We are all familiar by now with the use of PIRs (Passive Infra-red Detectors) to trigger the switching of lights (and increasingly - given our carbon reduction targets – HVAC) when people enter a room or zone and, of course, to ensure that they do not stay switched on any longer than necessary. So it’s just a case of dropping into the wholesaler and picking one up for the next job, isn’t it? No such luck because you’ve got a whole list of specification choices to make.
If, like the people at Timeguard, you believe that an installers early morning visit to the wholesaler ought not to be for pouring over spec sheets but to pick up goods quickly, then you will want to be prepared. So here’s a quick checklist of what to look for in a PIR detector.
The Movement of Presence Detector
You can find a basic PIR from as little as £9.99. On the other hand, a top-end super-sensitive presence detector can set you back as much as £249.00 or more. Similarly you will pay more for a more stylish design than you will for a real workhorse of a detector and you need to decide what the job in hand is. If you just need to detect a body walking into an area, a corridor or toilet for instance, than a fairly basic PIR movement (or motion) detector will suffice. If, however, you want to manage an area where people will be present, but not necessarily moving much more than fingers on a keyboard or the pages of a book, then you will need to look for the greater sensitivity of presence detectors. The presence detectors benefit from higher quality detector units and lens design. They can also offer constant light control to provide a facility for brightening and dimming lights in response to natural lighting conditions rather than just flicking them on and off.There is no official standard or definition of the difference between a PIR movement or motion detector and a presence detector, and no agreed British or European standard of sensitivity, so for now you pay your money and take your choice - in this way, picking a manufacturer you know and can rely on will be a high priority. You need to know that what is inside the box can really do what it says on the outside. Reliability is also a big issue because even though wiring is relatively straightforward, most detectors are mounted high up or on ceilings and in an office or commercial building accessing them to replace failed units is never going to be an easy job.
The Loading taken by the PIR
Make sure you check out the loading. While 2000W for filament or halogen lighting is fairly standard across the board, the rating for switching low energy or fluorescent lighting varies because of the initial surge always needed to switch these lights on. We have often pointed out that a combination of automatic PIR switching and low energy bulb or tubes is not always the most energy efficient option where switching is going to be frequent such as in an area where people are walking in and out a lot.There are also options to have two channel PIRs, controlling for example lights and ventilation fans. This might be typically employed in a toilet to keep the fan running for a few minutes after the person has left the room and the lights have gone out.
The Detection angle and field
Manufacturing costs these days have been driven down so far that there is no need for compromise on detection fields. 360 degrees for ceiling mounts and 180 degrees for wall mounts is the minimum you should accept. I’d be surprised if you could find anything with a lower specification these days. Expect a detection range of five to seven metres diameter. Detection fields are measured in diameters from a central point. However, we introduced the concept of square pattern detection with the Theben Compact Office Presence Detector, which makes it easy to plan the installation in a grid matrix of PIRs to completely cover a large area such as an open plan office. Of course the circular fields make it difficult to cover long, thin areas like corridors and the solution has been to install multiple detectors at intervals. Theben’s Compact Passage detector, which packs two detectors, facing in opposite directions (giving a 30m range), into one small casing can be mounted centrally meaning you only need one device and one installation.The Installation and set up of the PIR
You will want to choose between surface and flush mounting, which will depend on the building concerned. The good news is that surface mounting detectors are looking pretty sleek these days, but do check out the cable entry for internal PIR detectors, as you may need side or bottom. The setting up should be straightforward but do check the options – you will probably need to be able to adjust for ambient light level to ensure that lights are not switched in daytime. You may also want to be able to adjust the detection field, which is when a detector like the Timeguard PDSM comes into its own with easy adjustments for ceiling height, lux levels and time on and the option of a hand held remote control setting unit. After all, once a detector is up on high ceiling, it’s not going to be easy to adjust it!In fact having a PIR which can be adjusted by remote control is becoming a specification requirement, because of the ease of adjustment not only due to Health and Safety issues but also potential damage to the ceiling when moving sensors away from the plaster work to get at the controls.
