Campbell Scientific PWS100 Present Weather Sensor - Manual (Page 91)

Section 8. Functional Description
8.4 PWS100 Control Unit
The PWS100 control unit, shown in Figure 8-5 as a block diagram, is a custom
designed DSP board comprising a DSP, memory, timing circuits and analogue
to digital converter.
FIGURE 8-5. Block diagram of PWS100 control unit
The DSP board controls all of the functions of the system, including switching
of heaters when the temperature sensors in each head pass certain thresholds,
laser modulation, signal analysis and communications. The on board memory
holds the program code, data tables and data for statistical manipulation.
8.5 Measurement Signal Processing
The PWS100 has two phases of operation based around a ten second cycle. The
main phase is run for nine seconds out of every ten during which it
continuously captures data from the optical detectors and processes the data to
analyze for particles. The second phase, which runs in the remaining second is
used for making measurements from other sensors both within the sensor itself
and from the external sensors. Precipitation amounts and rates are corrected
for the 90% particle duty cycle, whilst counts of particles are not. As a result of
this ten second cycle statistical data are only updated every ten seconds.
The algorithm descriptions in this user guide give details as to how particles
are detected and used to give certain output relevant to present weather
monitoring.
8-5