Noise Equivalent Power (NEP) is a key figure of merit for infrared detectors. It quantifies the minimum detectable signal power. This article explains what NEP means for PIR sensors and how to use it in design.<\/p>\n
NEP is the amount of incident infrared power required to produce a signal-to-noise ratio of 1 (i.e., signal equals noise). It is typically specified in watts per square root hertz (W\/\u221aHz) or simply in watts for a given bandwidth.<\/p>\n
Lower NEP = Better sensitivity.<\/strong><\/p>\n For the Murata IRA-S200ST01, NEP is specified as 1.5\u00d710\u207b\u2079 W\/\u221aHz. This means that in a 1 Hz bandwidth, the sensor can detect 1.5 nW of infrared power.<\/p>\n To find the minimum detectable signal power in your application:<\/p>\n P_min = NEP \u00d7 \u221a(\u0394f)<\/strong><\/p>\n Where \u0394f is the noise bandwidth of your system. For a PIR system with a 10 Hz bandwidth:<\/p>\n P_min = 1.5e-9 \u00d7 \u221a10 = 1.5e-9 \u00d7 3.16 = 4.74e-9 W (4.74 nW).<\/p>\n The infrared power received from a human at distance d depends on:<\/p>\n A rough estimate: at 10m, received power might be on the order of 1-10 nW, which is near the NEP limit. This explains why range is limited.<\/p>\n Detectivity (D*) is another common figure, defined as:<\/p>\n D* = \u221a(A_d \u00d7 \u0394f) \/ NEP<\/strong><\/p>\n Where A_d is the detector area. D* normalizes for area, allowing comparison between different sensors. Higher D* is better.<\/p>\n NEP helps you:<\/p>\n HC-SR501 uses a cheap pyroelectric element (likely PZT-based) with higher NEP (less sensitive) than the Murata. This explains why HC-SR501 has shorter range and more false triggers.<\/p>\n NEP is a fundamental specification that quantifies a PIR sensor’s sensitivity. Understanding it helps in selecting the right sensor and designing optimal signal conditioning.<\/p>\n","protected":false},"excerpt":{"rendered":" Introduction Noise Equivalent Power (NEP) is a key figure of merit for infrared detectors. It quantifies the minimum detectable signal power. This article explains what NEP means for PIR sensors and how to use it in design. Definition of NEP NEP is the amount of incident infrared power required to produce a signal-to-noise ratio of […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[6],"tags":[],"class_list":["post-3306","post","type-post","status-publish","format-standard","hentry","category-reference"],"blocksy_meta":[],"yoast_head":"\r\nNEP in PIR Sensor Datasheets<\/h2>\n
Calculating Minimum Detectable Signal<\/h2>\n
Relating NEP to Detection Distance<\/h2>\n
\n
NEP vs. Detectivity (D*)<\/h2>\n
Factors Affecting NEP<\/h2>\n
\n
Using NEP in System Design<\/h2>\n
\n
Example: HC-SR501 vs. Murata IRA-S200ST01<\/h2>\n
Conclusion<\/h2>\n