Introduction
The Murata IRA-S200ST01 is a high-performance pyroelectric infrared sensor widely used in security systems, automatic doors, and occupancy detection. This article provides a complete technical analysis of its specifications, characteristics, and integration requirements.
Key Specifications
| Parameter | Value |
|---|---|
| Package | TO-5 metal can (3-pin) |
| Detector Element | Dual-element (series connection) |
| Window Material | Silicon with IR filter |
| Spectral Response | 7-14 µm (human detection band) |
| Responsivity | 3.3 kV/W (typical at 1 Hz, 500K blackbody) |
| Noise Equivalent Power (NEP) | 1.5×10⁻⁹ W/√Hz |
| Detectivity (D*) | 1.5×10⁸ cm·√Hz/W |
| Operating Voltage | 2-15 V (via external circuit) |
| Operating Temperature | -40°C to +70°C |
| Storage Temperature | -40°C to +80°C |
Internal Structure
The IRA-S200ST01 contains two pyroelectric elements connected in series with opposite polarity. This differential configuration provides excellent common-mode rejection of ambient temperature changes and vibration-induced signals.
The sensor includes an integrated JFET impedance converter configured as a source follower. A built-in resistor (typically 10-50 GΩ) provides the necessary DC bias path.
Electrical Characteristics
Output Signal
The sensor outputs a voltage signal that varies with incident IR radiation. Typical signal levels:
- Human walking at 5m: 10-50 mV peak-to-peak
- Noise floor: 1-5 mV (depending on bandwidth)
Frequency Response
The sensor’s response rolls off below approximately 0.1 Hz due to the electrical time constant (sensor capacitance × load resistance). The upper cutoff is determined by the thermal time constant of the elements, typically 10-100 Hz.
Equivalent Circuit
The IRA-S200ST01 can be modeled as:
- Pyroelectric current source (i_p) in parallel with sensor capacitance (C_s ≈ 20-50 pF)
- Parallel resistance (R_s > 10¹³ Ω)
- Series JFET source follower with gain ≈ 0.7-0.9
Application Circuit
A typical interface circuit requires:
- Load resistor (R_L) from source pin to GND: 10-100 kΩ
- Drain resistor (R_D) from drain pin to VCC: 10-100 kΩ
- Coupling capacitor to remove DC bias
- Subsequent amplification stages (gain 60-80 dB)
Typical circuit:
VCC ──── R_D (47k) ────┬──── Drain pin
│
├──── Output to AC coupling
│
Source pin ──── R_L (47k) ──── GND
Comparison with Other Murata Models
| Model | Package | Elements | Typical Use |
|---|---|---|---|
| IRA-S200ST01 | TO-5 | Dual (series) | General purpose |
| IRA-S210ST01 | TO-5 | Dual (parallel) | Higher signal |
| IRA-E700 | SMD | Single | Compact designs |
| IRA-S230ST01 | TO-5 | Quad | Direction detection |
PCB Layout Guidelines
- Keep traces short, especially to the JFET gate (internal to sensor).
- Guard ring around the input pins to minimize leakage currents.
- Avoid running high-speed digital traces near the sensor.
- Provide adequate decoupling on the power supply.
Lens Selection
The IRA-S200ST01 requires an external Fresnel lens. Murata offers compatible lenses with various patterns:
- IRA-L408B: Wide angle (100°)
- IRA-L409B: Long range (curtain)
- IRA-L410B: Pet immune
Conclusion
The Murata IRA-S200ST01 is a versatile, high-quality pyroelectric sensor suitable for a wide range of motion detection applications. Understanding its characteristics enables optimal circuit design and system integration.