Timers & Controls Watching the detectors
Too much choice and too many new products to get your head around? Timeguard’sTechnical Manager, Peter Staniforth, explains some of the considerations for wholesalers when it comes to selling PIR detectors.
P
IR detectors have become big and profitable business in the channel. There was a blip when we saw low
cost challengers to the quality brands but the wheat was soon sorted from the chaff. Installers know that if they really want to be
able to ‘fit and forget’ they need reliability and transparency: the products need to be clearly rated for the jobs they are good for. Predicting the inrush current is not a simple calculation. A better approach is to choose detectors that are already tested an specifically rated for the LED lighting you want to install. In my view, if the LED rating is not on the box, then that PIR detector and switch has no place on your shelves. Once you’ve sorted the wheat from the chaff when it comes to brands and quality guarantees, you need to decide what to stock. With more choice coming on the market next month, we at Timeguard admit to having have a vested interest in explaining the difference between motion and/or presence detection with PIR and the affordable microwave (higher frequency) detection) that is now also becoming a mainstream option. Broadly, detectors fall into two categories: Active and Passive.
Active detection Active motion sensors continuously emit energy. Energy field disturbances are detected by the motion sensor. Active motion detectors can be categorised into three types: microwave, tomographic and ultrasonic motion sensors. It is microwave technology that is now making a big impact in the wholesale channel. A microwave motion
detector can be a separate wall or ceiling mounted unit or integrated into fittings like our new ceiling lights, emits pulses at microwave frequencies, then measures reflection off objects (like walls) when those waves return to the sensor. So, the whole area is filled, and the detector senses reflections changing when there is a moving object (like a person) in
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the area. You can think of it as very much like police speed radar guns. The reflection mechanism means that
having line-of-sight is not an issue (PIR sensors can’t detect movement if it occurs around the corner. Also, microwaves can penetrate most building materials (but not metal). This also means that sensors can be integrated into light fittings for protection against dust and moisture With typical detection ranges up to 15
metres, microwave detectors are ideal for controlling multi segment areas. They have long been used in applications such as indicating the flow of products in pipelines and conveyor belts, etc. In buildings, they are ideal in offices, toilets and shower blocks where there are walls and partitions, and you want to avoid the cost of installing multiple detectors. However, do remember that you need to avoid nuisance triggering from adjacent corridors and
rooms. Other active technologies are
Timeguard's flush mounted microwave ceiling detector – more products are promised this summer.
With Timeguard’s innovative corner bracket, PIRs can now see around corners.
ultrasonic sensors, typically used in alarm systems and for wildlife photography, and tomographic radio wave sensors for automation and security in high-risk areas and to protect high value assets areas like banks.
Passive detection Passive sensors don’t emit any radiation; they only absorb it. They are still the most common form of detection in the built environment, where they are used mostly for indoor or outdoor lighting and HVAC applications. A PIR sensor is essentially a pyroelectric sensor divided into two halves that compare notes. If they are not receiving the same levels of IR, because the heat-emitting object is moving, then the PIR detector acts accordingly – typically triggering a light to switch on. PIR detectors cannot detect stationary or very slow motion objects. They are usually installed high up or in ceilings so installers really do need them to be reliable ‘fit and forget’ items. Prices will vary according to both specification and quality, and there are different PIR sensor units available with different ranges and coverage areas. You can also choose between motion (walking people) and presence (sedentary staff) detection or a combination of both.
www.timeguard.com June 2017 electrical wholesaler | 19
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