VID for flame detection is looking in part for:
- Flicker
- Color
- Size
- Brightness
- Dynaxmic texture analysis
VID for smoke detection, on the other hand, has algorithms for:
- Contrast change
- Edge lost
- Motion
- Color
- Fractal encoding of the image
- Temporal and spatial wavelet transformation
Smoke is more difficult to model than flame due to irregular motion characteristics, unstable cameras, dynamic backgrounds and lighting. Systems are now available that provide coverage for both flame and smoke.
System Design Characteristics
Camera selection can affect the outcome and sensitivity of a VID system. This is more so with the multiple camera configuration, as the single camera systems are configured by the VID manufacturer. Items that should be considered when selecting a camera include:
- Brightness
- Sharpness
- Flicker suppression
- Color balance
When selecting a camera, conferring with the VID manufacturer should take place to verify product compatibility with the system.
Ambient light within the spaces to be protected is also an important factor. A minimum of 1 foot candle is required for smoke detection. This is the same level of illumination required by NFPA 101 Life Safety Code for emergency lighting, and as such most facilities have this level. Illumination may be by either infrared (IR) or white light. For most applications, white light should be considered. A large fire could flood an IR receptor.
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Connection to a fire alarm system will be either through a relay output or by means of a 4-20mA signal. VID will also allow for v
isual review and interpretation via monitors.
In siting VID, the cameras will be required to have a direct line of view of the area that is to be covered. There must be no obstructions. Consideration should also be given to ventilation and smoke dilution. As discussed, light and illumination of the target area must also be considered.
Systems on the market today are listed by Factory Mutual (FM) Approvals through the organization’s Standard 3260, Standard for Radiant Energy-Sensing Fire Detectors for Automatic Fire Alarm Signaling. Two new standards are under development: FM 3232 (for VID) and UL 268B (video image smoke detectors). UL 268B is an outline at this time, but may be developed into a standard at a later date.
The integrator needs to be aware of and continue to remain up to date on this new VID technology, its applications and where it can and cannot be used. A “How can this be done?” application may now be possible thanks to VID.
Shane Clary, Ph.D., has more than 37 years of security and fire alarm industry experience. He serves on a number of NFPA technical committees, and is Vice President of Codes and Standards Compliance for Pacheco, Calif.-headquartered Bay Alarm Co.
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