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

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

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195 CHAPTER 22 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. L1306/frame/pt03 Page 195 Friday, June 23, 2000 2:16 PM © 2001 by CRC Press LLC 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.) L1306/frame/pt03 Page 196 Friday, June 23, 2000 2:16 PM © 2001 by CRC Press LLC GRAB SAMPLERS 197 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.) L1306/frame/pt03 Page 197 Friday, June 23, 2000 2:16 PM © 2001 by CRC Press LLC 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.) L1306/frame/pt03 Page 198 Friday, June 23, 2000 2:16 PM © 2001 by CRC Press LLC GRAB SAMPLERS 199 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. L1306/frame/pt03 Page 199 Friday, June 23, 2000 2:16 PM © 2001 by CRC Press LLC . 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. 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,. 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

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  • Table of Contents

  • CHAPTER 22: Grab Samplers

    • A. EQUIPMENT FEATURES

      • 1. Sample Delivery System

      • 2. Packaging

      • 3. Counting Features

      • 4. Computer Interface

      • Appendix 1: Manufacturer Listing

      • Appendix 2: Application Papers and Books on Particle Counting

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