Các quầy hạt sản xuất nước uống tất cả các lái xe sử dụng tia laser và mạch phát hiện tương tự như trong mục đích. Các chi tiết của các mạch không có sẵn cho công chúng, và bất kỳ cuộc thảo luận quan trọng của họ sẽ được vượt quá phạm vi của cuốn sách này. Điện tử đếm và nguồn cung cấp năng lượng cung cấp sẽ được thảo luận một thời gian ngắn. | 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 of these circuits are not made available to the public and any significant discussion of them would be beyond the scope of this book. The counting electronics and power supplies provided will be discussed briefly. A. COUNTING ELECTRONICS 1. Met One The Met One PCX employs a 12-bit PHA counting circuit. Up to 4096 count channels are theoretically possible. Eight channels are standard while up to 32 are available for online use. These size ranges are set through the digital interface with the manufacturers software. For best sizing accuracy the upper size range should be set at or below 20 pm. This allows all 4096 channels to cover the 0 to 1 V range. If a larger upper value is used these channels are spread out over 10 V up to 750 pm . This reduces the sizing accuracy by an order of magnitude. For most applications the 20 pm upper limit is sufficient. This mode should certainly be used if resolution and count correlation between instruments is important. The 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 calibrated in the field. The Met One model PCT analog output particle counter along with the older model 215W and model 203 units employ voltage comparator counting circuits. Each has only two size channels which provide only total counts. Unlike the PCX these channels are cumulative only except for the version of the PCT that does not have a local display. That unit provides a jumper setting that allows the first channel to be set to a differential mode. The size thresholds on all of these units are set manually with trimpots. Although they may be adjusted by the user they are not 151 2001 by CRC Press LLC 152 A PRACTICAL GUIDE TO PARTICLE COUNTING designed to be .
