tailieunhanh - A Practical Guide to Particle Counting for Drinking Water Treatment - Chapter 13

Lấy mẫu lấy được bảo hiểm trong một chương riêng biệt bởi vì họ hoạt động một cách đáng kể khác nhau từ các hệ thống trực tuyến. Các mô hình hiện đang sử dụng được thiết kế cho tính di động, mặc dù hầu hết thời gian họ được vận hành trong phòng thí nghiệm nhà máy nước uống. | CHAPTER 13 Grab Samplers Grab samplers are covered in a separate chapter because they operate in a manner substantially different from online systems. The models currently in use are designed for portability although most of the time they are operated in the drinking water plant laboratory. A. EQUIPMENT FEATURES For the most part the components of the grab-sampling particle counter are identical to those of the online system. The distinguishing feature is the addition of a sample delivery system designed to draw the sample through the particle sensor. The packaging and software must be suited to the different applications requirements. This section presents an overview of these additional features as well as any considerations regarding similar features used for a different purpose. One of the most useful features is the ability to function as an online unit. In this mode a grab sampler can be used as a temporary replacement for an online unit that must be taken out of service or in a sample location where a permanent online unit has not been installed. 1. Sample Delivery System a. Portable Grab Samplers As described in Part I the grab sampler employs a pump to pull the sample through the particle counter flow cell. In the units currently available on the market a small gear pump is used. This pump is small and lightweight and produces a virtually pulseless sample flow. It draws very little power allowing for battery operation. It is a fairly quiet running unit compared with the peristaltic pumps commonly found in laboratory applications. 127 2001 by CRC Press LLC 128 A PRACTICAL GUIDE TO PARTICLE COUNTING These small gear pumps are not designed for continuous operation and have an operating life of only a few hundred hours. This will provide several years of operation with grab samples but precludes long term online usage. The sample passes through the gear mechanism and large particles or concentrations of particles can jam the pump. This is not usually a problem