Siemens Cerberus Pyrotronics PB-1191 Manual page 4

Operating principle
The transmitter (IRLED) emits an invisible infrared (IR) pulse through the transmitter lens. The IR
pulse crosses over the measuring section and reaches the reflector located opposite the detector. The
reflector deflects the IR pulse back to the point of origin. The receiver lens directs the reflected IR
pulse to a silicon photodiode. The resulting electrical signal is evaluated by the electronics.
Receiver
Transmitter
Detector
PBA-1191
If smoke penetrates the measuring section, part of the light beam is absorbed by the smoke particles
while another part is scattered by the smoke particles; that is, the light beams merely change direction.
The remaining light reaches the reflector. The remaining light is then reflected and once again passes
through the measuring section and is further attenuated. Thus only a small portion of the beam
reaches the receiver and the signal (S
Measuring principle of the linear smoke detector with smoke
Coverage Area
Figure 2
Linear smoke detector without smoke
) becomes smaller.
smoke
Figure 3
Attenuation = Absorption + Scattering
PB-1191 Beam Detector
Scattering
Scattering
Light Beam Absorption
Smoke
Particles
Scattering
Reflector
PBR-1191
3