8-12 Model 3772/3771 Condensation Particle Counter
Viewing A n a log Pul s e s
You may want to observe the pulse shape of droplets passing through the
CPC optics by looking at the electronic signal produced in the
photodetector. This signal is produced when detecting scattered light from
the droplets passing through the laser beam. In general, the pulses will be
fairly uniform in shape and size regardless of the initial size of the particles
detected.
Notes: ❑ Viewing analog pulses should only be attempted by someone
who is familiar with the operation of the CPC and who is
technically qualified.
❑ When removing the cover of the CPC, observe the laser
warning label on the inside of the instrument.
W A R N I N G
The use of controls, adjustments, or procedures other than those
specified in this manual may result in exposure to hazardous optical
radiation.
C a u t i o n
Whenever performing service on internal components avoid damage to
the CPC circuitry by not stressing internal wiring, through bumping,
snagging or pulling. Also use electrostatic discharge (ESD) precautions:
Use only a table top with a grounded conducting surface.
Wear a grounded, static-discharging wrist strap
Using an oscilloscope, observe the analog electrical pulses from the
photodetector by following these steps:
1. Remove power from the CPC.
2. Remove the CPC cover.
3. Connect a “SMC Plug to BNC male” cable (not included) from J101 on
the detector board to an oscilloscope as shown in Figure 8-9. The
oscilloscope should be 50-ohm terminated. When viewing the signal on
the scope, the signal height should be scaled down by a factor of 10.
For a typical pulse of 3 volts, the scope will read only 300 mV.
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