CHAPTER 21 The Complete System Now that the various features of the different brands of equipment have been presented, it is time to put them all together and take a brief look at the to
Trang 1CHAPTER 21 The Complete System
Now that the various features of the different brands of equipment have been presented, it is time to put them all together and take a brief look at the total system The reader should bear in mind the limitations of such an undertaking, as features change and new models are introduced If this book is used properly, enough knowledge should be gained to allow one to evaluate these changes sufficiently It would be unfair to the manufacturers and the end user to take the brief comments made in this chapter as sufficient grounds for making a decision These comments are provided to help the reader to see better the “big picture” when undertaking a thorough evaluation They are not based on exhaustive empirical studies, or head-to-head tests on every feature The manufacturers specification’s and claims have been taken at face value, and have not been independently verified The information presented is based on informed opinion, gathered through much experience with a broad spectrum of operators and applications, but still subject to the many biases and flaws of fallen human nature Caveat Emptor
A THE TREATMENT PLANT/APPLICATION
All the equipment reviewed is designed for drinking water treatment applications
As such, each should perform adequately Most of the important decisions will have
to be based upon the service record and equipment reliability of each manufacturer, which will have to be accessed by consulting references It is important to consult
a sufficient number of references to overcome individual biases and offset the occasional “black hole” installation that will happen to everyone Make sure that proper account is taken for the age of the equipment installed Many improvements have been made in the past few years, as the market has matured Often complaints stem from frustration with the functionally limited equipment sold in earlier years, especially before adequate computer interface was provided Many operators have never properly learned how to use the equipment, and blame the equipment unfairly
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Complaints about Hiac Royco early on helped Met One to get a foothold in the market Similar complaints are now heard about some of these early Met One applications While Hiac Royco made little attempt to improve its products before selling the line to IBR, Met One has made great strides in the past few years It is important to get enough information to take these factors into account On the other hand, do not assume that the largest number of installations necessarily means the best product
Most of the other considerations will have to do with the ability of the operators
to operate and maintain the system Some of the systems require a little more effort
to clean and maintain, and a particular style of software presentation may be more suited to a given set of operators Although it is becoming less practical to have each manufacturer set up a demonstration system on site, each will provide demo software, which should be set up for the operators to try out Get copies of the manuals in advance The “simpler is better” approach is not always true Assuming that a computer will make the system too complicated is not usually wise It is precisely the ability to see the trended particle counter data that makes the equipment easier to use The same goes for auxiliary inputs Trending particle counts and turbidity together will be the best way to help the operations staff assimilate the technology Do not skimp on training Initial and follow-up training will make a great deal of difference
Most of the turnkey systems are designed to accommodate a large number of particle counters, so adding units piecemeal or after a plant expansion should not
be a problem If the turnkey system is to be used for only a couple of years before
a complete SCADA integration is undertaken, the various SCADA integration options should be studied in detail prior to making the initial purchase As this is usually the least-understood aspect of the technology, it is easy to “worry about it later,” which is unwise Although the manufacturers typically provide less-than-optimal support for SCADA integration, it stands to reason that the larger firms should be able to handle such requests more easily Met One has certainly had the most opportunity to have developed expertise in this area, with the largest installed base of equipment in the water market, as well as experience in other market segments The ARTI use of the Modbus RTU protocol is a welcome development The Chemtrac protocol was built around the optomux standard in a conscious attempt
to make SCADA integration easier, but most of the standard SCADA optomux drivers are incomplete and must be modified to accommodate it Any of the manu-facturers may have developed an interface for a particular SCADA package, so it never hurts to check
B EQUIPMENT FEATURES
1 Packaging
Packaging is integral to functionality All the units are designed for use in filter galleries and other damp environments It is an advantage to be able to clean the
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flow cell without opening the NEMA enclosure, since water may be spilled into the enclosure ARTI and Chemtrac offer the easiest access to the sensor, which sticks out of the NEMA enclosure, while the others allow access to cleaning without opening the NEMA enclosure Clogs or partial obstruction may require opening the NEMA enclosure of these other units Met One and IBR have pressure limitations that could be exceeded if compressed air is used to clear a clogged flow cell The removable bottom panel on the Chemtrac counter allows analog I/O signals
to be quickly disconnected and reconnected via plug-in connectors The IBR and Met One enclosures leave the power supplies mounted and isolated, but require individual removal of the analog signals
2 Sensor Characteristics
All of the units use light-blocking particle sensors All of them work according
to the same principles outlined in Part I of the book The largest deviations appear
in the use of less-rugged materials in the Met One sensor, and the nonvolumetric design of the older Hach/PMS equipment The former is important as a maintenance consideration only, in that it must be treated with more care than the others The nonvolumetric design of the older Hach sensor could result in the loss of sizing resolution accuracy Until tighter standards are developed, this will not be an issue
3 Counter Electronics
For most online applications, the type of counter electronics is not critical, as only a few size ranges are ever used Chemtrac and Met One employ multichannel analyzers (MCA) type counters, as opposed to the standard comparator types Met One uses the MCA card for calibration, which allows the complete system to be optimized for better performance
Chemtrac, ARTI, and Met One all offer versatility with regard to analog I/O
4 Software
A thorough evaluation of the software provided by each manufacturer shows that less difference exists than one may expect While certain features may be more appealing to a given operator, all the manufacturers provide the important features necessary to a well-run particle counting system
ARTI, Met One, and Chemtrac offer similar packages, with Aquarius and WQS being a little more up-to-date with multiple graphing features The IBR Intellitest program is not as developed as the others, but is functional, and will likely keep evolving
All in all, our recommendation would be that the software offered by all of the manufacturers is adequate, and should not be the driving factor in the system selection All other things being equal, then perhaps the look and feel of a given program might be a deciding factor
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5 Experience
Met One is the leader in providing in-house expertise It is the company with the most installations, as well as the longest tenure in drinking water applications
It is larger than the other companies, and should be strengthened by its merger with Hach Hach has a tremendous installed base of turbidimeters and other plant instru-mentation
Chemtrac is a small company with a good marketing channel but with little technical expertise If serious efforts at tightening standards are pursued by the industry, it is doubtful that Chemtrac will be able to keep up Equipment must be improved over time, or it will become dated The Chemtrac equipment had some excellent features when it was introduced, but it has never matured as a product The IBR equipment has been around since 1988, and it remains to be seen to what degree it will be improved and advanced
ARTI has a staff of experienced designers, many having been formerly associated with Met One Its alliance with US Filter will give it a good presence in the market
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