In newer systems, it would be desirable to integrate the measurement of turbidity with the measurement of color. In general, a turbidimeter employing light absorption can be used to measure either turbidity or color but not both simultaneously. Although no work has been done on this, some thought has been given to the use of different colored rotating filters, one of which would be glass with little absorption capacity, to permit detection of selected colors as well as turbidity with one device. (f) Sunlight intensity: For measuring sunlight intensity a pyrheliometer is employed consisting of two concentric circles 10 mils and 5 mils in diameter respectively. The outer circle is coated with magnesium oxide and the inner circle with lampblack. Each circle is electrically insulated from the other. Incident sunlight causes a temperature difference which generates a voltage in a thermocouple. One wire is an alloy of 60-percent gold and 40-percent paladium while the second is an alloy of 90-percent platinum and 10-percent rhodium. The device produces 90 percent or better of its output when exposed to radiation having wave lengths between 0.35 micron and 2.6 microns. This limitation is imposed upon the device by a sodium lime glass enclosure. (g) Conductivity: Measurement of conductivity is made by applying an alternating current voltage across a pair of platinum electrodes. The cell forms one arm of a wheatstone bridge and the unbalanced output is amplified and rectified by the analyzers, and recorded as conductance. Alternating current is employed in this measurement to prevent polarizations of the cells. A line frequency of 60 cycles has been shown to be satisfactory, although in several cases frequencies of 400 to 1000 cycles per second have been employed. The current carrying ability of a solution depends upon the ions present and their mobilities. Mobility is temperature dependent so that temperature compensation is required and is effected by the application of sensistors. Although present conductivity devices are satisfactory for measurements below 10,000 micromhos, and in "rather clear waters," difficulties have arisen in measurements an order of magnitude higher, so that additional research in conductivity measurements is desirable. 2. Analyzers. The integrated system equipment employs the more recent electronic operational amplifier technology in the analyzer phase of the integrated system in preference to conventional alternating current amplifiers. This technology provides greater stability and reliability, and lends itself to modular design, thereby facilitating maintenance. Research is now being carried on to determine the feasibility of employing solid state devices in the analyzer phase of the integrated system. One primary difficulty of the application of solid state devices is their sensitivity to temperature change. Current through a solid state device is exponentially related to temperature. A possible engineering solution to this dilemma might be controlled temperature environment for the analyzer section, although advanced research in solid state physics may also provide a solution. 3. Recorders. The integrated system employs one multipoint strip chart recorder which displays all parameters on a single chart, a technique facilitating visual analysis and reducing the number of instruments requiring maintenance and replacement. 4. Telemetering.-The transmission of water quality data from remote localities to a central monitoring and processing facility can also be provided in an integrated automatic data acquisition system. There are two general methods for transmitting signals from a monitor to a central locality, radiofrequency and telephone lines. The radiofrequency or microwave transmission employs carrier frequencies which are modulated by the telemetered signal. The transmitter may be keyed by a form of information which can cause a contact closure or which can be used to vary the frequencies in an oscillator circuit. These alternatives are classified as either amplitude or frequency modulated techniques. Microwave telemetering is generally directional in that its transmission is focused on the receiving antenna at a distant point. As a general rule microwave transmission is limited to line-of-sight operation for dependable results. Repeater stations may be employed where longer distances are required. When telephone lines are employed several methods of data transmission can be used. (a) Techniques can be employed which involve the conversion of the quantity to be measured into an electric current proportional to the variable measured. (b) Voltage transmission methods vary the voltage at the receiving end so that it is proportional to the quantity measured. (c) Impulse telemetering consists of the transmission of square type pulses which may or may not be uniformly spaced. One method of impulse telemetering produces a single pulse for each unit of the parameter measured, transmitted at equal time intervals. In other systems the interval between impulses may be proportional to the parameter measured, and the pulse amplitude held constant. (d) Another form of telemetering employs frequency techniques. In this approach the frequency of a carrier is directly proportional to the amplitude of the parameter measured. This type of telemetry is employed by the ORSANCO equipment for transmitting pH and other values in which a carrier frequency between 5 and 15 cycles per second is employed. Thus, 5 cycles per second represents 0 pH, 10 cycles per second represents a pH of 6, and 15 cycles per second represents a pH of 12. Telemetering makes it possible to eliminate a great deal of manual translation, which is often accompanied by errors that are costly and hard to find. Data processing The increasing sophistication of computers and their adaptability has made it possible to utilize fully, large quantities of data from continuous observations of natural phenomena, and to summarize and analyze them in days-only a few years ago the job would have been virtually impossible of achievement. The use of computers, therefore, has greatly refined the theoretical approaches, has provided greater insight into physical phenomena, and has enabled a reduction in errors incurred during manual manipulation of large quantities of data. It has made it possible to greatly increase the number of quality parameters which can be summarized and used in making judgments regarding control measures and management problems. Analog computers are a very useful tool. The analog has made it possible to simulate a stream system by reducing the observations made to an electronic circuit which reacts to stimuli as does the river 85974-62-7 or body of water, the stimuli in the analog computer being that corresponding to and applied by the manipulator in accordance with the observed condition in the river. This has made it possible to inject additional variables or increased amounts of stimuli to gain further insight and to predict what will occur in a stream or lake under different sets of circumstances. 1. Analog to digital conversion.-As previously noted, recorded data must be processed either manually or automatically. To provide the capability for automatically processing data from an integrated system, analog to digital conversion is required. There are essentially two devices used for analog to digital conversion: (a) Electromechanical devices called encoders, and (b) analog to digital converters which employ either magnetic amplifiers, vacuum tubes, or solid state devices. If the conversion occurs at the monitor, it is possible to produce the output as binary coded decimal information on magnetic tape, as BCD information on punched paper tape, or as decimal information on binary cards. Although the magnetic tape output device is fastest and directly compatible to most digital computers, it is the most expensive and most delicate. Research in the application of magnetic tape under field conditions would be desirable to exploit the two advantages of speed and computer compatibility. A more economical but slower method for producing digital output is the paper tape technique. There are basically two paper tape methods: (a) Binary coded decimal in serial fashion, and (b) binary coded decimal employing 16 channel tape. In the latter technique a single row of holes represents one specified number, and in the former technique a block of holes 6 by 8 in size would represent a specific number. The 16 channel paper requires a special tape reading device for producing punched cards. A third alternative to producing information for digital computer processing employs an analog to digital converter and a mechanical summary punch or key punch. Although this technique would produce cards that would be directly compatible to digital processing, the equipment employed would be quite cumbersome and transfer of cards from monitoring station to control data processing point would present a problem for continuous water quality monitoring. Of the three alternatives, punched paper tape at this time seems to be the cheapest, the most reliable, and the simplest from a field operation view, though it is the most time consuming from a data processing point of view. A peripheral operation from paper tape to cards generally is required before punched paper tape can be utilized by a computer. 2. Digital computers. For processing water quality data, various types of digital computers can be employed. These include the IBM series 704, 1401, 1620, 650, the Honeywell 400 and 800, and similar systems. At the present time, the Robert A. Taft Sanitary Engineering Center is employing a Minneapolis-Honeywell 400 digital computer for data processing. The basic system consists of a central processor, 4 magnetic tapes units, a high-speed printer (900 lines per minute) and a high-speed card reader (650 cards per minute). The central processor includes an arithmetic unit, a control unit, one block of memory (12,288 decimal digits, which can be expanded to a total of 49,135 decimal digits), and an independent console. Figure 19 shows |