TIDUF52 December   2023 MSPM0L1303 , MSPM0L1304 , MSPM0L1305 , MSPM0L1306 , MSPM0L1343 , MSPM0L1344 , MSPM0L1345 , MSPM0L1346

 

  1.   1
  2.   Description
  3.   Resources
  4.   Features
  5.   Applications
  6.   6
  7. 1System Description
    1. 1.1 Key System Specifications
  8. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Design Considerations
      1. 2.2.1 Photoelectric Smoke Detector Background – DC-Based Signal Chain
      2. 2.2.2 Modulation-Based Smoke Detection Signal Chain
      3. 2.2.3 Optical Sensing AFE Design
        1. 2.2.3.1 TIA
        2. 2.2.3.2 BPF
        3. 2.2.3.3 Demodulator and Integrator
        4. 2.2.3.4 LED Driver
      4. 2.2.4 Optical and Mechanical Design
    3. 2.3 Highlighted Products
      1. 2.3.1 MSPM0L1306
      2. 2.3.2 TLV9062S
      3. 2.3.3 TPS7A24
      4. 2.3.4 TS5A623157
      5. 2.3.5 SN74LVC1G66
      6. 2.3.6 HDC2010
  9. 3Hardware, Software, Testing Requirements, and Test Results
    1. 3.1 Hardware Requirements
      1. 3.1.1 Power
      2. 3.1.2 Communication Interface
      3. 3.1.3 Headers
    2. 3.2 Software Requirements
      1. 3.2.1 Getting Started Firmware
      2. 3.2.2 Measurements and Smoke Detection
      3. 3.2.3 Additional Demonstration Functionality
      4. 3.2.4 Smoke Detector GUI
    3. 3.3 Test Setup
      1. 3.3.1 UL217 Smoke Box and Fire Testing Setup
      2. 3.3.2 Ambient Light Testing Setup
      3. 3.3.3 Air-Quality Sensing Test Setup
    4. 3.4 Test Results
      1. 3.4.1 UL217 Testing Results
      2. 3.4.2 Ambient Light Testing Results
      3. 3.4.3 Air-Quality Sensing Test Results
      4. 3.4.4 Power Testing Results
      5. 3.4.5 Fire Room Smoke Testing
  10. 4Design and Documentation Support
    1. 4.1 Design Files
      1. 4.1.1 Schematics
      2. 4.1.2 BOM
      3. 4.1.3 CAD Files
    2. 4.2 Tools and Software
    3. 4.3 Documentation Support
    4. 4.4 Support Resources
    5. 4.5 Trademarks
  11. 5About the Author

1 System Description

Recent changes to the UL217 standard for residential smoke alarms (eighth and ninth editions) have been made to improve the performance of smoke alarms; first to keep up with modern construction techniques and materials, such as lighter more flammable materials in open floor plans that lead to hotter and faster burning fires which reduce the egress time needed for escape, and secondly to cover smoldering polyurethane fires which are not reliably detected with today’s alarms. Additionally, to further improve reliability, the ability to distinguish between real sources of fire and nuisance sources, for example, from cooking, steam from a shower, and so on, is required. Smoke from these nuisance sources tend to contain particle sizes much smaller than those found in sources from real fires. However, flaming polyurethane is an exception, where the particle sizes in this type of smoke consists of sizes in the upper range as those found in nuisance sources. Currently available, single wavelength photoelectric detectors using simple threshold-based detection algorithms, do not have the capability to distinguish between certain types of smoke particles (for example, flaming polyurethane) and nuisance sources. The UL268 standard covering commercial smoke detectors has similar updated requirements for smoke sensing performance. The TIDA-010941 demonstrates a multi-wavelength, multi-angle design capable of passing the new UL217 9th edition sensitivity and fire room testing requirements.

This reference design uses a modulation-based signal chain to overcome several shortcomings of a traditional DC-based architecture. The two main advantages of this approach are the improvement of ambient light rejection and improved signal-to-noise ratio (SNR) for the signal chain. Low cost is paramount for smoke detector applications. The improved ambient light rejection of this design enables the potential to implement a chamberless smoke detector design. Removing the optical chamber in a photoelectric detector represents a significant savings in terms of both BOM and assembly costs. However, despite the benefits of not having a chamber, significant environmental challenges exist, such as rejection of disturbances due to insects or collection of dust in the optical path over time. Using a multi-wavelength architecture, in this case Blue and Infrared (IR), allows for an increased signal response from smaller particle sizes typically found in nuisance sources, thereby, increasing the effective particle size detection range of the signal chain. The multi-angle aspect of this design consists of measuring the light scattering response at different scattering angles such as a typical forward scatter angle and a back scatter angle. This allows the estimation of particle size by taking the ratio of the measurements from the two angles. These two techniques; multi-wavelength and multi-angle, together, allow for a robust multiple-criteria approach for distinguishing between real sources of smoke and nuisance sources.

The improved SNR for the signal chain in this design not only enables the implementation of robust algorithms for reduced false alarms in smoke detection, but also enables the ability to sense particulates in air quality sensing application. Very accurate particle size estimates as well as mass concentration measurements are possible with this reference design. The implication is that this design opens the door for a smoke detector capable of not only meeting the latest standards for smoke detection but also sensing indoor air quality using the same optical design.

Lastly, low power is a key concern for smoke alarms that are battery operated since changing batteries frequently is inconvenient and quite challenging in certain installations for the consumer. The TIDA-010941 is capable of providing 10 years of battery life from a single 9-V alkaline battery to make sure smoke detection remains operable for as long a possible.