Think you know PIRs..?

IFSEC returns 16–18th May 2023

INTRUDER

Think you know PIRs?

PIRs are the bread and butter of the security industry, but how much do you actually know about them and how they have evolved to counteract unwanted activations?

In a recent PSI podcast we spoke to Mike Burgess, EMEA Sales Manager for Takex Europe about detection and its place in the electronic security sector. It was clear that the Passive Infrared Detector is still very much an integral part of the picture when it comes to alarms systems and improving the performance of CCTV, but what was also apparent is that there is more than one type of detector on the market and quite a difference in price across the range. So why are there so many options for such a basic component of the system?

“What we need to remember is that the PIR is the trigger of the security installation and any issues with incorrect product specification or positioning will result in a failing or underperforming system,” says John Angell, General Sales Manager at Takex. “This is why installers need to be aware of the differing capabilities of PIRs and how the technology has developed to provide the best results for each environment.”

While the basic function of a PIR sensor is to detect an intruder, there are differences to consider between those installed internally compared to those being used outside the premises. For the external detector, incorrect choice of PIR can lead to situations when there is too much triggering – usually by animals, moving bushes or changes in sunlight. This is not the fault of the unit; it is down to the wrong product being used. This is why companies like Takex have a range of technologies with varying detector setups to negate problems with unwanted activations.

So let’s take a closer look at the technology behind a PIR to find out how it does its job.

The technology

“In essence PIRs are made of a pyroelectric sensor (pyro) which can detect levels of infrared radiation,” says Mike Burgess. “Everything emits radiation, albeit at a low level, and the more radiation is emitted the hotter something is. In a PIR the pyro is split into two or four segments, because the detector is looking for motion rather than a change in ambient radiation levels. The two halves or four quarters of the segment are wired to cancel each other out, so when one section sees less or more radiation than its partner, there is a change of state which results in a trigger.”

If it was just the pyro on its own, the segments would see the same thing all of the time and it would be difficult to sense movement, so it is necessary to separate what the pyro sees into zones, which can be done using either a Fresnel lens or mirrors.

Pyros vary in quality and sensitivity tremendously, as do Fresnel lenses, which of course will affect dramatically the effectiveness of the device.

“In some locations it is possible to use the budget end of the market sensor and the results will be fine,” explains Mike. “This would be the case with scenarios like a domestic setting with no pets or vermin where the only likely cause of activation will be a person. However if you put domestic animals into the mix then you need to look at getting something “pet immune” which is usually achieved by designing the Fresnel lens with wider spaced zones, requiring a much bigger infrared radiation source to cause an activation, usually only effective for something the size of a spaniel.”

Once you move to more industrial internal applications you have to consider what else could generate radiation, air-conditioning outlets, vermin, machinery, and also the required coverage distances tend to be greater, meaning a more sensitive pyro and better“What we need to remember is that the PIR is the trigger of the security installation and any issues with incorrect product specification or positioning will result in a failing or underperforming system”

INTRUDER

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“As you move higher up the price range you will find devices with two or more pyros looking at the same area, to ensure the stability of the detector in a more difficult environment”

quality Fresnel lens, or mirrored optics (more expensive, but greater zone clarity).

So let’s look at some of the choices for PIR detection and how the latest systems operate without the unwanted activations associated with cheaper technologies.

Better options

“As you move higher up the price range you will find devices with two or more pyros looking at the same area, to ensure the stability of the detector in a more difficult environment,” says John Angell. “Moving outside is where we should look away from the budget choices, this is where the detectors are subject to the environment and mother nature with all of her moods, rather than the controlled environment inside. Depending where you are in the world will depend on what you have to make allowances for, be it massively fluctuating temperatures, heavy rainfall on a regular basis and/or wildlife of varying proportions.”

A typical dual zone example would be the MS-12TE/FE PIR, designed with the challenges of our feathered and furry friends, be they domestic or wild, the MS-12 series overcomes the usual problems experienced using external PIRs by using two detectors to cover each zone. The sensor covers an angle up to 90° and uses both a horizontal curtain and a variable downward curtain, and for a confirmed alarm both need to be broken together. Therefore if installed around one metre from the ground, then something more than one metre tall would be needed to generate an activation across the two detectors in the same area.

The 90° coverage could be achieved anywhere to the front of the device, or there are masks supplied which will reduce that 90° all the way down to 13° (ideal for wall/window detection). To enhance this device further the sensitivity can be varied from 30% all the way to 170%, and the Pulse Count (how many fingers of detection need to be activated to generate an alarm) can be changed from one to three, essential for locations where there is an abundance of movement in a zone such as flora or fauna.

But using a dual zone unit is not the only way to rule out unwanted activations, there are triple zone detectors such as the PIR-T15WAM and PIRT-40NAM available.

With either a 15m wide angle or a 45m vertical curtain (ideal for CCTV applications), each unit is fitted with three pyros and uses mirrored optics (a huge advantage for zone definition, particularly at long range); two pyros are for the main coverage, the third is dedicated to the creep zone directly below the unit. The PIR-T40NAM also has an auxiliary zone that will detect intruders below the unit before they even enter the creep zone. The optics inside the units can be rotated through 180° meaning it is impossible for an intruder to know where the coverage area is. These can be installed at extreme mounting heights for even wider coverage.

Detection selection

As the initial phase of a security system it is vital that the PIR chosen for the job, fits the job. In the past external PIRs in particular have had a bad press due to the levels of unwanted alarms that have resulted from incorrect specification or positioning. Now that there are dual and triple zone detectors available the problems associated with using basic sensors outdoors have been overcome. What’s more, using the sensors to trigger CCTV can help improve the visual verification process.

“Installers should be aware that we have been doing a lot of work behind the scenes to improve the performance and reliability of detectors compared to the ones they may have tried in the past,” says John Angell. “Nobody wants unwanted activations of security systems and in developing the innovations of dual and triple zone detectors we have increased the numbers of applications that PIRs can be used for. With the addition of battery-powered units to the range we’ve further extended what installers can do for their customers and made verification of alarms with cameras even more responsive.”

Think you know about PIRs? Think again.