HEALTH & SAFETY
Figure 4
The smoke particles scatter some of this light back onto the photodiodes (see the cross-section of the ADPD188BI in Figure 3). The analogue front end (AFE)
includes the transimpedance amplifier, band- pass filter, integrator, ADC, LED drivers, and digital control (see the middle of Figure 4). There are many options inside the AFE to enable optimization for different applications and use cases. The AFE also provides the ability to reject ambient light, such as from lamps or solar radiation, at levels up to 80 dB. This principle provides many significant advantages. The short distance between the LED and PD results in much more efficient use of light, which reduces the power dissipation of the system for a required sensitivity and results in a longer battery lifetime. Two different LED colours are included in the device. The amount of light scattered by the particles is a function of wavelength. This provides limited use for separating the hamburger and flaming
polyurethane smokes, but can be used to distinguish between relatively small smoke particles (100 nm to 300 nm diameter) and much larger smouldering plastic or steam particles (10 μm diameter). The highly configurable AFE inside the ADPD188BI provides for a very high dynamic range that is software configurable and can be adjusted on the fly. The SNR of the system can also be easily adjusted to optimize for power or performance on the fly. One example would be to dynamically increase the sample rate or SNR when smoke has been detected to more accurately differentiate between a nuisance source or a real fire. Integrating the system also enables Analog Devices to calibrate the loop response (LED driver LED PD AFE) of the parts and burn calibration coefficients into the AFE to limit the part-to-part variation to better than ±10%, which reduces or eliminates the need for expensive and time-consuming sensitivity calibrations in smoke tunnels. The ADPD188BI provides the features and
capabilities to increase the performance of smoke detectors to more accurately separate nuisance sources from fire events. As well as performance, there are further advantages: the integration of LEDs means separate LED sourcing and stocking is eliminated, and the small form factor allows for integrated smoke detection across intelligent building components.
Analog Devices
www.analog.com
Christoph Kämmerer has worked at Analog Devices in Germany since February 2015. He graduated in 2014 from the Friedrich Alexander University in Erlangen with a master’s in physics. He then worked as an intern in process development at Analog Devices in Limerick. Having completed the trainee program in December 2016, he now works as a field applications engineer at Analog Devices and specializes in emer- ging applications. He can be reached at christoph.
kaemmerer@analog.com.
FACTORY&HANDLINGSOLUTIONS | FEBRUARY 2022 27
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