Hach Met One 6000 Series, User Manual

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General information
Important Note: A yellow LED can be activated from the central monitoring software with
ModBus protocol to flash for count alert. The yellow LED cannot be activated with FX
protocol. If not activated by the software, the yellow LED will only turn on during startup
initialization.
For a description of the Ethernet LED indicators, refer to section 4.2.2.2 on page 36 . For
a description of the Wireless LED indicators, refer to section 4.3.1.5 on page 40 .
2.5 Theory of operation
The sensor in the Met One 6000 air particle counter contains a laser diode light source
that illuminates an area called the view volume with intense light. Particles in the sample
pass through the view volume and scatter the laser light, which is then collected through
the collection optics and focused onto a photodiode. The intensity of scattered light varies
depending on the size of the particle. The photodiode detects and converts the light
signal to electrical pulses, the magnitude of which is proportional to the particle size. The
information processed by the on-board controller electronics are then communicated to
the central monitoring system through the communication electronics.
The pulses are counted and measured by electronics on a circuit board containing
counting operations circuitry. Comparators are used to measure pulse height and sort the
signals into channels according to size. Counting circuits count the pulses in each
channel. The results indicate the particle counts for each size channel.
Calculations, if required by the operator, are performed and the data is available to the
I/O circuits for the facility monitoring system software through suitable communication
protocol or for peripheral devices. The firmware that controls counter operations is stored
in flash memory. The counting operations circuitry can also process external analog
signals from environmental probes when used.
Additional circuitry provides device controls for the sample flow and external accessories.
Power regulation and distribution circuits control the proper levels and internal application
of DC voltages.
Isokinetic sampling probes
The isokinetic sampling probe is designed for accurate sampling in laminar flow
environments. The velocity of air in the probe is close to that of a typical vertical or
horizontal laminar flow environment such as a clean room or clean hood. The probe will
match the vertical (or horizontal) flow speed of the air in order to collect representative
samples of the cleanroom laminar flow for the particle counter. Refer to
Figure 4 for a
comparison of sampling with and without the isokinetic probe.
Table 1 LED indicator description
LED color Indication System status
Green Flashing (3 second) Normal operation sampling
Green Steady Normal operation not sampling
Red Solid or flashing Count alarm
Blue Steady Sensor failure
Blue Flashing Communication failure
Blue One short flash, one long flash Flow failure