A Practical Guide to Particle Counting for Drinking Water Treatment - Chapter 22 potx

EQUIPMENT FEATURES The ARTI WQA 2000, Met One WGS-267 Grab Sampler, and the Chemtrac 2400 PS are designed to operate in grab or continuous, online mode.. This allows the sample flow to b

Grab Samplers

All four of the manufacturers offer grab samplers, with Met One, Chemtrac, and ARTI leading the way IBR still offers the Hiac Royco unit originally designed for Hach as the “Log Easy.” Each of the units is similar in size and weight, and operates

in like manner

A EQUIPMENT FEATURES

The ARTI WQA 2000, Met One WGS-267 Grab Sampler, and the Chemtrac

2400 PS are designed to operate in grab or continuous, online mode The IBR can

as well, although its internal pump cannot be bypassed The pumps in each of these units are not designed for continual operation, so it is recommended that long-term online applications be set up using a constant-head overflow weir and gravity flow

1 Sample Delivery System

All of the units employ small DC gear pumps that pull the sample through the sensor The speed of the pump is controlled by a DC voltage source, which is not user adjustable The ARTI WQA 2000 and the Met One WGS-267 employ a user-adjustable needle valve rotometer to allow the operator to adjust the flow rate The other units provide no flow adjustment or display The gear pumps provide a smooth, quiet, pulseless flow and can clog if large concentrations of particles are present They are designed for around 400 hours of operating life, which will cover several years worth of grab sampling, but only a few weeks of continuous operation The ARTI, Chemtrac, and Met One units are easily converted to continuous, online operation by moving a couple of pieces of tubing This allows for the pump

to be bypassed, and connection made to a gravity flow system

196 A PRACTICAL GUIDE TO PARTICLE COUNTING

All of the units operate off AC power and rechargeable DC batteries Battery operation provides ease of portability, as well as reducing the electrical shock hazard when operated in a wet environment

2 Packaging

The Chemtrac 2400 PS is packaged in a standard NEMA 4X plastic box, with the sensor extending from the side This allows the sample flow to be completely separated from the battery and electronics The AC power adapter is a sealed “desk-top” power supply similar to the type used for laptop computers This smaller NEMA box is mounted on a simple adjustable stand and stored in a rugged watertight ABS plastic equipment case for ease of storage and portability The 2400 PS has a local display and a membrane touch keypad operator interface No printer is available See Figure 22.1

The Met One WGS 267 is built into a folding deep-drawn aluminum case, with the counting electronics mounted in the door, and the sensor, power supply, battery, and sample delivery system in the larger body of the case Unlike the Chemtrac unit, the model 267 must be taken apart to access the sensor for cleaning Liquid does pass into the case, allowing for the potential for leakage into the power supply A fault isolation circuit breaker is built into the power cord to shut off the system if the power supply is shorted A membrane keypad and local display are provided, along with a small thermal printer See Figure 22.2

Figure 22.1 Chemtrac PC2400PS grab sampler (Courtesy of Chemtrac Systems, Inc.,

Nor-cross, GA.)

The ARTI WQA 2000 comes in a cast aluminum housing with side panels that

open to provide access to the sensor sample ports An LCD graphic display

mea-suring 128 × 128 pixels is mounted on the top between a membrane keypad and

thermal graphics printer The top is sloped downward to provide a comfortable

working angle for the operator The unit has a retractable handle and shoulder strap,

and comes with an optional ruggedized plastic storage case (Figure 22.3)

The IBR VersaCount has a handle attached for portability, but does not have an

external case The front of the unit incorporates a keypad and display, along with a

series of bar codes A bar code reader is attached to the unit This rather odd feature

is included because the unit is a modified version of a Hiac Royco portable air

particle counter Air particle counters are designed to be moved from room to room,

since air is difficult to “grab-sample.” Bar codes were mounted at various locations

where the samples were taken, and provided a quick way of tagging the data

Drinking water plants are not set up the same way, and the considerably heavier

water version is not convenient to carry around It is reported that some of the early

customers would stick the bar code wand into the sample, thinking that it was the

particle sensor

The IBR VersaCount is designed such that the sample passes through the

enclo-sure that houses the electronics, power supply, battery, and sample delivery system

A small standalone thermal printer is available as an option

Figure 22.2 Met One WGS 267 grab sampler (Courtesy of Pacific Scientifc Instruments, Grants

Pass, OR.)

