MEMS sensors play role in LED lighting revolution
By Fabrizio Petris, Omron Electronics
LED lighting system costs can be reduced with good control circuit design and component selection.
More and more commercial contractors are installing low-power lighting in the drive to reduce energy costs and shrink carbon footprints, but automation and intelligent control offer further savings by switching off services in unused areas
Lighting accounts for about 25% of the commercial building sector’s energy use and, although it is less significant in the home, this remains one of the easiest ways for end-users to reduce their costs. Switching to less power-hungry light sources, such as compact fluorescent lighting and LEDs, is having a huge impact on energy use and cost, but domestic and business users can reduce costs further by improving control and applying automation.
Implementing automation in the home or office can reduce lighting consumption by up to 50 per cent according to market intelligence firm Pike Research, and the savings can be even more dramatic in warehouses and industrial plants. Not surprisingly, the global market for intelligent lighting control is set for very strong growth, doubling to $2.6 billion by 2016.
Lighting controls offer significant potential for reducing that energy use, and new sensor, switch and relay technologies are making a wide range of innovative strategies possible, from room-level awareness of occupancy and daylight sensing, to building-wide coordination of a fully networked system.
Perhaps the greatest potential for energy savings comes from the ability to automatically switch lights off when they are unnecessary and on when they are required. This is the drive behind a resurgence of interest in infrared sensors.
According to a 2012 report from the market research organization Yole Développement: “Even if this motion detector business is mature, it will continue to grow at a significant rate (CAGR 2010-2016 in value: + 9 %) driven by the concern for energy savings”. The overall IR detector business is predicted to expand from $152m in 2010 at a rate of + 11 %/ year to reach $286m in 2016.
New infrared sensor technologies, capable of detecting stationary heat-emitting objects, are able to take a larger share of the opportunities this growth brings by occupying territory inaccessible to the familiar PIR detector, traditionally used for presence detection in home and building automation systems.
The reason is this: PIRs use the pyroelectric effect to sense people or animals in its field of view and, as the pyroelectric phenomenon is a temporary change in a material’s structure during heating or cooling, the detection circuitry depends on measuring a difference in the heat pattern. It is only detecting motion rather than presence.
Absolute vs. relative – quite a difference
New thermal sensors based on microelectromechanical systems (MEMS) do not suffer this disadvantage. MEMS thermopiles, essentially nano-scale arrays of thermocouples, measure the actual temperature of the sources rather than a differential value, so they detect people in a room even when they are not moving. Presence detection opens whole new applications that motion-detecting pyroelectric sensors cannot touch.
For example presence detectors can be used as inputs to lighting, reliably switching to energy saving modes when there are no people in the zone that is being monitored. Indeed the applications extend out to heating, air-conditioning and security systems.
Arrays for more accurate position
MEMS sensors, like Omron’s D6T, measure temperature across the whole field of view. Compare that with conventional thermal sensors, which are restricted to measurements at a single point.
Configured as an array (1x8 and 4x4 arrays are available currently), the sensor can assign temperature information to a specific cell, adding a positional dimension to its presence and temperature data. The result is higher accuracy, lower crosstalk and a wider field of view. Using several sensors in a room multiplies these benefits: a quad 4x4 array sensor module can be used to obtain higher resolution or broader coverage, for example, identifying a person’s location within 1m across a 16m² area.
The technology behind these new thermal sensors combines a MEMS micro-mirror structure for efficient IR radiation detection with a high-performance silicon lens to focus the infrared rays onto its thermopiles.
Proprietary application-specific integrated circuits then make the necessary computations and convert sensor signals into meaningful digital outputs. The result is +/- 0.14 C° resolution with noise immunity (measured as noise equivalent temperature difference) of 140mK.
Larger 16x16 MEMS sensor arrays are currently being developed, which will provide finer lighting control, especially in open space environments.
Coping with inrush currents
Although presence detection offers the greatest potential to improve lighting automation, innovation in switches and relays also presents substantial prospects.
For example, the high inrush currents and long lifetimes of modern lighting installations pose new challenges for switch and sensor makers. Switching fluorescent lamps in particular need to handle the high peak of current when a lamp turns on.
Capacitive loads are even more critical: a capacitor connected in parallel with a lamp driver is a very common circuit configuration, also for LEDs, and the peak of current generated from its discharge can easily exceed 10 to 15 times the rated current. Designing-in the wrong relay can drastically reduce the life of the whole system.
Relay manufacturers are rising to the challenge with advanced materials for contacts. Consider, for example, the use of a Silver-Indium-Tin alloy, which is extremely hard, has a high melting point and exhibits excellent resistance to arcing and welding - making it ideal for high inrush loads. A further advantage is that the alloy is cadmium-free so meets RoHS requirements.
These Ag-In-Sn contacts enable relays, depending on the models, to handle up to 100A inrush current, even for fluorescent or tungsten lamps. A 16A relay is suitable for all types of lamps available in the market, from fluorescent to LEDs, though lower-capacity relays can be specified for some lighting applications.
Smaller and quieter relays
Growing use of power saving LED means there is less need for 16A capability, which means that lighting control systems can take advantage of the size-reduction innovations that come with lower power consumption. Compact and slimline relays are especially useful in the switching modules used to control LED lights: 6,5mm devices like the G6D-ASI 5A relay, also using a Silver-Indium-Tin alloy contact, bring space as well as cost reductions.
Relays are getting quieter as well as smaller; removing a major source of distraction that can arise after lighting control has been installed.
In addition to the use of power relays in ballasts and lighting system management, DIP switches are commonly used to set the function of each device in the module. It is important that these devices be dependable in operation as well as compatible with the latest automated production methods.
Whether it's electromechanical devices like as DIP switches and relays, or state-of-the-art electronic components such as MEMS sensors, component manufacturers are producing innovative products specifically focused on lighting applications.
By delivering tangible advantages to lighting control equipment these new devices are helping OEMs to achieve more efficient control and to reduce costs and space in their products, making a substantial contribution to lower energy consumption overall.
Fabrizio Petris is Global Application Oriented Team Manager - Building Automation and Security for Omron Electronic Components Europe