TSI Instruments 3786 User Manual

1-6 Model 3786 Ultrafine Water-based Condensation Particle Counter
Totalizer allows for increased statistical precision at low particle
concentrations through the use of longer sample times.
When a particle enters the optical viewing volume and is being
detected, no other particles can be counted. As the particle
concentration increases, the amount of time blocked by the
presence of particles becomes significant. If the particle
concentration were computed using elapsed time, the value would
be under reported. The actual sample time needs to be corrected for
this blocked or dead-time. To adjust for this particle coincidence
effect, the UWCPC measures the dead-time resulting from the
presence of particles in the viewing volume and subtracts it from
the sample time. This sample live-time value is used in place of the
sample time for the concentration calculations for the primary
display when not using the totalizer.
At very high concentrations, the dead-time value grows and the
adjustment becomes large. Single particle events may not even be
detected since particles are nearly continually in the measurement
viewing volume and the accuracy of the live-time measurement
begins to diminish. When the measured live-time value drops below
40% of elapse (real time), the display will show an “OVER”
annotation indicating that the measured concentration exceeds its
specified operating range. When the live-time value drops below
10% of elapse time, the display will show a concentration of 9.99E5
particles/cm
3
indicating an extreme overload condition.
During operation the UWCPC collects: single particle counts and
dead-time corrected sample time every tenth of second. The
concentration value reported on the primary concentration display
is updated each second. It uses data collected over the previous
second of elapsed time to calculate concentration. If the
concentration is less than 20.0 particles/cm
3
, a six-second running
average of particle count data is used to calculate the displayed
value. A single particle counted during this six-second sample is
displayed as 0.03 particles/cm
3
which is the minimum value that
can be displayed (other than 0.00) without using the totalizer.
Concentration data is also available from the data communications
ports and it is “aggregated” or summed from each tenth-second
measurement with programmable sample periods from 0.1 second
to 3600 seconds.

TSI Instruments 3786 Specifications

General

Brand	TSI Instruments
Model	3786
Category	Cash Counter
Language	English