Tamper-Evident Fasteners for PIR Sensor Lens Replacement
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Solution Overview
Problem
Existing passive infra-red motion detectors face challenges in replacing optical systems without exposing and potentially damaging the sensitive electronics, as the optical system must be removed from the inside, requiring disassembly and increasing the risk of component damage.
Innovation Solution
A security device design allowing the optical system, such as a lens, to be removable from the outside of the housing without disassembling the electronics, with a locking feature that prevents unauthorized removal and triggers a tamper signal if attempted, ensuring the electronics remain protected during replacement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of repair
If the optical system is removed from the inside of the housing, then the optical system can be replaced, but the electronics are exposed and at risk of damage
Solution Approach 1:
The housing is divided into a front section and a rear section, with the optical system located in the front section that can be accessed and removed independently. The front section is designed to be removable from the rear section, allowing optical system replacement without exposing the electronics in the rear section.
Solution Approach 2:
The optical system is extracted as a separate, independently accessible component within the front section. This allows the optical system to be removed and replaced without needing to access the interior of the entire housing or expose the electronics located in the rear section.
2Ease of repair
If the front section is made removable for optical system access, then optical system replacement is easier, but tamper security is reduced
Solution Approach 1:
Different security characteristics are applied to different sections: the front section is designed for easy removal and replacement of the optical system, while the rear section containing the electronics maintains a more secure, fixed attachment. This local differentiation allows convenient optical system access without compromising overall tamper security.
Solution Approach 2:
The front section acts as an intermediary layer between the user and the electronics. It provides controlled access to the optical system while physically shielding the electronics in the rear section, allowing optical replacement without direct exposure to or risk to the electronic components.
3Object-affected harmful factors
If a locking feature is added to prevent unauthorized removal, then tamper security is improved, but device complexity increases
Solution Approach 1:
The locking feature is merged with the existing fastening mechanism that connects the front and rear sections. The same mechanical interface that allows the front section to be attached and removed also incorporates the tamper detection functionality, eliminating the need for separate locking components while maintaining security.
Solution Approach 2:
The fastening mechanism automatically provides tamper detection and reporting functionality without requiring additional active components. When the front section is removed or tampered with, the mechanism itself generates the tamper signal that is communicated to the control panel, making the system self-monitoring.
Data Source
AI summary
A security device, such as a passive infra-red motion detector (1) is provided with a plurality of fasteners (15, 25). One fastener (25) removably fastens a lens (4) to a housing of the passive infra-red detector, such that the lens (4) can be removed from the outside of the housing, whilst the other fastener (15) fastens a front section (2) of the housing to the rear section (3). Both fasteners (15, 25) are transparent/translucent and act as light guides.