to draw air through pipes into the sensor. Application areas include listed buildings and museums or dusty environments such as animal enclosures. Intake filters remove larger dust particles which would clog the detection chamber. ASDs often use laser diodes as the light source in the scattered-light chamber to detect even the slightest particle scattering.
Flame detectors
Flame detectors are inexpensive, low-power sensors that detect infrared radiation, especially the flickering of flames. When the sensor is triggered, a microprocessor activates an alarm. More expensive systems use additional ultraviolet detectors. These IR plus UV units are more expensive but give fewer false alarms.
Bosch 420 Series Detectors
Two eyes are better than one
Based on the idea that two eyes are better than one, the Bosch 420 Series detectors boast dual-optical chambers for extra sensitivity and flexibility. All sensor signals from the chambers are continually evaluated by the internal electronics and linked together with the aid of an integrated microprocessor. Because the chambers are linked, the detectors can be used where light smoke, vapor, or dust due to operational conditions is present. Apart from fre and carbon monoxide detection, the 425 LSNi can identify the presence of hydrogen and nitrogen monoxide.
Ei208iDW Carbon Monoxide Sensor
Digital canary bird
Around a hundred years ago miners could only protect themselves from deadly mine gases, such as carbon monoxide, by using canary birds to give a warning. Today’s electronic canary is the smartphone app, such as the one from Ei Electronics. The company’s Ei208iDW carbon monoxide sensor connects to its Internet app not only to send alarms but also to provide information on air quality trends. The detector’s long-life 3 V lithium battery lasts about ten years.
Renesas SGAS711
Gassing up
There is an obvious need to detect the presence of flammable gases before their concentration levels approach explosive proportions. The SGAS711 by Renesas is a solid-state chemiresistor sensor designed to detect flammable gases in air. The SGAS711 sensor uses an integrated heater with highly sensitive MOx material tailored for detection of flammable gases. The device is ideal to be used as a methane gas sensor, propane gas sensor, hydrogen gas sensor, liquefied petroleum gas sensor (LPG sensor), and more.
At the more expensive end, thermal-imaging cameras are the newest components of fire protection. Unlike IR sensors, they are designed to detect potential fires long before they break out by helping to identify areas of sharply rising temperature. Thermal imaging is particularly useful in areas, such as hay storage shelters or waste dumps, where spontaneous combustion can occur, or to monitor the heating effect of wear and tear on machinery.
Thermal cameras may be more expensive but their advantage is that they can be used from a distance to view and protect a wider area. The resolution is much lower than visible light cameras, much less than 1 megapixel, but indicating where the problem area lies rarely requires high definition – though higher resolutions are available at extra cost.
Gas detectors
Gas detectors are often installed alongside smoke detectors to sense natural-gas leaks, which could lead to a fire or even an explosion. They are usually designed to detect poisonous carbon monoxide, too, which could be leaking from gas cookers or central heating boilers. Carbon monoxide is colorless and odorless and can cause headaches, fainting, and, in higher concentrations, death.
NXP MC145010
Setting a standard
The MC145010 microprocessor by NXP is already used in millions of homes. It has become the standard chip in low-cost smoke detectors. In a scattered-light chamber, a photodiode receives the light emitted by the internal LED. Motorola’s chip evaluates any changes in the amount of light received by the photodiode to determine if smoke is present and, on detection, the chip can cause a warning light to flash and set off a piezoelectric horn. The MC145010 can operate at voltages between 6V and12V, so it will continue to work even with weakening batteries. Its current usage is an extremely modest 12 µA which further preserves battery life.
Draeger Gas Detector
A warning from the Cloud
An industrial gas detector from Draeger can be equipped with up to six sensors. Status queries and alarms are sent via SMS if required and more-detailed data can be sent periodically via email. A cloud service records name, type, and concentration of gases and other relevant data. Optionally, gas concentrations can be displayed in an online table or a single trend on a visualization panel that can be accessed on a local network through a web browser.
Flir-One Camera
See the fire before it starts
The Flir-One camera is Flir Systems’ entry-level model to the world of thermal imaging. It is intended for service engineers who want to get an at-a-glance overview of overheating, defective components so they can intervene before a fire breaks out. The camera connects to an Android or iOS smartphone’s USB socket, allowing photos and videos to be sent from the field. The resolution is 160 pixels by 120 pixels and the camera can record temperature differences of up to 0.1°C.
Some detectors also monitor for sound changes to detect the ultrasonic noise created as pressurized gas is forced through a crack in a pipe. Early warnings would mean that remedial actions could be taken before a buildup happens.
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