Quads offer the most discerning passive infrared detection.

What’s the best passive infrared  sensor technology available today for intrusion detection systems?

A: KING of pure passive infrared intrusion detectors is the quadruple element sensor. It works on a different principle to the dual edge units that monitor passage from 1 part of a zone to another.

The quad principle of detection aims to reduce the chance of false alarm caused by pets or small animals by clever design and without using tune-out processing, which cab lower a sensor’s overall detection discernment.

Combining quad element and advanced signal processing should mean an even better sensor. Quads break each zone into 4 separate parts – imagine them as 4 boxes forming a square but remaining distinct from each other. Each of the elements has a different value. The 2 upper boxes are designated A+ and A- while the lower 2 boxes are B+ and B-. Quads monitor these to see if they are being filled by the IRE signal of an intruder.

It works like this. Each A box is matched negative and positive and it’s the same with the B boxes. As the processor monitors each of the 4 elements in a zone it considers the IRE level. When this breaks a certain threshold, the processor starts to calculate an equation over and over. This equation is [A+B] – [A-B] = 0. So long as the result of this calculation adds up to 0 then no alarm is activated.

If a mouse moves in the target area and its signal fills only 1 zone element with an IRE signal having a value of 2uJ. The processor computes this as [0+2] – [0-2] = [+2] – [-2] = 0 and there’s no alarm signal generated. But if an intruder with a value of 10uJ disturbs 2 elements then the processor calculates [10+10] – [10-10] = 20 – [0] = 20 – 0 = 20. As 10 is the alarm threshold, a value of 20 means alarm activation.

In the field the quad is constantly running computations which essentially represent questions like: “Was there a disturbance in any of the 4 elements? What was its value? Is it still there? Has it moved?” Are quad PIRs better than microwave/PIR dual technology sensors? It sidles towards applications with your conclusions governed by your definition of ‘better’.