198 A PRACTICAL GUIDE TO PARTICLE COUNTING

3 Counting Features

The Chemtrac 2400 PS uses the same counter electronics as the standard online

unit, but uses different firmware (“Firmware” is operating code that is programmed

into the electronics It is designed to be a more permanent part of the system than

“software.”) This change allows for up to 16 user-adjustable size channels to be

programmed, along with other parameters Up to 16 tagnames can be programmed

by the user as well, so that the data can be stored according to the location where

the sample was taken The keypad is used to cycle through several options for sample

time, number of runs, and tagname Up to 320 samples can be stored in the unit

The liquid crystal display shows the tagname, sample number, and cycles through

the particle size data

The Met One WGS-267 uses a comparator-based counter, which provides six

particle size channels preset at the factory The operator keypad is used to set the

sample period and interval, time and date, the number of sample runs, and several

counting modes Total counts, counts per milliliter, or counts per 100 ml can be

selected A special concentration mode provides a quick measure of the particle

concentration, so that the need for dilution may be quickly ascertained An audible

alarm will indicate sensor problems, dirty cell, or overconcentration An ID number

Figure 22.3 ARTI WQA 2000 Portable Water Quality Analyzer (Courtesy of Art Instruments,

Inc., Grants Pass, OR.)

can be programmed in to tag the data in memory or on the printout A log removal

function allows instant calculation of log removal between two samples Up to 250

samples can be stored in a rotating buffer (“rotating” means that the first sample

will be overwritten by the 251st sample, etc., so that the most recent samples will

be saved in memory if the limit is exceeded)

The ARTI WQA 2000 uses the same counting electronics as the online unit and

is available with either of the sensors The keypad can be used to select from several

preset sample and purge volumes Eight particle size channels are provided, and

the user may choose between cumulative or differential counts in particles per

milliliter Samples may be labeled to provide for log removal calculations between

the first record of a label and all the other records of the same label A large storage

buffer allows for storing data from up to 500 samples

The WQA 2000 also accepts inputs for the measurement of other water quality

parameters, such as pH, turbidity, conductivity, etc

The IBR VersaCount provides eight size ranges preset at the factory Data can

be displayed in counts per milliliter or total counts, and log removals can be

calcu-lated and displayed User-selectable alarms provide an audible alarm when count

limits are exceeded The above-mentioned bar code panel is used to input settings

Up to 350 sample runs can be stored in memory for download

4 Computer Interface

All the grab samplers are equipped with RS-232 serial data interface to allow

the stored data to be downloaded to a PC Both Met One and IBR provide only

DOS-based software for this purpose Chemtrac has a 16-bit Windows program

called “Grabbit,” which is used to download tagnames and size ranges into the

counter electronics, along with a range of sample times and numbers of sample runs

that provide the options selectable from the operator keypad This allows the user

to customize selection options This program also includes reporting software, which

is built around the Crystal Reports program used by the online TracWare software

Met One does have an optional counter electronics and software package

designed for those desiring particle distribution data The counter electronics is a

2048-channel multichannel analyzer, which is mounted in an ISA slot in the PC A

package called WGS is used to collect and view the data This system is not

compatible with Windows software, and must be run in DOS mode It is designed

to take the particle pulses directly from the sensor, bypassing the built-in

grab-sampler electronics

ARTI provides a Windows-based software package for accessing data from the

Aquarion