Healthy lifestyles are growing the market for air quality sensors

Air pollution and mortality rate are closely linked. Public Health England (PHE) published a report in April 2014 that estimated the number of deaths in UK local authorities attributable to long term exposure to man-made particles less than 2.5 microns in diameter. It concluded that 8% of deaths in London (and possibly almost double this number) could be attributed to long-term exposure to particulate pollution – most of which is created by motor vehicles. All cities suffer from this kind of pollution, some more than others, depending on traffic density, other sources of particulates, weather conditions and various geographic factors.

However, particulates are not the only pollutants that damage health. Carbon monoxide (CO), excess levels of carbon dioxide (CO²), and high concentrations of gases such as propane or methane also have adverse, and sometimes fatal consequences for humans.

Some air conditioners in offices and homes no longer just operate on the basis of controlling temperature. Smart sensors also take account of humidity, particulates of various sizes and even the presence of tobacco smoke.

One US company, Sensorcon, developed a multi-sensor tool, called Sensodrone, for use with a smartphone. Funded through KickStarter, the firm describes the product as 'the world’s first mobile, wearable, programmable sensing computer' and one journalist described it as “a Swiss Army Knife of environmental input.”

Sensordrone incorporates a carbon monoxide detector, non-contact thermometer, gas leak detector, lux meter, weather station, diagnostic tool, breath analyser and more

The much-vaunted Internet of Things will involve billions of sensors from which data is processed and communicated, and new products that control and safeguard our environment will be developed in their droves over the next few years. Here are just a few examples of CO², humidity and temperature sensors.

Amphenol air quality sensors include the Telair T6613/66715 series of modules for CO² detection (right). They come in single and dual channel versions and there are complementary duct-mount or wall-mount transmitters. Humidity and temperature models of the wall-mount versions are available too. Accurate sensing results in well-controlled environments in which energy consumption is minimised, realising considerable cost savings.

Alps humidity sensors are used in everything from home appliances to health care devices. Various versions provide absolute or relative humidity measurement based upon changes in the mechanical or electrical state of hygroscopic materials inside the devices. The most popular type, the HSHCA, translates changes in humidity to changes in capacitance to produce a highly linear response without the need for temperature compensation circuits. The Alps HTUD sensor is a plug-and-play device that combines humidity and temperature sensing in one compact, DFN package.

Amphenol EMD-4000 sensors are resistive devices for measuring relative humidity. They’re used in air conditioning systems for commercial premises, homes and automobiles and have a measurement range of 20% to 95% relative humidity at 25°C.

TDK also uses resistive humidity sensing in its CHS family of humidity sensors. The products are particularly resistant to the ingress of water and various gases, and exhibit no hysteresis when measuring between 5% and 95% relatively humidity levels.

Hygrometers and air humidifiers are the primary applications for capacitive atmospheric humidity sensors from Vishay. Each sensor consists of a non-conductive foil, which is covered on both sides with a layer of gold. The dielectric constant of the foil changes as a function of the relative humidity of the ambient atmosphere and, accordingly, the capacitance value of the sensor is a measure of relative humidity. Relative humidity from 10% to 90% is measured and the devices can be used from 0 to 85°C, a wider temperature range than most of the resistive types.

Humidity sensors and humidity/temperature sensor modules are also made by Measurement Specialties. These sensors employ a capacitive cell for humidity measurement and a Negative Temperature Coefficient (NTC) thermistor for temperature measurement. They’re useful in applications where dew point, absolute humidity measurements or humidity compensation are required. 

Measurement Specialties mini-modules combine humidity and temperature sensing

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