Pyroelectric Effect

Modern motion detectors are based on well established and field proven technologies and are compatible with the construction industry. Haggul_MotionDetector_sml.jpgThey are used to secure buildings, but can also contribute to lower electricity costs through intelligent light control within the context of a “Smart Home”, which means their popularity is likely to continue unabated. Although pyroelectric sensors are the key element of these motion detectors, their implementation requires controllers which provide a high degree of flexibility. LSI/CSI have been developing customized components for these PIR-detectors since the mid-90’s, and technically mature standard-ICs are part of their product range.

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PIRSensorD203B_01.png Passive infrared technology or PIR provides a cost effective and reliable means for detecting infrared sources, such as humans or animals, and is therefore deployed in millions of motion & presence detectors. The technology is based on the so-called pyroelectric effect or pyroelectric polarisation, the capacity of piezoelectric crystals, e.g. tourmaline, to react to temperature change with charge separations. Hence, they only detect IR emitters when they move and thus provide clear advantages compared with competing technologies such as ultrasound or microwaves. PIR sensors are generally designed as double or quadruple elements in order to exclude erroneous triggering due to light changes. A Fresnel lens design can be used increase incoming light levels, enhancing the effective signal.

PIR-Sensors need controllers

L6506_BlockDiagram_01_sml.jpgBuilding on its expertise in the field of HV-CMOS processes, the chip manufacturer LSI Computer Systems (LSI/CSI) has been manufacturing PIR sensor interface controllers for more than a decade.

Following the initial customized ASIC implementations, the LS6511N was the first standard controller driving a light-modulation triac. The current product range includes the LS6506R controller which was specifically designed to trigger impulse relays. Contrary to triacs, relays are also able to switch other resistive loads such as heating & air conditioning equipment. The use of current pulse relays, or, as the case may be, of bistable relays means that the power consumption of motion detectors is as low as comparable triac solutions. (The IC is also available as LS6507R for triac solutions).

Overview PIR-Sensor Interface-ICs from LSI/CSI

Relay advantage

The ability to switch loads with bistable relays significantly increases the deployment possibilities of the detector, permitting trouble-free switching of air conditioning equipment with powerful inductive components and of neon tubes fitted with compensating inductors and energy-saving light bulbs, as these are often sensitive to cyclic power cuts caused by triac controllers and thus require continuous mains power supply. On the other hand, the component also requires a separate DC current supply, which is generally supplied via a Graetz rectifier with voltage divider and filtering. The supply current is then grounded via protective earthing and should not exceed 500uArms. Bistable relays are also required to keep power consumption low, of course, but they are currently still more expensive than classic, monostable designs.