...
151
CHAPTER
17
Particle Counter Electronics
The particle counters manufactured for drinking water all employ laser driver
and detector circuits that are similar in purpose. The details ... PHA card is used to calibrate the Met One sensor. All 4096 channels may
be downloaded to provide a histogram of particle sizes. This allows each particle
counter to be calibr...
... Packaged Treatment Plants
Packaged treatment plants, as touched on above, are prefabricated plants, which
are more cost-effective than ground-up plants for smaller applications. A packaged
plant ... removal. (Courtesy of Pacific Scientific Instruments, Grants Pass, OR.)
28 A PRACTICAL GUIDE TO PARTICLE COUNTING
manufacturers of packaged treatment plants employ particle c...
... at a time. If a spare
is available it can be rotated into service. The maintenance log should be kept up-
to- date, and calibration stickers displaying the date of calibration placed on each
particle ... practical.
2. Particle Counter Calibration Verification
Verifying calibration is an easier and more practical step for the water plant
operator. Only a couple of partic...
... PRACTICAL GUIDE TO PARTICLE COUNTING
The disadvantage to this approach is that the particle counter data are collected
and displayed separately from the other plant data, requiring separate training ... second alternative is the direct interface of the particle counters to SCADA
using serial data communications. All count data, as well as status and alarm
information, are t...
... case of online particle counting, trending the grab-sample data
with other plant parameters will add to its value. If these data are available in a
usable file format that can be imported into ... prior to each
use. Certainly an acid washer and particle- free storage area would be ideal, but these
are usually not necessary for 2- m particle counting. It is a good idea to k...
... detected
and measured if it produces a signal with a minimum 2 to 1 signal -to- noise ratio.
B. SIGNAL -TO- NOISE RATIO
All electronic instruments are subject to various forms of “noise,” or random,
meaningless ... mentioned is Section A, the smallest particle that can be reliably measured
must produce a signal amplitude at least twice that of the noise, or a 2 to 1 signa...
...
82 A PRACTICAL GUIDE TO PARTICLE COUNTING
The cell window materials vary in optical quality. Small imperfections in the
material diffuse the light and are a source of resolution and sizing ... reflected back into
the laser, it can disrupt this process, and cause variations in the beam intensity. This
is another reason that aluminum flow cells are anodized a dark color, as the...
... called a voltage comparator
input stage. The more complex approach involves analog -to- digital (A/ D) conversion.
1. Voltage Comparator
A comparator is simply a small circuit that “compares” an ... typically
communicated every minute.
The comparator provides a simple way to convert the particle size information
from an analog pulse to a digital count value. It is a very...
... voltage range of a chart recorder or SCADA analog
input is 1 to 5 V. A 250
Ω
resistor is required to convert a 4 to 20 mA signal into a
1 to 5 V signal.
Another benefit of the 4 to 20 mA current ... some cases, flow alarms can be signaled by the particle
counter via the computer data collection system.
A. DIAGNOSTIC SIGNALS, ALARMS, AND DISPLAYS
The most common alar...