Overview

In modern security, smart home, and automation control, pyroelectric infrared sensors (PIR) have become indispensable core components. The RE200B, a classic and widely used pyroelectric sensor, is highly valued for its cost-effectiveness, reliability, and mature manufacturing process. It accurately detects infrared radiation changes caused by human movement while ignoring stationary objects. Based on years of sensor R&D experience, Nexisense has optimized the principles and applications of RE200B sensors. This article systematically explains the working mechanism from basic physics to practical enhancements, helping engineers and developers better understand and utilize this technology.

Core Physical Principle: Pyroelectric Effect

The RE200B operates based on the pyroelectric effect. Certain special crystal materials (such as lithium tantalate or modified lead zirconate titanate ceramics) exhibit unique properties: when the temperature changes, the polarization intensity inside the crystal changes, causing relative displacement of positive and negative charge centers and producing equal but opposite bound charges on the crystal surfaces, generating measurable voltage or charge signals.

The key is that the sensor responds to the rate of temperature change (dT/dt), not the absolute temperature. This makes it insensitive to slow, uniform temperature variations (like ambient temperature changes) but highly responsive to localized, transient temperature fluctuations, such as infrared radiation changes caused by human movement. A human body, as a ~37°C heat source, continuously emits far-infrared radiation in the 8–14μm band. When a person enters or leaves the detection area, the sensor detects a sudden change in radiation flux, triggering a pyroelectric current.

This characteristic defines typical applications: the RE200B excels at detecting dynamic targets (e.g., walking people) while ignoring stationary heat sources (like radiators), effectively reducing false alarms.

Internal Structure: Dual-Element Complementary and Signal Conversion

The RE200B is not just a single crystal but uses a precise internal structure to balance high sensitivity and interference immunity.

Dual-Element Complementary Structure

The sensor contains two pyroelectric elements with opposite polarities, connected in series (dual-element design). This symmetric layout offers two advantages:

• Environmental interference suppression: Slow environmental temperature changes (like gradual sunlight or air conditioning) affect both elements equally, producing signals of the same amplitude and polarity. Series connection cancels these signals, resulting in near-zero output.

• Dynamic signal enhancement: When a moving target passes, infrared radiation sequentially illuminates the two elements, generating opposite pulse signals in sequence. Series connection creates a pronounced alternating output, which is easy for circuitry to recognize.

This differential design greatly improves the signal-to-noise ratio, keeping the sensor sensitive to even small movements.

Impedance Conversion and Preliminary Amplification

The charge generated by the pyroelectric elements is extremely small (picoCoulomb level) and has very high source impedance (10^9–10^12Ω), making direct output difficult to process. The RE200B integrates a high-input-impedance JFET to:

• Convert the high-impedance charge signal into a low-impedance voltage signal.

• Provide initial voltage amplification (gain typically 10–100×).

• Act as a source follower to reduce output impedance for external circuitry.

The JFET-processed signal typically reaches millivolt levels, suitable for further amplification, filtering, and comparison by subsequent circuits.

Fresnel Lens: The "Magnifying Glass" for Detection

The bare RE200B sensor has a narrow detection field (~tens of degrees) and a limited distance of a few meters. In practical applications, a Fresnel lens is essential for usable detection distances (5–12 meters) and wide-angle coverage (90°–120°).

The Fresnel lens does more than focus infrared radiation:

• Infrared focusing: Concentrates far-infrared radiation onto the sensor, increasing sensitivity and effective range.

  
  

• Zone segmentation: Composed of dozens to hundreds of small lens units, dividing the space into alternating sensitive and blind zones. Moving humans repeatedly cross these zones, generating a series of infrared pulses. This "chopping" converts slow changes into high-frequency alternating signals, easily detected and distinguished from noise.

Lens selection depends on the application: narrow-angle long-distance for corridors, wide-angle long-distance for halls, and pet-immune lenses that adjust blind zone height to avoid small animals triggering the sensor.

Nexisense Application Optimization and Practice

While classic, RE200B performance heavily depends on peripheral circuitry and system design. Nexisense emphasizes:

• Advanced signal processing: Multi-stage filtering (high-pass + low-pass) and adaptive threshold algorithms suppress common false alarm sources like light, fans, or pets.

• Lens and field-of-view matching: Provides multiple Fresnel lens options and supports custom detection patterns.

• Electromagnetic compatibility and stability: Industrial-grade PCB layout, power filtering, and shielding ensure long-term reliability under strong EM interference.

• Digital and analog output: Analog voltage models (e.g., HDA series) and digital interface models (e.g., GDA series supporting I²C or custom protocols) for integration into smart systems.

These optimizations make Nexisense pyroelectric sensors widely recognized in security alarms, smart lighting, automatic doors, and foot traffic counting.

FAQ

1. Why can't RE200B detect stationary humans? It responds to temperature change rate; stationary targets do not generate flux changes, so no signal output.

2. How does the dual-element structure reduce false alarms? Slow environmental changes affect both elements equally, cancelling signals; moving targets generate differential pulses for effective distinction.

3. What is the function of the Fresnel lens? Focuses infrared radiation and segments the detection zone, converting movement into pulse signals to improve sensitivity and range.

4. What does the JFET do in RE200B? Converts high-impedance to low-impedance signals and provides preliminary amplification for weak signal processing.

5. How to adjust detection distance and angle? Mainly through Fresnel lens design; different lenses achieve 5–15m distance and 60°–180° angle.

6. Does RE200B have a temperature range requirement? Typical operating temperature is -20°C to +70°C; sensitivity decreases outside this range.

7. How to avoid sunlight or lamp interference? Dual-element structure cancels slow changes; appropriate lens and filtering circuits reduce false alarms.

8. Will pets trigger RE200B? Standard lenses may trigger; pet-immune lenses (blind zone ~1m) are recommended.

9. Does Nexisense pyroelectric sensor support digital output? Yes, digital models (e.g., GDA series) are suitable for MCU or IoT integration.

10. Typical applications of RE200B? Security alarms, smart lighting, automatic doors, foot traffic counting, robot obstacle avoidance, etc.

Conclusion

The RE200B pyroelectric infrared sensor leverages the pyroelectric effect, dual-element complementary structure for interference suppression, JFET for signal conversion, and Fresnel lens for extended detection range, forming an efficient and reliable human motion detection solution. Nexisense further optimizes the classic component, providing complete solutions from component to system level, enabling accurate and stable sensing in security and smart control. Understanding and utilizing these sensors is a crucial step in building efficient environmental perception systems in the IoT and smart era.