2–8
Model 3760 Condensation Nucleus Counter
adjustments are needed. The minimum detectable particle size is controlled by the
supersaturation ratio of the butanol vapor in the condenser. Since the butanol
droplets grow to nearly the same size, there is no particle size discrimination by
electrical pulse-height measurement. Particle detection is unaffected by slight
degradation in laser power or dirty optics. Finally, since the CNC is a single-
particle counter, there is no photometric calibration for concentration.
Figure 2-5
Analog Pulse Trace of the Photodetector Signal While the CNC Samples Ambient
Laboratory Room Air. The bottom trace is a 100x expansion of one of the pulses from the
top trace. The pulse on the bottom trace is approximately 320 millivolts in amplitude and
0.25 microsecond wide.
