Occupancy detection systems are widely used as a security mechanism and to detect human presence for automatically controlling room temperature, lighting or ventilation. A key factor to an effective alarm system is to ignore to the presence of small dogs. The ProxFusion® series allows for implementing pet immunity, while reducing the number of analogue components used in conventional PIR alarm systems.
How Pet Detection works
ProxFusion® is a range of multi sensor IC’s. A single ProxFusion® IC can control up to two PIR sensors. A Fresnel lens is used to project the IR onto the PIR elements as seen in Figure 1. The field of view and range of the dual PIR sensor is dependent on the type of Fresnel lens used.
Figure 1: PIR Fresnel Lens
The dual PIR detection setup is shown in Figure 2. The aim is to create two unique detection zones: one for pets and one for adult humans. This is done by directing one Fresnel lens upwards and one downwards. Small dogs will only trigger the bottom facing PIR sensor (lower zone), while both PIR’s will be trigged by an adult human.
It is recommended to place the sensor at a height of 1.7m as this will allow enough black body radiation from an adult to trigger the top PIR sensor, while not triggering the sensor when a pet in the detection zone. The best placement for a motion sensor is in a corner of the room, as this allows the sensor to monitor the entire room. The data displayed in Figure 3 and Figure 4 shows the delta values for the top and bottom PIR sensors, calculated as: Delta = Counts – LTA
Typical human movement causes large fluctuations in both the upper and the lower PIR sensor readings simultaneously. Both PIR sensors receive a large change in in the measured IR signal, due to the large amount of black body radiation emitted by humans. The received signal on the top PIR sensor from a pet’s movement is significantly smaller than any human movement. When implementing a sensor trigger for the PIR sensor, the threshold needs to be set above the max pet signal received. The threshold on the top PIR sensor can be set more sensitive than the bottom.
Figure 3: Human walking upright at four meters in front of sensor.
Figure 4: Pet moving 1-6m from sensor