Introduction
Just as cold weather affects PIR sensors, high temperatures can also cause problems. When ambient temperature approaches human body temperature (37°C), the contrast between a person and the background disappears, making detection difficult or impossible.
Why High Temperature Causes Problems
PIR sensors detect the difference in infrared radiation between a warm object (like a person) and the background. When the background temperature is close to skin temperature, the difference becomes very small. At 35-40°C ambient, a person may be nearly invisible to a PIR sensor.
Symptoms
- Sensor works at night or in cool conditions but fails during hot days.
- Detection range shrinks dramatically in hot weather.
- People are detected only when very close to the sensor.
Solutions
1. Increase Sensitivity
If your sensor has an adjustable potentiometer, turn it to maximum. This may help detect the small remaining signal.
2. Use a Sensor with Better Temperature Compensation
High-quality sensors like the Panasonic EKMB series have built-in temperature compensation that maintains sensitivity across a wide range.
3. Choose a Sensor with Different Spectral Response
Some sensors are optimized for high-temperature environments (e.g., industrial applications). They may use different filter wavelengths.
4. Provide Cooling
In extreme cases, you can cool the sensor itself using a Peltier cooler or by mounting it in a shaded, ventilated enclosure. This is rarely practical.
5. Use a Different Technology
For environments regularly above 35°C, consider microwave or mmWave radar sensors, which are unaffected by ambient temperature.
Case Study: Desert Outdoor Camera
A security camera in the Arizona desert used a PIR sensor for motion activation. In summer, when temperatures reached 45°C, the sensor stopped detecting people. The solution was to switch to a microwave sensor, which worked reliably regardless of temperature.
Conclusion
High-temperature environments challenge PIR sensors. If your application must work in hot climates, select sensors with good temperature compensation or consider alternative technologies.